/* global BlobView, ID3v1Metadata, LazyLoader */
/* exported ID3v2Metadata */
'use strict';

/**
 * Parse files with ID3v2 metadata.
 *
 * Format information:
 *   http://id3.org/Developer%20Information
 */
var ID3v2Metadata = (function() {
  // Map id3v2 frame ids to metadata property names. Each line has two mappings:
  // one for id3v2.3+ and one for id3v2.2.
  var ID3V2FRAMES = {
    TPE1: 'artist',   TP1: 'artist',
    TALB: 'album',    TAL: 'album',
    TIT2: 'title',    TT2: 'title',
    TRCK: 'tracknum', TRK: 'tracknum',
    TPOS: 'discnum',  TPA: 'discnum',
    APIC: 'picture',  PIC: 'picture'
  };
  var ID3V2SECONDARYFRAMES = {
    TRCK: 'trackcount', TRK: 'trackcount',
    TPOS: 'disccount',  TPA: 'disccount'
  };

  /**
   * Parse a file and return a Promise with the metadata.
   *
   * @param {BlobView} blobview The audio file to parse.
   * @return {Promise} A Promise returning the parsed metadata object.
   */
  function parse(blobview) {
    return new Promise((resolve, reject) => {
      var header = parseHeader(blobview);
      if (header.version > 4) {
        console.warn('mp3 file with unknown metadata version');
        reject();
        return;
      }

      blobview.getMore(blobview.index, header.length, (moreview, err) => {
        if (err) {
          reject(err);
          return;
        }

        try {
          resolve(parseFrames(header, moreview));
        } catch(e) {
          console.warn('Invalid ID3v2 data for', blobview.blob.name, ':', e);
          reject(e);
        }
      });
    }).catch((e) => {
      return LazyLoader.load('js/metadata/id3v1.js').then(() => {
        return ID3v1Metadata.parse(blobview);
      });
    });
  }

  /**
   * Parse the header of an ID3 tag.
   *
   * @param {BlobView} blobview The audio file to parse.
   * @return {Object} An object describing the header's values.
   */
  function parseHeader(blobview) {
    // First three bytes are "ID3" or we wouldn't be here
    blobview.seek(3);

    var header = {
      get versionString() {
        return 'id3v2.' + this.version + '.' + this.revision;
      },

      get tag_unsynchronized() {
        return (this.flags & 0x80) !== 0;
      },

      get has_extended_header() {
        return (this.flags & 0x40) !== 0;
      }
    };

    header.version = blobview.readUnsignedByte();
    header.revision = blobview.readUnsignedByte();

    header.flags = blobview.readUnsignedByte();
    header.length = blobview.readID3Uint28BE();

    return header;
  }

  /**
   * Parse all the ID3 frames in this tag.
   *
   * @param {Object} header The header object for this ID3 tag.
   * @param {BlobView} blobview The audio file to parse.
   * @return {Object} The metadata extracted from the ID3 tag.
   */
  function parseFrames(header, blobview) {
    var metadata = {};
    metadata.tag_format = header.versionString;

    // In id3v2.3, the "unsynchronized" flag in the tag header applies to
    // the whole tag (excluding the tag header). In id3v2.4, the flag is just
    // an indicator that we should expect to see the "unsynchronized" flag
    // set on all the frames.
    if (header.tag_unsynchronized && header.version === 3) {
      blobview = deunsync(blobview, header.length);
    }

    // Skip the extended header, if there is one.
    if (header.has_extended_header) {
      var extended_header_size;
      if (header.version === 4) {
        // In id3v2.4, the size includes itself, i.e. the rest of the header
        // is |extended_header_size - 4|.
        extended_header_size = blobview.readID3Uint28BE() - 4;
      } else { // id3version === 3
        // In id3v2.3, the size *excludes* itself, i.e. the rest of the header
        // is |extended_header_size|.
        extended_header_size = blobview.readUnsignedInt();
      }
      blobview.advance(extended_header_size);
    }

    while (blobview.index < blobview.byteLength) {
      // If there is a null byte here, then we've found padding and we're done.
      if (blobview.getUint8(blobview.index) === 0) {
        break;
      }
      parseFrame(header, blobview, metadata);
    }

    return metadata;
  }

  /**
   * Parse an individual ID3 frame.
   *
   * @param {Object} header The header object for this ID3 tag.
   * @param {BlobView} blobview The audio file being parsed.
   * @param {Metadata} metadata The (partially filled-in) metadata object.
   */
  function parseFrame(header, blobview, metadata) {
    var frameid, framesize, frame_format_flags, frame_unsynchronized = false,
        data_len_indicator = false, unsupported_flags = false;

    switch (header.version) {
    case 2:
      frameid = blobview.readBinaryText(3);
      framesize = blobview.readUint24();
      break;
    case 3:
      frameid = blobview.readBinaryText(4);
      framesize = blobview.readUnsignedInt();
      // Ignore the frame status flags, since they only apply when modifying the
      // file/tag.
      blobview.readUnsignedByte();
      frame_format_flags = blobview.readUnsignedByte();

