/* Copyright (c) 2012-2014 LevelUP contributors
 * See list at <https://github.com/rvagg/node-levelup#contributing>
 * MIT License <https://github.com/rvagg/node-levelup/blob/master/LICENSE.md>
 */

// NOTE: we are fixed to readable-stream@1.0.x for now
// for pure Streams2 across Node versions
import ReadableStreamCore from 'readable-stream';
import inherits from 'inherits';

var Readable = ReadableStreamCore.Readable;

function ReadStream(options, makeData) {
  if (!(this instanceof ReadStream)) {
    return new ReadStream(options, makeData);
  }

  Readable.call(this, { objectMode: true, highWaterMark: options.highWaterMark });

  // purely to keep `db` around until we're done so it's not GCed if the user doesn't keep a ref

  this._waiting = false;
  this._options = options;
  this._makeData = makeData;
}

inherits(ReadStream, Readable);

ReadStream.prototype.setIterator = function (it) {
  this._iterator = it;
  /* istanbul ignore if */
  if (this._destroyed) {
    return it.end(function () {});
  }
  /* istanbul ignore if */
  if (this._waiting) {
    this._waiting = false;
    return this._read();
  }
  return this;
};

ReadStream.prototype._read = function read() {
  var self = this;
  /* istanbul ignore if */
  if (self._destroyed) {
    return;
  }
  /* istanbul ignore if */
  if (!self._iterator) {
    return this._waiting = true;
  }

  self._iterator.next(function (err, key, value) {
    if (err || (key === undefined && value === undefined)) {
      if (!err && !self._destroyed) {
        self.push(null);
      }
      return self._cleanup(err);
    }


    value = self._makeData(key, value);
    if (!self._destroyed) {
      self.push(value);
    }
  });
};

ReadStream.prototype._cleanup = function (err) {
  if (this._destroyed) {
    return;
  }

  this._destroyed = true;

  var self = this;
  /* istanbul ignore if */
  if (err) {
    self.emit('error', err);
  }

  /* istanbul ignore else */
  if (self._iterator) {
    self._iterator.end(function () {
      self._iterator = null;
      self.emit('close');
    });
  } else {
    self.emit('close');
  }
};

ReadStream.prototype.destroy = function () {
  this._cleanup();
};

export default ReadStream;