# encoding: UTF-8
#
# Copyright 2011, 2012 Keith Rarick
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

# See https://github.com/kr/okjson for updates.

require 'stringio'

# Some parts adapted from
# http://golang.org/src/pkg/json/decode.go and
# http://golang.org/src/pkg/utf8/utf8.go
module Xplenty
  class API
    module OkJson
      extend self


      # Decodes a json document in string s and
      # returns the corresponding ruby value.
      # String s must be valid UTF-8. If you have
      # a string in some other encoding, convert
      # it first.
      #
      # String values in the resulting structure
      # will be UTF-8.
      def decode(s)
        ts = lex(s)
        v, ts = textparse(ts)
        if ts.length > 0
          raise Error, 'trailing garbage'
        end
        v
      end


      # Parses a "json text" in the sense of RFC 4627.
      # Returns the parsed value and any trailing tokens.
      # Note: this is almost the same as valparse,
      # except that it does not accept atomic values.
      def textparse(ts)
        if ts.length < 0
          raise Error, 'empty'
        end

        typ, _, val = ts[0]
        case typ
        when '{' then objparse(ts)
        when '[' then arrparse(ts)
        else
          raise Error, "unexpected #{val.inspect}"
        end
      end


      # Parses a "value" in the sense of RFC 4627.
      # Returns the parsed value and any trailing tokens.
      def valparse(ts)
        if ts.length < 0
          raise Error, 'empty'
        end

        typ, _, val = ts[0]
        case typ
        when '{' then objparse(ts)
        when '[' then arrparse(ts)
        when :val,:str then [val, ts[1..-1]]
        else
          raise Error, "unexpected #{val.inspect}"
        end
      end


      # Parses an "object" in the sense of RFC 4627.
      # Returns the parsed value and any trailing tokens.
      def objparse(ts)
        ts = eat('{', ts)
        obj = {}

        if ts[0][0] == '}'
          return obj, ts[1..-1]
        end

        k, v, ts = pairparse(ts)
        obj[k] = v

        if ts[0][0] == '}'
          return obj, ts[1..-1]
        end

        loop do
          ts = eat(',', ts)

          k, v, ts = pairparse(ts)
          obj[k] = v

          if ts[0][0] == '}'
            return obj, ts[1..-1]
          end
        end
      end


      # Parses a "member" in the sense of RFC 4627.
      # Returns the parsed values and any trailing tokens.
      def pairparse(ts)
        (typ, _, k), ts = ts[0], ts[1..-1]
        if typ != :str
          raise Error, "unexpected #{k.inspect}"
        end
        ts = eat(':', ts)
        v, ts = valparse(ts)
        [k, v, ts]
      end


      # Parses an "array" in the sense of RFC 4627.
      # Returns the parsed value and any trailing tokens.
      def arrparse(ts)
        ts = eat('[', ts)
        arr = []

        if ts[0][0] == ']'
          return arr, ts[1..-1]
        end

        v, ts = valparse(ts)
        arr << v

        if ts[0][0] == ']'
          return arr, ts[1..-1]
        end

        loop do
          ts = eat(',', ts)

          v, ts = valparse(ts)
          arr << v

          if ts[0][0] == ']'
            return arr, ts[1..-1]
          end
        end
      end


      def eat(typ, ts)
        if ts[0][0] != typ
          raise Error, "expected #{typ} (got #{ts[0].inspect})"
        end
        ts[1..-1]
      end


      # Scans s and returns a list of json tokens,
      # excluding white space (as defined in RFC 4627).
      def lex(s)
        ts = []
        while s.length > 0
          typ, lexeme, val = tok(s)
          if typ == nil
            raise Error, "invalid character at #{s[0,10].inspect}"
          end
          if typ != :space
            ts << [typ, lexeme, val]
          end
          s = s[lexeme.length..-1]
        end
        ts
      end


