// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of mime;


/**
 * A Mime Multipart class representing each part parsed by
 * [MimeMultipartTransformer]. The data is streamed in as it become available.
 */
abstract class MimeMultipart extends Stream<List<int>> {
  Map<String, String> get headers;
}

class _MimeMultipart extends MimeMultipart {
  final Map<String, String> headers;
  final Stream<List<int>> _stream;

  _MimeMultipart(this.headers, this._stream);

  StreamSubscription<List<int>> listen(void onData(List<int> data),
                                       {void onDone(),
                                        void onError(error),
                                        bool cancelOnError}) {
    return _stream.listen(onData,
                          onDone: onDone,
                          onError: onError,
                          cancelOnError: cancelOnError);
  }
}

class _Const {
  // Bytes for '()<>@,;:\\"/[]?={} \t'.
  static const SEPARATORS = const [40, 41, 60, 62, 64, 44, 59, 58, 92, 34, 47,
                                   91, 93, 63, 61, 123, 125, 32, 9];
}

class _CharCode {
  static const int HT = 9;
  static const int LF = 10;
  static const int CR = 13;
  static const int SP = 32;
  static const int DASH = 45;
  static const int COLON = 58;
}

/**
 * Parser for MIME multipart types of data as described in RFC 2046
 * section 5.1.1. The data is transformed into [MimeMultipart] objects, each
 * of them streaming the multipart data.
 */
class MimeMultipartTransformer
    implements StreamTransformer<List<int>, MimeMultipart> {
  static const int _START = 0;
  static const int _FIRST_BOUNDARY_ENDING = 111;
  static const int _FIRST_BOUNDARY_END = 112;
  static const int _BOUNDARY_ENDING = 1;
  static const int _BOUNDARY_END = 2;
  static const int _HEADER_START = 3;
  static const int _HEADER_FIELD = 4;
  static const int _HEADER_VALUE_START = 5;
  static const int _HEADER_VALUE = 6;
  static const int _HEADER_VALUE_FOLDING_OR_ENDING = 7;
  static const int _HEADER_VALUE_FOLD_OR_END = 8;
  static const int _HEADER_ENDING = 9;
  static const int _CONTENT = 10;
  static const int _LAST_BOUNDARY_DASH2 = 11;
  static const int _LAST_BOUNDARY_ENDING = 12;
  static const int _LAST_BOUNDARY_END = 13;
  static const int _DONE = 14;
  static const int _FAILURE = 15;

  StreamController _controller;
  StreamSubscription _subscription;

  StreamController _multipartController;
  Map<String, String> _headers;

  List<int> _boundary;
  int _state = _START;
  int _boundaryIndex = 2;

  // Current index in the data buffer. If index is negative then it
  // is the index into the artificial prefix of the boundary string.
  int _index;
  List<int> _buffer;

  StringBuffer _headerField = new StringBuffer();
  StringBuffer _headerValue = new StringBuffer();

  /**
   * Construct a new MIME multipart parser with the boundary
   * [boundary]. The boundary should be as specified in the content
   * type parameter, that is without the -- prefix.
   */
  MimeMultipartTransformer(String boundary) {
    List<int> charCodes = boundary.codeUnits;
    _boundary = new Uint8List(4 + charCodes.length);
    // Set-up the matching boundary preceding it with CRLF and two
    // dashes.
    _boundary[0] = _CharCode.CR;
    _boundary[1] = _CharCode.LF;
    _boundary[2] = _CharCode.DASH;
    _boundary[3] = _CharCode.DASH;
    _boundary.setRange(4, 4 + charCodes.length, charCodes);
  }

  void _resumeStream() {
    _subscription.resume();
  }

  void _pauseStream() {
    _subscription.pause();
  }

  Stream<MimeMultipart> bind(Stream<List<int>> stream) {
    _controller = new StreamController(
        sync: true,
        onPause: _pauseStream,
        onResume:_resumeStream,
        onCancel: () {
          _subscription.cancel();
        },
        onListen: () {
          _subscription = stream.listen(
              (data) {
                assert(_buffer == null);
                _pauseStream();
                _buffer = data;
                _index = 0;
                _parse();
              },
              onDone: () {
                if (_state != _DONE) {
                  _controller.addError(
                      new MimeMultipartException("Bad multipart ending"));
                }
                _controller.close();
              },
              onError: (error) {
                _controller.addError(error);
              });
        });
    return _controller.stream;
  }

  void _parse() {
    // Number of boundary bytes to artificially place before the supplied data.
    int boundaryPrefix = 0;
    // Position where content starts. Will be null if no known content
    // start exists. Will be negative of the content starts in the
    // boundary prefix. Will be zero or position if the content starts
    // in the current buffer.
    int contentStartIndex;

