text: var ID3v2 = require('./id3v2frames');
  
  ID3v2.frames = {
      // v2.2
      "BUF": "Recommended buffer size",
      "CNT": "Play counter",
      "COM": "Comments",
      "CRA": "Audio encryption",
      "CRM": "Encrypted meta frame",
      "ETC": "Event timing codes",
      "EQU": "Equalization",
      "GEO": "General encapsulated object",
      "IPL": "Involved people list",
      "LNK": "Linked information",
      "MCI": "Music CD Identifier",
      "MLL": "MPEG location lookup table",
      "PIC": "Attached picture",
      "POP": "Popularimeter",
      "REV": "Reverb",
      "RVA": "Relative volume adjustment",
      "SLT": "Synchronized lyric/text",
      "STC": "Synced tempo codes",
      "TAL": "Album/Movie/Show title",
      "TBP": "BPM (Beats Per Minute)",
      "TCM": "Composer",
      "TCO": "Content type",
      "TCR": "Copyright message",
      "TDA": "Date",
      "TDY": "Playlist delay",
      "TEN": "Encoded by",
      "TFT": "File type",
      "TIM": "Time",
      "TKE": "Initial key",
      "TLA": "Language(s)",
      "TLE": "Length",
      "TMT": "Media type",
      "TOA": "Original artist(s)/performer(s)",
      "TOF": "Original filename",
      "TOL": "Original Lyricist(s)/text writer(s)",
      "TOR": "Original release year",
      "TOT": "Original album/Movie/Show title",
      "TP1": "Lead artist(s)/Lead performer(s)/Soloist(s)/Performing group",
      "TP2": "Band/Orchestra/Accompaniment",
      "TP3": "Conductor/Performer refinement",
      "TP4": "Interpreted, remixed, or otherwise modified by",
      "TPA": "Part of a set",
      "TPB": "Publisher",
      "TRC": "ISRC (International Standard Recording Code)",
      "TRD": "Recording dates",
      "TRK": "Track number/Position in set",
      "TSI": "Size",
      "TSS": "Software/hardware and settings used for encoding",
      "TT1": "Content group description",
      "TT2": "Title/Songname/Content description",
      "TT3": "Subtitle/Description refinement",
      "TXT": "Lyricist/text writer",
      "TXX": "User defined text information frame",
      "TYE": "Year",
      "UFI": "Unique file identifier",
      "ULT": "Unsychronized lyric/text transcription",
      "WAF": "Official audio file webpage",
      "WAR": "Official artist/performer webpage",
      "WAS": "Official audio source webpage",
      "WCM": "Commercial information",
      "WCP": "Copyright/Legal information",
      "WPB": "Publishers official webpage",
      "WXX": "User defined URL link frame",
      // v2.3
      "AENC": "Audio encryption",
      "APIC": "Attached picture",
      "COMM": "Comments",
      "COMR": "Commercial frame",
      "ENCR": "Encryption method registration",
      "EQUA": "Equalization",
      "ETCO": "Event timing codes",
      "GEOB": "General encapsulated object",
      "GRID": "Group identification registration",
      "IPLS": "Involved people list",
      "LINK": "Linked information",
      "MCDI": "Music CD identifier",
      "MLLT": "MPEG location lookup table",
      "OWNE": "Ownership frame",
      "PRIV": "Private frame",
      "PCNT": "Play counter",
      "POPM": "Popularimeter",
      "POSS": "Position synchronisation frame",
      "RBUF": "Recommended buffer size",
      "RVAD": "Relative volume adjustment",
      "RVRB": "Reverb",
      "SYLT": "Synchronized lyric/text",
      "SYTC": "Synchronized tempo codes",
      "TALB": "Album/Movie/Show title",
      "TBPM": "BPM (beats per minute)",
      "TCOM": "Composer",
      "TCON": "Content type",
      "TCOP": "Copyright message",
      "TDAT": "Date",
      "TDLY": "Playlist delay",
      "TENC": "Encoded by",
      "TEXT": "Lyricist/Text writer",
      "TFLT": "File type",
      "TIME": "Time",
      "TIT1": "Content group description",
      "TIT2": "Title/songname/content description",
      "TIT3": "Subtitle/Description refinement",
      "TKEY": "Initial key",
      "TLAN": "Language(s)",
      "TLEN": "Length",
      "TMED": "Media type",
      "TOAL": "Original album/movie/show title",
      "TOFN": "Original filename",
      "TOLY": "Original lyricist(s)/text writer(s)",
      "TOPE": "Original artist(s)/performer(s)",
      "TORY": "Original release year",
      "TOWN": "File owner/licensee",
      "TPE1": "Lead performer(s)/Soloist(s)",
      "TPE2": "Band/orchestra/accompaniment",
      "TPE3": "Conductor/performer refinement",
      "TPE4": "Interpreted, remixed, or otherwise modified by",
      "TPOS": "Part of a set",
      "TPUB": "Publisher",
      "TRCK": "Track number/Position in set",
      "TRDA": "Recording dates",
      "TRSN": "Internet radio station name",
      "TRSO": "Internet radio station owner",
      "TSIZ": "Size",
      "TSRC": "ISRC (international standard recording code)",
      "TSSE": "Software/Hardware and settings used for encoding",
      "TYER": "Year",
      "TXXX": "User defined text information frame",
      "UFID": "Unique file identifier",
      "USER": "Terms of use",
      "USLT": "Unsychronized lyric/text transcription",
      "WCOM": "Commercial information",
      "WCOP": "Copyright/Legal information",
      "WOAF": "Official audio file webpage",
      "WOAR": "Official artist/performer webpage",
      "WOAS": "Official audio source webpage",
      "WORS": "Official internet radio station homepage",
      "WPAY": "Payment",
      "WPUB": "Publishers official webpage",
      "WXXX": "User defined URL link frame"
  };
  
