Updating what seems to be outdated documentation. (#6949)

defmodule System do
  @moduledoc """
  The `System` module provides functions that interact directly
  with the VM or the host system.

  ## Time

  The `System` module also provides functions that work with time,
  returning different times kept by the system with support for
  different time units.

  One of the complexities in relying on system times is that they
  may be adjusted. For example, when you enter and leave daylight
  saving time, the system clock will be adjusted, often adding
  or removing one hour. We call such changes "time warps". In
  order to understand how such changes may be harmful, imagine
  the following code:

      ## DO NOT DO THIS
      prev = System.os_time()
      # ... execute some code ...
      next = System.os_time()
      diff = next - prev

  If, while the code is executing, the system clock changes,
  some code that executed in 1 second may be reported as taking
  over 1 hour! To address such concerns, the VM provides a
  monotonic time via `System.monotonic_time/0` which never
  decreases and does not leap:

      ## DO THIS
      prev = System.monotonic_time()
      # ... execute some code ...
      next = System.monotonic_time()
      diff = next - prev

  Generally speaking, the VM provides three time measurements:

    * `os_time/0` - the time reported by the OS. This time may be
      adjusted forwards or backwards in time with no limitation;

    * `system_time/0` - the VM view of the `os_time/0`. The system time and OS
      time may not match in case of time warps although the VM works towards
      aligning them. This time is not monotonic (i.e., it may decrease)
      as its behaviour is configured [by the VM time warp
      mode](http://www.erlang.org/doc/apps/erts/time_correction.html#Time_Warp_Modes);

    * `monotonic_time/0` - a monotonically increasing time provided
      by the Erlang VM.

  The time functions in this module work in the `:native` unit
  (unless specified otherwise), which is OS dependent. Most of
  the time, all calculations are done in the `:native` unit, to
  avoid loss of precision, with `convert_time_unit/3` being
  invoked at the end to convert to a specific time unit like
  `:millisecond` or `:microsecond`. See the `t:time_unit/0` type for
  more information.

  For a more complete rundown on the VM support for different
  times, see the [chapter on time and time
  correction](http://www.erlang.org/doc/apps/erts/time_correction.html)
  in the Erlang docs.
  """

  @typedoc """
  The time unit to be passed to functions like `monotonic_time/1` and others.

  The `:second`, `:millisecond`, `:microsecond` and `:nanosecond` time
  units controls the return value of the functions that accept a time unit.

  A time unit can also be a strictly positive integer. In this case, it
  represents the "parts per second": the time will be returned in `1 /
  parts_per_second` seconds. For example, using the `:millisecond` time unit
  is equivalent to using `1000` as the time unit (as the time will be returned
  in 1/1000 seconds - milliseconds).

  Keep in mind the Erlang API prior to version 19.1 will use `:milli_seconds`,
  `:micro_seconds` and `:nano_seconds` as time units although Elixir normalizes
  their spelling to match the SI convention.
  """
  # TODO: Warn all old mappings once Elixir requires Erlang/OTP 19.1+
  @type time_unit ::
          :second
          | :millisecond
          | :microsecond
          | :nanosecond
          | pos_integer
          | :seconds
          | :milliseconds
          | :microseconds
          | :nanoseconds

  @base_dir :filename.join(__DIR__, "../../..")
  @version_file :filename.join(@base_dir, "VERSION")

  defp strip(iodata) do
    :re.replace(iodata, "^[\s\r\n\t]+|[\s\r\n\t]+$", "", [:global, return: :binary])
  end

  defp read_stripped(path) do
    case :file.read_file(path) do
      {:ok, binary} ->
        strip(binary)

      _ ->
        ""
    end
  end

  # Read and strip the version from the VERSION file.
  defmacrop get_version do
    case read_stripped(@version_file) do
      "" -> raise RuntimeError, message: "could not read the version number from VERSION"
      data -> data
    end
  end

  # Returns OTP version that Elixir was compiled with.
  defmacrop get_otp_release do
    :erlang.list_to_binary(:erlang.system_info(:otp_release))
  end

  # Tries to run "git rev-parse --short HEAD". In the case of success returns
  # the short revision hash. If that fails, returns an empty string.
  defmacrop get_revision do
    null =
      case :os.type() do
        {:win32, _} -> 'NUL'
        _ -> '/dev/null'
      end

    'git rev-parse --short HEAD 2> '
    |> Kernel.++(null)
    |> :os.cmd()
    |> strip
  end

  defp revision, do: get_revision()

  # Get the date at compilation time.
  defmacrop get_date do
    IO.iodata_to_binary(:httpd_util.rfc1123_date())
  end

  @doc """
  Returns the endianness.
  """
  def endianness do
    :erlang.system_info(:endian)
  end

  @doc """
  Returns the endianness the system was compiled with.
  """
  @endianness :erlang.system_info(:endian)
  def compiled_endianness do
    @endianness
  end

  @doc """
  Elixir version information.

  Returns Elixir's version as binary.
  """
  @spec version() :: String.t()
  def version, do: get_version()

  @doc """
  Elixir build information.

  Returns a keyword list with Elixir version, Git short revision hash and compilation date.
  """
  @spec build_info() :: map
  def build_info do
    %{
      build: build(),
      date: get_date(),
      revision: revision(),
      version: version(),
      otp_release: get_otp_release()
    }
  end

  # Returns a string of the build info
  defp build do
    {:ok, v} = Version.parse(version())

    revision_string = if v.pre != [] and revision() != "", do: " (#{revision()})", else: ""
    otp_version_string = " (compiled with OTP #{get_otp_release()})"

    version() <> revision_string <> otp_version_string
  end

  @doc """
  Lists command line arguments.

  Returns the list of command line arguments passed to the program.
  """
  @spec argv() :: [String.t()]
  def argv do
    :elixir_config.get(:argv)
  end

  @doc """
  Modifies command line arguments.

  Changes the list of command line arguments. Use it with caution,
  as it destroys any previous argv information.
  """
  @spec argv([String.t()]) :: :ok
  def argv(args) do
    :elixir_config.put(:argv, args)
  end

  @doc """
  Current working directory.

  Returns the current working directory or `nil` if one
  is not available.
  """
  def cwd do
    case :file.get_cwd() do
      {:ok, base} -> IO.chardata_to_string(fix_drive_letter(base))
      _ -> nil
    end
  end

  defp fix_drive_letter([l, ?:, ?/ | rest] = original) when l in ?A..?Z do
    case :os.type() do
      {:win32, _} -> [l + ?a - ?A, ?:, ?/ | rest]
      _ -> original
    end
  end

  defp fix_drive_letter(original), do: original

  @doc """
  Current working directory, exception on error.

  Returns the current working directory or raises `RuntimeError`.
  """
  def cwd! do
    cwd() ||
      raise RuntimeError,
        message: "could not get a current working directory, the current location is not accessible"
  end

  @doc """
  User home directory.

  Returns the user home directory (platform independent).
  """
  def user_home do
    :elixir_config.get(:home)
  end

  @doc """
  User home directory, exception on error.

  Same as `user_home/0` but raises `RuntimeError`
  instead of returning `nil` if no user home is set.
  """
  def user_home! do
    user_home() ||
      raise RuntimeError,
        message: "could not find the user home, please set the HOME environment variable"
  end

  @doc ~S"""
  Writable temporary directory.

  Returns a writable temporary directory.
  Searches for directories in the following order:

    1. the directory named by the TMPDIR environment variable
    2. the directory named by the TEMP environment variable
    3. the directory named by the TMP environment variable
    4. `C:\TMP` on Windows or `/tmp` on Unix
    5. as a last resort, the current working directory

  Returns `nil` if none of the above are writable.
  """
  def tmp_dir do
    write_env_tmp_dir('TMPDIR') || write_env_tmp_dir('TEMP') || write_env_tmp_dir('TMP') ||
      write_tmp_dir('/tmp') || ((cwd = cwd()) && write_tmp_dir(cwd))
  end

  @doc """
  Writable temporary directory, exception on error.

  Same as `tmp_dir/0` but raises `RuntimeError`
  instead of returning `nil` if no temp dir is set.
  """
  def tmp_dir! do
    tmp_dir() ||
      raise RuntimeError,
        message: "could not get a writable temporary directory, " <>
          "please set the TMPDIR environment variable"
  end

  defp write_env_tmp_dir(env) do
    case :os.getenv(env) do
      false -> nil
      tmp -> write_tmp_dir(tmp)
    end
  end

  defp write_tmp_dir(dir) do
    case File.stat(dir) do
      {:ok, stat} ->
        case {stat.type, stat.access} do
          {:directory, access} when access in [:read_write, :write] ->
            IO.chardata_to_string(dir)

          _ ->
            nil
        end

      {:error, _} ->
        nil
    end
  end

  @doc """
  Registers a program exit handler function.

  Registers a function that will be invoked at the end of program execution.
  Useful for invoking a hook in "script" mode.

  The handler always executes in a different process from the one it was
  registered in. As a consequence, any resources managed by the calling process
  (ETS tables, open files, etc.) won't be available by the time the handler
  function is invoked.

  The function must receive the exit status code as an argument.
  """
  def at_exit(fun) when is_function(fun, 1) do
    :elixir_config.update(:at_exit, &[fun | &1])
  end

  @doc """
  Locates an executable on the system.

  This function looks up an executable program given
  its name using the environment variable PATH on Unix
  and Windows. It also considers the proper executable
  extension for each OS, so for Windows it will try to
  lookup files with `.com`, `.cmd` or similar extensions.
  """
  @spec find_executable(binary) :: binary | nil
  def find_executable(program) when is_binary(program) do
    assert_no_null_byte!(program, "System.find_executable/1")

    case :os.find_executable(String.to_charlist(program)) do
      false -> nil
      other -> List.to_string(other)
    end
  end

  @doc """
  Returns all system environment variables.

  The returned value is a map containing name-value pairs.
  Variable names and their values are strings.
  """
  @spec get_env() :: %{optional(String.t()) => String.t()}
  def get_env do
    Enum.into(:os.getenv(), %{}, fn var ->
      var = IO.chardata_to_string(var)
      [k, v] = String.split(var, "=", parts: 2)
      {k, v}
    end)
  end

  @doc """
  Returns the value of the given environment variable.

  The returned value of the environment variable
  `varname` is a string, or `nil` if the environment
  variable is undefined.
  """
  @spec get_env(String.t()) :: String.t() | nil
  def get_env(varname) when is_binary(varname) do
    case :os.getenv(String.to_charlist(varname)) do
      false -> nil
      other -> List.to_string(other)
    end
  end

  @doc """
  Erlang VM process identifier.

  Returns the process identifier of the current Erlang emulator
  in the format most commonly used by the operating system environment.

  For more information, see `:os.getpid/0`.
  """
  @spec get_pid() :: binary
  def get_pid, do: IO.iodata_to_binary(:os.getpid())

  @doc """
  Sets an environment variable value.

  Sets a new `value` for the environment variable `varname`.
  """
  @spec put_env(binary, binary) :: :ok
  def put_env(varname, value) when is_binary(varname) and is_binary(value) do
    case :binary.match(varname, "=") do
      {_, _} ->
        raise ArgumentError,
              "cannot execute System.put_env/2 for key with \"=\", got: #{inspect(varname)}"

      :nomatch ->
        :os.putenv(String.to_charlist(varname), String.to_charlist(value))
        :ok
    end
  end

  @doc """
  Sets multiple environment variables.

  Sets a new value for each environment variable corresponding
  to each `{key, value}` pair in `enum`.
  """
  @spec put_env(Enumerable.t()) :: :ok
  def put_env(enum) do
    Enum.each(enum, fn {key, val} -> put_env(key, val) end)
  end

  @doc """
  Deletes an environment variable.