      # Scans the first token in s and
      # returns a 3-element list, or nil
      # if s does not begin with a valid token.
      #
      # The first list element is one of
      # '{', '}', ':', ',', '[', ']',
      # :val, :str, and :space.
      #
      # The second element is the lexeme.
      #
      # The third element is the value of the
      # token for :val and :str, otherwise
      # it is the lexeme.
      def tok(s)
        case s[0]
        when ?{  then ['{', s[0,1], s[0,1]]
        when ?}  then ['}', s[0,1], s[0,1]]
        when ?:  then [':', s[0,1], s[0,1]]
        when ?,  then [',', s[0,1], s[0,1]]
        when ?[  then ['[', s[0,1], s[0,1]]
        when ?]  then [']', s[0,1], s[0,1]]
        when ?n  then nulltok(s)
        when ?t  then truetok(s)
        when ?f  then falsetok(s)
        when ?"  then strtok(s)
        when Spc then [:space, s[0,1], s[0,1]]
        when ?\t then [:space, s[0,1], s[0,1]]
        when ?\n then [:space, s[0,1], s[0,1]]
        when ?\r then [:space, s[0,1], s[0,1]]
        else          numtok(s)
        end
      end


      def nulltok(s);  s[0,4] == 'null'  ? [:val, 'null',  nil]   : [] end
      def truetok(s);  s[0,4] == 'true'  ? [:val, 'true',  true]  : [] end
      def falsetok(s); s[0,5] == 'false' ? [:val, 'false', false] : [] end


      def numtok(s)
        m = /-?([1-9][0-9]+|[0-9])([.][0-9]+)?([eE][+-]?[0-9]+)?/.match(s)
        if m && m.begin(0) == 0
          if m[3] && !m[2]
            [:val, m[0], Integer(m[1])*(10**Integer(m[3][1..-1]))]
          elsif m[2]
            [:val, m[0], Float(m[0])]
          else
            [:val, m[0], Integer(m[0])]
          end
        else
          []
        end
      end


      def strtok(s)
        m = /"([^"\\]|\\["\/\\bfnrt]|\\u[0-9a-fA-F]{4})*"/.match(s)
        if ! m
          raise Error, "invalid string literal at #{abbrev(s)}"
        end
        [:str, m[0], unquote(m[0])]
      end


      def abbrev(s)
        t = s[0,10]
        p = t['`']
        t = t[0,p] if p
        t = t + '...' if t.length < s.length
        '`' + t + '`'
      end


      # Converts a quoted json string literal q into a UTF-8-encoded string.
      # The rules are different than for Ruby, so we cannot use eval.
      # Unquote will raise an error if q contains control characters.
      def unquote(q)
        q = q[1...-1]
        rubydoesenc = false
        # In ruby >= 1.9, a[w] is a codepoint, not a byte.
        if q.class.method_defined?(:force_encoding)
          q.force_encoding('UTF-8')
          rubydoesenc = true
        end
        a = q.dup # allocate a big enough string
        r, w = 0, 0
        while r < q.length
          c = q[r]
          case true
          when c == ?\\
            r += 1
            if r >= q.length
              raise Error, "string literal ends with a \"\\\": \"#{q}\""
            end

            case q[r]
            when ?",?\\,?/,?'
              a[w] = q[r]
              r += 1
              w += 1
            when ?b,?f,?n,?r,?t
              a[w] = Unesc[q[r]]
              r += 1
              w += 1
            when ?u
              r += 1
              uchar = begin
                hexdec4(q[r,4])
              rescue RuntimeError => e
                raise Error, "invalid escape sequence \\u#{q[r,4]}: #{e}"
              end
              r += 4
              if surrogate? uchar
                if q.length >= r+6
                  uchar1 = hexdec4(q[r+2,4])
                  uchar = subst(uchar, uchar1)
                  if uchar != Ucharerr
                    # A valid pair; consume.
                    r += 6
                  end
                end
              end
              if rubydoesenc
                a[w] = '' << uchar
                w += 1
              else
                w += ucharenc(a, w, uchar)
              end
            else
              raise Error, "invalid escape char #{q[r]} in \"#{q}\""
            end
          when c == ?", c < Spc
            raise Error, "invalid character in string literal \"#{q}\""
          else
            # Copy anything else byte-for-byte.
            # Valid UTF-8 will remain valid UTF-8.
            # Invalid UTF-8 will remain invalid UTF-8.
            # In ruby >= 1.9, c is a codepoint, not a byte,
            # in which case this is still what we want.
            a[w] = c
            r += 1
            w += 1
          end
        end
        a[0,w]
      end


