define(function(require, exports, module) {
'use strict';

var Responder = require('common/responder');
var core = require('core');
var debug = require('common/debug')('controllers/recurring_events');
var nextTick = require('common/next_tick');

function RecurringEvents() {
  this.accounts = core.storeFactory.get('Account');
  Responder.call(this);
}
module.exports = RecurringEvents;

RecurringEvents.prototype = {
  __proto__: Responder.prototype,

  startEvent: 'expandStart',
  completeEvent: 'expandComplete',

  /**
   * Adds N number of days to the window to expand
   * events until. Its very important for this number
   * to be greater then the maximum number of days displayed
   * in the month view (or a view with more days) otherwise
   * the view may be loaded without actually expanding all
   * the visible days.
   *
   * @type Number
   */
  paddingInDays: 85,

  /**
   * Amount of time (in MS) to wait between triggering
   * the recurring event expansions.
   */
  waitBeforeMove: 750,

  /**
   * We need to limit the number of tries on expansions
   * otherwise its possible we never complete during error
   * or long recurring event.
   */
  maximumExpansions: 25,

  /**
   * private timeout (as in setTimeout id) use with waitBeforeMove.
   */
  _moveTimeout: null,

  /**
   * True when queue is running...
   */
  pending: false,

  unobserve: function() {
    core.timeController.removeEventListener(
      'monthChange',
      this
    );

    core.syncController.removeEventListener(
      'syncComplete',
      this
    );
  },

  observe: function() {
    var time = core.timeController;

    // expand initial time this is necessary
    // for cases where user has device off for long periods of time.
    if (time.position) {
      this.queueExpand(time.position);
    }

    // register observers
    time.on('monthChange', this);

    // we must re-expand after sync so events at least
    // expand to the current position....
    core.syncController.on('syncComplete', this);
  },

  handleEvent: function(event) {
    switch (event.type) {
      case 'syncComplete':
        this.queueExpand(
          core.timeController.position
        );
        break;

      case 'monthChange':
        if (this._moveTimeout !== null) {
          clearTimeout(this._moveTimeout);
          this._moveTimeout = null;
        }

        // trigger the event queue when we move
        this._moveTimeout = setTimeout(
          // data[0] is the new date.
          this.queueExpand.bind(this, event.data[0]),
          this.waitBeforeMove
        );
        break;
    }
  },

  /**
   * Attempts to expand provider until no events require expansion.
   *
   * @param {Date} expandDate expands up to this date.
   * @param {Calendar.Provider.Abstract} provider instance.
   * @param {Function} callback
   *  fired when maximumExpansions is hit or
   *  no more events require expansion.
   *
   */
  _expandProvider: function(expandDate, provider, callback) {
    debug('Will attempt to expand provider until:', expandDate);
    var tries = 0;
    var max = this.maximumExpansions;

    function attemptCompleteExpand() {
      debug('Will try to complete expansion (tries = ' + tries + ')');
      if (tries >= max) {
        return callback(new Error(
          'could not complete expansion after "' + tries + '"'
        ));
      }

      provider.ensureRecurrencesExpanded(expandDate, function(err, didExpand) {
        if (err) {
          return callback(err);
        }

        debug('Expansion attempt did expand:', didExpand);

        if (!didExpand) {
          // successfully expanded and no events need expansion
          // for this date anymore...
          callback();
        } else {
          tries++;
          // attempt another expand without stack.
          nextTick(attemptCompleteExpand);
        }
      });
    }

    attemptCompleteExpand();
  },

  /**
   * Queues an expansion. If the given date is before
   * any dates in the stack it will be discarded.
   */
  queueExpand: function(expandTo) {
    if (this.pending) {
      if (!this._next) {
        this._next = expandTo;
      } else if (expandTo > this._next) {
        this._next = expandTo;
      }
      // don't start the queue if pending...
      return;
    }

    // either way we need to process an event
    // so increment pending for running and non-running cases.
    this.pending = true;
    this.emit('expandStart');

    var self = this;
    function expandNext(date) {
      self.expand(date, function() {
        if (date === self._next) {
          self._next = null;
        }

        var next = self._next;

        // when the queue is empty emit expandComplete
        if (!next) {
          self.pending = false;
          self.emit('expandComplete');
          return;
        }

        expandNext(next);
      });
    }

    expandNext(expandTo);
  },

  /**
   * Ensures we have time converage until the given date.
   * Additional time will be added to the date see .paddingInDays.
   *
   * @param {Date} expandTo date to expand to.
   */
  expand: function(expandTo, callback) {
    debug('expand', expandTo);

    this.accounts.all((err, accounts) => {
      if (err) {
        return callback(err);
      }

      // add minimum padding...
      var expandDate = new Date(expandTo.valueOf());
      expandDate.setDate(expandDate.getDate() + this.paddingInDays);

      var providers = this._getExpandableProviders(accounts);
      var pending = providers.length;

      if (!pending) {
        return nextTick(callback);
      }

      providers.forEach(provider => {
        this._expandProvider(expandDate, provider, () => {
          if (--pending <= 0) {
            callback();
          }
        });
      });
    });
  },

  _getExpandableProviders: function(accounts) {
    var providers = [];
    Object.keys(accounts).forEach(key => {
      var account = accounts[key];
      var provider = core.providerFactory.get(account.providerType);
      if (provider &&
          provider.canExpandRecurringEvents &&
          providers.indexOf(provider) === -1) {
        providers.push(provider);
      }
    });

    return providers;
  }
};

});