  Removes the variable `varname` from the environment.
  """
  @spec delete_env(String.t()) :: :ok
  def delete_env(varname) do
    :os.unsetenv(String.to_charlist(varname))
    :ok
  end

  @doc """
  Last exception stacktrace.

  Note that the Erlang VM (and therefore this function) does not
  return the current stacktrace but rather the stacktrace of the
  latest exception.

  Inlined by the compiler into `:erlang.get_stacktrace/0`.
  """
  def stacktrace do
    :erlang.get_stacktrace()
  end

  @doc """
  Immediately halts the Erlang runtime system.

  Terminates the Erlang runtime system without properly shutting down
  applications and ports. Please see `stop/1` for a careful shutdown of the
  system.

  `status` must be a non-negative integer, the atom `:abort` or a binary.

    * If an integer, the runtime system exits with the integer value which
      is returned to the operating system.

    * If `:abort`, the runtime system aborts producing a core dump, if that is
      enabled in the operating system.

    * If a string, an Erlang crash dump is produced with status as slogan,
      and then the runtime system exits with status code 1.

  Note that on many platforms, only the status codes 0-255 are supported
  by the operating system.

  For more information, see `:erlang.halt/1`.

  ## Examples

      System.halt(0)
      System.halt(1)
      System.halt(:abort)

  """
  @spec halt(non_neg_integer | binary | :abort) :: no_return
  def halt(status \\ 0)

  def halt(status) when is_integer(status) or status == :abort do
    :erlang.halt(status)
  end

  def halt(status) when is_binary(status) do
    :erlang.halt(String.to_charlist(status))
  end

  @doc """
  Carefully stops the Erlang runtime system.

  All applications are taken down smoothly, all code is unloaded, and all ports
  are closed before the system terminates by calling `halt/1`.

  `status` must be a non-negative integer value which is returned by the
  runtime system to the operating system.

  Note that on many platforms, only the status codes 0-255 are supported
  by the operating system.

  For more information, see `:init.stop/1`.

  ## Examples

      System.stop(0)
      System.stop(1)

  """
  @spec stop(non_neg_integer | binary) :: no_return
  def stop(status \\ 0)

  def stop(status) when is_integer(status) do
    :init.stop(status)
  end

  def stop(status) when is_binary(status) do
    :init.stop(String.to_charlist(status))
  end

  @doc ~S"""
  Executes the given `command` with `args`.

  `command` is expected to be an executable available in PATH
  unless an absolute path is given.

  `args` must be a list of binaries which the executable will receive
  as its arguments as is. This means that:

    * environment variables will not be interpolated
    * wildcard expansion will not happen (unless `Path.wildcard/2` is used
      explicitly)
    * arguments do not need to be escaped or quoted for shell safety

  This function returns a tuple containing the collected result
  and the command exit status.

  Internally, this function uses a `Port` for interacting with the
  outside world. However, if you plan to run a long-running program,
  ports guarantee stdin/stdout devices will be closed but it does not
  automatically terminate the program. The documentation for the
  `Port` module describes this problem and possible solutions under
  the "Zombie processes" section.

  ## Examples

      iex> System.cmd "echo", ["hello"]
      {"hello\n", 0}

      iex> System.cmd "echo", ["hello"], env: [{"MIX_ENV", "test"}]
      {"hello\n", 0}

      iex> System.cmd "echo", ["hello"], into: IO.stream(:stdio, :line)
      hello
      {%IO.Stream{}, 0}

  ## Options

    * `:into` - injects the result into the given collectable, defaults to `""`
    * `:cd` - the directory to run the command in
    * `:env` - an enumerable of tuples containing environment key-value as binary
    * `:arg0` - sets the command arg0
    * `:stderr_to_stdout` - redirects stderr to stdout when `true`
    * `:parallelism` - when `true`, the VM will schedule port tasks to improve
      parallelism in the system. If set to `false`, the VM will try to perform
      commands immediately, improving latency at the expense of parallelism.
      The default can be set on system startup by passing the "+spp" argument
      to `--erl`.

  ## Error reasons

  If invalid arguments are given, `ArgumentError` is raised by
  `System.cmd/3`. `System.cmd/3` also expects a strict set of
  options and will raise if unknown or invalid options are given.

  Furthermore, `System.cmd/3` may fail with one of the POSIX reasons
  detailed below:

    * `:system_limit` - all available ports in the Erlang emulator are in use

    * `:enomem` - there was not enough memory to create the port

    * `:eagain` - there are no more available operating system processes

    * `:enametoolong` - the external command given was too long

    * `:emfile` - there are no more available file descriptors
      (for the operating system process that the Erlang emulator runs in)

    * `:enfile` - the file table is full (for the entire operating system)

    * `:eacces` - the command does not point to an executable file

    * `:enoent` - the command does not point to an existing file

  ## Shell commands

  If you desire to execute a trusted command inside a shell, with pipes,
  redirecting and so on, please check `:os.cmd/1`.
  """
  @spec cmd(binary, [binary], keyword) :: {Collectable.t(), exit_status :: non_neg_integer}
  def cmd(command, args, opts \\ []) when is_binary(command) and is_list(args) do
    assert_no_null_byte!(command, "System.cmd/3")

    unless Enum.all?(args, &is_binary/1) do
      raise ArgumentError, "all arguments for System.cmd/3 must be binaries"
    end

    cmd = String.to_charlist(command)

    cmd =
      if Path.type(cmd) == :absolute do
        cmd
      else
        :os.find_executable(cmd) || :erlang.error(:enoent, [command, args, opts])
      end

    {into, opts} = cmd_opts(opts, [:use_stdio, :exit_status, :binary, :hide, args: args], "")
    {initial, fun} = Collectable.into(into)

    try do
      do_cmd(Port.open({:spawn_executable, cmd}, opts), initial, fun)
    catch
      kind, reason ->
        stacktrace = System.stacktrace()
        fun.(initial, :halt)
        :erlang.raise(kind, reason, stacktrace)
    else
      {acc, status} -> {fun.(acc, :done), status}
    end
  end

  defp do_cmd(port, acc, fun) do
    receive do
      {^port, {:data, data}} ->
        do_cmd(port, fun.(acc, {:cont, data}), fun)

      {^port, {:exit_status, status}} ->
        {acc, status}
    end
  end

  defp cmd_opts([{:into, any} | t], opts, _into), do: cmd_opts(t, opts, any)

  defp cmd_opts([{:cd, bin} | t], opts, into) when is_binary(bin),
    do: cmd_opts(t, [{:cd, bin} | opts], into)

  defp cmd_opts([{:arg0, bin} | t], opts, into) when is_binary(bin),
    do: cmd_opts(t, [{:arg0, bin} | opts], into)

  defp cmd_opts([{:stderr_to_stdout, true} | t], opts, into),
    do: cmd_opts(t, [:stderr_to_stdout | opts], into)

  defp cmd_opts([{:stderr_to_stdout, false} | t], opts, into), do: cmd_opts(t, opts, into)

  defp cmd_opts([{:parallelism, bool} | t], opts, into) when is_boolean(bool),
    do: cmd_opts(t, [{:parallelism, bool} | opts], into)

  defp cmd_opts([{:env, enum} | t], opts, into),
    do: cmd_opts(t, [{:env, validate_env(enum)} | opts], into)

  defp cmd_opts([{key, val} | _], _opts, _into),
    do: raise(ArgumentError, "invalid option #{inspect(key)} with value #{inspect(val)}")

  defp cmd_opts([], opts, into), do: {into, opts}

  defp validate_env(enum) do
    Enum.map(enum, fn
      {k, nil} ->
        {String.to_charlist(k), false}

      {k, v} ->
        {String.to_charlist(k), String.to_charlist(v)}

      other ->
        raise ArgumentError, "invalid environment key-value #{inspect(other)}"
    end)
  end

  @doc """
  Returns the current monotonic time in the `:native` time unit.

  This time is monotonically increasing and starts in an unspecified
  point in time.

  Inlined by the compiler into `:erlang.monotonic_time/0`.
  """
  @spec monotonic_time() :: integer
  def monotonic_time do
    :erlang.monotonic_time()
  end

  @doc """
  Returns the current monotonic time in the given time unit.

  This time is monotonically increasing and starts in an unspecified
  point in time.
  """
  @spec monotonic_time(time_unit) :: integer
  def monotonic_time(unit) do
    :erlang.monotonic_time(normalize_time_unit(unit))
  end

  @doc """
  Returns the current system time in the `:native` time unit.

  It is the VM view of the `os_time/0`. They may not match in
  case of time warps although the VM works towards aligning
  them. This time is not monotonic.

  Inlined by the compiler into `:erlang.system_time/0`.
  """
  @spec system_time() :: integer
  def system_time do
    :erlang.system_time()
  end

  @doc """
  Returns the current system time in the given time unit.

  It is the VM view of the `os_time/0`. They may not match in
  case of time warps although the VM works towards aligning
  them. This time is not monotonic.
  """
  @spec system_time(time_unit) :: integer
  def system_time(unit) do
    :erlang.system_time(normalize_time_unit(unit))
  end

  @doc """
  Converts `time` from time unit `from_unit` to time unit `to_unit`.

  The result is rounded via the floor function.

  `convert_time_unit/3` accepts an additional time unit (other than the
  ones in the `t:time_unit/0` type) called `:native`. `:native` is the time
  unit used by the Erlang runtime system. It's determined when the runtime
  starts and stays the same until the runtime is stopped. To determine what
  the `:native` unit amounts to in a system, you can call this function to
  convert 1 second to the `:native` time unit (i.e.,
  `System.convert_time_unit(1, :second, :native)`).
  """
  @spec convert_time_unit(integer, time_unit | :native, time_unit | :native) :: integer
  def convert_time_unit(time, from_unit, to_unit) do
    :erlang.convert_time_unit(time, normalize_time_unit(from_unit), normalize_time_unit(to_unit))
  end

  @doc """
  Returns the current time offset between the Erlang VM monotonic
  time and the Erlang VM system time.

  The result is returned in the `:native` time unit.

  See `time_offset/1` for more information.

  Inlined by the compiler into `:erlang.time_offset/0`.
  """
  @spec time_offset() :: integer
  def time_offset do
    :erlang.time_offset()
  end

  @doc """
  Returns the current time offset between the Erlang VM monotonic
  time and the Erlang VM system time.

  The result is returned in the given time unit `unit`. The returned
  offset, added to an Erlang monotonic time (e.g., obtained with
  `monotonic_time/1`), gives the Erlang system time that corresponds
  to that monotonic time.
  """
  @spec time_offset(time_unit) :: integer
  def time_offset(unit) do
    :erlang.time_offset(normalize_time_unit(unit))
  end

  @doc """
  Returns the current OS time.

  The result is returned in the `:native` time unit.

  This time may be adjusted forwards or backwards in time
  with no limitation and is not monotonic.

  Inlined by the compiler into `:os.system_time/0`.
  """
  @spec os_time() :: integer
  def os_time do
    :os.system_time()
  end

  @doc """
  Returns the current OS time in the given time `unit`.

  This time may be adjusted forwards or backwards in time
  with no limitation and is not monotonic.
  """
  @spec os_time(time_unit) :: integer
  def os_time(unit) do
    :os.system_time(normalize_time_unit(unit))
  end

  @doc """
  Returns the OTP release number.
  """
  @spec otp_release :: String.t()
  def otp_release do
    :erlang.list_to_binary(:erlang.system_info(:otp_release))
  end

  @doc """
  Returns the number of schedulers in the VM.
  """
  @spec schedulers :: pos_integer
  def schedulers do
    :erlang.system_info(:schedulers)
  end

  @doc """
  Returns the number of schedulers online in the VM.
  """
  @spec schedulers_online :: pos_integer
  def schedulers_online do
    :erlang.system_info(:schedulers_online)
  end

  @doc """
  Generates and returns an integer that is unique in the current runtime
  instance.

