text: import os
  
  from .script import ScriptDirectory
  from .runtime.environment import EnvironmentContext
  from . import util
  from . import autogenerate as autogen
  
  
  def list_templates(config):
      """List available templates
  
      :param config: a :class:`.Config` object.
  
      """
  
      config.print_stdout("Available templates:\n")
      for tempname in os.listdir(config.get_template_directory()):
          with open(
              os.path.join(config.get_template_directory(), tempname, "README")
          ) as readme:
              synopsis = next(readme)
          config.print_stdout("%s - %s", tempname, synopsis)
  
      config.print_stdout("\nTemplates are used via the 'init' command, e.g.:")
      config.print_stdout("\n  alembic init --template generic ./scripts")
  
  
  def init(config, directory, template="generic"):
      """Initialize a new scripts directory.
  
      :param config: a :class:`.Config` object.
  
      :param directory: string path of the target directory
  
      :param template: string name of the migration environment template to
       use.
  
      """
  
      if os.access(directory, os.F_OK):
          raise util.CommandError("Directory %s already exists" % directory)
  
      template_dir = os.path.join(config.get_template_directory(), template)
      if not os.access(template_dir, os.F_OK):
          raise util.CommandError("No such template %r" % template)
  
      util.status(
          "Creating directory %s" % os.path.abspath(directory), os.makedirs, directory
      )
  
      versions = os.path.join(directory, "versions")
      util.status(
          "Creating directory %s" % os.path.abspath(versions), os.makedirs, versions
      )
  
      script = ScriptDirectory(directory)
  
      for file_ in os.listdir(template_dir):
          file_path = os.path.join(template_dir, file_)
          if file_ == "alembic.ini.mako":
              config_file = os.path.abspath(config.config_file_name)
              if os.access(config_file, os.F_OK):
                  util.msg("File %s already exists, skipping" % config_file)
              else:
                  script._generate_template(
                      file_path, config_file, script_location=directory
                  )
          elif os.path.isfile(file_path):
              output_file = os.path.join(directory, file_)
              script._copy_file(file_path, output_file)
  
      util.msg(
          "Please edit configuration/connection/logging "
          "settings in %r before proceeding." % config_file
      )
  
  
  def revision(
      config,
      message=None,
      autogenerate=False,
      sql=False,
      head="head",
      splice=False,
      branch_label=None,
      version_path=None,
      rev_id=None,
      depends_on=None,
      process_revision_directives=None,
  ):
      """Create a new revision file.
  
      :param config: a :class:`.Config` object.
  
      :param message: string message to apply to the revision; this is the
       ``-m`` option to ``alembic revision``.
  
      :param autogenerate: whether or not to autogenerate the script from
       the database; this is the ``--autogenerate`` option to ``alembic revision``.
  
      :param sql: whether to dump the script out as a SQL string; when specified,
       the script is dumped to stdout.  This is the ``--sql`` option to
       ``alembic revision``.
  
      :param head: head revision to build the new revision upon as a parent;
       this is the ``--head`` option to ``alembic revision``.
  
      :param splice: whether or not the new revision should be made into a
       new head of its own; is required when the given ``head`` is not itself
       a head.  This is the ``--splice`` option to ``alembic revision``.
  
      :param branch_label: string label to apply to the branch; this is the
       ``--branch-label`` option to ``alembic revision``.
  
      :param version_path: string symbol identifying a specific version path
       from the configuration; this is the ``--version-path`` option to
       ``alembic revision``.
  
      :param rev_id: optional revision identifier to use instead of having
       one generated; this is the ``--rev-id`` option to ``alembic revision``.
  
      :param depends_on: optional list of "depends on" identifiers; this is the
       ``--depends-on`` option to ``alembic revision``.
  
      :param process_revision_directives: this is a callable that takes the
       same form as the callable described at
       :paramref:`.EnvironmentContext.configure.process_revision_directives`;
       will be applied to the structure generated by the revision process
       where it can be altered programmatically.   Note that unlike all
       the other parameters, this option is only available via programmatic
       use of :func:`.command.revision`
  
       .. versionadded:: 0.9.0
  
      """
  
      script_directory = ScriptDirectory.from_config(config)
  
      command_args = dict(
          message=message,
          autogenerate=autogenerate,
          sql=sql,
          head=head,
          splice=splice,
          branch_label=branch_label,
          version_path=version_path,
          rev_id=rev_id,
          depends_on=depends_on,
      )
      revision_context = autogen.RevisionContext(
          config,
          script_directory,
          command_args,
          process_revision_directives=process_revision_directives,
      )
  
      environment = util.asbool(config.get_main_option("revision_environment"))
  
      if autogenerate:
          environment = True
  
          if sql:
              raise util.CommandError(
                  "Using --sql with --autogenerate does not make any sense"
              )
  
