import Ember from 'ember';

/**
  The post stream is an object which represents the posts in a discussion as
  they are displayed on the discussion page, from top to bottom. ...
 */
export default Ember.ArrayProxy.extend(Ember.Evented, {

  // An array of all of the post IDs, in chronological order, in the discussion.
  ids: null,

  content: null,

  store: null,
  discussion: null,

  postLoadCount: 20,

  count: Ember.computed.alias('ids.length'),

  loadedCount: Ember.computed('content.@each', function() {
    return this.get('content').filterBy('content').length;
  }),

  firstLoaded: Ember.computed('content.@each', function() {
    var first = this.objectAt(0);
    return first && first.content;
  }),

  lastLoaded: Ember.computed('content.@each', function() {
    var last = this.objectAt(this.get('length') - 1);
    return last && last.content;
  }),

  init: function() {
    this._super();
    this.set('ids', Ember.A());
    this.clear();
  },

  setup: function(ids) {
    // Set our ids to the array provided and reset the content of the
    // stream to a big gap that covers the amount of posts we now have.
    this.set('ids', ids);
    this.clear();
  },

  // Clear the contents of the post stream, resetting it to one big gap.
  clear: function() {
    var content = Ember.A();
    content.clear().pushObject(this.makeItem(0, this.get('count') - 1).set('loading', true));
    this.set('content', content);
  },

  loadRange: function(start, end, backwards) {
    var limit = this.get('postLoadCount');

    // Find the appropriate gap objects in the post stream. When we find
    // one, we will turn on its loading flag.
    this.get('content').forEach(function(item) {
      if (!item.content && ((item.indexStart >= start && item.indexStart <= end) || (item.indexEnd >= start && item.indexEnd <= end))) {
        item.set('loading', true);
        item.set('direction', backwards ? 'up' : 'down');
      }
    });

    // Get a list of post numbers that we'll want to retrieve. If there are
    // more post IDs than the number of posts we want to load, then take a
    // slice of the array in the appropriate direction.
    var ids = this.get('ids').slice(start, end + 1);
    ids = backwards ? ids.slice(-limit) : ids.slice(0, limit);

    return this.loadPosts(ids);
  },

  loadPosts: function(ids) {
    if (!ids.length) {
      return Ember.RSVP.resolve();
    }

    var stream = this;
    return this.store.find('post', {ids: ids}).then(function(posts) {
      stream.addPosts(posts);
    });
  },

  loadNearNumber: function(number) {
    // Find the item in the post stream which is nearest to this number. If
    // it turns out the be the actual post we're trying to load, then we can
    // return a resolved promise (i.e. we don't need to make an API
    // request.) Or, if it's a gap, we'll switch on its loading flag.
    var item = this.findNearestToNumber(number);
    if (item) {
      if (item.get('content.number') == number) {
        return Ember.RSVP.resolve([item.get('content')]);
      } else if (! item.content) {
        item.set('direction', 'down').set('loading', true);
      }
    }

    var stream = this;
    return this.store.find('post', {
      discussions: this.get('discussion.id'),
      near: number,
      count: this.get('postLoadCount')
    }).then(function(posts) {
      stream.addPosts(posts);
    });
  },

  loadNearIndex: function(index, backwards) {
    // Find the item in the post stream which is nearest to this index. If
    // it turns out the be the actual post we're trying to load, then we can
    // return a resolved promise (i.e. we don't need to make an API
    // request.) Or, if it's a gap, we'll switch on its loading flag.
    var item = this.findNearestToIndex(index);
    if (item) {
      if (item.content) {
        return Ember.RSVP.resolve([item.get('content')]);
      }
      return this.loadRange(Math.max(item.indexStart, index - this.get('postLoadCount') / 2), item.indexEnd, backwards);
    }

    return Ember.RSVP.reject();
  },

  addPosts: function(posts) {
    this.trigger('postsLoaded', posts);

    var stream = this;
    var content = this.get('content');
    content.beginPropertyChanges();
    posts.forEach(function(post) {
      stream.addPost(post);
    });
    content.endPropertyChanges();

    this.trigger('postsAdded');
  },

  addPost: function(post) {
    var index = this.get('ids').indexOf(post.get('id'));
    var content = this.get('content');
    var makeItem = this.makeItem;

    // Here we loop through each item in the post stream, and find the gap
    // in which this post should be situated. When we find it, we can replace
    // it with the post, and new gaps either side if appropriate.
    content.some(function(item, i) {
      if (item.indexStart <= index && item.indexEnd >= index) {
        var newItems = [];
        if (item.indexStart < index) {
          newItems.push(makeItem(item.indexStart, index - 1));
        }
        newItems.push(makeItem(index, index, post));
        if (item.indexEnd > index) {
          newItems.push(makeItem(index + 1, item.indexEnd));
        }
        content.replace(i, 1, newItems);
        return true;
      }
    });
  },

  addPostToEnd: function(post) {
    this.get('ids').pushObject(post.get('id'));
    var index = this.get('count') - 1;
    this.get('content').pushObject(this.makeItem(index, index, post));
  },

  removePost: function(post) {
    this.get('ids').removeObject(post.get('id'));
    var content = this.get('content');
    content.removeObject(content.findBy('content', post));
  },

  makeItem: function(indexStart, indexEnd, post) {
    var item = Ember.Object.create({
      indexStart: indexStart,
      indexEnd: indexEnd
    });
    if (post) {
      item.setProperties({
        content: post,
        component: 'discussion/post-'+post.get('type')
      });
    }
    return item;
  },

  findNearestTo: function(index, property) {
    var nearestItem;
    this.get('content').some(function(item) {
      if (item.get(property) > index) {
        return true;
      }
      nearestItem = item;
    });
    return nearestItem;
  },

  findNearestToNumber: function(number) {
    return this.findNearestTo(number, 'content.number');
  },

  findNearestToIndex: function(index) {
    return this.findNearestTo(index, 'indexStart');
  }
});