  "Unique" means that this function, called with the same list of `modifiers`,
  will never return the same integer more than once on the current runtime
  instance.

  If `modifiers` is `[]`, then a unique integer (that can be positive or negative) is returned.
  Other modifiers can be passed to change the properties of the returned integer:

    * `:positive` - the returned integer is guaranteed to be positive.
    * `:monotonic` - the returned integer is monotonically increasing. This
      means that, on the same runtime instance (but even on different
      processes), integers returned using the `:monotonic` modifier will always
      be strictly less than integers returned by successive calls with the
      `:monotonic` modifier.

  All modifiers listed above can be combined; repeated modifiers in `modifiers`
  will be ignored.

  Inlined by the compiler into `:erlang.unique_integer/1`.
  """
  @spec unique_integer([:positive | :monotonic]) :: integer
  def unique_integer(modifiers \\ []) do
    :erlang.unique_integer(modifiers)
  end

  defp assert_no_null_byte!(binary, operation) do
    case :binary.match(binary, "\0") do
      {_, _} ->
        raise ArgumentError,
              "cannot execute #{operation} for program with null byte, got: #{inspect(binary)}"

      :nomatch ->
        binary
    end
  end

  defp normalize_time_unit(:native), do: :native

  defp normalize_time_unit(:second), do: :seconds
  defp normalize_time_unit(:millisecond), do: :milli_seconds
  defp normalize_time_unit(:microsecond), do: :micro_seconds
  defp normalize_time_unit(:nanosecond), do: :nano_seconds

  defp normalize_time_unit(:seconds), do: :seconds
  defp normalize_time_unit(:milliseconds), do: :milli_seconds
  defp normalize_time_unit(:microseconds), do: :micro_seconds
  defp normalize_time_unit(:nanoseconds), do: :nano_seconds

  defp normalize_time_unit(unit) when is_integer(unit) and unit > 0, do: unit

  defp normalize_time_unit(erlang_unit)
       when erlang_unit in [:milli_seconds, :micro_seconds, :nano_seconds] do
    erlang_unit
  end

  defp normalize_time_unit(other) do
    raise ArgumentError,
          "unsupported time unit. Expected :second, :millisecond, " <>
            ":microsecond, :nanosecond, or a positive integer, " <> "got #{inspect(other)}"
  end
end

defmodule System do
  @moduledoc """
  The `System` module provides functions that interact directly
  with the VM or the host system.

  ## Time

  The `System` module also provides functions that work with time,
  returning different times kept by the system with support for
  different time units.

  One of the complexities in relying on system times is that they
  may be adjusted. For example, when you enter and leave daylight
  saving time, the system clock will be adjusted, often adding
  or removing one hour. We call such changes "time warps". In
  order to understand how such changes may be harmful, imagine
  the following code:

      ## DO NOT DO THIS
      prev = System.os_time()
      # ... execute some code ...
      next = System.os_time()
      diff = next - prev

  If, while the code is executing, the system clock changes,
  some code that executed in 1 second may be reported as taking
  over 1 hour! To address such concerns, the VM provides a
  monotonic time via `System.monotonic_time/0` which never
  decreases and does not leap:

      ## DO THIS
      prev = System.monotonic_time()
      # ... execute some code ...
      next = System.monotonic_time()
      diff = next - prev

  Generally speaking, the VM provides three time measurements:

    * `os_time/0` - the time reported by the OS. This time may be
      adjusted forwards or backwards in time with no limitation;

    * `system_time/0` - the VM view of the `os_time/0`. The system time and OS
      time may not match in case of time warps although the VM works towards
      aligning them. This time is not monotonic (i.e., it may decrease)
      as its behaviour is configured [by the VM time warp
      mode](http://www.erlang.org/doc/apps/erts/time_correction.html#Time_Warp_Modes);

    * `monotonic_time/0` - a monotonically increasing time provided
      by the Erlang VM.

  The time functions in this module work in the `:native` unit
  (unless specified otherwise), which is OS dependent. Most of
  the time, all calculations are done in the `:native` unit, to
  avoid loss of precision, with `convert_time_unit/3` being
  invoked at the end to convert to a specific time unit like
  `:millisecond` or `:microsecond`. See the `t:time_unit/0` type for
  more information.

  For a more complete rundown on the VM support for different
  times, see the [chapter on time and time
  correction](http://www.erlang.org/doc/apps/erts/time_correction.html)
  in the Erlang docs.
  """

  @typedoc """
  The time unit to be passed to functions like `monotonic_time/1` and others.

  The `:second`, `:millisecond`, `:microsecond` and `:nanosecond` time
  units controls the return value of the functions that accept a time unit.

  A time unit can also be a strictly positive integer. In this case, it
  represents the "parts per second": the time will be returned in `1 /
  parts_per_second` seconds. For example, using the `:millisecond` time unit
  is equivalent to using `1000` as the time unit (as the time will be returned
  in 1/1000 seconds - milliseconds).

  Keep in mind the Erlang API prior to version 19.1 will use `:milli_seconds`,
  `:micro_seconds` and `:nano_seconds` as time units although Elixir normalizes
  their spelling to match the SI convention.
  """
  # TODO: Warn all old mappings once Elixir requires Erlang/OTP 19.1+
  @type time_unit ::
          :second
          | :millisecond
          | :microsecond
          | :nanosecond
          | pos_integer
          | :seconds
          | :milliseconds
          | :microseconds
          | :nanoseconds

  @base_dir :filename.join(__DIR__, "../../..")
  @version_file :filename.join(@base_dir, "VERSION")

  defp strip(iodata) do
    :re.replace(iodata, "^[\s\r\n\t]+|[\s\r\n\t]+$", "", [:global, return: :binary])
  end

  defp read_stripped(path) do
    case :file.read_file(path) do
      {:ok, binary} ->
        strip(binary)

      _ ->
        ""
    end
  end

  # Read and strip the version from the VERSION file.
  defmacrop get_version do
    case read_stripped(@version_file) do
      "" -> raise RuntimeError, message: "could not read the version number from VERSION"
      data -> data
    end
  end

  # Returns OTP version that Elixir was compiled with.
  defmacrop get_otp_release do
    :erlang.list_to_binary(:erlang.system_info(:otp_release))
  end

  # Tries to run "git rev-parse --short HEAD". In the case of success returns
  # the short revision hash. If that fails, returns an empty string.
  defmacrop get_revision do
    null =
      case :os.type() do
        {:win32, _} -> 'NUL'
        _ -> '/dev/null'
      end

    'git rev-parse --short HEAD 2> '
    |> Kernel.++(null)
    |> :os.cmd()
    |> strip
  end

  defp revision, do: get_revision()

  # Get the date at compilation time.
  defmacrop get_date do
    IO.iodata_to_binary(:httpd_util.rfc1123_date())
  end

  @doc """
  Returns the endianness.
  """
  def endianness do
    :erlang.system_info(:endian)
  end

  @doc """
  Returns the endianness the system was compiled with.
  """
  @endianness :erlang.system_info(:endian)
  def compiled_endianness do
    @endianness
  end

  @doc """
  Elixir version information.

  Returns Elixir's version as binary.
  """
  @spec version() :: String.t()
  def version, do: get_version()

  @doc """
  Elixir build information.

  Returns a keyword list with Elixir version, Git short revision hash and compilation date.
  """
  @spec build_info() :: map
  def build_info do
    %{
      build: build(),
      date: get_date(),
      revision: revision(),
      version: version(),
      otp_release: get_otp_release()
    }
  end

  # Returns a string of the build info
  defp build do
    {:ok, v} = Version.parse(version())

    revision_string = if v.pre != [] and revision() != "", do: " (#{revision()})", else: ""
    otp_version_string = " (compiled with OTP #{get_otp_release()})"

    version() <> revision_string <> otp_version_string
  end

  @doc """
  Lists command line arguments.

  Returns the list of command line arguments passed to the program.
  """
  @spec argv() :: [String.t()]
  def argv do
    :elixir_config.get(:argv)
  end

  @doc """
  Modifies command line arguments.

  Changes the list of command line arguments. Use it with caution,
  as it destroys any previous argv information.
  """
  @spec argv([String.t()]) :: :ok
  def argv(args) do
    :elixir_config.put(:argv, args)
  end

  @doc """
  Current working directory.

  Returns the current working directory or `nil` if one
  is not available.
  """
  def cwd do
    case :file.get_cwd() do
      {:ok, base} -> IO.chardata_to_string(fix_drive_letter(base))
      _ -> nil
    end
  end

  defp fix_drive_letter([l, ?:, ?/ | rest] = original) when l in ?A..?Z do
    case :os.type() do
      {:win32, _} -> [l + ?a - ?A, ?:, ?/ | rest]
      _ -> original
    end
  end

  defp fix_drive_letter(original), do: original

  @doc """
  Current working directory, exception on error.

  Returns the current working directory or raises `RuntimeError`.
  """
  def cwd! do
    cwd() ||
      raise RuntimeError,
        message: "could not get a current working directory, the current location is not accessible"
  end

  @doc """
  User home directory.

  Returns the user home directory (platform independent).
  """
  def user_home do
    :elixir_config.get(:home)
  end

  @doc """
  User home directory, exception on error.

  Same as `user_home/0` but raises `RuntimeError`
  instead of returning `nil` if no user home is set.
  """
  def user_home! do
    user_home() ||
      raise RuntimeError,
        message: "could not find the user home, please set the HOME environment variable"
  end

  @doc ~S"""
  Writable temporary directory.

  Returns a writable temporary directory.
  Searches for directories in the following order:

    1. the directory named by the TMPDIR environment variable
    2. the directory named by the TEMP environment variable
    3. the directory named by the TMP environment variable
    4. `C:\TMP` on Windows or `/tmp` on Unix
    5. as a last resort, the current working directory

  Returns `nil` if none of the above are writable.
  """
  def tmp_dir do
    write_env_tmp_dir('TMPDIR') || write_env_tmp_dir('TEMP') || write_env_tmp_dir('TMP') ||
      write_tmp_dir('/tmp') || ((cwd = cwd()) && write_tmp_dir(cwd))
  end

  @doc """
  Writable temporary directory, exception on error.

  Same as `tmp_dir/0` but raises `RuntimeError`
  instead of returning `nil` if no temp dir is set.
  """
  def tmp_dir! do
    tmp_dir() ||
      raise RuntimeError,
        message: "could not get a writable temporary directory, " <>
          "please set the TMPDIR environment variable"
  end

  defp write_env_tmp_dir(env) do
    case :os.getenv(env) do
      false -> nil
      tmp -> write_tmp_dir(tmp)
    end
  end

  defp write_tmp_dir(dir) do
    case File.stat(dir) do
      {:ok, stat} ->
        case {stat.type, stat.access} do
          {:directory, access} when access in [:read_write, :write] ->
            IO.chardata_to_string(dir)

          _ ->
            nil
        end

      {:error, _} ->
        nil
    end
  end

  @doc """
  Registers a program exit handler function.

  Registers a function that will be invoked at the end of program execution.
  Useful for invoking a hook in "script" mode.

  The handler always executes in a different process from the one it was
  registered in. As a consequence, any resources managed by the calling process
  (ETS tables, open files, etc.) won't be available by the time the handler
  function is invoked.

  The function must receive the exit status code as an argument.
  """
  def at_exit(fun) when is_function(fun, 1) do
    :elixir_config.update(:at_exit, &[fun | &1])
  end

  @doc """
  Locates an executable on the system.

