BlazeComponent.extendComponent({
  template: function() {
    return 'list';
  },

  // Proxies
  openForm: function(options) {
    this.componentChildren('listBody')[0].openForm(options);
  },

  onCreated: function() {
    this.newCardFormIsVisible = new ReactiveVar(true);
  },

  // The jquery UI sortable library is the best solution I've found so far. I
  // tried sortable and dragula but they were not powerful enough four our use
  // case. I also considered writing/forking a drag-and-drop + sortable library
  // but it's probably too much work.
  // By calling asking the sortable library to cancel its move on the `stop`
  // callback, we basically solve all issues related to reactive updates. A
  // comment below provides further details.
  onRendered: function() {
    var self = this;
    if (! Meteor.userId() || ! Meteor.user().isBoardMember())
      return;

    var boardComponent = self.componentParent();
    var itemsSelector = '.js-minicard:not(.placeholder, .js-card-composer)';
    var $cards = self.$('.js-minicards');
    $cards.sortable({
      connectWith: '.js-minicards',
      tolerance: 'pointer',
      appendTo: '#surface',
      helper: function(evt, item) {
        var helper = item.clone();
        if (MultiSelection.isActive()) {
          var andNOthers = $cards.find('.js-minicard.is-checked').length - 1;
          if (andNOthers > 0) {
            helper.append($(Blaze.toHTML(HTML.DIV(
              // XXX Super bad class name
              {'class': 'and-n-other'},
              // XXX Need to translate
              'and ' + andNOthers + ' other cards.'
            ))));
          }
        }
        return helper;
      },
      distance: 7,
      items: itemsSelector,
      scroll: false,
      placeholder: 'minicard-wrapper placeholder',
      start: function(evt, ui) {
        ui.placeholder.height(ui.helper.height());
        EscapeActions.executeUpTo('popup');
        boardComponent.setIsDragging(true);
      },
      stop: function(evt, ui) {
        // To attribute the new index number, we need to get the DOM element
        // of the previous and the following card -- if any.
        var prevCardDom = ui.item.prev('.js-minicard').get(0);
        var nextCardDom = ui.item.next('.js-minicard').get(0);
        var nCards = MultiSelection.isActive() ? MultiSelection.count() : 1;
        var sortIndex = Utils.calculateIndex(prevCardDom, nextCardDom, nCards);
        var listId = Blaze.getData(ui.item.parents('.list').get(0))._id;

        // Normally the jquery-ui sortable library moves the dragged DOM element
        // to its new position, which disrupts Blaze reactive updates mechanism
        // (especially when we move the last card of a list, or when multiple
        // users move some cards at the same time). To prevent these UX glitches
        // we ask sortable to gracefully cancel the move, and to put back the
        // DOM in its initial state. The card move is then handled reactively by
        // Blaze with the below query.
        $cards.sortable('cancel');

        if (MultiSelection.isActive()) {
          Cards.find(MultiSelection.getMongoSelector()).forEach(function(c, i) {
            Cards.update(c._id, {
              $set: {
                listId: listId,
                sort: sortIndex.base + i * sortIndex.increment
              }
            });
          });
        } else {
          var cardDomElement = ui.item.get(0);
          var cardId = Blaze.getData(cardDomElement)._id;
          Cards.update(cardId, {
            $set: {
              listId: listId,
              sort: sortIndex.base
            }
          });
        }
        boardComponent.setIsDragging(false);
      }
    });

    // We want to re-run this function any time a card is added.
    self.autorun(function() {
      var currentBoardId = Tracker.nonreactive(function() {
        return Session.get('currentBoard');
      });
      Cards.find({ boardId: currentBoardId }).fetch();
      Tracker.afterFlush(function() {
        $cards.find(itemsSelector).droppable({
          hoverClass: 'draggable-hover-card',
          accept: '.js-member,.js-label',
          drop: function(event, ui) {
            var cardId = Blaze.getData(this)._id;
            var addToSet;

            if (ui.draggable.hasClass('js-member')) {
              var memberId = Blaze.getData(ui.draggable.get(0)).userId;
              addToSet = { members: memberId };
            } else {
              var labelId = Blaze.getData(ui.draggable.get(0))._id;
              addToSet = { labelIds: labelId };
            }
            Cards.update(cardId, { $addToSet: addToSet });
          }
        });
      });
    });
  }
}).register('list');