      # Encodes unicode character u as UTF-8
      # bytes in string a at position i.
      # Returns the number of bytes written.
      def ucharenc(a, i, u)
        case true
        when u <= Uchar1max
          a[i] = (u & 0xff).chr
          1
        when u <= Uchar2max
          a[i+0] = (Utag2 | ((u>>6)&0xff)).chr
          a[i+1] = (Utagx | (u&Umaskx)).chr
          2
        when u <= Uchar3max
          a[i+0] = (Utag3 | ((u>>12)&0xff)).chr
          a[i+1] = (Utagx | ((u>>6)&Umaskx)).chr
          a[i+2] = (Utagx | (u&Umaskx)).chr
          3
        else
          a[i+0] = (Utag4 | ((u>>18)&0xff)).chr
          a[i+1] = (Utagx | ((u>>12)&Umaskx)).chr
          a[i+2] = (Utagx | ((u>>6)&Umaskx)).chr
          a[i+3] = (Utagx | (u&Umaskx)).chr
          4
        end
      end


      def hexdec4(s)
        if s.length != 4
          raise Error, 'short'
        end
        (nibble(s[0])<<12) | (nibble(s[1])<<8) | (nibble(s[2])<<4) | nibble(s[3])
      end


      def subst(u1, u2)
        if Usurr1 <= u1 && u1 < Usurr2 && Usurr2 <= u2 && u2 < Usurr3
          return ((u1-Usurr1)<<10) | (u2-Usurr2) + Usurrself
        end
        return Ucharerr
      end


      def surrogate?(u)
        Usurr1 <= u && u < Usurr3
      end


      def nibble(c)
        case true
        when ?0 <= c && c <= ?9 then c.ord - ?0.ord
        when ?a <= c && c <= ?z then c.ord - ?a.ord + 10
        when ?A <= c && c <= ?Z then c.ord - ?A.ord + 10
        else
          raise Error, "invalid hex code #{c}"
        end
      end


      # Encodes x into a json text. It may contain only
      # Array, Hash, String, Numeric, true, false, nil.
      # (Note, this list excludes Symbol.)
      # X itself must be an Array or a Hash.
      # No other value can be encoded, and an error will
      # be raised if x contains any other value, such as
      # Nan, Infinity, Symbol, and Proc, or if a Hash key
      # is not a String.
      # Strings contained in x must be valid UTF-8.
      def encode(x)
        case x
        when Hash    then objenc(x)
        when Array   then arrenc(x)
        else
          raise Error, 'root value must be an Array or a Hash'
        end
      end


      def valenc(x)
        case x
        when Hash    then objenc(x)
        when Array   then arrenc(x)
        when String  then strenc(x)
        when Numeric then numenc(x)
        when true    then "true"
        when false   then "false"
        when nil     then "null"
        else
          raise Error, "cannot encode #{x.class}: #{x.inspect}"
        end
      end


      def objenc(x)
        '{' + x.map{|k,v| keyenc(k) + ':' + valenc(v)}.join(',') + '}'
      end


      def arrenc(a)
        '[' + a.map{|x| valenc(x)}.join(',') + ']'
      end


      def keyenc(k)
        case k
        when String then strenc(k)
        else
          raise Error, "Hash key is not a string: #{k.inspect}"
        end
      end