  This function looks up an executable program given
  its name using the environment variable PATH on Unix
  and Windows. It also considers the proper executable
  extension for each OS, so for Windows it will try to
  lookup files with `.com`, `.cmd` or similar extensions.
  """
  @spec find_executable(binary) :: binary | nil
  def find_executable(program) when is_binary(program) do
    assert_no_null_byte!(program, "System.find_executable/1")

    case :os.find_executable(String.to_charlist(program)) do
      false -> nil
      other -> List.to_string(other)
    end
  end

  @doc """
  Returns all system environment variables.

  The returned value is a map containing name-value pairs.
  Variable names and their values are strings.
  """
  @spec get_env() :: %{optional(String.t()) => String.t()}
  def get_env do
    Enum.into(:os.getenv(), %{}, fn var ->
      var = IO.chardata_to_string(var)
      [k, v] = String.split(var, "=", parts: 2)
      {k, v}
    end)
  end

  @doc """
  Returns the value of the given environment variable.

  The returned value of the environment variable
  `varname` is a string, or `nil` if the environment
  variable is undefined.
  """
  @spec get_env(String.t()) :: String.t() | nil
  def get_env(varname) when is_binary(varname) do
    case :os.getenv(String.to_charlist(varname)) do
      false -> nil
      other -> List.to_string(other)
    end
  end

  @doc """
  Erlang VM process identifier.

  Returns the process identifier of the current Erlang emulator
  in the format most commonly used by the operating system environment.

  For more information, see `:os.getpid/0`.
  """
  @spec get_pid() :: binary
  def get_pid, do: IO.iodata_to_binary(:os.getpid())

  @doc """
  Sets an environment variable value.

  Sets a new `value` for the environment variable `varname`.
  """
  @spec put_env(binary, binary) :: :ok
  def put_env(varname, value) when is_binary(varname) and is_binary(value) do
    case :binary.match(varname, "=") do
      {_, _} ->
        raise ArgumentError,
              "cannot execute System.put_env/2 for key with \"=\", got: #{inspect(varname)}"

      :nomatch ->
        :os.putenv(String.to_charlist(varname), String.to_charlist(value))
        :ok
    end
  end

  @doc """
  Sets multiple environment variables.

  Sets a new value for each environment variable corresponding
  to each key in `dict`.
  """
  @spec put_env(Enumerable.t()) :: :ok
  def put_env(enum) do
    Enum.each(enum, fn {key, val} -> put_env(key, val) end)
  end

  @doc """
  Deletes an environment variable.

  Removes the variable `varname` from the environment.
  """
  @spec delete_env(String.t()) :: :ok
  def delete_env(varname) do
    :os.unsetenv(String.to_charlist(varname))
    :ok
  end

  @doc """
  Last exception stacktrace.

  Note that the Erlang VM (and therefore this function) does not
  return the current stacktrace but rather the stacktrace of the
  latest exception.

  Inlined by the compiler into `:erlang.get_stacktrace/0`.
  """
  def stacktrace do
    :erlang.get_stacktrace()
  end

  @doc """
  Immediately halts the Erlang runtime system.

  Terminates the Erlang runtime system without properly shutting down
  applications and ports. Please see `stop/1` for a careful shutdown of the
  system.

  `status` must be a non-negative integer, the atom `:abort` or a binary.

    * If an integer, the runtime system exits with the integer value which
      is returned to the operating system.

    * If `:abort`, the runtime system aborts producing a core dump, if that is
      enabled in the operating system.

    * If a string, an Erlang crash dump is produced with status as slogan,
      and then the runtime system exits with status code 1.

  Note that on many platforms, only the status codes 0-255 are supported
  by the operating system.

  For more information, see `:erlang.halt/1`.

  ## Examples

      System.halt(0)
      System.halt(1)
      System.halt(:abort)

  """
  @spec halt(non_neg_integer | binary | :abort) :: no_return
  def halt(status \\ 0)

  def halt(status) when is_integer(status) or status == :abort do
    :erlang.halt(status)
  end

  def halt(status) when is_binary(status) do
    :erlang.halt(String.to_charlist(status))
  end

  @doc """
  Carefully stops the Erlang runtime system.

  All applications are taken down smoothly, all code is unloaded, and all ports
  are closed before the system terminates by calling `halt/1`.

  `status` must be a non-negative integer value which is returned by the
  runtime system to the operating system.

  Note that on many platforms, only the status codes 0-255 are supported
  by the operating system.

  For more information, see `:init.stop/1`.

  ## Examples

      System.stop(0)
      System.stop(1)

  """
  @spec stop(non_neg_integer | binary) :: no_return
  def stop(status \\ 0)

  def stop(status) when is_integer(status) do
    :init.stop(status)
  end

  def stop(status) when is_binary(status) do
    :init.stop(String.to_charlist(status))
  end

  @doc ~S"""
  Executes the given `command` with `args`.

  `command` is expected to be an executable available in PATH
  unless an absolute path is given.

  `args` must be a list of binaries which the executable will receive
  as its arguments as is. This means that:

    * environment variables will not be interpolated
    * wildcard expansion will not happen (unless `Path.wildcard/2` is used
      explicitly)
    * arguments do not need to be escaped or quoted for shell safety

  This function returns a tuple containing the collected result
  and the command exit status.

  Internally, this function uses a `Port` for interacting with the
  outside world. However, if you plan to run a long-running program,
  ports guarantee stdin/stdout devices will be closed but it does not
  automatically terminate the program. The documentation for the
  `Port` module describes this problem and possible solutions under
  the "Zombie processes" section.

  ## Examples

      iex> System.cmd "echo", ["hello"]
      {"hello\n", 0}

      iex> System.cmd "echo", ["hello"], env: [{"MIX_ENV", "test"}]
      {"hello\n", 0}

      iex> System.cmd "echo", ["hello"], into: IO.stream(:stdio, :line)
      hello
      {%IO.Stream{}, 0}

  ## Options

    * `:into` - injects the result into the given collectable, defaults to `""`
    * `:cd` - the directory to run the command in
    * `:env` - an enumerable of tuples containing environment key-value as binary
    * `:arg0` - sets the command arg0
    * `:stderr_to_stdout` - redirects stderr to stdout when `true`
    * `:parallelism` - when `true`, the VM will schedule port tasks to improve
      parallelism in the system. If set to `false`, the VM will try to perform
      commands immediately, improving latency at the expense of parallelism.
      The default can be set on system startup by passing the "+spp" argument
      to `--erl`.

  ## Error reasons

  If invalid arguments are given, `ArgumentError` is raised by
  `System.cmd/3`. `System.cmd/3` also expects a strict set of
  options and will raise if unknown or invalid options are given.

  Furthermore, `System.cmd/3` may fail with one of the POSIX reasons
  detailed below:

    * `:system_limit` - all available ports in the Erlang emulator are in use

    * `:enomem` - there was not enough memory to create the port

    * `:eagain` - there are no more available operating system processes

    * `:enametoolong` - the external command given was too long

    * `:emfile` - there are no more available file descriptors
      (for the operating system process that the Erlang emulator runs in)

    * `:enfile` - the file table is full (for the entire operating system)

    * `:eacces` - the command does not point to an executable file

    * `:enoent` - the command does not point to an existing file

  ## Shell commands

  If you desire to execute a trusted command inside a shell, with pipes,
  redirecting and so on, please check `:os.cmd/1`.
  """
  @spec cmd(binary, [binary], keyword) :: {Collectable.t(), exit_status :: non_neg_integer}
  def cmd(command, args, opts \\ []) when is_binary(command) and is_list(args) do
    assert_no_null_byte!(command, "System.cmd/3")

    unless Enum.all?(args, &is_binary/1) do
      raise ArgumentError, "all arguments for System.cmd/3 must be binaries"
    end

    cmd = String.to_charlist(command)

    cmd =
      if Path.type(cmd) == :absolute do
        cmd
      else
        :os.find_executable(cmd) || :erlang.error(:enoent, [command, args, opts])
      end

    {into, opts} = cmd_opts(opts, [:use_stdio, :exit_status, :binary, :hide, args: args], "")
    {initial, fun} = Collectable.into(into)

    try do
      do_cmd(Port.open({:spawn_executable, cmd}, opts), initial, fun)
    catch
      kind, reason ->
        stacktrace = System.stacktrace()
        fun.(initial, :halt)
        :erlang.raise(kind, reason, stacktrace)
    else
      {acc, status} -> {fun.(acc, :done), status}
    end
  end

  defp do_cmd(port, acc, fun) do
    receive do
      {^port, {:data, data}} ->
        do_cmd(port, fun.(acc, {:cont, data}), fun)

      {^port, {:exit_status, status}} ->
        {acc, status}
    end
  end

  defp cmd_opts([{:into, any} | t], opts, _into), do: cmd_opts(t, opts, any)

  defp cmd_opts([{:cd, bin} | t], opts, into) when is_binary(bin),
    do: cmd_opts(t, [{:cd, bin} | opts], into)

  defp cmd_opts([{:arg0, bin} | t], opts, into) when is_binary(bin),
    do: cmd_opts(t, [{:arg0, bin} | opts], into)

  defp cmd_opts([{:stderr_to_stdout, true} | t], opts, into),
    do: cmd_opts(t, [:stderr_to_stdout | opts], into)

  defp cmd_opts([{:stderr_to_stdout, false} | t], opts, into), do: cmd_opts(t, opts, into)

  defp cmd_opts([{:parallelism, bool} | t], opts, into) when is_boolean(bool),
    do: cmd_opts(t, [{:parallelism, bool} | opts], into)

  defp cmd_opts([{:env, enum} | t], opts, into),
    do: cmd_opts(t, [{:env, validate_env(enum)} | opts], into)

  defp cmd_opts([{key, val} | _], _opts, _into),
    do: raise(ArgumentError, "invalid option #{inspect(key)} with value #{inspect(val)}")

  defp cmd_opts([], opts, into), do: {into, opts}

  defp validate_env(enum) do
    Enum.map(enum, fn
      {k, nil} ->
        {String.to_charlist(k), false}

      {k, v} ->
        {String.to_charlist(k), String.to_charlist(v)}

      other ->
        raise ArgumentError, "invalid environment key-value #{inspect(other)}"
    end)
  end

  @doc """
  Returns the current monotonic time in the `:native` time unit.

  This time is monotonically increasing and starts in an unspecified
  point in time.

  Inlined by the compiler into `:erlang.monotonic_time/0`.
  """
  @spec monotonic_time() :: integer
  def monotonic_time do
    :erlang.monotonic_time()
  end

  @doc """
  Returns the current monotonic time in the given time unit.

  This time is monotonically increasing and starts in an unspecified
  point in time.
  """
  @spec monotonic_time(time_unit) :: integer
  def monotonic_time(unit) do
    :erlang.monotonic_time(normalize_time_unit(unit))
  end

  @doc """
  Returns the current system time in the `:native` time unit.

  It is the VM view of the `os_time/0`. They may not match in
  case of time warps although the VM works towards aligning
  them. This time is not monotonic.

  Inlined by the compiler into `:erlang.system_time/0`.
  """
  @spec system_time() :: integer
  def system_time do
    :erlang.system_time()
  end

  @doc """
  Returns the current system time in the given time unit.

  It is the VM view of the `os_time/0`. They may not match in
  case of time warps although the VM works towards aligning
  them. This time is not monotonic.
  """
  @spec system_time(time_unit) :: integer
  def system_time(unit) do
    :erlang.system_time(normalize_time_unit(unit))
  end

  @doc """
  Converts `time` from time unit `from_unit` to time unit `to_unit`.

  The result is rounded via the floor function.