          def retrieve_migrations(rev, context):
              revision_context.run_autogenerate(rev, context)
              return []
  
      elif environment:
  
          def retrieve_migrations(rev, context):
              revision_context.run_no_autogenerate(rev, context)
              return []
  
      elif sql:
          raise util.CommandError(
              "Using --sql with the revision command when "
              "revision_environment is not configured does not make any sense"
          )
  
      if environment:
          with EnvironmentContext(
              config,
              script_directory,
              fn=retrieve_migrations,
              as_sql=sql,
              template_args=revision_context.template_args,
              revision_context=revision_context,
          ):
              script_directory.run_env()
  
      scripts = [script for script in revision_context.generate_scripts()]
      if len(scripts) == 1:
          return scripts[0]
      else:
          return scripts
  
  
  def merge(config, revisions, message=None, branch_label=None, rev_id=None):
      """Merge two revisions together.  Creates a new migration file.
  
      .. versionadded:: 0.7.0
  
      :param config: a :class:`.Config` instance
  
      :param message: string message to apply to the revision
  
      :param branch_label: string label name to apply to the new revision
  
      :param rev_id: hardcoded revision identifier instead of generating a new
       one.
  
      .. seealso::
  
          :ref:`branches`
  
      """
  
      script = ScriptDirectory.from_config(config)
      template_args = {
          "config": config  # Let templates use config for
          # e.g. multiple databases
      }
      return script.generate_revision(
          rev_id or util.rev_id(),
          message,
          refresh=True,
          head=revisions,
          branch_labels=branch_label,
          **template_args
      )
  
  
  def upgrade(config, revision, sql=False, tag=None):
      """Upgrade to a later version.
  
      :param config: a :class:`.Config` instance.
  
      :param revision: string revision target or range for --sql mode
  
      :param sql: if True, use ``--sql`` mode
  
      :param tag: an arbitrary "tag" that can be intercepted by custom
       ``env.py`` scripts via the :meth:`.EnvironmentContext.get_tag_argument`
       method.
  
      """
  
      script = ScriptDirectory.from_config(config)
  
      starting_rev = None
      if ":" in revision:
          if not sql:
              raise util.CommandError("Range revision not allowed")
          starting_rev, revision = revision.split(":", 2)
  
      def upgrade(rev, context):
          return script._upgrade_revs(revision, rev)
  
      with EnvironmentContext(
          config,
          script,
          fn=upgrade,
          as_sql=sql,
          starting_rev=starting_rev,
          destination_rev=revision,
          tag=tag,
      ):
          script.run_env()
  
  
  def downgrade(config, revision, sql=False, tag=None):
      """Revert to a previous version.
  
      :param config: a :class:`.Config` instance.
  
      :param revision: string revision target or range for --sql mode
  
      :param sql: if True, use ``--sql`` mode
  
      :param tag: an arbitrary "tag" that can be intercepted by custom
       ``env.py`` scripts via the :meth:`.EnvironmentContext.get_tag_argument`
       method.
  
      """
  
      script = ScriptDirectory.from_config(config)
      starting_rev = None
      if ":" in revision:
          if not sql:
              raise util.CommandError("Range revision not allowed")
          starting_rev, revision = revision.split(":", 2)
      elif sql:
          raise util.CommandError("downgrade with --sql requires <fromrev>:<torev>")
  
      def downgrade(rev, context):
          return script._downgrade_revs(revision, rev)
  
      with EnvironmentContext(
          config,
          script,
          fn=downgrade,
          as_sql=sql,
          starting_rev=starting_rev,
          destination_rev=revision,
          tag=tag,
      ):
          script.run_env()
  
  
  def show(config, rev):
      """Show the revision(s) denoted by the given symbol.
  
      :param config: a :class:`.Config` instance.
  
      :param revision: string revision target
  
      """
  
      script = ScriptDirectory.from_config(config)
  
      if rev == "current":
  
          def show_current(rev, context):
              for sc in script.get_revisions(rev):
                  config.print_stdout(sc.log_entry)
              return []
  
          with EnvironmentContext(config, script, fn=show_current):
              script.run_env()
      else:
          for sc in script.get_revisions(rev):
              config.print_stdout(sc.log_entry)
  
  
  def history(config, rev_range=None, verbose=False, indicate_current=False):
      """List changeset scripts in chronological order.
  
      :param config: a :class:`.Config` instance.
  
      :param rev_range: string revision range
  
      :param verbose: output in verbose mode.
  
      :param indicate_current: indicate current revision.
  
