class Rack::Multipart::Parser

def self.parse(io, content_length, content_type, tmpfile, bufsize, qp)
  return EMPTY if 0 == content_length
  boundary = parse_boundary content_type
  return EMPTY unless boundary
  if boundary.length > 70
    # RFC 1521 Section 7.2.1 imposes a 70 character maximum for the boundary.
    # Most clients use no more than 55 characters.
    raise Error, "multipart boundary size too large (#{boundary.length} characters)"
  end
  io = BoundedIO.new(io, content_length) if content_length
  parser = new(boundary, tmpfile, bufsize, qp)
  parser.parse(io)
  parser.result
end

def self.parse_boundary(content_type)
  return unless content_type
  data = content_type.match(MULTIPART)
  return unless data
  data[1]
end

def consume_boundary
  if read_buffer = @sbuf.scan_until(@body_regex)
    read_buffer.end_with?(EOL) ? :BOUNDARY : :END_BOUNDARY
  else
    @sbuf.terminate
    nil
  end
end

def dequote(str) # From WEBrick::HTTPUtils
  ret = (/\A"(.*)"\Z/ =~ str) ? $1 : str.dup
  ret.gsub!(/\\(.)/, "\\1")
  ret
end

def get_filename(head)
  filename = nil
  case head
  when RFC2183
    params = Hash[*head.scan(DISPPARM).flat_map(&:compact)]
    if filename = params['filename*']
      encoding, _, filename = filename.split("'", 3)
    elsif filename = params['filename']
      filename = $1 if filename =~ /^"(.*)"$/
    end
  when BROKEN
    filename = $1
    filename = $1 if filename =~ /^"(.*)"$/
  end
  return unless filename
  if filename.scan(/%.?.?/).all? { |s| /%[0-9a-fA-F]{2}/.match?(s) }
    filename = Utils.unescape_path(filename)
  end
  filename.scrub!
  if filename !~ /\\[^\\"]/
    filename = filename.gsub(/\\(.)/, '\1')
  end
  if encoding
    filename.force_encoding ::Encoding.find(encoding)
  end
  filename
end

def handle_consume_token
  tok = consume_boundary
  # break if we're at the end of a buffer, but not if it is the end of a field
  @state = if tok == :END_BOUNDARY || (@sbuf.eos? && tok != :BOUNDARY)
    :DONE
  else
    :MIME_HEAD
  end
end

def handle_empty_content!(content)
  if content.nil? || content.empty?
    raise EmptyContentError
  end
end

def handle_fast_forward
  while true
    case consume_boundary
    when :BOUNDARY
      # found opening boundary, transition to next state
      @state = :MIME_HEAD
      return
    when :END_BOUNDARY
      # invalid multipart upload
      if @sbuf.pos == @end_boundary_size && @sbuf.rest == EOL
        # stop parsing a buffer if a buffer is only an end boundary.
        @state = :DONE
        return
      end
      # retry for opening boundary
    else
      # no boundary found, keep reading data
      return :want_read
    end
  end
end

def handle_mime_body
  if (body_with_boundary = @sbuf.check_until(@body_regex)) # check but do not advance the pointer yet
    body = body_with_boundary.sub(/#{@body_regex}\z/m, '') # remove the boundary from the string
    @collector.on_mime_body @mime_index, body
    @sbuf.pos += body.length + 2 # skip \r\n after the content
    @state = :CONSUME_TOKEN
    @mime_index += 1
  else
    # Save what we have so far
    if @rx_max_size < @sbuf.rest_size
      delta = @sbuf.rest_size - @rx_max_size
      @collector.on_mime_body @mime_index, @sbuf.peek(delta)
      @sbuf.pos += delta
      @sbuf.string = @sbuf.rest
    end
    :want_read
  end
end

def handle_mime_head
  if @sbuf.scan_until(@head_regex)
    head = @sbuf[1]
    content_type = head[MULTIPART_CONTENT_TYPE, 1]
    if name = head[MULTIPART_CONTENT_DISPOSITION, 1]
      name = dequote(name)
    else
      name = head[MULTIPART_CONTENT_ID, 1]
    end
    filename = get_filename(head)
    if name.nil? || name.empty?
      name = filename || "#{content_type || TEXT_PLAIN}[]".dup
    end
    @collector.on_mime_head @mime_index, head, filename, content_type, name
    @state = :MIME_BODY
  else
    :want_read
  end
end

def initialize(boundary, tempfile, bufsize, query_parser)
  @query_parser   = query_parser
  @params         = query_parser.make_params
  @bufsize        = bufsize
  @state = :FAST_FORWARD
  @mime_index = 0
  @collector = Collector.new tempfile
  @sbuf = StringScanner.new("".dup)
  @body_regex = /(?:#{EOL}|\A)--#{Regexp.quote(boundary)}(?:#{EOL}|--)/m
  @end_boundary_size = boundary.bytesize + 4 # (-- at start, -- at finish)
  @rx_max_size = boundary.bytesize + 6 # (\r\n-- at start, either \r\n or -- at finish)
  @head_regex = /(.*?#{EOL})#{EOL}/m
end

def parse(io)
  outbuf = String.new
  read_data(io, outbuf)
  loop do
    status =
      case @state
      when :FAST_FORWARD
        handle_fast_forward
      when :CONSUME_TOKEN
        handle_consume_token
      when :MIME_HEAD
        handle_mime_head
      when :MIME_BODY
        handle_mime_body
      else # when :DONE
        return
      end
    read_data(io, outbuf) if status == :want_read
  end
end

def read_data(io, outbuf)
  content = io.read(@bufsize, outbuf)
  handle_empty_content!(content)
  @sbuf.concat(content)
end

def result
  @collector.each do |part|
    part.get_data do |data|
      tag_multipart_encoding(part.filename, part.content_type, part.name, data)
      @query_parser.normalize_params(@params, part.name, data)
    end
  end
  MultipartInfo.new @params.to_params_hash, @collector.find_all(&:file?).map(&:body)
end

def tag_multipart_encoding(filename, content_type, name, body)
  name = name.to_s
  encoding = Encoding::UTF_8
  name.force_encoding(encoding)
  return if filename
  if content_type
    list         = content_type.split(';')
    type_subtype = list.first
    type_subtype.strip!
    if TEXT_PLAIN == type_subtype
      rest = list.drop 1
      rest.each do |param|
        k, v = param.split('=', 2)
        k.strip!
        v.strip!
        v = v[1..-2] if v.start_with?('"') && v.end_with?('"')
        if k == "charset"
          encoding = begin
            Encoding.find v
          rescue ArgumentError
            Encoding::BINARY
          end
        end
      end
    end
  end
  name.force_encoding(encoding)
  body.force_encoding(encoding)
end