  `convert_time_unit/3` accepts an additional time unit (other than the
  ones in the `t:time_unit/0` type) called `:native`. `:native` is the time
  unit used by the Erlang runtime system. It's determined when the runtime
  starts and stays the same until the runtime is stopped. To determine what
  the `:native` unit amounts to in a system, you can call this function to
  convert 1 second to the `:native` time unit (i.e.,
  `System.convert_time_unit(1, :second, :native)`).
  """
  @spec convert_time_unit(integer, time_unit | :native, time_unit | :native) :: integer
  def convert_time_unit(time, from_unit, to_unit) do
    :erlang.convert_time_unit(time, normalize_time_unit(from_unit), normalize_time_unit(to_unit))
  end

  @doc """
  Returns the current time offset between the Erlang VM monotonic
  time and the Erlang VM system time.

  The result is returned in the `:native` time unit.

  See `time_offset/1` for more information.

  Inlined by the compiler into `:erlang.time_offset/0`.
  """
  @spec time_offset() :: integer
  def time_offset do
    :erlang.time_offset()
  end

  @doc """
  Returns the current time offset between the Erlang VM monotonic
  time and the Erlang VM system time.

  The result is returned in the given time unit `unit`. The returned
  offset, added to an Erlang monotonic time (e.g., obtained with
  `monotonic_time/1`), gives the Erlang system time that corresponds
  to that monotonic time.
  """
  @spec time_offset(time_unit) :: integer
  def time_offset(unit) do
    :erlang.time_offset(normalize_time_unit(unit))
  end

  @doc """
  Returns the current OS time.

  The result is returned in the `:native` time unit.

  This time may be adjusted forwards or backwards in time
  with no limitation and is not monotonic.

  Inlined by the compiler into `:os.system_time/0`.
  """
  @spec os_time() :: integer
  def os_time do
    :os.system_time()
  end

  @doc """
  Returns the current OS time in the given time `unit`.

  This time may be adjusted forwards or backwards in time
  with no limitation and is not monotonic.
  """
  @spec os_time(time_unit) :: integer
  def os_time(unit) do
    :os.system_time(normalize_time_unit(unit))
  end

  @doc """
  Returns the OTP release number.
  """
  @spec otp_release :: String.t()
  def otp_release do
    :erlang.list_to_binary(:erlang.system_info(:otp_release))
  end

  @doc """
  Returns the number of schedulers in the VM.
  """
  @spec schedulers :: pos_integer
  def schedulers do
    :erlang.system_info(:schedulers)
  end

  @doc """
  Returns the number of schedulers online in the VM.
  """
  @spec schedulers_online :: pos_integer
  def schedulers_online do
    :erlang.system_info(:schedulers_online)
  end

  @doc """
  Generates and returns an integer that is unique in the current runtime
  instance.

  "Unique" means that this function, called with the same list of `modifiers`,
  will never return the same integer more than once on the current runtime
  instance.

  If `modifiers` is `[]`, then a unique integer (that can be positive or negative) is returned.
  Other modifiers can be passed to change the properties of the returned integer:

    * `:positive` - the returned integer is guaranteed to be positive.
    * `:monotonic` - the returned integer is monotonically increasing. This
      means that, on the same runtime instance (but even on different
      processes), integers returned using the `:monotonic` modifier will always
      be strictly less than integers returned by successive calls with the
      `:monotonic` modifier.

  All modifiers listed above can be combined; repeated modifiers in `modifiers`
  will be ignored.

  Inlined by the compiler into `:erlang.unique_integer/1`.
  """
  @spec unique_integer([:positive | :monotonic]) :: integer
  def unique_integer(modifiers \\ []) do
    :erlang.unique_integer(modifiers)
  end

  defp assert_no_null_byte!(binary, operation) do
    case :binary.match(binary, "\0") do
      {_, _} ->
        raise ArgumentError,
              "cannot execute #{operation} for program with null byte, got: #{inspect(binary)}"

      :nomatch ->
        binary
    end
  end

  defp normalize_time_unit(:native), do: :native

  defp normalize_time_unit(:second), do: :seconds
  defp normalize_time_unit(:millisecond), do: :milli_seconds
  defp normalize_time_unit(:microsecond), do: :micro_seconds
  defp normalize_time_unit(:nanosecond), do: :nano_seconds

  defp normalize_time_unit(:seconds), do: :seconds
  defp normalize_time_unit(:milliseconds), do: :milli_seconds
  defp normalize_time_unit(:microseconds), do: :micro_seconds
  defp normalize_time_unit(:nanoseconds), do: :nano_seconds

  defp normalize_time_unit(unit) when is_integer(unit) and unit > 0, do: unit

  defp normalize_time_unit(erlang_unit)
       when erlang_unit in [:milli_seconds, :micro_seconds, :nano_seconds] do
    erlang_unit
  end

  defp normalize_time_unit(other) do
    raise ArgumentError,
          "unsupported time unit. Expected :second, :millisecond, " <>
            ":microsecond, :nanosecond, or a positive integer, " <> "got #{inspect(other)}"
  end
end


Typo: Phhoenix

Typo: Phhoenix

defmodule Phoenix.HTML.Form do
  @moduledoc ~S"""
  Helpers related to producing HTML forms.

  The functions in this module can be used in three
  distinct scenario:

    * with model data - when information to populate
      the form comes from a model

    * with connection data - when a form is created based
      on the information in the connection (aka `Plug.Conn`)

    * without form data - when the functions are used directly,
      outside of a form

  We will explore all three scenarios below.

  ## With model data

  The entry point for defining forms in Phoenix is with
  the `form_for/4` function. For this example, we will
  use `Ecto.Changeset`, which integrate nicely with Phoenix
  forms via the `phoenix_ecto` package.

  Imagine you have the following action in your controller:

      def new(conn, _params) do
        changeset = User.changeset(%User{})
        render conn, "new.html", changeset: changeset
      end

  where `User.changeset/2` is defined as follows:

      def changeset(user, params \\ nil) do
        cast(user, params)
      end

  Now a `@changeset` assign is available in views which we
  can pass to the form:

      <%= form_for @changeset, user_path(@conn, :create), fn f -> %>
        <label>
          Name: <%= text_input f, :name %>
        </label>

        <label>
          Age: <%= select f, :age, 18..100 %>
        </label>

        <%= submit "Submit" %>
      <% end %>

  `form_for/4` receives the `Ecto.Changeset` and converts it
  to a form, which is passed to the function as the argument
  `f`. All the remaining functions in this module receive
  the form and automatically generate the input fields, often
  by extracting information from the given changeset. For example,
  if the user had a default value for age set, it will
  automatically show up as selected in the form.

  ## With connection data

  `form_for/4` expects as first argument any data structure that
  implements the `Phoenix.HTML.FormData` protocol. By default,
  Phoenix implements this protocol for `Plug.Conn`, allowing us
  to create forms based only on connection information.

  This is useful when you are creating forms that are not backed
  by any kind of model data, like a search form.

      <%= form_for @conn, search_path(@conn, :new), [name: :search], fn f -> %>
        <%= text_input f, :for %>
        <%= submit "Search" %>
      <% end %>

  ## Without form data

  Sometimes we may want to generate a `text_input/3` or any other
  tag outside of a form. The functions in this module also support
  such usage by simply passing an atom as first argument instead
  of the form.

      <%= text_input :user, :name, value: "This is a prepopulated value" %>

  """

  alias Phoenix.HTML.Form
  import Phoenix.HTML
  import Phoenix.HTML.Tag

  @doc """
  Defines the Phoenix.HTML.Form struct.

  Its fields are:

    * `:source` - the data structure given to `form_for/4` that
      implements the form data protocol

    * `:name` - the name to be used when generating input fields

    * `:model` - the model used to lookup field data

    * `:params` - the parameters associated to this form in case
      they were sent as part of a previous request

    * `:hidden` - a keyword list of fields that are required for
      submitting the form behind the scenes as hidden inputs

    * `:options` - a copy of the options given when creating the
      form via `form_for/4` without any form data specific key

    * `:errors` - a keyword list of errors that associated with
      the form

    * `:validations` - a keyword list of validations for the given
      inputs
  """
  defstruct source: nil, name: nil, model: %{}, hidden: [], params: %{},
            errors: [], validations: [], options: []

  @type t :: %Form{source: term, name: String.t, model: %{atom => term},
                   params: %{binary => term}, hidden: Keyword.t, options: Keyword.t,
                   errors: Keyword.t, validations: Keyword.t}

  @doc """
  Generates a form tag with a form builder.

  See the module documentation for examples of using this function.

  ## Options

    * `:name` - the name to be used in the form. May be inflected
      if a model is available

    * `:method` - the HTTP method. If the method is not "get" nor "post",
      an input tag with name `_method` is generated along-side the form tag.
      Defaults to "post".

    * `:multipart` - when true, sets enctype to "multipart/form-data".
      Required when uploading files

    * `:csrf_token` - for "post" requests, the form tag will automatically
      include an input tag with name `_csrf_token`. When set to false, this
      is disabled

    * `:enforce_utf8` - when false, does not enforce utf8

  See `Phoenix.HTML.Tag.form_tag/2` for more information on the
  options above.
  """
  @spec form_for(Phoenix.HTML.FormData.t, String.t,
                 Keyword.t, (t -> Phoenix.HTML.unsafe)) :: Phoenix.HTML.safe
  def form_for(form_data, action, options \\ [], fun) when is_function(fun, 1) do
    form = Phoenix.HTML.FormData.to_form(form_data, options)
    safe_concat [form_tag(action, form.options), fun.(form), safe("</form>")]
  end

  ## Form helpers

  @doc """
  Generates a text input.

  The form should either be a `Phoenix.HTML.Form` emitted
  by `form_for` or an atom.

  All given options are forwarded to the underlying input,
  default values are provided for id, name and value if
  possible.

  ## Examples

      # Assuming form contains a User model
      text_input(form, :name)
      #=> <input id="user_name" name="user[name]" type="text" value="">

      text_input(:user, :name)
      #=> <input id="user_name" name="user[name]" type="text" value="">

  """
  def text_input(form, field, opts \\ []) do
    generic_input(:text, form, field, opts)
  end

  @doc """
  Generates a hidden input.

  See `text_input/3` for example and docs.
  """
  def hidden_input(form, field, opts \\ []) do
    generic_input(:hidden, form, field, opts)
  end

  @doc """
  Generates an email input.

  See `text_input/3` for example and docs.
  """
  def email_input(form, field, opts \\ []) do
    generic_input(:email, form, field, opts)
  end

  @doc """
  Generates a number input.

  See `text_input/3` for example and docs.
  """
  def number_input(form, field, opts \\ []) do
    generic_input(:number, form, field, opts)
  end

  defp generic_input(type, form, field, opts) when is_atom(field) and is_list(opts) do
    opts =
      opts
      |> Keyword.put_new(:type, type)
      |> Keyword.put_new(:id, id_from(form, field))
      |> Keyword.put_new(:name, name_from(form, field))
      |> Keyword.put_new(:value, value_from(form, field))
    tag(:input, opts)
  end

  @doc """
  Generates a file input.

  It requires the given form to be configured with `multipart: true`
  when invokig `form_for/4`, otherwise it fails with `ArgumentError`.

  See `text_input/3` for example and docs.
  """
  def file_input(form, field, opts \\ []) do
    if match?(%Form{}, form) and !form.options[:multipart] do
      raise ArgumentError, "file_input/3 requires the enclosing form_for/4 " <>
                           "to be configured with multipart: true"
    end

    opts =
      opts
      |> Keyword.put_new(:type, :file)
      |> Keyword.put_new(:id, id_from(form, field))
      |> Keyword.put_new(:name, name_from(form, field))

    tag(:input, opts)
  end

  @doc """
  Generates a submit input to send the form.

  All options are forwarded to the underlying input tag.

