Clean up code

js/src/forum/components/DiscussionList.js

@@ -4,6 +4,13 @@ import Button from '../../common/components/Button';
 import LoadingIndicator from '../../common/components/LoadingIndicator';
 import Placeholder from '../../common/components/Placeholder';
 
+/**
+ * How many discussions do we show / load per page?
+ *
+ * @type {number}
+ */
+const DISCUSSIONS_PER_PAGE = 20;
+
 /**
  * The `DiscussionList` component displays a list of discussions.
  *
@@ -15,11 +22,18 @@ import Placeholder from '../../common/components/Placeholder';
 export default class DiscussionList extends Component {
   init() {
     /**
-     * Whether or not discussion results are loading.
+     * Whether or not discussion results are loading for the next page.
      *
      * @type {Boolean}
      */
-    this.loading = true;
+    this.loadingNext = true;
+
+    /**
+     * Whether or not discussion results are loading for the previous page.
+     *
+     * @type {Boolean}
+     */
+    this.loadingPrev = false;
 
     /**
      * Whether or not there are more results that can be loaded.
@@ -28,6 +42,34 @@ export default class DiscussionList extends Component {
      */
     this.moreResults = false;
 
+    /**
+     * Current page in discussion list
+     *
+     * @type {number}
+     */
+    this.page = Number(m.route.param('page')) || 1;
+
+    /**
+     * First page loaded in discussion list
+     *
+     * @type {number}
+     */
+    this.firstLoadedPage = this.page;
+
+    /**
+     * Last page loaded in discussion list
+     *
+     * @type {number}
+     */
+    this.lastLoadedPage = this.page;
+
+    /**
+     * Number of discussions to offset for pagination
+     *
+     * @type {number}
+     */
+    this.offset = (this.page - 1) * DISCUSSIONS_PER_PAGE;
+
     /**
      * The discussions in the discussion list.
      *
@@ -35,30 +77,29 @@ export default class DiscussionList extends Component {
      */
     this.discussions = [];
 
+    /**
+     * When getting more discussions, put the new discussions at the top of the discussion list
+     *
+     * @type {boolean}
+     */
+    this.addResultsToBeginning = false;
+
     this.refresh();
   }
 
   view() {
     const params = this.props.params;
-    let loading;
 
-    if (this.loading) {
-      loading = LoadingIndicator.component();
-    } else if (this.moreResults) {
-      loading = Button.component({
-        children: app.translator.trans('core.forum.discussion_list.load_more_button'),
-        className: 'Button',
-        onclick: this.loadMore.bind(this),
-      });
-    }
-
-    if (this.discussions.length === 0 && !this.loading) {
+    if (this.discussions.length === 0 && !this.loadingNext) {
       const text = app.translator.trans('core.forum.discussion_list.empty_text');
       return <div className="DiscussionList">{Placeholder.component({ text })}</div>;
     }
 
     return (
       <div className={'DiscussionList' + (this.props.params.q ? ' DiscussionList--searchResults' : '')}>
+        {this.loadingPrev
+          ? LoadingIndicator.component()
+          : this.firstLoadedPage !== 1 && <div className="DiscussionList-loadMore">{this.getLoadPrevButton()}</div>}
         <ul className="DiscussionList-discussions">
           {this.discussions.map((discussion) => {
             return (
@@ -68,7 +109,9 @@ export default class DiscussionList extends Component {
             );
           })}
         </ul>
-        <div className="DiscussionList-loadMore">{loading}</div>
+        <div className="DiscussionList-loadMore">
+          {this.loadingNext ? LoadingIndicator.component() : this.moreResults && this.getLoadNextButton()}
+        </div>
       </div>
     );
   }
@@ -121,7 +164,7 @@ export default class DiscussionList extends Component {
    */
   refresh(clear = true) {
     if (clear) {
-      this.loading = true;
+      this.loadingNext = true;
       this.discussions = [];
     }
 
