RoomView: Use platform specific search if our platform supports it.

This patch extends our search to include our platform specific event
index.

There are 3 search scenarios and are handled differently when platform
support for indexing is present:

    - Search a single non-encrypted room: Use the server-side search
        like before.
    - Search a single encrypted room: Search using our platform specific
        event index.
    - Search across all rooms: Search encrypted rooms using our local
        event index. Search non-encrypted rooms using the classic
        server-side search. Combine the results.

The combined search will result in having twice the amount of search
results since comparing the scores fairly wasn't deemed sensible.

src/components/structures/RoomView.js

@@ -34,6 +34,7 @@ import { _t } from '../../languageHandler';
 import {RoomPermalinkCreator} from '../../utils/permalinks/Permalinks';
 
 import MatrixClientPeg from '../../MatrixClientPeg';
+import PlatformPeg from "../../PlatformPeg";
 import ContentMessages from '../../ContentMessages';
 import Modal from '../../Modal';
 import sdk from '../../index';
@@ -1140,12 +1141,116 @@ module.exports = createReactClass({
         }
 
         debuglog("sending search request");
+        const platform = PlatformPeg.get();
 
+        if (platform.supportsEventIndexing()) {
+            const combinedSearchFunc = async (searchTerm) => {
+                // Create two promises, one for the local search, one for the
+                // server-side search.
+                const client = MatrixClientPeg.get();
+                const serverSidePromise = client.searchRoomEvents({
+                    term: searchTerm,
+                });
+                const localPromise = localSearchFunc(searchTerm);
+
+                // Wait for both promises to resolve.
+                await Promise.all([serverSidePromise, localPromise]);
+
+                // Get both search results.
+                const localResult = await localPromise;
+                const serverSideResult = await serverSidePromise;
+
+                // Combine the search results into one result.
+                const result = {};
+
+                // Our localResult and serverSideResult are both ordered by
+                // recency separetly, when we combine them the order might not
+                // be the right one so we need to sort them.
+                const compare = (a, b) => {
+                    const aEvent = a.context.getEvent().event;
+                    const bEvent = b.context.getEvent().event;
+
+                    if (aEvent.origin_server_ts >
+                        bEvent.origin_server_ts) return -1;
+                    if (aEvent.origin_server_ts <
+                        bEvent.origin_server_ts) return 1;
+                    return 0;
+                };
+
+                result.count = localResult.count + serverSideResult.count;
+                result.results = localResult.results.concat(
+                    serverSideResult.results).sort(compare);
+                result.highlights = localResult.highlights.concat(
+                    serverSideResult.highlights);
+
+                return result;
+            };
+
+            const localSearchFunc = async (searchTerm, roomId = undefined) => {
+                const searchArgs = {
+                    search_term: searchTerm,
+                    before_limit: 1,
+                    after_limit: 1,
+                    order_by_recency: true,
+                };
+
+                if (roomId !== undefined) {
+                    searchArgs.room_id = roomId;
+                }
+
+                const localResult = await platform.searchEventIndex(
+                    searchArgs);
+
+                const response = {
+                    search_categories: {
+                        room_events: localResult,
+                    },
+                };
+
+                const emptyResult = {
+                    results: [],
+                    highlights: [],
+                };
+
+                // TODO is there a better way to convert our result into what
+                // is expected by the handler method.
+                const result = MatrixClientPeg.get()._processRoomEventsSearch(
+                    emptyResult, response);
+
+                return result;
+            };
+
+            let searchPromise;
+
+            if (scope === "Room") {
+                const roomId = this.state.room.roomId;
+
+                if (MatrixClientPeg.get().isRoomEncrypted(roomId)) {
+                    // The search is for a single encrypted room, use our local
+                    // search method.
+                    searchPromise = localSearchFunc(term, roomId);
+                } else {
+                    // The search is for a single non-encrypted room, use the
+                    // server-side search.
+                    searchPromise = MatrixClientPeg.get().searchRoomEvents({
+                        filter: filter,
+                        term: term,
+                    });
+                }
+            } else {
+                // Search across all rooms, combine a server side search and a
+                // local search.
+                searchPromise = combinedSearchFunc(term);
+            }
+
+            this._handleSearchResult(searchPromise).done();
+        } else {
             const searchPromise = MatrixClientPeg.get().searchRoomEvents({
                 filter: filter,
                 term: term,
             });
             this._handleSearchResult(searchPromise).done();
+        }
     },
 
     _handleSearchResult: function(searchPromise) {