  ## Examples

      submit "Submit"
      #=> <input type="submit" value="Submit">

  """
  def submit(value, opts \\ []) do
    opts =
      opts
      |> Keyword.put_new(:type, "submit")
      |> Keyword.put_new(:value, value)
    tag(:input, opts)
  end

  @doc """
  Generates a radio button.

  Invoke this function for each possible value you to be
  sent to the server.

  ## Examples

      # Assuming form contains a User model
      radio_button(form, :role, "admin")
      #=> <input id="user_role_admin" name="user[role]" type="radio" value="admin">

  ## Options

  All options are simply forwarded to the underlying HTML tag.
  """
  def radio_button(form, field, value, opts \\ []) do
    value = html_escape(value)

    opts =
      opts
      |> Keyword.put_new(:type, "radio")
      |> Keyword.put_new(:id, id_from(form, field) <> "_" <> elem(value, 1))
      |> Keyword.put_new(:name, name_from(form, field))

    if value == html_escape(value_from(form, field)) do
      opts = Keyword.put_new(opts, :checked, true)
    end

    tag(:input, [value: value] ++ opts)
  end

  @doc """
  Generates a checkbox.

  This function is useful for sending boolean values to the server.

  ## Examples

      # Assuming form contains a User model
      checkbox(form, :famous)
      #=> <input name="user[famous]" type="hidden" value="false">
          <input checked="checked" id="user_famous" name="user[famous]"> type="checkbox" value="true")

  ## Options

    * `:checked_value` - the value to be sent when the checkbox is checked.
      Defaults to "true"

    * `:unchecked_value` - the value to be sent then the checkbox is unchecked,
      Defaults to "false"

    * `:value` - the value used to check if a checkbox is checked or unchecked.
      The default value is extracted from the model if a model is available

  All other options are forwarded to the underlying HTML tag.

  ## Hidden fields

  Because an unchecked checkbox is not sent to the server, Phoenix
  automatically generates a hidden field with the unchecked_value
  *before* the checkbox field to ensure the `unchecked_value` is sent
  when the checkbox is not marked.
  """
  def checkbox(form, field, opts \\ []) do
    opts =
      opts
      |> Keyword.put_new(:type, "checkbox")
      |> Keyword.put_new(:id, id_from(form, field))
      |> Keyword.put_new(:name, name_from(form, field))

    {value, opts}           = Keyword.pop(opts, :value, value_from(form, field))
    {checked_value, opts}   = Keyword.pop(opts, :checked_value, true)
    {unchecked_value, opts} = Keyword.pop(opts, :unchecked_value, false)

    # We html escape all values to be sure we are comparing
    # apples to apples. After all we may have true in the model
    # but "true" in the params and both need to match.
    value           = html_escape(value)
    checked_value   = html_escape(checked_value)
    unchecked_value = html_escape(unchecked_value)

    if value == checked_value do
      opts = Keyword.put_new(opts, :checked, true)
    end

    safe_concat tag(:input, name: Keyword.get(opts, :name), type: "hidden", value: unchecked_value),
                tag(:input, [value: checked_value] ++ opts)
  end

  @doc """
  Generates a select tag with the given `values`.

  Values are expected to be an Enumerable containing two-item tuples
  (like maps and keyword lists) or any Enumerable where the element
  will be used both as key and value for the generated select.

  ## Examples

      # Assuming form contains a User model
      select(form, :age, 0..120)
      #=> <select id="user_age" name="user[age]">
          <option value="0">0</option>
          ...
          <option value="120">120</option>
          </select>

      select(form, :role, [admin: "Admin", user: "User"])
      #=> <select id="user_role" name="user[role]">
          <option value="admin">Admin</option>
          <option value="user">User</option>
          </select>

      select(form, :role, [admin: "Admin", user: "User"], prompt: "Choose your role")
      #=> <select id="user_role" name="user[role]">
          <option value="">Choose your role</option>
          <option value="admin">Admin</option>
          <option value="user">User</option>
          </select>

  ## Options

    * `:prompt` - an option to include at the top of the options with
      the given prompt text

    * `:value` - the value used to select a given option.
      The default value is extracted from the model if a model is available

    * `:default` - the default value to use when none was given in
      `:value` and none was available in the model

  All other options are forwarded to the underlying HTML tag.
  """
  def select(form, field, values, opts \\ []) do
    {default, opts} = Keyword.pop(opts, :default)
    {value, opts}   = Keyword.pop(opts, :value, value_from(form, field) || default)

    {options, opts} = case Keyword.pop(opts, :prompt) do
      {nil, opts}    -> {safe(""), opts}
      {prompt, opts} -> {content_tag(:option, prompt, value: ""), opts}
    end

    opts =
      opts
      |> Keyword.put_new(:id, id_from(form, field))
      |> Keyword.put_new(:name, name_from(form, field))

    options = options_for_select(values, options, html_escape(value))
    content_tag(:select, options, opts)
  end

  defp options_for_select(values, options, value) do
    Enum.reduce values, options, fn
      {option_value, option_key}, acc ->
        option_key   = html_escape(option_key)
        option_value = html_escape(option_value)
        option(option_key, option_value, value, acc)
      option, acc ->
        option = html_escape(option)
        option(option, option, value, acc)
    end
  end

  defp option(option_key, option_value, value, acc) do
    opts = [value: option_value, selected: value == option_value]
    safe_concat acc, content_tag(:option, option_key, opts)
  end

  ## Datetime

  @doc ~S"""
  Generates select tags for datetime.

  ## Examples

      # Assuming form contains a User model
      datetime_select form, :born_at
      #=> <select id="user_born_at_year" name="user[born_at][year]">...</select> /
          <select id="user_born_at_month" name="user[born_at][month]">...</select> /
          <select id="user_born_at_day" name="user[born_at][day]">...</select> —
          <select id="user_born_at_hour" name="user[born_at][hour]">...</select> :
          <select id="user_born_at_min" name="user[born_at][min]">...</select>

  If you want to include the seconds field (hidden by default), pass `sec: []`:

      # Assuming form contains a User model
      datetime_select form, :born_at, sec: []

  If you want to configure the years range:

      # Assuming form contains a User model
      datetime_select form, :born_at, year: [options: 1900..2100]

  You are also able to configure `:month`, `:day`, `:hour`, `:min` and
  `:sec`. All options given to those keys will be forwarded to the
  underlying select. See `select/4` for more information.

  ## Options

    * `:value` - the value used to select a given option.
      The default value is extracted from the model if a model is available

    * `:default` - the default value to use when none was given in
      `:value` and none was available in the model

    * `:year`, `:month`, `:day`, `:hour`, `:min`, `:sec` - options passed
      to the underlying select. See `select/4` for more information.
      The available values can be given in `:options`.

    * `:builder` - specify how the select can be build. It must be a function
      that receives a builder that should be invoked with the select name
      and a set of options. See builder below for more information.

  ## Builder

  The generated datetime_select can be customized at will by providing a
  builder option. Here is an example from EEx:

      <%= datetime_select form, :born_at, builder: fn b -> %>
        Date: <%= b.(:day, []) %> / <%= b.(:month, []) %> / <%= b.(:hour, []) %>
        Time: <%= b.(:hour, []) %> : <%= b.(:min, []) %>
      <% end %>

  Although we have passed empty lists as options (they are required), you
  could pass any option there and it would be given to the underlying select
  input.

  In practice, we recommend you to create your own helper with your default
  builder:

      def my_datetime_select(form, field, opts \\ []) do
        builder = fn b ->
          ~e"\""
          Date: <%= b.(:day, []) %> / <%= b.(:month, []) %> / <%= b.(:hour, []) %>
          Time: <%= b.(:hour, []) %> : <%= b.(:min, []) %>
          "\""
        end

        datetime_select(form, field, [builder: builder] ++ opts)
      end

  Then you are able to use your own datetime_select throughout your whole
  application.

  ## Supported date values

  The following values are supported as date:

    * a map containing the `year`, `month` and `day` keys (either as strings or atoms)
    * a tuple with three elements: `{year, month, day}`
    * `nil`

  ## Supported time values

  The following values are supported as time:

    * a map containing the `hour` and `min` keys and an optional `sec` key (either as strings or atoms)
    * a tuple with three elements: `{hour, min, sec}`
    * a tuple with four elements: `{hour, min, sec, usec}`
    * `nil`

  """
  def datetime_select(form, field, opts \\ []) do
    value = Keyword.get(opts, :value, value_from(form, field) || Keyword.get(opts, :default))

    builder =
      Keyword.get(opts, :builder) || fn b ->
        date = date_builder(b, opts)
        time = time_builder(b, opts)
        safe_concat [date, safe(" — "), time]
      end

    builder.(datetime_builder(form, field, date_value(value), time_value(value), opts))
  end

  @doc """
  Generates select tags for date.

  Check `datetime_select/3` for more information on options and supported values.
  """
  def date_select(form, field, opts \\ []) do
    value   = Keyword.get(opts, :value, value_from(form, field) || Keyword.get(opts, :default))
    builder = Keyword.get(opts, :builder) || &date_builder(&1, opts)
    builder.(datetime_builder(form, field, date_value(value), nil, opts))
  end

  defp date_builder(b, _opts) do
    safe_concat [b.(:year, []), safe(" / "), b.(:month, []), safe(" / "), b.(:day, [])]
  end

  defp date_value(%{"year" => year, "month" => month, "day" => day}),
    do: %{year: year, month: month, day: day}
  defp date_value(%{year: year, month: month, day: day}),
    do: %{year: year, month: month, day: day}

  defp date_value({{year, month, day}, _}),
    do: %{year: year, month: month, day: day}
  defp date_value({year, month, day}),
    do: %{year: year, month: month, day: day}

  defp date_value(nil),
    do: %{year: nil, month: nil, day: nil}
  defp date_value(other),
    do: raise(ArgumentError, "unrecognized date #{inspect other}")

  @doc """
  Generates select tags for time.

  Check `datetime_select/3` for more information on options and supported values.
  """
  def time_select(form, field, opts \\ []) do
    value   = Keyword.get(opts, :value, value_from(form, field) || Keyword.get(opts, :default))
    builder = Keyword.get(opts, :builder) || &time_builder(&1, opts)
    builder.(datetime_builder(form, field, nil, time_value(value), opts))
  end

  defp time_builder(b, opts) do
    time = safe_concat [b.(:hour, []), safe(" : "), b.(:min, [])]

    if Keyword.get(opts, :sec) do
      safe_concat [time, safe(" : "), b.(:sec, [])]
    else
      time
    end
  end

  defp time_value(%{"hour" => hour, "min" => min} = map),
    do: %{hour: hour, min: min, sec: Map.get(map, "sec", 0)}
  defp time_value(%{hour: hour, min: min} = map),
    do: %{hour: hour, min: min, sec: Map.get(map, :sec, 0)}

  defp time_value({_, {hour, min, sec, _msec}}),
    do: %{hour: hour, min: min, sec: sec}
  defp time_value({hour, min, sec, _mseg}),
    do: %{hour: hour, min: min, sec: sec}
  defp time_value({_, {hour, min, sec}}),
    do: %{hour: hour, min: min, sec: sec}
  defp time_value({hour, min, sec}),
    do: %{hour: hour, min: min, sec: sec}

  defp time_value(nil),
    do: %{hour: nil, min: nil, sec: nil}
  defp time_value(other),
    do: raise(ArgumentError, "unrecognized time #{inspect other}")

  @months %{
    "1"  => "January",
    "2"  => "February",
    "3"  => "March",
    "4"  => "April",
    "5"  => "May",
    "6"  => "June",
    "7"  => "July",
    "8"  => "August",
    "9"  => "September",
    "10" => "October",
    "11" => "November",
    "12" => "December"
  }

  map = &Enum.into(&1, %{}, fn i ->
    i = Integer.to_string(i)
    {i, String.rjust(i, 2, ?0)}
  end)

