[Room] Add method to get an event by the ID.

lib/src/Room.dart

@@ -468,4 +468,17 @@ class Room {
 
     return participants;
   }
+
+  /// Searches for the event in the store. If it isn't found, try to request it
+  /// from the server. Returns null if not found.
+  Future<Event> getEventById(String eventID) async {
+    if (client.store != null) {
+      final Event storeEvent = await client.store.getEventById(eventID, this);
+      if (storeEvent != null) return storeEvent;
+    }
+    final dynamic resp = await client.connection.jsonRequest(
+        type: "GET", action: "/client/r0/rooms/$id/event/$eventID");
+    if (resp is ErrorResponse) return null;
+    return Event.fromJson(resp, this);
+  }
 }

lib/src/Store.dart

@@ -597,6 +597,14 @@ class Store {
     return;
   }
 
+  /// Searches for the event in the store.
+  Future<Event> getEventById(String eventID, Room room) async {
+    List<Map<String, dynamic>> res = await db.rawQuery(
+        "SELECT * FROM Events WHERE id=? AND chat_id=?", [eventID, room.id]);
+    if (res.length == 0) return null;
+    return Event.fromJson(res[0], room);
+  }
+
   /// The database sheme for the Client class.
   static final String ClientsScheme = 'CREATE TABLE IF NOT EXISTS Clients(' +
       'client TEXT PRIMARY KEY, ' +

test/FakeMatrixApi.dart

@@ -62,6 +62,20 @@ class FakeMatrixApi extends MockClient {
 
   static final Map<String, Map<String, dynamic>> api = {
     "GET": {
+      "/client/r0/rooms/!localpart:server.abc/event/1234": (var req) => {
+            "content": {
+              "body": "This is an example text message",
+              "msgtype": "m.text",
+              "format": "org.matrix.custom.html",
+              "formatted_body": "<b>This is an example text message</b>"
+            },
+            "type": "m.room.message",
+            "event_id": "143273582443PhrSn:example.org",
+            "room_id": "!localpart:server.abc",
+            "sender": "@example:example.org",
+            "origin_server_ts": 1432735824653,
+            "unsigned": {"age": 1234}
+          },
       "/client/r0/rooms/!1234:example.com/messages": (var req) => {
             "start": "t47429-4392820_219380_26003_2265",
             "end": "t47409-4357353_219380_26003_2265",

test/Room_test.dart

@@ -24,6 +24,7 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:famedlysdk/src/Room.dart';
 import 'package:famedlysdk/src/Client.dart';
+import 'package:famedlysdk/src/Event.dart';
 import 'package:famedlysdk/src/User.dart';
 import 'FakeMatrixApi.dart';
 
@@ -140,5 +141,10 @@ void main() {
       expect(user.avatarUrl.mxc, "mxc://example.org/SEsfnsuifSDFSSEF");
       expect(user.room.id, "!localpart:server.abc");
     });
+
+    test("getEventByID", () async {
+      final Event event = await room.getEventById("1234");
+      expect(event.id, "143273582443PhrSn:example.org");
+    });
   });
 }