src/utils/vttparser.js

/*
 * Source: https://github.com/mozilla/vtt.js/blob/master/dist/vtt.js#L1716
 */
 
import VTTCue from './vttcue';
 
const StringDecoder = function StringDecoder () {
  return {
    decode: function (data) {
      if (!data) {
        return '';
      }
 
      if (typeof data !== 'string') {
        throw new Error('Error - expected string data.');
      }
 
      return decodeURIComponent(encodeURIComponent(data));
    }
  };
};
 
function VTTParser () {
  this.window = window;
  this.state = 'INITIAL';
  this.buffer = '';
  this.decoder = new StringDecoder();
  this.regionList = [];
}
 
// Try to parse input as a time stamp.
function parseTimeStamp (input) {
  function computeSeconds (h, m, s, f) {
    return (h | 0) * 3600 + (m | 0) * 60 + (s | 0) + (f | 0) / 1000;
  }
 
  let m = input.match(/^(\d+):(\d{2})(:\d{2})?\.(\d{3})/);
  if (!m) {
    return null;
  }
 
  if (m[3]) {
    // Timestamp takes the form of [hours]:[minutes]:[seconds].[milliseconds]
    return computeSeconds(m[1], m[2], m[3].replace(':', ''), m[4]);
  } else if (m[1] > 59) {
    // Timestamp takes the form of [hours]:[minutes].[milliseconds]
    // First position is hours as it's over 59.
    return computeSeconds(m[1], m[2], 0, m[4]);
  } else {
    // Timestamp takes the form of [minutes]:[seconds].[milliseconds]
    return computeSeconds(0, m[1], m[2], m[4]);
  }
}
 
// A settings object holds key/value pairs and will ignore anything but the first
// assignment to a specific key.
function Settings () {
  this.values = Object.create(null);
}
 
Settings.prototype = {
  // Only accept the first assignment to any key.
  set: function (k, v) {
    if (!this.get(k) && v !== '') {
      this.values[k] = v;
    }
  },
  // Return the value for a key, or a default value.
  // If 'defaultKey' is passed then 'dflt' is assumed to be an object with
  // a number of possible default values as properties where 'defaultKey' is
  // the key of the property that will be chosen; otherwise it's assumed to be
  // a single value.
  get: function (k, dflt, defaultKey) {
    if (defaultKey) {
      return this.has(k) ? this.values[k] : dflt[defaultKey];
    }
 
    return this.has(k) ? this.values[k] : dflt;
  },
  // Check whether we have a value for a key.
  has: function (k) {
    return k in this.values;
  },
  // Accept a setting if its one of the given alternatives.
  alt: function (k, v, a) {
    for (let n = 0; n < a.length; ++n) {
      if (v === a[n]) {
        this.set(k, v);
        break;
      }
    }
  },
  // Accept a setting if its a valid (signed) integer.
  integer: function (k, v) {
    if (/^-?\d+$/.test(v)) { // integer
      this.set(k, parseInt(v, 10));
    }
  },
  // Accept a setting if its a valid percentage.
  percent: function (k, v) {
    let m;
    if ((m = v.match(/^([\d]{1,3})(\.[\d]*)?%$/))) {
      v = parseFloat(v);
      if (v >= 0 && v <= 100) {
        this.set(k, v);
        return true;
      }
    }
    return false;
  }
};
 
// Helper function to parse input into groups separated by 'groupDelim', and
// interprete each group as a key/value pair separated by 'keyValueDelim'.
function parseOptions (input, callback, keyValueDelim, groupDelim) {
  let groups = groupDelim ? input.split(groupDelim) : [input];
  for (let i in groups) {
    if (typeof groups[i] !== 'string') {
      continue;
    }
 
    let kv = groups[i].split(keyValueDelim);
    if (kv.length !== 2) {
      continue;
    }
 
    let k = kv[0];
    let v = kv[1];
    callback(k, v);
  }
}
 
let defaults = new VTTCue(0, 0, 0);
// 'middle' was changed to 'center' in the spec: https://github.com/w3c/webvtt/pull/244
//  Safari doesn't yet support this change, but FF and Chrome do.
let center = defaults.align === 'middle' ? 'middle' : 'center';
 
function parseCue (input, cue, regionList) {
  // Remember the original input if we need to throw an error.
  let oInput = input;
  // 4.1 WebVTT timestamp
  function consumeTimeStamp () {
    let ts = parseTimeStamp(input);
    if (ts === null) {
      throw new Error('Malformed timestamp: ' + oInput);
    }
 