  @days   map.(1..31)
  @hours  map.(0..23)
  @minsec map.(0..59)

  defp datetime_builder(form, field, date, time, parent) do
    id   = Keyword.get(parent, :id, id_from(form, field))
    name = Keyword.get(parent, :name, name_from(form, field))

    fn
      :year, opts when date != nil ->
        {year, _, _}  = :erlang.date()
        {value, opts} = datetime_options(:year, year-5..year+5, id, name, parent, date, opts)
        select(:datetime, :year, value, opts)
      :month, opts when date != nil ->
        {value, opts} = datetime_options(:month, @months, id, name, parent, date, opts)
        select(:datetime, :month, value, opts)
      :day, opts when date != nil ->
        {value, opts} = datetime_options(:day, @days, id, name, parent, date, opts)
        select(:datetime, :day, value, opts)
      :hour, opts when time != nil ->
        {value, opts} = datetime_options(:hour, @hours, id, name, parent, time, opts)
        select(:datetime, :hour, value, opts)
      :min, opts when time != nil ->
        {value, opts} = datetime_options(:min, @minsec, id, name, parent, time, opts)
        select(:datetime, :min, value, opts)
      :sec, opts when time != nil ->
        {value, opts} = datetime_options(:sec, @minsec, id, name, parent, time, opts)
        select(:datetime, :sec, value, opts)
    end
  end

  defp datetime_options(type, values, id, name, parent, datetime, opts) do
    opts = Keyword.merge Keyword.get(parent, type, []), opts
    suff = Atom.to_string(type)

    {value, opts} = Keyword.pop(opts, :options, values)

    {value,
      opts
      |> Keyword.put_new(:id, id <> "_" <> suff)
      |> Keyword.put_new(:name, name <> "[" <> suff <> "]")
      |> Keyword.put_new(:value, Map.get(datetime, type))}
  end

  ## Helpers

  defp value_from(%{model: model, params: params}, field),
    do: Map.get(params, Atom.to_string(field)) || Map.get(model, field)
  defp value_from(name, _field) when is_atom(name),
    do: nil

  defp id_from(%{name: name}, field),
    do: "#{name}_#{field}"
  defp id_from(name, field) when is_atom(name),
    do: "#{name}_#{field}"

  defp name_from(%{name: name}, field),
    do: "#{name}[#{field}]"
  defp name_from(name, field) when is_atom(name),
    do: "#{name}[#{field}]"
end

defmodule Phoenix.HTML.Form do
  @moduledoc ~S"""
  Helpers related to producing HTML forms.

  The functions in this module can be used in three
  distinct scenario:

    * with model data - when information to populate
      the form comes from a model

    * with connection data - when a form is created based
      on the information in the connection (aka `Plug.Conn`)

    * without form data - when the functions are used directly,
      outside of a form

  We will explore all three scenarios below.

  ## With model data

  The entry point for defining forms in Phhoenix is with
  the `form_for/4` function. For this example, we will
  use `Ecto.Changeset`, which integrate nicely with Phoenix
  forms via the `phoenix_ecto` package.

  Imagine you have the following action in your controller:

      def new(conn, _params) do
        changeset = User.changeset(%User{})
        render conn, "new.html", changeset: changeset
      end

  where `User.changeset/2` is defined as follows:

      def changeset(user, params \\ nil) do
        cast(user, params)
      end

  Now a `@changeset` assign is available in views which we
  can pass to the form:

      <%= form_for @changeset, user_path(@conn, :create), fn f -> %>
        <label>
          Name: <%= text_input f, :name %>
        </label>

        <label>
          Age: <%= select f, :age, 18..100 %>
        </label>

        <%= submit "Submit" %>
      <% end %>

  `form_for/4` receives the `Ecto.Changeset` and converts it
  to a form, which is passed to the function as the argument
  `f`. All the remaining functions in this module receive
  the form and automatically generate the input fields, often
  by extracting information from the given changeset. For example,
  if the user had a default value for age set, it will
  automatically show up as selected in the form.

  ## With connection data

  `form_for/4` expects as first argument any data structure that
  implements the `Phoenix.HTML.FormData` protocol. By default,
  Phoenix implements this protocol for `Plug.Conn`, allowing us
  to create forms based only on connection information.

  This is useful when you are creating forms that are not backed
  by any kind of model data, like a search form.

      <%= form_for @conn, search_path(@conn, :new), [name: :search], fn f -> %>
        <%= text_input f, :for %>
        <%= submit "Search" %>
      <% end %>

  ## Without form data

  Sometimes we may want to generate a `text_input/3` or any other
  tag outside of a form. The functions in this module also support
  such usage by simply passing an atom as first argument instead
  of the form.

      <%= text_input :user, :name, value: "This is a prepopulated value" %>

  """

  alias Phoenix.HTML.Form
  import Phoenix.HTML
  import Phoenix.HTML.Tag

  @doc """
  Defines the Phoenix.HTML.Form struct.

  Its fields are:

    * `:source` - the data structure given to `form_for/4` that
      implements the form data protocol

    * `:name` - the name to be used when generating input fields

    * `:model` - the model used to lookup field data

    * `:params` - the parameters associated to this form in case
      they were sent as part of a previous request

    * `:hidden` - a keyword list of fields that are required for
      submitting the form behind the scenes as hidden inputs

    * `:options` - a copy of the options given when creating the
      form via `form_for/4` without any form data specific key

    * `:errors` - a keyword list of errors that associated with
      the form

    * `:validations` - a keyword list of validations for the given
      inputs
  """
  defstruct source: nil, name: nil, model: %{}, hidden: [], params: %{},
            errors: [], validations: [], options: []

  @type t :: %Form{source: term, name: String.t, model: %{atom => term},
                   params: %{binary => term}, hidden: Keyword.t, options: Keyword.t,
                   errors: Keyword.t, validations: Keyword.t}

  @doc """
  Generates a form tag with a form builder.

  See the module documentation for examples of using this function.

  ## Options

    * `:name` - the name to be used in the form. May be inflected
      if a model is available

    * `:method` - the HTTP method. If the method is not "get" nor "post",
      an input tag with name `_method` is generated along-side the form tag.
      Defaults to "post".

    * `:multipart` - when true, sets enctype to "multipart/form-data".
      Required when uploading files

    * `:csrf_token` - for "post" requests, the form tag will automatically
      include an input tag with name `_csrf_token`. When set to false, this
      is disabled

    * `:enforce_utf8` - when false, does not enforce utf8

  See `Phoenix.HTML.Tag.form_tag/2` for more information on the
  options above.
  """
  @spec form_for(Phoenix.HTML.FormData.t, String.t,
                 Keyword.t, (t -> Phoenix.HTML.unsafe)) :: Phoenix.HTML.safe
  def form_for(form_data, action, options \\ [], fun) when is_function(fun, 1) do
    form = Phoenix.HTML.FormData.to_form(form_data, options)
    safe_concat [form_tag(action, form.options), fun.(form), safe("</form>")]
  end

  ## Form helpers

  @doc """
  Generates a text input.

  The form should either be a `Phoenix.HTML.Form` emitted
  by `form_for` or an atom.

  All given options are forwarded to the underlying input,
  default values are provided for id, name and value if
  possible.

  ## Examples

      # Assuming form contains a User model
      text_input(form, :name)
      #=> <input id="user_name" name="user[name]" type="text" value="">

      text_input(:user, :name)
      #=> <input id="user_name" name="user[name]" type="text" value="">

  """
  def text_input(form, field, opts \\ []) do
    generic_input(:text, form, field, opts)
  end

  @doc """
  Generates a hidden input.

  See `text_input/3` for example and docs.
  """
  def hidden_input(form, field, opts \\ []) do
    generic_input(:hidden, form, field, opts)
  end

  @doc """
  Generates an email input.

  See `text_input/3` for example and docs.
  """
  def email_input(form, field, opts \\ []) do
    generic_input(:email, form, field, opts)
  end

  @doc """
  Generates a number input.

  See `text_input/3` for example and docs.
  """
  def number_input(form, field, opts \\ []) do
    generic_input(:number, form, field, opts)
  end

  defp generic_input(type, form, field, opts) when is_atom(field) and is_list(opts) do
    opts =
      opts
      |> Keyword.put_new(:type, type)
      |> Keyword.put_new(:id, id_from(form, field))
      |> Keyword.put_new(:name, name_from(form, field))
      |> Keyword.put_new(:value, value_from(form, field))
    tag(:input, opts)
  end

  @doc """
  Generates a file input.

  It requires the given form to be configured with `multipart: true`
  when invokig `form_for/4`, otherwise it fails with `ArgumentError`.

  See `text_input/3` for example and docs.
  """
  def file_input(form, field, opts \\ []) do
    if match?(%Form{}, form) and !form.options[:multipart] do
      raise ArgumentError, "file_input/3 requires the enclosing form_for/4 " <>
                           "to be configured with multipart: true"
    end

    opts =
      opts
      |> Keyword.put_new(:type, :file)
      |> Keyword.put_new(:id, id_from(form, field))
      |> Keyword.put_new(:name, name_from(form, field))

    tag(:input, opts)
  end

  @doc """
  Generates a submit input to send the form.

  All options are forwarded to the underlying input tag.

  ## Examples

      submit "Submit"
      #=> <input type="submit" value="Submit">

  """
  def submit(value, opts \\ []) do
    opts =
      opts
      |> Keyword.put_new(:type, "submit")
      |> Keyword.put_new(:value, value)
    tag(:input, opts)
  end

  @doc """
  Generates a radio button.

  Invoke this function for each possible value you to be
  sent to the server.

  ## Examples

      # Assuming form contains a User model
      radio_button(form, :role, "admin")
      #=> <input id="user_role_admin" name="user[role]" type="radio" value="admin">

  ## Options

  All options are simply forwarded to the underlying HTML tag.
  """
  def radio_button(form, field, value, opts \\ []) do
    value = html_escape(value)

    opts =
      opts
      |> Keyword.put_new(:type, "radio")
      |> Keyword.put_new(:id, id_from(form, field) <> "_" <> elem(value, 1))
      |> Keyword.put_new(:name, name_from(form, field))

    if value == html_escape(value_from(form, field)) do
      opts = Keyword.put_new(opts, :checked, true)
    end

    tag(:input, [value: value] ++ opts)
  end

  @doc """
  Generates a checkbox.

  This function is useful for sending boolean values to the server.

  ## Examples

      # Assuming form contains a User model
      checkbox(form, :famous)
      #=> <input name="user[famous]" type="hidden" value="false">
          <input checked="checked" id="user_famous" name="user[famous]"> type="checkbox" value="true")

  ## Options

    * `:checked_value` - the value to be sent when the checkbox is checked.
      Defaults to "true"

    * `:unchecked_value` - the value to be sent then the checkbox is unchecked,
      Defaults to "false"

    * `:value` - the value used to check if a checkbox is checked or unchecked.
      The default value is extracted from the model if a model is available

  All other options are forwarded to the underlying HTML tag.

  ## Hidden fields

  Because an unchecked checkbox is not sent to the server, Phoenix
  automatically generates a hidden field with the unchecked_value
  *before* the checkbox field to ensure the `unchecked_value` is sent
  when the checkbox is not marked.
  """
  def checkbox(form, field, opts \\ []) do
    opts =
      opts
      |> Keyword.put_new(:type, "checkbox")
      |> Keyword.put_new(:id, id_from(form, field))
      |> Keyword.put_new(:name, name_from(form, field))

    {value, opts}           = Keyword.pop(opts, :value, value_from(form, field))
    {checked_value, opts}   = Keyword.pop(opts, :checked_value, true)
    {unchecked_value, opts} = Keyword.pop(opts, :unchecked_value, false)

    # We html escape all values to be sure we are comparing
    # apples to apples. After all we may have true in the model
    # but "true" in the params and both need to match.
    value           = html_escape(value)
    checked_value   = html_escape(checked_value)
    unchecked_value = html_escape(unchecked_value)

    if value == checked_value do
      opts = Keyword.put_new(opts, :checked, true)
    end

    safe_concat tag(:input, name: Keyword.get(opts, :name), type: "hidden", value: unchecked_value),
                tag(:input, [value: checked_value] ++ opts)
  end

  @doc """
  Generates a select tag with the given `values`.