    // Function to report content data for the current part. The data
    // reported is from the current content start index up til the
    // current index. As the data can be artificially prefixed with a
    // prefix of the boundary both the content start index and index
    // can be negative.
    void reportData() {
      if (contentStartIndex < 0) {
        var contentLength = boundaryPrefix + _index - _boundaryIndex;
        if (contentLength <= boundaryPrefix) {
          _multipartController.add(
              _boundary.sublist(0, contentLength));
        } else {
          _multipartController.add(
              _boundary.sublist(0, boundaryPrefix));
          _multipartController.add(
              _buffer.sublist(0, contentLength - boundaryPrefix));
        }
      } else {
        var contentEndIndex = _index - _boundaryIndex;
        _multipartController.add(
            _buffer.sublist(contentStartIndex, contentEndIndex));
      }
    }

    if (_state == _CONTENT && _boundaryIndex == 0) {
      contentStartIndex = 0;
    } else {
      contentStartIndex = null;
    }
    // The data to parse might be "artificially" prefixed with a
    // partial match of the boundary.
    boundaryPrefix = _boundaryIndex;

    while ((_index < _buffer.length) && _state != _FAILURE && _state != _DONE) {
      if (_multipartController != null && _multipartController.isPaused) {
        return;
      }
      int byte;
      if (_index < 0) {
        byte = _boundary[boundaryPrefix + _index];
      } else {
        byte = _buffer[_index];
      }
      switch (_state) {
        case _START:
          if (byte == _boundary[_boundaryIndex]) {
            _boundaryIndex++;
            if (_boundaryIndex == _boundary.length) {
              _state = _FIRST_BOUNDARY_ENDING;
              _boundaryIndex = 0;
            }
          } else {
            // Restart matching of the boundary.
            _index = _index - _boundaryIndex;
            _boundaryIndex = 0;
          }
          break;

        case _FIRST_BOUNDARY_ENDING:
          if (byte == _CharCode.CR) {
            _state = _FIRST_BOUNDARY_END;
          } else {
            _expectWS(byte);
          }
          break;

        case _FIRST_BOUNDARY_END:
          _expect(byte, _CharCode.LF);
          _state = _HEADER_START;
          break;

        case _BOUNDARY_ENDING:
          if (byte == _CharCode.CR) {
            _state = _BOUNDARY_END;
          } else if (byte == _CharCode.DASH) {
            _state = _LAST_BOUNDARY_DASH2;
          } else {
            _expectWS(byte);
          }
          break;

        case _BOUNDARY_END:
          _expect(byte, _CharCode.LF);
          _multipartController.close();
          _multipartController = null;
          _state = _HEADER_START;
          break;

        case _HEADER_START:
          _headers = new Map<String, String>();
          if (byte == _CharCode.CR) {
            _state = _HEADER_ENDING;
          } else {
            // Start of new header field.
            _headerField.writeCharCode(_toLowerCase(byte));
            _state = _HEADER_FIELD;
          }
          break;

        case _HEADER_FIELD:
          if (byte == _CharCode.COLON) {
            _state = _HEADER_VALUE_START;
          } else {
            if (!_isTokenChar(byte)) {
              throw new MimeMultipartException("Invalid header field name");
            }
            _headerField.writeCharCode(_toLowerCase(byte));
          }
          break;

        case _HEADER_VALUE_START:
          if (byte == _CharCode.CR) {
            _state = _HEADER_VALUE_FOLDING_OR_ENDING;
          } else if (byte != _CharCode.SP && byte != _CharCode.HT) {
            // Start of new header value.
            _headerValue.writeCharCode(byte);
            _state = _HEADER_VALUE;
          }
          break;