      def strenc(s)
        t = StringIO.new
        t.putc(?")
        r = 0

        # In ruby >= 1.9, s[r] is a codepoint, not a byte.
        rubydoesenc = s.class.method_defined?(:encoding)

        while r < s.length
          case s[r]
          when ?"  then t.print('\\"')
          when ?\\ then t.print('\\\\')
          when ?\b then t.print('\\b')
          when ?\f then t.print('\\f')
          when ?\n then t.print('\\n')
          when ?\r then t.print('\\r')
          when ?\t then t.print('\\t')
          else
            c = s[r]
            case true
            when rubydoesenc
              begin
                c.ord # will raise an error if c is invalid UTF-8
                t.write(c)
              rescue
                t.write(Ustrerr)
              end
            when Spc <= c && c <= ?~
              t.putc(c)
            else
              n = ucharcopy(t, s, r) # ensure valid UTF-8 output
              r += n - 1 # r is incremented below
            end
          end
          r += 1
        end
        t.putc(?")
        t.string
      end


      def numenc(x)
        if ((x.nan? || x.infinite?) rescue false)
          raise Error, "Numeric cannot be represented: #{x}"
        end
        "#{x}"
      end


      # Copies the valid UTF-8 bytes of a single character
      # from string s at position i to I/O object t, and
      # returns the number of bytes copied.
      # If no valid UTF-8 char exists at position i,
      # ucharcopy writes Ustrerr and returns 1.
      def ucharcopy(t, s, i)
        n = s.length - i
        raise Utf8Error if n < 1

        c0 = s[i].ord

        # 1-byte, 7-bit sequence?
        if c0 < Utagx
          t.putc(c0)
          return 1
        end

        raise Utf8Error if c0 < Utag2 # unexpected continuation byte?

        raise Utf8Error if n < 2 # need continuation byte
        c1 = s[i+1].ord
        raise Utf8Error if c1 < Utagx || Utag2 <= c1

        # 2-byte, 11-bit sequence?
        if c0 < Utag3
          raise Utf8Error if ((c0&Umask2)<<6 | (c1&Umaskx)) <= Uchar1max
          t.putc(c0)
          t.putc(c1)
          return 2
        end

        # need second continuation byte
        raise Utf8Error if n < 3

        c2 = s[i+2].ord
        raise Utf8Error if c2 < Utagx || Utag2 <= c2

        # 3-byte, 16-bit sequence?
        if c0 < Utag4
          u = (c0&Umask3)<<12 | (c1&Umaskx)<<6 | (c2&Umaskx)
          raise Utf8Error if u <= Uchar2max
          t.putc(c0)
          t.putc(c1)
          t.putc(c2)
          return 3
        end

        # need third continuation byte
        raise Utf8Error if n < 4
        c3 = s[i+3].ord
        raise Utf8Error if c3 < Utagx || Utag2 <= c3

        # 4-byte, 21-bit sequence?
        if c0 < Utag5
          u = (c0&Umask4)<<18 | (c1&Umaskx)<<12 | (c2&Umaskx)<<6 | (c3&Umaskx)
          raise Utf8Error if u <= Uchar3max
          t.putc(c0)
          t.putc(c1)
          t.putc(c2)
          t.putc(c3)
          return 4
        end

        raise Utf8Error
      rescue Utf8Error
        t.write(Ustrerr)
        return 1
      end


      class Utf8Error < ::StandardError
      end


      class Error < ::StandardError
      end


      Utagx = 0x80 # 1000 0000
      Utag2 = 0xc0 # 1100 0000
      Utag3 = 0xe0 # 1110 0000
      Utag4 = 0xf0 # 1111 0000
      Utag5 = 0xF8 # 1111 1000
      Umaskx = 0x3f # 0011 1111
      Umask2 = 0x1f # 0001 1111
      Umask3 = 0x0f # 0000 1111
      Umask4 = 0x07 # 0000 0111
      Uchar1max = (1<<7) - 1
      Uchar2max = (1<<11) - 1
      Uchar3max = (1<<16) - 1
      Ucharerr = 0xFFFD # unicode "replacement char"
      Ustrerr = "\xef\xbf\xbd" # unicode "replacement char"
      Usurrself = 0x10000
      Usurr1 = 0xd800
      Usurr2 = 0xdc00
      Usurr3 = 0xe000

      Spc = ' '[0]
      Unesc = {?b=>?\b, ?f=>?\f, ?n=>?\n, ?r=>?\r, ?t=>?\t}
    end
  end
end