  var _shortcuts = {
      "title": ["TIT2", "TT2"],
      "artist": ["TPE1", "TP1"],
      "album": ["TALB", "TAL"],
      "year": ["TYER", "TYE"],
      "comment": ["COMM", "COM"],
      "track": ["TRCK", "TRK"],
      "genre": ["TCON", "TCO"],
      "picture": ["APIC", "PIC"],
      "lyrics": ["USLT", "ULT"]
  };
  var _defaultShortcuts = ["title", "artist", "album", "track"];
  
  function getTagsFromShortcuts(shortcuts) {
      var tags = [];
      for (var i = 0, shortcut; shortcut = shortcuts[i]; i++) {
          tags = tags.concat(_shortcuts[shortcut] || [shortcut]);
      }
      return tags;
  }
  
  // The ID3v2 tag/frame size is encoded with four bytes where the most significant bit (bit 7) is set to zero in every byte, making a total of 28 bits. The zeroed bits are ignored, so a 257 bytes long tag is represented as $00 00 02 01.
  function readSynchsafeInteger32At(offset, data) {
      var size1 = data.getByteAt(offset);
      var size2 = data.getByteAt(offset + 1);
      var size3 = data.getByteAt(offset + 2);
      var size4 = data.getByteAt(offset + 3);
      // 0x7f = 0b01111111
      var size = size4 & 0x7f | ((size3 & 0x7f) << 7) | ((size2 & 0x7f) << 14) | ((size1 & 0x7f) << 21);
  
      return size;
  }
  
  function readFrameFlags(data, offset) {
      var flags = {
          message: {
              tag_alter_preservation: data.isBitSetAt(offset, 6),
              file_alter_preservation: data.isBitSetAt(offset, 5),
              read_only: data.isBitSetAt(offset, 4)
          },
          format: {
              grouping_identity: data.isBitSetAt(offset + 1, 7),
              compression: data.isBitSetAt(offset + 1, 3),
              encription: data.isBitSetAt(offset + 1, 2),
              unsynchronisation: data.isBitSetAt(offset + 1, 1),
              data_length_indicator: data.isBitSetAt(offset + 1, 0)
          }
      };
  
      return flags;
  }
  
  /** All the frames consists of a frame header followed by one or more fields containing the actual information.
   * The frame ID made out of the characters capital A-Z and 0-9. Identifiers beginning with "X", "Y" and "Z" are for experimental use and free for everyone to use, without the need to set the experimental bit in the tag header. Have in mind that someone else might have used the same identifier as you. All other identifiers are either used or reserved for future use.
   * The frame ID is followed by a size descriptor, making a total header size of ten bytes in every frame. The size is calculated as frame size excluding frame header (frame size - 10).
   */
  function readFrames(offset, end, data, id3header, tags) {
      var frames = {};
      var frameDataSize;
      var major = id3header["major"];
  
      tags = getTagsFromShortcuts(tags || _defaultShortcuts);
  
      while (offset < end) {
          var readFrameFunc = null;
          var frameData = data;
          var frameDataOffset = offset;
          var flags = null;
  