@@ -131,7 +174,7 @@ export default class DiscussionList extends Component {
         this.parseResults(results);
       },
       () => {
-        this.loading = false;
+        this.loadingNext = false;
         m.redraw();
       }
     );
@@ -140,10 +183,10 @@ export default class DiscussionList extends Component {
   /**
    * Load a new page of discussion results.
    *
-   * @param {Integer} offset The index to start the page at.
+   * @param {Number} offset The index to start the page at.
    * @return {Promise}
    */
-  loadResults(offset) {
+  loadResults(offset = this.offset) {
     const preloadedDiscussions = app.preloadedApiDocument();
 
     if (preloadedDiscussions) {
@@ -157,32 +200,77 @@ export default class DiscussionList extends Component {
     return app.store.find('discussions', params);
   }
 
+  /**
+   * Load the previous page of discussion results.
+   *
+   * @public
+   */
+  loadPrev() {
+    if (this.firstLoadedPage !== 1) {
+      this.loadingPrev = true;
+      this.page = --this.firstLoadedPage;
+      this.addResultsToBeginning = true;
+    }
+
+    this.loadResults((this.offset = (this.page - 1) * DISCUSSIONS_PER_PAGE)).then(this.parseResults.bind(this));
+  }
+
   /**
    * Load the next page of discussion results.
    *
    * @public
    */
-  loadMore() {
-    this.loading = true;
+  loadNext() {
+    this.loadingNext = true;
+    this.page = ++this.lastLoadedPage;
 
-    this.loadResults(this.discussions.length).then(this.parseResults.bind(this));
+    this.loadResults((this.offset = (this.page - 1) * DISCUSSIONS_PER_PAGE)).then(this.parseResults.bind(this));
   }
 
   /**
    * Parse results and append them to the discussion list.
    *
    * @param {Discussion[]} results
-   * @return {Discussion[]}
    */
   parseResults(results) {
-    [].push.apply(this.discussions, results);
+    // If the results need to be added to the beginning of the discussion list
+    // do so, and reset the value for the variable keeping track of this necessity
+    if (this.addResultsToBeginning) {
+      [].unshift.apply(this.discussions, results);
+      this.addResultsToBeginning = false;
+    } else {
+      [].push.apply(this.discussions, results);
+    }
 
-    this.loading = false;
+    this.loadingNext = false;
+    this.loadingPrev = false;
     this.moreResults = !!results.payload.links.next;
 
     m.lazyRedraw();
+    this.updateUrl();
+  }
 
-    return results;
+  /**
+   * Update the "page" parameter in the URL shown to the user.
+   *
+   * Constructs a URL to this discussion with the updated page, then
+   * replaces it into the window's history and our own history stack.
+   */
+  updateUrl() {
+    // Bail out if the browser does not support updating the URL.
+    if (typeof window.URL !== 'function') return;
+
+    const query = m.route.parseQueryString(document.location.search);
+    query.page = this.page;
+
+    if (this.page === 1) {
+      delete query.page;
+    }
+
+    const url = new URL(document.location.href);
+    url.search = m.route.buildQueryString(query);
+
+    window.history.replaceState(null, '', url.toString());
   }
 
   /**
@@ -208,4 +296,30 @@ export default class DiscussionList extends Component {
   addDiscussion(discussion) {
     this.discussions.unshift(discussion);
   }
+
+  /**
+   * Get the "Load Previous" page button.
+   *
+   * @return {Button}
+   */
+  getLoadPrevButton() {
+    return Button.component({
+      children: app.translator.trans(`core.forum.discussion_list.load_prev_button`),
+      className: 'Button',
+      onclick: this.loadPrev.bind(this),
+    });
+  }
+
+  /**
+   * Get the "Load More" page button.
+   *
+   * @return {Button}
+   */
+  getLoadNextButton() {
+    return Button.component({
+      children: app.translator.trans(`core.forum.discussion_list.load_more_button`),
+      className: 'Button',
+      onclick: this.loadNext.bind(this),
+    });
+  }
 }