import { jsExtend as extend } from 'pouchdb-utils';
import Promise from 'pouchdb-promise';
import {
  replicate,
  toPouch
} from './replicateWrapper';
import inherits from 'inherits';
import { EventEmitter as EE } from 'events';
import { clone } from 'pouchdb-utils';

inherits(Sync, EE);
export default sync;
function sync(src, target, opts, callback) {
  if (typeof opts === 'function') {
    callback = opts;
    opts = {};
  }
  if (typeof opts === 'undefined') {
    opts = {};
  }
  opts = clone(opts);
  /*jshint validthis:true */
  opts.PouchConstructor = opts.PouchConstructor || this;
  src = toPouch(src, opts);
  target = toPouch(target, opts);
  return new Sync(src, target, opts, callback);
}

function Sync(src, target, opts, callback) {
  var self = this;
  this.canceled = false;

  var optsPush = opts.push ? extend({}, opts, opts.push) : opts;
  var optsPull = opts.pull ? extend({}, opts, opts.pull) : opts;

  this.push = replicate(src, target, optsPush);
  this.pull = replicate(target, src, optsPull);

  this.pushPaused = true;
  this.pullPaused = true;

  function pullChange(change) {
    self.emit('change', {
      direction: 'pull',
      change: change
    });
  }
  function pushChange(change) {
    self.emit('change', {
      direction: 'push',
      change: change
    });
  }
  function pushDenied(doc) {
    self.emit('denied', {
      direction: 'push',
      doc: doc
    });
  }
  function pullDenied(doc) {
    self.emit('denied', {
      direction: 'pull',
      doc: doc
    });
  }
  function pushPaused() {
    self.pushPaused = true;
    /* istanbul ignore if */
    if (self.pullPaused) {
      self.emit('paused');
    }
  }
  function pullPaused() {
    self.pullPaused = true;
    /* istanbul ignore if */
    if (self.pushPaused) {
      self.emit('paused');
    }
  }
  function pushActive() {
    self.pushPaused = false;
    /* istanbul ignore if */
    if (self.pullPaused) {
      self.emit('active', {
        direction: 'push'
      });
    }
  }
  function pullActive() {
    self.pullPaused = false;
    /* istanbul ignore if */
    if (self.pushPaused) {
      self.emit('active', {
        direction: 'pull'
      });
    }
  }

  var removed = {};

  function removeAll(type) { // type is 'push' or 'pull'
    return function (event, func) {
      var isChange = event === 'change' &&
        (func === pullChange || func === pushChange);
      var isDenied = event === 'denied' &&
        (func === pullDenied || func === pushDenied);
      var isPaused = event === 'paused' &&
        (func === pullPaused || func === pushPaused);
      var isActive = event === 'active' &&
        (func === pullActive || func === pushActive);

      if (isChange || isDenied || isPaused || isActive) {
        if (!(event in removed)) {
          removed[event] = {};
        }
        removed[event][type] = true;
        if (Object.keys(removed[event]).length === 2) {
          // both push and pull have asked to be removed
          self.removeAllListeners(event);
        }
      }
    };
  }

  if (opts.live) {
    this.push.on('complete', self.pull.cancel.bind(self.pull));
    this.pull.on('complete', self.push.cancel.bind(self.push));
  }

  function addOneListener(ee, event, listener) {
    if (ee.listeners(event).indexOf(listener) == -1) {
      ee.on(event, listener);
    }
  }

  this.on('newListener', function (event) {
    if (event === 'change') {
      addOneListener(self.pull, 'change', pullChange);
      addOneListener(self.push, 'change', pushChange);
    } else if (event === 'denied') {
      addOneListener(self.pull, 'denied', pullDenied);
      addOneListener(self.push, 'denied', pushDenied);
    } else if (event === 'active') {
      addOneListener(self.pull, 'active', pullActive);
      addOneListener(self.push, 'active', pushActive);
    } else if (event === 'paused') {
      addOneListener(self.pull, 'paused', pullPaused);
      addOneListener(self.push, 'paused', pushPaused);
    }
  });

  this.on('removeListener', function (event) {
    if (event === 'change') {
      self.pull.removeListener('change', pullChange);
      self.push.removeListener('change', pushChange);
    } else if (event === 'denied') {
      self.pull.removeListener('denied', pullDenied);
      self.push.removeListener('denied', pushDenied);
    } else if (event === 'active') {
      self.pull.removeListener('active', pullActive);
      self.push.removeListener('active', pushActive);
    } else if (event === 'paused') {
      self.pull.removeListener('paused', pullPaused);
      self.push.removeListener('paused', pushPaused);
    }
  });

  this.pull.on('removeListener', removeAll('pull'));
  this.push.on('removeListener', removeAll('push'));

  var promise = Promise.all([
    this.push,
    this.pull
  ]).then(function (resp) {
    var out = {
      push: resp[0],
      pull: resp[1]
    };
    self.emit('complete', out);
    if (callback) {
      callback(null, out);
    }
    self.removeAllListeners();
    return out;
  }, function (err) {
    self.cancel();
    if (callback) {
      // if there's a callback, then the callback can receive
      // the error event
      callback(err);
    } else {
      // if there's no callback, then we're safe to emit an error
      // event, which would otherwise throw an unhandled error
      // due to 'error' being a special event in EventEmitters
      self.emit('error', err);
    }
    self.removeAllListeners();
    if (callback) {
      // no sense throwing if we're already emitting an 'error' event
      throw err;
    }
  });

  this.then = function (success, err) {
    return promise.then(success, err);
  };

  this.catch = function (err) {
    return promise.catch(err);
  };
}

Sync.prototype.cancel = function () {
  if (!this.canceled) {
    this.canceled = true;
    this.push.cancel();
    this.pull.cancel();
  }
};