Implement active users chart

Resolve #3904

src/chart/active-users.ts

@@ -0,0 +1,48 @@
+import autobind from 'autobind-decorator';
+import Chart, { Obj } from '.';
+import { IUser, isLocalUser } from '../models/user';
+
+/**
+ * アクティブユーザーに関するチャート
+ */
+type ActiveUsersLog = {
+	local: {
+		/**
+		 * アクティブユーザー数
+		 */
+		count: number;
+	};
+
+	remote: ActiveUsersLog['local'];
+};
+
+class ActiveUsersChart extends Chart<ActiveUsersLog> {
+	constructor() {
+		super('activeUsers');
+	}
+
+	@autobind
+	protected async getTemplate(init: boolean, latest?: ActiveUsersLog): Promise<ActiveUsersLog> {
+		return {
+			local: {
+				count: 0
+			},
+			remote: {
+				count: 0
+			}
+		};
+	}
+
+	@autobind
+	public async update(user: IUser) {
+		const update: Obj = {
+			count: 1
+		};
+
+		await this.incIfUnique({
+			[isLocalUser(user) ? 'local' : 'remote']: update
+		}, 'users', user._id.toHexString());
+	}
+}
+
+export default new ActiveUsersChart();