osr-discourse-src/app/assets/javascripts/discourse/lib/posts-with-placeholders.js.es6

import EmberObject from "@ember/object";
import { default as computed } from "ember-addons/ember-computed-decorators";

export function Placeholder(viewName) {
  this.viewName = viewName;
}

export default EmberObject.extend(Ember.Array, {
  posts: null,
  _appendingIds: null,

  init() {
    this._appendingIds = {};
  },

  @computed
  length() {
    return (
      this.get("posts.length") + Object.keys(this._appendingIds || {}).length
    );
  },

  nextObject(index) {
    return this.objectAt(index);
  },

  _changeArray(cb, offset, removed, inserted) {
    this.arrayContentWillChange(offset, removed, inserted);
    cb();
    this.arrayContentDidChange(offset, removed, inserted);
    this.notifyPropertyChange("length");
  },

  clear(cb) {
    this._changeArray(cb, 0, this.get("posts.length"), 0);
  },

  appendPost(cb) {
    this._changeArray(cb, this.get("posts.length"), 0, 1);
  },

  removePost(cb) {
    this._changeArray(cb, this.get("posts.length") - 1, 1, 0);
  },

  refreshAll(cb) {
    const length = this.get("posts.length");
    this._changeArray(cb, 0, length, length);
  },

  appending(postIds) {
    this._changeArray(
      () => {
        const appendingIds = this._appendingIds;
        postIds.forEach(pid => (appendingIds[pid] = true));
      },
      this.length,
      0,
      postIds.length
    );
  },

  finishedAppending(postIds) {
    this._changeArray(
      () => {
        const appendingIds = this._appendingIds;
        postIds.forEach(pid => delete appendingIds[pid]);
      },
      this.get("posts.length") - postIds.length,
      postIds.length,
      postIds.length
    );
  },

  finishedPrepending(postIds) {
    this._changeArray(function() {}, 0, 0, postIds.length);
  },

  objectAt(index) {
    const posts = this.posts;
    return index < posts.length
      ? posts[index]
      : new Placeholder("post-placeholder");
  }
});