    // Remove time stamp from input.
    input = input.replace(/^[^\sa-zA-Z-]+/, '');
    return ts;
  }
 
  // 4.4.2 WebVTT cue settings
  function consumeCueSettings (input, cue) {
    let settings = new Settings();
 
    parseOptions(input, function (k, v) {
      switch (k) {
      case 'region':
        // Find the last region we parsed with the same region id.
        for (let i = regionList.length - 1; i >= 0; i--) {
          if (regionList[i].id === v) {
            settings.set(k, regionList[i].region);
            break;
          }
        }
        break;
      case 'vertical':
        settings.alt(k, v, ['rl', 'lr']);
        break;
      case 'line':
        var vals = v.split(','),
          vals0 = vals[0];
        settings.integer(k, vals0);
        if (settings.percent(k, vals0)) {
          settings.set('snapToLines', false);
        }
 
        settings.alt(k, vals0, ['auto']);
        if (vals.length === 2) {
          settings.alt('lineAlign', vals[1], ['start', center, 'end']);
        }
 
        break;
      case 'position':
        vals = v.split(',');
        settings.percent(k, vals[0]);
        if (vals.length === 2) {
          settings.alt('positionAlign', vals[1], ['start', center, 'end', 'line-left', 'line-right', 'auto']);
        }
 
        break;
      case 'size':
        settings.percent(k, v);
        break;
      case 'align':
        settings.alt(k, v, ['start', center, 'end', 'left', 'right']);
        break;
      }
    }, /:/, /\s/);
 
    // Apply default values for any missing fields.
    cue.region = settings.get('region', null);
    cue.vertical = settings.get('vertical', '');
    let line = settings.get('line', 'auto');
    if (line === 'auto' && defaults.line === -1) {
      // set numeric line number for Safari
      line = -1;
    }
    cue.line = line;
    cue.lineAlign = settings.get('lineAlign', 'start');
    cue.snapToLines = settings.get('snapToLines', true);
    cue.size = settings.get('size', 100);
    cue.align = settings.get('align', center);
    let position = settings.get('position', 'auto');
    if (position === 'auto' && defaults.position === 50) {
      // set numeric position for Safari
      position = cue.align === 'start' || cue.align === 'left' ? 0 : cue.align === 'end' || cue.align === 'right' ? 100 : 50;
    }
    cue.position = position;
  }
 
  function skipWhitespace () {
    input = input.replace(/^\s+/, '');
  }
 
  // 4.1 WebVTT cue timings.
  skipWhitespace();
  cue.startTime = consumeTimeStamp(); // (1) collect cue start time
  skipWhitespace();
  if (input.substr(0, 3) !== '-->') { // (3) next characters must match '-->'
    throw new Error('Malformed time stamp (time stamps must be separated by \'-->\'): ' +
      oInput);
  }
  input = input.substr(3);
  skipWhitespace();
  cue.endTime = consumeTimeStamp(); // (5) collect cue end time
 
  // 4.1 WebVTT cue settings list.
  skipWhitespace();
  consumeCueSettings(input, cue);
}
 
function fixLineBreaks (input) {
  return input.replace(/<br(?: \/)?>/gi, '\n');
}
 
VTTParser.prototype = {
  parse: function (data) {
    let self = this;
 
    // If there is no data then we won't decode it, but will just try to parse
    // whatever is in buffer already. This may occur in circumstances, for
    // example when flush() is called.
    if (data) {
      // Try to decode the data that we received.
      self.buffer += self.decoder.decode(data, { stream: true });
    }
 
    function collectNextLine () {
      let buffer = self.buffer;
      let pos = 0;
 
      buffer = fixLineBreaks(buffer);
 
      while (pos < buffer.length && buffer[pos] !== '\r' && buffer[pos] !== '\n') {
        ++pos;
      }
 
      let line = buffer.substr(0, pos);
      // Advance the buffer early in case we fail below.
      if (buffer[pos] === '\r') {
        ++pos;
      }
 
      if (buffer[pos] === '\n') {
        ++pos;
      }
 
      self.buffer = buffer.substr(pos);
      return line;
    }
 
    // 3.2 WebVTT metadata header syntax
    function parseHeader (input) {
      parseOptions(input, function (k, v) {
        switch (k) {
        case 'Region':
          // 3.3 WebVTT region metadata header syntax
          // console.log('parse region', v);
          // parseRegion(v);
          break;
        }
      }, /:/);
    }
 