        case _HEADER_VALUE:
          if (byte == _CharCode.CR) {
            _state = _HEADER_VALUE_FOLDING_OR_ENDING;
          } else {
            _headerValue.writeCharCode(byte);
          }
          break;

        case _HEADER_VALUE_FOLDING_OR_ENDING:
          _expect(byte, _CharCode.LF);
          _state = _HEADER_VALUE_FOLD_OR_END;
          break;

        case _HEADER_VALUE_FOLD_OR_END:
          if (byte == _CharCode.SP || byte == _CharCode.HT) {
            _state = _HEADER_VALUE_START;
          } else {
            String headerField = _headerField.toString();
            String headerValue =_headerValue.toString();
            _headers[headerField.toLowerCase()] = headerValue;
            _headerField = new StringBuffer();
            _headerValue = new StringBuffer();
            if (byte == _CharCode.CR) {
              _state = _HEADER_ENDING;
            } else {
              // Start of new header field.
              _headerField.writeCharCode(_toLowerCase(byte));
              _state = _HEADER_FIELD;
            }
          }
          break;

        case _HEADER_ENDING:
          _expect(byte, _CharCode.LF);
          _multipartController = new StreamController(
              sync: true,
              onPause: () {
                _pauseStream();
              },
              onResume: () {
                _resumeStream();
                _parse();
              });
          _controller.add(
              new _MimeMultipart(_headers, _multipartController.stream));
          _headers = null;
          _state = _CONTENT;
          contentStartIndex = _index + 1;
          break;

        case _CONTENT:
          if (byte == _boundary[_boundaryIndex]) {
            _boundaryIndex++;
            if (_boundaryIndex == _boundary.length) {
              if (contentStartIndex != null) {
                _index++;
                reportData();
                _index--;
              }
              _multipartController.close();
              _boundaryIndex = 0;
              _state = _BOUNDARY_ENDING;
            }
          } else {
            // Restart matching of the boundary.
            _index = _index - _boundaryIndex;
            if (contentStartIndex == null) contentStartIndex = _index;
            _boundaryIndex = 0;
          }
          break;

        case _LAST_BOUNDARY_DASH2:
          _expect(byte, _CharCode.DASH);
          _state = _LAST_BOUNDARY_ENDING;
          break;

        case _LAST_BOUNDARY_ENDING:
          if (byte == _CharCode.CR) {
            _state = _LAST_BOUNDARY_END;
          } else {
            _expectWS(byte);
          }
          break;

        case _LAST_BOUNDARY_END:
          _expect(byte, _CharCode.LF);
          _multipartController.close();
          _multipartController = null;
          _state = _DONE;
          break;

        default:
          // Should be unreachable.
          assert(false);
          break;
      }

      // Move to the next byte.
      _index++;
    }

    // Report any known content.
    if (_state == _CONTENT && contentStartIndex != null) {
      reportData();
    }

    // Resume if at end.
    if (_index == _buffer.length) {
      _buffer = null;
      _index = null;
      _resumeStream();
    }
  }

  bool _isTokenChar(int byte) {
    return byte > 31 && byte < 128 && _Const.SEPARATORS.indexOf(byte) == -1;
  }

  int _toLowerCase(int byte) {
    final int aCode = "A".codeUnitAt(0);
    final int zCode = "Z".codeUnitAt(0);
    final int delta = "a".codeUnitAt(0) - aCode;
    return (aCode <= byte && byte <= zCode) ? byte + delta : byte;
  }

  void _expect(int val1, int val2) {
    if (val1 != val2) {
      throw new MimeMultipartException("Failed to parse multipart mime 1");
    }
  }

  void _expectWS(int byte) {
    if (byte != _CharCode.SP && byte != _CharCode.HT) {
      throw new MimeMultipartException("Failed to parse multipart mime 2");
    }
  }
}


class MimeMultipartException implements Exception {
  const MimeMultipartException([String this.message = ""]);
  String toString() => "MimeMultipartException: $message";
  final String message;
}