class Sass::Source::Map

def to_json(options)
  css_uri, css_path, sourcemap_path =
    options[:css_uri], options[:css_path], options[:sourcemap_path]
  unless css_uri || (css_path && sourcemap_path)
    raise ArgumentError.new("Sass::Source::Map#to_json requires either " \
      "the :css_uri option or both the :css_path and :soucemap_path options.")
  end
  css_path &&= Sass::Util.pathname(File.absolute_path(css_path))
  sourcemap_path &&= Sass::Util.pathname(File.absolute_path(sourcemap_path))
  css_uri ||= Sass::Util.file_uri_from_path(
    Sass::Util.relative_path_from(css_path, sourcemap_path.dirname))
  result = "{\n"
  write_json_field(result, "version", 3, true)
  source_uri_to_id = {}
  id_to_source_uri = {}
  id_to_contents = {} if options[:type] == :inline
  next_source_id = 0
  line_data = []
  segment_data_for_line = []
  # These track data necessary for the delta coding.
  previous_target_line = nil
  previous_target_offset = 1
  previous_source_line = 1
  previous_source_offset = 1
  previous_source_id = 0
  @data.each do |m|
    file, importer = m.input.file, m.input.importer
    next unless importer
    if options[:type] == :inline
      source_uri = file
    else
      sourcemap_dir = sourcemap_path && sourcemap_path.dirname.to_s
      sourcemap_dir = nil if options[:type] == :file
      source_uri = importer.public_url(file, sourcemap_dir)
      next unless source_uri
    end
    current_source_id = source_uri_to_id[source_uri]
    unless current_source_id
      current_source_id = next_source_id
      next_source_id += 1
      source_uri_to_id[source_uri] = current_source_id
      id_to_source_uri[current_source_id] = source_uri
      if options[:type] == :inline
        id_to_contents[current_source_id] =
          importer.find(file, {}).instance_variable_get('@template')
      end
    end
    [
      [m.input.start_pos, m.output.start_pos],
      [m.input.end_pos, m.output.end_pos]
    ].each do |source_pos, target_pos|
      if previous_target_line != target_pos.line
        line_data.push(segment_data_for_line.join(",")) unless segment_data_for_line.empty?
        (target_pos.line - 1 - (previous_target_line || 0)).times {line_data.push("")}
        previous_target_line = target_pos.line
        previous_target_offset = 1
        segment_data_for_line = []
      end
      # `segment` is a data chunk for a single position mapping.
      segment = ""
      # Field 1: zero-based starting offset.
      segment << Sass::Util.encode_vlq(target_pos.offset - previous_target_offset)
      previous_target_offset = target_pos.offset
      # Field 2: zero-based index into the "sources" list.
      segment << Sass::Util.encode_vlq(current_source_id - previous_source_id)
      previous_source_id = current_source_id
      # Field 3: zero-based starting line in the original source.
      segment << Sass::Util.encode_vlq(source_pos.line - previous_source_line)
      previous_source_line = source_pos.line
      # Field 4: zero-based starting offset in the original source.
      segment << Sass::Util.encode_vlq(source_pos.offset - previous_source_offset)
      previous_source_offset = source_pos.offset
      segment_data_for_line.push(segment)
      previous_target_line = target_pos.line
    end
  end
  line_data.push(segment_data_for_line.join(","))
  write_json_field(result, "mappings", line_data.join(";"))
  source_names = []
  (0...next_source_id).each {|id| source_names.push(id_to_source_uri[id].to_s)}
  write_json_field(result, "sources", source_names)
  if options[:type] == :inline
    write_json_field(result, "sourcesContent",
      (0...next_source_id).map {|id| id_to_contents[id]})
  end
  write_json_field(result, "names", [])
  write_json_field(result, "file", css_uri)
  result << "\n}"
  result
end