Remove app.search instance, cache app.cache.searched (#2151)

* Moved search state logic into search state

js/src/forum/states/GlobalSearchState.js

@@ -0,0 +1,95 @@
+import SearchState from './SearchState';
+
+export default class GlobalSearchState extends SearchState {
+  constructor(cachedSearches = [], searchRoute = 'index') {
+    super(cachedSearches);
+    this.searchRoute = searchRoute;
+  }
+
+  getValue() {
+    if (this.value === undefined) {
+      this.value = this.getInitialSearch() || '';
+    }
+
+    return super.getValue();
+  }
+
+  /**
+   * Clear the search input and the current controller's active search.
+   */
+  clear() {
+    super.clear();
+
+    if (this.getInitialSearch()) {
+      this.clearInitialSearch();
+    } else {
+      m.redraw();
+    }
+  }
+
+  /**
+   * Get URL parameters that stick between filter changes.
+   *
+   * @return {Object}
+   */
+  stickyParams() {
+    return {
+      sort: m.route.param('sort'),
+      q: m.route.param('q'),
+    };
+  }
+
+  /**
+   * Get parameters to pass to the DiscussionList component.
+   *
+   * @return {Object}
+   */
+  params() {
+    const params = this.stickyParams();
+
+    params.filter = m.route.param('filter');
+
+    return params;
+  }
+
+  /**
+   * Redirect to the index page using the given sort parameter.
+   *
+   * @param {String} sort
+   */
+  changeSort(sort) {
+    const params = this.params();
+
+    if (sort === Object.keys(app.cache.discussionList.sortMap())[0]) {
+      delete params.sort;
+    } else {
+      params.sort = sort;
+    }
+
+    m.route(app.route(this.searchRoute, params));
+  }
+
+  /**
+   * Return the current search query, if any. This is implemented to activate
+   * the search box in the header.
+   *
+   * @see Search
+   * @return {String}
+   */
+  getInitialSearch() {
+    return app.current.constructor.providesInitialSearch && this.params().q;
+  }
+
+  /**
+   * Redirect to the index page without a search filter. This is called when the
+   * 'x' is clicked in the search box in the header.
+   *
+   * @see Search
+   */
+  clearInitialSearch() {
+    const params = this.params();
+    delete params.q;
+
+    m.route(app.route(this.searchRoute, params));
+  }
+}