      unsupported_flags = (frame_format_flags !== 0);
      break;
    case 4:
      frameid = blobview.readBinaryText(4);
      framesize = blobview.readID3Uint28BE();
      blobview.readUnsignedByte(); // As above, ignore the frame status flags.
      frame_format_flags = blobview.readUnsignedByte();

      data_len_indicator   = ((frame_format_flags & 0b00000001) !== 0);
      frame_unsynchronized = ((frame_format_flags & 0b00000010) !== 0);
      unsupported_flags    = ((frame_format_flags & 0b11111100) !== 0);
      break;
    }

    var nextframe = blobview.index + framesize;
    var propname = ID3V2FRAMES[frameid];

    // Skip frames we don't care about.
    if (!propname) {
      blobview.seek(nextframe);
      return;
    }

    // Skip frames with flags we don't understand.
    if (unsupported_flags) {
      console.warn('Skipping', frameid, 'frame with unsupported format flags',
                   '0b' + frame_format_flags.toString(2));
      blobview.seek(nextframe);
      return;
    }

    try {
      var frameview, framevalue, data_len;

      if (data_len_indicator) {
        data_len = blobview.readID3Uint28BE();
        framesize -= 4;
      }

      if (frame_unsynchronized) {
        frameview = deunsync(blobview, framesize);
        framesize = frameview.sliceLength;
        if (data_len !== undefined && framesize != data_len) {
          console.warn('de-unsynced frame size (' + framesize + ') doesn\'t' +
                       'match data length indicator (' + data_len + ')');
        }
      } else {
        frameview = blobview;
      }

      switch (frameid) {
      case 'TPE1': case 'TP1': // artist
      case 'TALB': case 'TAL': // album
      case 'TIT2': case 'TT2': // title
        framevalue = readTextFrame(header, frameview, framesize);
        break;
      case 'TRCK': case 'TRK': // track
      case 'TPOS': case 'TPA': // disc
        framevalue = readNumericPairFrame(header, frameview, framesize);
        if (framevalue[1] !== null) {
          metadata[ID3V2SECONDARYFRAMES[frameid]] = framevalue[1];
        }
        framevalue = framevalue[0];
        break;
      case 'APIC': case 'PIC': // picture
        framevalue = readPicFrame(header, frameview, framesize);
        break;
      default:
        console.error('Should not have gotten here');
      }

      if (framevalue !== null) {
        metadata[propname] = framevalue;
      }
    } catch (e) {
      console.warn('Error parsing mp3 metadata frame', frameid, ':', e);
    }

    // Make sure we're at the start of the next frame before continuing
    blobview.seek(nextframe);
  }

  /**
   * Reverse the ID3 unsynchronization so that we get the unescaped data. This
   * will advance the view to the end of the unsynchronized block so that you
   * can continue to use the original view once you're finished with the
   * deunsynced view.
   *
   * @param {BlobView} view The original BlobView for the ID3 tag.
   * @param {Number} framesize The size of the unsynchronized frame.
   * @return {BlobView} A new BlobView with the deunsynced data.
   */
  function deunsync(view, framesize) {
    // To de-unsychronize a frame, we need to convert all instances of
    // |0xff 00| to |0xff|.
    var data = new Uint8Array(framesize), was0xff = false, dataIndex = 0;
    for (var i = 0; i < framesize; i++) {
      var b = view.readUnsignedByte();
      if (was0xff && b === 0x00) {
        continue;
      }
      was0xff = (b === 0xff);
      data[dataIndex++] = b;
    }

    // Create a new BlobView with the de-unsynchronized data.
    var deunsynced_view = new BlobView.getFromArrayBuffer(
      data.buffer, 0, dataIndex, view.littleEndian
    );
    deunsynced_view.deunsynced = true;
    return deunsynced_view;
  }

  /**
   * Read the value from a textual ID3 frame (one whose name starts with "T",
   * and isn't "TXXX").
   *
   * @param {Object} header The header object for this ID3 tag.
   * @param {BlobView} view The audio file being parsed.
   * @param {Number} size The size in bytes of this frame's value.
   * @param {Number} encoding The encoding for this string (0: latin-1,
   *   1: utf16, 2: utf16-be, 3: utf-8). If null, determine the encoding from
   *   the first byte of the value.
   * @param {String} The value of this frame.
   */
  function readTextFrame(header, view, size, encoding) {
    if (encoding === undefined) {
      encoding = view.readUnsignedByte();
      size = size - 1;
    }
    if (header.version === 4) {
      // In id3v2.4, all text frames can have multiple values, separated by
      // the null character. For now, we join them together to make one big
      // string.
      return readEncodedTextArray(view, size, encoding);
    } else {
      // In id3v2.3, some text frames can have multiple values, separated by
      // '/', so we don't need to do anything special here. In fact, even if
      // we start treating multi-value text frames as an array, we probably
      // shouldn't do anything, since '/' is a bad delimiter.
      return readEncodedText(view, size, encoding);
    }
  }

