msimerson/safe-log-reader

'use strict';

// https://nodejs.org/api/stream.html#stream_object_mode

const StringDecoder = require('string_decoder').StringDecoder;
const Transform = require('stream').Transform;

class LineSplitter extends Transform {

  constructor (options) {

    if (!options) options = {};
    if (!options.transform) options.transform = { objectMode: true };

    super(options.transform)

    this._encoding  = options.encoding  || 'utf8';
    this._seperator = options.seperator || '\n';
    this._buffer = '';
    this._decoder = new StringDecoder(this._encoding);

    this.bytes = options.bytes || 0;
  }

  _transform (chunk, encoding, done) {
    this.bytes += chunk.length;

    if (encoding !== this._encoding) {
      // this is likely 'buffer' when the source file is an archive
      this._buffer += this._decoder.write(chunk);
    }
    else {
      // already decoded by fs.createReadStream
      this._buffer += chunk;
    }

    const lines = this._buffer.split(this._seperator);
    this._buffer = lines.pop();

    for (const line of lines) this.push(line);

    done();
  }

  _flush (done) {
    // trailing text (after last seperator)
    const rem = this._buffer.trim();
    if (rem) this.push(rem);
    this._buffer = '';
    done();
  }
}

module.exports = function (options) {
  return new LineSplitter(options);
}