       ..versionadded:: 0.9.9
  
      """
  
      script = ScriptDirectory.from_config(config)
      if rev_range is not None:
          if ":" not in rev_range:
              raise util.CommandError(
                  "History range requires [start]:[end], " "[start]:, or :[end]"
              )
          base, head = rev_range.strip().split(":")
      else:
          base = head = None
  
      environment = (
          util.asbool(config.get_main_option("revision_environment")) or indicate_current
      )
  
      def _display_history(config, script, base, head, currents=()):
          for sc in script.walk_revisions(base=base or "base", head=head or "heads"):
  
              if indicate_current:
                  sc._db_current_indicator = sc.revision in currents
  
              config.print_stdout(
                  sc.cmd_format(
                      verbose=verbose,
                      include_branches=True,
                      include_doc=True,
                      include_parents=True,
                  )
              )
  
      def _display_history_w_current(config, script, base, head):
          def _display_current_history(rev, context):
              if head == "current":
                  _display_history(config, script, base, rev, rev)
              elif base == "current":
                  _display_history(config, script, rev, head, rev)
              else:
                  _display_history(config, script, base, head, rev)
              return []
  
          with EnvironmentContext(config, script, fn=_display_current_history):
              script.run_env()
  
      if base == "current" or head == "current" or environment:
          _display_history_w_current(config, script, base, head)
      else:
          _display_history(config, script, base, head)
  
  
  def heads(config, verbose=False, resolve_dependencies=False):
      """Show current available heads in the script directory
  
      :param config: a :class:`.Config` instance.
  
      :param verbose: output in verbose mode.
  
      :param resolve_dependencies: treat dependency version as down revisions.
  
      """
  
      script = ScriptDirectory.from_config(config)
      if resolve_dependencies:
          heads = script.get_revisions("heads")
      else:
          heads = script.get_revisions(script.get_heads())
  
      for rev in heads:
          config.print_stdout(
              rev.cmd_format(verbose, include_branches=True, tree_indicators=False)
          )
  
  
  def branches(config, verbose=False):
      """Show current branch points.
  
      :param config: a :class:`.Config` instance.
  
      :param verbose: output in verbose mode.
  
      """
      script = ScriptDirectory.from_config(config)
      for sc in script.walk_revisions():
          if sc.is_branch_point:
              config.print_stdout(
                  "%s\n%s\n",
                  sc.cmd_format(verbose, include_branches=True),
                  "\n".join(
                      "%s -> %s"
                      % (
                          " " * len(str(sc.revision)),
                          rev_obj.cmd_format(
                              False, include_branches=True, include_doc=verbose
                          ),
                      )
                      for rev_obj in (script.get_revision(rev) for rev in sc.nextrev)
                  ),
              )
  
  
  def current(config, verbose=False, head_only=False):
      """Display the current revision for a database.
  
      :param config: a :class:`.Config` instance.
  
      :param verbose: output in verbose mode.
  
      :param head_only: deprecated; use ``verbose`` for additional output.
  
      """
  
      script = ScriptDirectory.from_config(config)
  
      if head_only:
          util.warn("--head-only is deprecated")
  
      def display_version(rev, context):
          if verbose:
              config.print_stdout(
                  "Current revision(s) for %s:",
                  util.obfuscate_url_pw(context.connection.engine.url),
              )
          for rev in script.get_all_current(rev):
              config.print_stdout(rev.cmd_format(verbose))
  
          return []
  
      with EnvironmentContext(config, script, fn=display_version):
          script.run_env()
  
  
  def stamp(config, revision, sql=False, tag=None):
      """'stamp' the revision table with the given revision; don't
      run any migrations.
  
      :param config: a :class:`.Config` instance.
  
      :param revision: target revision.
  
      :param sql: use ``--sql`` mode
  
      :param tag: an arbitrary "tag" that can be intercepted by custom
       ``env.py`` scripts via the :class:`.EnvironmentContext.get_tag_argument`
       method.
  
      """
  
      script = ScriptDirectory.from_config(config)
  
      starting_rev = None
      if ":" in revision:
          if not sql:
              raise util.CommandError("Range revision not allowed")
          starting_rev, revision = revision.split(":", 2)
  
      def do_stamp(rev, context):
          return script._stamp_revs(revision, rev)
  
      with EnvironmentContext(
          config,
          script,
          fn=do_stamp,
          as_sql=sql,
          destination_rev=revision,
          starting_rev=starting_rev,
          tag=tag,
      ):
          script.run_env()
  
  
  def edit(config, rev):
      """Edit revision script(s) using $EDITOR.
  
      :param config: a :class:`.Config` instance.
  
      :param rev: target revision.
  
      """
  
      script = ScriptDirectory.from_config(config)
  
      if rev == "current":
  
          def edit_current(rev, context):
              if not rev:
                  raise util.CommandError("No current revisions")
              for sc in script.get_revisions(rev):
                  util.edit(sc.path)
              return []
  
          with EnvironmentContext(config, script, fn=edit_current):
              script.run_env()
      else:
          revs = script.get_revisions(rev)
          if not revs:
              raise util.CommandError("No revision files indicated by symbol '%s'" % rev)
          for sc in revs:
              util.edit(sc.path)
  