  Values are expected to be an Enumerable containing two-item tuples
  (like maps and keyword lists) or any Enumerable where the element
  will be used both as key and value for the generated select.

  ## Examples

      # Assuming form contains a User model
      select(form, :age, 0..120)
      #=> <select id="user_age" name="user[age]">
          <option value="0">0</option>
          ...
          <option value="120">120</option>
          </select>

      select(form, :role, [admin: "Admin", user: "User"])
      #=> <select id="user_role" name="user[role]">
          <option value="admin">Admin</option>
          <option value="user">User</option>
          </select>

      select(form, :role, [admin: "Admin", user: "User"], prompt: "Choose your role")
      #=> <select id="user_role" name="user[role]">
          <option value="">Choose your role</option>
          <option value="admin">Admin</option>
          <option value="user">User</option>
          </select>

  ## Options

    * `:prompt` - an option to include at the top of the options with
      the given prompt text

    * `:value` - the value used to select a given option.
      The default value is extracted from the model if a model is available

    * `:default` - the default value to use when none was given in
      `:value` and none was available in the model

  All other options are forwarded to the underlying HTML tag.
  """
  def select(form, field, values, opts \\ []) do
    {default, opts} = Keyword.pop(opts, :default)
    {value, opts}   = Keyword.pop(opts, :value, value_from(form, field) || default)

    {options, opts} = case Keyword.pop(opts, :prompt) do
      {nil, opts}    -> {safe(""), opts}
      {prompt, opts} -> {content_tag(:option, prompt, value: ""), opts}
    end

    opts =
      opts
      |> Keyword.put_new(:id, id_from(form, field))
      |> Keyword.put_new(:name, name_from(form, field))

    options = options_for_select(values, options, html_escape(value))
    content_tag(:select, options, opts)
  end

  defp options_for_select(values, options, value) do
    Enum.reduce values, options, fn
      {option_value, option_key}, acc ->
        option_key   = html_escape(option_key)
        option_value = html_escape(option_value)
        option(option_key, option_value, value, acc)
      option, acc ->
        option = html_escape(option)
        option(option, option, value, acc)
    end
  end

  defp option(option_key, option_value, value, acc) do
    opts = [value: option_value, selected: value == option_value]
    safe_concat acc, content_tag(:option, option_key, opts)
  end

  ## Datetime

  @doc ~S"""
  Generates select tags for datetime.

  ## Examples

      # Assuming form contains a User model
      datetime_select form, :born_at
      #=> <select id="user_born_at_year" name="user[born_at][year]">...</select> /
          <select id="user_born_at_month" name="user[born_at][month]">...</select> /
          <select id="user_born_at_day" name="user[born_at][day]">...</select> —
          <select id="user_born_at_hour" name="user[born_at][hour]">...</select> :
          <select id="user_born_at_min" name="user[born_at][min]">...</select>

  If you want to include the seconds field (hidden by default), pass `sec: []`:

      # Assuming form contains a User model
      datetime_select form, :born_at, sec: []

  If you want to configure the years range:

      # Assuming form contains a User model
      datetime_select form, :born_at, year: [options: 1900..2100]

  You are also able to configure `:month`, `:day`, `:hour`, `:min` and
  `:sec`. All options given to those keys will be forwarded to the
  underlying select. See `select/4` for more information.

  ## Options

    * `:value` - the value used to select a given option.
      The default value is extracted from the model if a model is available

    * `:default` - the default value to use when none was given in
      `:value` and none was available in the model

    * `:year`, `:month`, `:day`, `:hour`, `:min`, `:sec` - options passed
      to the underlying select. See `select/4` for more information.
      The available values can be given in `:options`.

    * `:builder` - specify how the select can be build. It must be a function
      that receives a builder that should be invoked with the select name
      and a set of options. See builder below for more information.

  ## Builder

  The generated datetime_select can be customized at will by providing a
  builder option. Here is an example from EEx:

      <%= datetime_select form, :born_at, builder: fn b -> %>
        Date: <%= b.(:day, []) %> / <%= b.(:month, []) %> / <%= b.(:hour, []) %>
        Time: <%= b.(:hour, []) %> : <%= b.(:min, []) %>
      <% end %>

  Although we have passed empty lists as options (they are required), you
  could pass any option there and it would be given to the underlying select
  input.

  In practice, we recommend you to create your own helper with your default
  builder:

      def my_datetime_select(form, field, opts \\ []) do
        builder = fn b ->
          ~e"\""
          Date: <%= b.(:day, []) %> / <%= b.(:month, []) %> / <%= b.(:hour, []) %>
          Time: <%= b.(:hour, []) %> : <%= b.(:min, []) %>
          "\""
        end

        datetime_select(form, field, [builder: builder] ++ opts)
      end

  Then you are able to use your own datetime_select throughout your whole
  application.

  ## Supported date values

  The following values are supported as date:

    * a map containing the `year`, `month` and `day` keys (either as strings or atoms)
    * a tuple with three elements: `{year, month, day}`
    * `nil`

  ## Supported time values

  The following values are supported as time:

    * a map containing the `hour` and `min` keys and an optional `sec` key (either as strings or atoms)
    * a tuple with three elements: `{hour, min, sec}`
    * a tuple with four elements: `{hour, min, sec, usec}`
    * `nil`

  """
  def datetime_select(form, field, opts \\ []) do
    value = Keyword.get(opts, :value, value_from(form, field) || Keyword.get(opts, :default))

    builder =
      Keyword.get(opts, :builder) || fn b ->
        date = date_builder(b, opts)
        time = time_builder(b, opts)
        safe_concat [date, safe(" — "), time]
      end

    builder.(datetime_builder(form, field, date_value(value), time_value(value), opts))
  end

  @doc """
  Generates select tags for date.

  Check `datetime_select/3` for more information on options and supported values.
  """
  def date_select(form, field, opts \\ []) do
    value   = Keyword.get(opts, :value, value_from(form, field) || Keyword.get(opts, :default))
    builder = Keyword.get(opts, :builder) || &date_builder(&1, opts)
    builder.(datetime_builder(form, field, date_value(value), nil, opts))
  end

  defp date_builder(b, _opts) do
    safe_concat [b.(:year, []), safe(" / "), b.(:month, []), safe(" / "), b.(:day, [])]
  end

  defp date_value(%{"year" => year, "month" => month, "day" => day}),
    do: %{year: year, month: month, day: day}
  defp date_value(%{year: year, month: month, day: day}),
    do: %{year: year, month: month, day: day}

  defp date_value({{year, month, day}, _}),
    do: %{year: year, month: month, day: day}
  defp date_value({year, month, day}),
    do: %{year: year, month: month, day: day}

  defp date_value(nil),
    do: %{year: nil, month: nil, day: nil}
  defp date_value(other),
    do: raise(ArgumentError, "unrecognized date #{inspect other}")

  @doc """
  Generates select tags for time.

  Check `datetime_select/3` for more information on options and supported values.
  """
  def time_select(form, field, opts \\ []) do
    value   = Keyword.get(opts, :value, value_from(form, field) || Keyword.get(opts, :default))
    builder = Keyword.get(opts, :builder) || &time_builder(&1, opts)
    builder.(datetime_builder(form, field, nil, time_value(value), opts))
  end

  defp time_builder(b, opts) do
    time = safe_concat [b.(:hour, []), safe(" : "), b.(:min, [])]

    if Keyword.get(opts, :sec) do
      safe_concat [time, safe(" : "), b.(:sec, [])]
    else
      time
    end
  end

  defp time_value(%{"hour" => hour, "min" => min} = map),
    do: %{hour: hour, min: min, sec: Map.get(map, "sec", 0)}
  defp time_value(%{hour: hour, min: min} = map),
    do: %{hour: hour, min: min, sec: Map.get(map, :sec, 0)}

  defp time_value({_, {hour, min, sec, _msec}}),
    do: %{hour: hour, min: min, sec: sec}
  defp time_value({hour, min, sec, _mseg}),
    do: %{hour: hour, min: min, sec: sec}
  defp time_value({_, {hour, min, sec}}),
    do: %{hour: hour, min: min, sec: sec}
  defp time_value({hour, min, sec}),
    do: %{hour: hour, min: min, sec: sec}

  defp time_value(nil),
    do: %{hour: nil, min: nil, sec: nil}
  defp time_value(other),
    do: raise(ArgumentError, "unrecognized time #{inspect other}")

  @months %{
    "1"  => "January",
    "2"  => "February",
    "3"  => "March",
    "4"  => "April",
    "5"  => "May",
    "6"  => "June",
    "7"  => "July",
    "8"  => "August",
    "9"  => "September",
    "10" => "October",
    "11" => "November",
    "12" => "December"
  }

  map = &Enum.into(&1, %{}, fn i ->
    i = Integer.to_string(i)
    {i, String.rjust(i, 2, ?0)}
  end)

  @days   map.(1..31)
  @hours  map.(0..23)
  @minsec map.(0..59)

  defp datetime_builder(form, field, date, time, parent) do
    id   = Keyword.get(parent, :id, id_from(form, field))
    name = Keyword.get(parent, :name, name_from(form, field))

    fn
      :year, opts when date != nil ->
        {year, _, _}  = :erlang.date()
        {value, opts} = datetime_options(:year, year-5..year+5, id, name, parent, date, opts)
        select(:datetime, :year, value, opts)
      :month, opts when date != nil ->
        {value, opts} = datetime_options(:month, @months, id, name, parent, date, opts)
        select(:datetime, :month, value, opts)
      :day, opts when date != nil ->
        {value, opts} = datetime_options(:day, @days, id, name, parent, date, opts)
        select(:datetime, :day, value, opts)
      :hour, opts when time != nil ->
        {value, opts} = datetime_options(:hour, @hours, id, name, parent, time, opts)
        select(:datetime, :hour, value, opts)
      :min, opts when time != nil ->
        {value, opts} = datetime_options(:min, @minsec, id, name, parent, time, opts)
        select(:datetime, :min, value, opts)
      :sec, opts when time != nil ->
        {value, opts} = datetime_options(:sec, @minsec, id, name, parent, time, opts)
        select(:datetime, :sec, value, opts)
    end
  end

  defp datetime_options(type, values, id, name, parent, datetime, opts) do
    opts = Keyword.merge Keyword.get(parent, type, []), opts
    suff = Atom.to_string(type)

    {value, opts} = Keyword.pop(opts, :options, values)

    {value,
      opts
      |> Keyword.put_new(:id, id <> "_" <> suff)
      |> Keyword.put_new(:name, name <> "[" <> suff <> "]")
      |> Keyword.put_new(:value, Map.get(datetime, type))}
  end

  ## Helpers

  defp value_from(%{model: model, params: params}, field),
    do: Map.get(params, Atom.to_string(field)) || Map.get(model, field)
  defp value_from(name, _field) when is_atom(name),
    do: nil

  defp id_from(%{name: name}, field),
    do: "#{name}_#{field}"
  defp id_from(name, field) when is_atom(name),
    do: "#{name}_#{field}"

  defp name_from(%{name: name}, field),
    do: "#{name}[#{field}]"
  defp name_from(name, field) when is_atom(name),
    do: "#{name}[#{field}]"
end