module ActiveSupport::JSON::Backends::Yaml

def convert_json_to_yaml(json) #:nodoc:
  require 'strscan' unless defined? ::StringScanner
  scanner, quoting, marks, pos, times = ::StringScanner.new(json), false, [], nil, []
  while scanner.scan_until(/(\\['"]|['":,\\]|\\.)/)
    case char = scanner[1]
    when '"', "'"
      if !quoting
        quoting = char
        pos = scanner.pos
      elsif quoting == char
        if json[pos..scanner.pos-2] =~ DATE_REGEX
          # found a date, track the exact positions of the quotes so we can
          # overwrite them with spaces later.
          times << pos << scanner.pos
        end
        quoting = false
      end
    when ":",","
      marks << scanner.pos - 1 unless quoting
    when "\\"
      scanner.skip(/\\/)
    end
  end
  if marks.empty?
    json.gsub(/\\([\\\/]|u[[:xdigit:]]{4})/) do
      ustr = $1
      if ustr.start_with?('u')
        [ustr[1..-1].to_i(16)].pack("U")
      elsif ustr == '\\'
        '\\\\'
      else
        ustr
      end
    end
  else
    left_pos  = [-1].push(*marks)
    right_pos = marks << scanner.pos + scanner.rest_size
    output    = []
    left_pos.each_with_index do |left, i|
      scanner.pos = left.succ
      chunk = scanner.peek(right_pos[i] - scanner.pos + 1)
      # overwrite the quotes found around the dates with spaces
      while times.size > 0 && times[0] <= right_pos[i]
        chunk[times.shift - scanner.pos - 1] = ' '
      end
      chunk.gsub!(/\\([\\\/]|u[[:xdigit:]]{4})/) do
        ustr = $1
        if ustr.start_with?('u')
          [ustr[1..-1].to_i(16)].pack("U")
        elsif ustr == '\\'
          '\\\\'
        else
          ustr
        end
      end
      output << chunk
    end
    output = output * " "
    output.gsub!(/\\\//, '/')
    output
  end
end

def decode(json)
  if json.respond_to?(:read)
    json = json.read
  end
  YAML.load(convert_json_to_yaml(json))
rescue ArgumentError
  raise ParseError, "Invalid JSON string"
end