    // 5.1 WebVTT file parsing.
    try {
      let line;
      if (self.state === 'INITIAL') {
        // We can't start parsing until we have the first line.
        if (!/\r\n|\n/.test(self.buffer)) {
          return this;
        }
 
        line = collectNextLine();
        // strip of UTF-8 BOM if any
        // https://en.wikipedia.org/wiki/Byte_order_mark#UTF-8
        let m = line.match(/^()?WEBVTT([ \t].*)?$/);
        if (!m || !m[0]) {
          throw new Error('Malformed WebVTT signature.');
        }
 
        self.state = 'HEADER';
      }
 
      let alreadyCollectedLine = false;
      while (self.buffer) {
        // We can't parse a line until we have the full line.
        if (!/\r\n|\n/.test(self.buffer)) {
          return this;
        }
 
        if (!alreadyCollectedLine) {
          line = collectNextLine();
        } else {
          alreadyCollectedLine = false;
        }
 
        switch (self.state) {
        case 'HEADER':
          // 13-18 - Allow a header (metadata) under the WEBVTT line.
          if (/:/.test(line)) {
            parseHeader(line);
          } else if (!line) {
            // An empty line terminates the header and starts the body (cues).
            self.state = 'ID';
          }
          continue;
        case 'NOTE':
          // Ignore NOTE blocks.
          if (!line) {
            self.state = 'ID';
          }
 
          continue;
        case 'ID':
          // Check for the start of NOTE blocks.
          if (/^NOTE($|[ \t])/.test(line)) {
            self.state = 'NOTE';
            break;
          }
          // 19-29 - Allow any number of line terminators, then initialize new cue values.
          if (!line) {
            continue;
          }
 
          self.cue = new VTTCue(0, 0, '');
          self.state = 'CUE';
          // 30-39 - Check if self line contains an optional identifier or timing data.
          if (line.indexOf('-->') === -1) {
            self.cue.id = line;
            continue;
          }
          // Process line as start of a cue.
          /* falls through */
        case 'CUE':
          // 40 - Collect cue timings and settings.
          try {
            parseCue(line, self.cue, self.regionList);
          } catch (e) {
            // In case of an error ignore rest of the cue.
            self.cue = null;
            self.state = 'BADCUE';
            continue;
          }
          self.state = 'CUETEXT';
          continue;
        case 'CUETEXT':
          var hasSubstring = line.indexOf('-->') !== -1;
          // 34 - If we have an empty line then report the cue.
          // 35 - If we have the special substring '-->' then report the cue,
          // but do not collect the line as we need to process the current
          // one as a new cue.
          if (!line || hasSubstring && (alreadyCollectedLine = true)) {
            // We are done parsing self cue.
            if (self.oncue) {
              self.oncue(self.cue);
            }
 
            self.cue = null;
            self.state = 'ID';
            continue;
          }
          if (self.cue.text) {
            self.cue.text += '\n';
          }
 
          self.cue.text += line;
          continue;
        case 'BADCUE': // BADCUE
          // 54-62 - Collect and discard the remaining cue.
          if (!line) {
            self.state = 'ID';
          }
 
          continue;
        }
      }
    } catch (e) {
      // If we are currently parsing a cue, report what we have.
      if (self.state === 'CUETEXT' && self.cue && self.oncue) {
        self.oncue(self.cue);
      }
 
      self.cue = null;
      // Enter BADWEBVTT state if header was not parsed correctly otherwise
      // another exception occurred so enter BADCUE state.
      self.state = self.state === 'INITIAL' ? 'BADWEBVTT' : 'BADCUE';
    }
    return this;
  },
  flush: function () {
    let self = this;
    try {
      // Finish decoding the stream.
      self.buffer += self.decoder.decode();
      // Synthesize the end of the current cue or region.
      if (self.cue || self.state === 'HEADER') {
        self.buffer += '\n\n';
        self.parse();
      }
      // If we've flushed, parsed, and we're still on the INITIAL state then
      // that means we don't have enough of the stream to parse the first
      // line.
      if (self.state === 'INITIAL') {
        throw new Error('Malformed WebVTT signature.');
      }
    } catch (e) {
      throw e;
    }
    if (self.onflush) {
      self.onflush();
    }
 
    return this;
  }
};
 
export { fixLineBreaks };
 
export default VTTParser;