          switch (major) {
              case 2:
                  var frameID = frameData.getStringAt(frameDataOffset, 3);
                  var frameSize = frameData.getInteger24At(frameDataOffset + 3, true);
                  var frameHeaderSize = 6;
                  break;
  
              case 3:
                  var frameID = frameData.getStringAt(frameDataOffset, 4);
                  var frameSize = frameData.getLongAt(frameDataOffset + 4, true);
                  var frameHeaderSize = 10;
                  break;
  
              case 4:
                  var frameID = frameData.getStringAt(frameDataOffset, 4);
                  var frameSize = readSynchsafeInteger32At(frameDataOffset + 4, frameData);
                  var frameHeaderSize = 10;
                  break;
          }
          // if last frame GTFO
          if (frameID == "") {
              break;
          }
  
          // advance data offset to the next frame data
          offset += frameHeaderSize + frameSize;
          // skip unwanted tags
          if (tags.indexOf(frameID) < 0) {
              continue;
          }
  
          // read frame message and format flags
          if (major > 2) {
              flags = readFrameFlags(frameData, frameDataOffset + 8);
          }
  
          frameDataOffset += frameHeaderSize;
  
          // the first 4 bytes are the real data size
          // (after unsynchronisation && encryption)
          if (flags && flags.format.data_length_indicator) {
              frameDataSize = readSynchsafeInteger32At(frameDataOffset, frameData);
              frameDataOffset += 4;
              frameSize -= 4;
          }
  
          // TODO: support unsynchronisation
          if (flags && flags.format.unsynchronisation) {
              //frameData = removeUnsynchronisation(frameData, frameSize);
              continue;
          }
  
          // find frame parsing function
          if (frameID in ID3v2.readFrameData) {
              readFrameFunc = ID3v2.readFrameData[frameID];
          } else if (frameID[0] == "T") {
              readFrameFunc = ID3v2.readFrameData["T*"];
          }
  
          var parsedData = readFrameFunc ? readFrameFunc(frameDataOffset, frameSize, frameData, flags) : undefined;
          var desc = frameID in ID3v2.frames ? ID3v2.frames[frameID] : 'Unknown';
  
          var frame = {
              id: frameID,
              size: frameSize,
              description: desc,
              data: parsedData
          };
  
          if (frameID in frames) {
              if (frames[frameID].id) {
                  frames[frameID] = [frames[frameID]];
              }
              frames[frameID].push(frame);
          } else {
              frames[frameID] = frame;
          }
      }
  
      return frames;
  }
  
  //function removeUnsynchronisation(data, size)
  //{
  //    return data;
  //}
  
  function getFrameData(frames, ids) {
      if (typeof ids == 'string') {
          ids = [ids];
      }
  
      for (var i = 0, id; id = ids[i]; i++) {
          if (id in frames) {
              return frames[id].data;
          }
      }
  }
  
  ID3v2.loadData = function(data, callback) {
      data.loadRange([0, readSynchsafeInteger32At(6, data)], callback);
  };
  
  // http://www.id3.org/id3v2.3.0
  ID3v2.readTagsFromData = function(data, tags) {
      var offset = 0;
      var major = data.getByteAt(offset + 3);
      if (major > 4) {
          return {
              version: '>2.4'
          };
      }
      var revision = data.getByteAt(offset + 4);
      var unsynch = data.isBitSetAt(offset + 5, 7);
      var xheader = data.isBitSetAt(offset + 5, 6);
      var xindicator = data.isBitSetAt(offset + 5, 5);
      var size = readSynchsafeInteger32At(offset + 6, data);
      offset += 10;
  
      if (xheader) {
          var xheadersize = data.getLongAt(offset, true);
          // The 'Extended header size', currently 6 or 10 bytes, excludes itself.
          offset += xheadersize + 4;
      }
  
      var id3 = {
          "version": '2.' + major + '.' + revision,
          "major": major,
          "revision": revision,
          "flags": {
              "unsynchronisation": unsynch,
              "extended_header": xheader,
              "experimental_indicator": xindicator
          },
          "size": size
      };
      var frames = unsynch ? {} : readFrames(offset, size - 10, data, id3, tags);
      // create shortcuts for most common data
      for (var name in _shortcuts)
          if (_shortcuts.hasOwnProperty(name)) {
              var data = getFrameData(frames, _shortcuts[name]);
              if (data) id3[name] = data;
          }
  
      for (var frame in frames) {
          if (frames.hasOwnProperty(frame)) {
              id3[frame] = frames[frame];
          }
      }
  
      return id3;
  };
  
  module.exports = ID3v2;