  /**
   * Read the value from a numeric pair frame (track number or disc number).
   *
   * @param {Object} header The header object for this ID3 tag.
   * @param {BlobView} view The audio file being parsed.
   * @param {Number} size The size in bytes of this frame's value.
   * @param {Number} encoding The encoding for this string (0: latin-1,
   *   1: utf16, 2: utf16-be, 3: utf-8). If null, determine the encoding from
   *   the first byte of the value.
   * @param {Array} The value of this frame, as two Numbers.
   */
  function readNumericPairFrame(header, view, size, encoding) {
    var text = readTextFrame(header, view, size, encoding);
    var pair = text.split('/', 2).map(function(val) {
      var i = parseInt(val, 10);
      return isNaN(i) || !isFinite(i) ? null : i;
    });
    if (pair.length === 1) {
      pair.push(null);
    }
    return pair;
  }

  /**
   * Read the value from a picture frame.
   *
   * @param {Object} header The header object for this ID3 tag.
   * @param {BlobView} view The audio file being parsed.
   * @param {Number} size The size in bytes of this frame's value.
   * @param {Picture} The value of this frame.
   */
  function readPicFrame(header, view, size) {
    var start = view.index;
    var encoding = view.readUnsignedByte();
    var mimetype;
    // mimetype is different for old PIC frames and new APIC frames
    if (header.version === 2) {
      mimetype = view.readLatin1Text(3);
      if (mimetype === 'JPG') {
        mimetype = 'image/jpeg';
      } else if (mimetype === 'PNG') {
        mimetype = 'image/png';
      }
    } else {
      mimetype = view.readNullTerminatedLatin1Text(size - 1);
      if (mimetype === '-->') {
        // XXX: We don't support URLs (the spec recommends against them anyway).
        console.error('URL for cover art is not supported.');
        return null;
      }
    }

    // We ignore these next two fields.
    view.readUnsignedByte(); // kind
    readEncodedText(view, size - (view.index - start), encoding); // desc

    var picstart = view.sliceOffset + view.viewOffset + view.index;
    var picsize = size - (view.index - start);
    var picend = picstart + picsize;

    if (view.deunsynced) {
      return {
        flavor: 'unsynced',
        blob: new Blob(
          [view.buffer.slice(picstart, picend)],
          {type: mimetype}
        )
      };
    } else {
      // Now return an object that specifies where to pull the image from
      // The properties of this object can be passed to blob.slice()
      return {
        flavor: 'embedded',
        start: picstart,
        end: picend,
        type: mimetype
      };
    }
  }

  /**
   * Read an array of strings from a frame.
   *
   * @param {BlobView} view The audio file being parsed.
   * @param {Number} size The size in bytes of this frame's value.
   * @param {Number} encoding The encoding for this string (0: latin-1,
   *   1: utf16, 2: utf16-be, 3: utf-8). If null, determine the encoding from
   *   the first byte of the value.
   * @param {String} The strings, joined by " / ".
   */
  function readEncodedTextArray(view, size, encoding) {
    var text;
    switch (encoding) {
    case 0:
      text = view.readLatin1Text(size);
      break;
    case 1:
      text = view.readUTF16Text(size, undefined);
      break;
    case 2:
      text = view.readUTF16Text(size, false);
      break;
    case 3:
      text = view.readUTF8Text(size);
      break;
    default:
      throw Error('unknown text encoding');
    }

    // Remove any trailing nulls and replace nulls in the middle with ' / '.
    // XXX: When the database supports arrays of values for each field, we
    // should split this into a proper array!
    return text.replace(/\0+$/, '').replace('\0', ' / ');
  }

  /**
   * Read a single string from a frame.
   *
   * @param {BlobView} view The audio file being parsed.
   * @param {Number} size The size in bytes of this frame's value.
   * @param {Number} encoding The encoding for this string (0: latin-1,
   *   1: utf16, 2: utf16-be, 3: utf-8). If null, determine the encoding from
   *   the first byte of the value.
   * @param {String} The string.
   */
  function readEncodedText(view, size, encoding) {
    switch (encoding) {
    case 0:
      return view.readNullTerminatedLatin1Text(size);
    case 1:
      // Round down to the nearest 16 bits.
      return view.readNullTerminatedUTF16Text(size - (size % 2), undefined);
    case 2:
      // Round down to the nearest 16 bits.
      return view.readNullTerminatedUTF16Text(size - (size % 2), false);
    case 3:
      return view.readNullTerminatedUTF8Text(size);
    default:
      throw Error('unknown text encoding');
    }
  }

  return {
    parse: parse
  };

})();