Add storeEvents impl.

lib/client.js

@@ -830,27 +830,38 @@ MatrixClient.prototype.roomState = function(roomId, callback) {
  */
 MatrixClient.prototype.scrollback = function(room, limit, callback) {
     if (utils.isFunction(limit)) { callback = limit; limit = undefined; }
+    limit = limit || 30;
+
     if (room.oldState.paginationToken === null) {
         return q(room); // already at the start.
     }
+    // attempt to grab more events from the store first
+    var numAdded = this.store.scrollback(room, limit).length;
+    if (numAdded === limit) {
+        // store contained everything we needed.
+        return q(room);
+    }
+    // reduce the required number of events appropriately
+    limit = limit - numAdded;
+
     var path = utils.encodeUri(
         "/rooms/$roomId/messages", {$roomId: room.roomId}
     );
-    limit = limit || 30;
     var params = {
         from: room.oldState.paginationToken,
         limit: limit,
         dir: 'b'
     };
     var defer = q.defer();
+    var self = this;
     this._http.authedRequest(callback, "GET", path, params).done(function(res) {
-        room.addEventsToTimeline(
-            utils.map(res.chunk, _PojoToMatrixEventMapper), true
-        );
+        var matrixEvents = utils.map(res.chunk, _PojoToMatrixEventMapper);
+        room.addEventsToTimeline(matrixEvents, true);
         room.oldState.paginationToken = res.end;
         if (res.chunk.length < limit) {
             room.oldState.paginationToken = null;
         }
+        self.store.storeEvents(room, matrixEvents, res.end, true);
         _resolve(callback, defer, room);
     }, function(err) {
         _reject(callback, defer, err);