diff --git a/build/publish.ts b/build/publish.ts
index 317fc0ce7..29f68ec2f 100644
--- a/build/publish.ts
+++ b/build/publish.ts
@@ -1,3 +1,4 @@
+/* eslint-disable no-console */
 /* eslint-disable import/no-extraneous-dependencies */
 /* eslint-disable consistent-return */
 /* eslint-disable no-await-in-loop */
diff --git a/build/start.ts b/build/start.ts
index 901bcddf5..3733ff5e7 100644
--- a/build/start.ts
+++ b/build/start.ts
@@ -1,3 +1,4 @@
+/* eslint-disable no-console */
 /* eslint-disable import/no-extraneous-dependencies */
 import os from 'os';
 import path from 'path';
diff --git a/build/utils.ts b/build/utils.ts
index a05a4ae8a..c13dfff47 100644
--- a/build/utils.ts
+++ b/build/utils.ts
@@ -1,3 +1,4 @@
+/* eslint-disable no-console */
 /* eslint-disable import/no-extraneous-dependencies */
 import path from 'path';
 import globby from 'globby';
diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index e260acf27..3550a18af 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "2.13.5",
+    "version": "2.13.6",
     "bin": "bin/hydrooj.js",
     "main": "dist/loader.js",
     "typings": "dist/loader.d.ts",
@@ -31,6 +31,7 @@
         "serialize-javascript": "^4.0.0",
         "sockjs": "^0.3.20",
         "superagent": "^6.1.0",
+        "supports-color": "^7.2.0",
         "systeminformation": "^4.27.3",
         "yargs": "^15.4.1"
     },
@@ -49,6 +50,7 @@
         "@types/serialize-javascript": "^4.0.0",
         "@types/sockjs": "^0.3.32",
         "@types/superagent": "^4.1.8",
+        "@types/supports-color": "^5.3.0",
         "@types/yargs": "^15.0.5"
     },
     "scripts": {
diff --git a/packages/hydrooj/src/entry/common.ts b/packages/hydrooj/src/entry/common.ts
index ec5b4fd6e..cc4370173 100644
--- a/packages/hydrooj/src/entry/common.ts
+++ b/packages/hydrooj/src/entry/common.ts
@@ -3,7 +3,9 @@
 import fs from 'fs';
 import path from 'path';
 import yaml from 'js-yaml';
-import { argv } from 'yargs';
+import { Logger } from '../logger';
+
+const logger = new Logger('common', true);
 
 export const builtinLib = [
     'jwt', 'download', 'i18n', 'mail', 'useragent',
@@ -46,14 +48,12 @@ export async function handler(pending: string[], fail: string[]) {
         const p = path.resolve(i, 'handler.js');
         if (fs.existsSync(p) && !fail.includes(i)) {
             try {
-                console.log(`Handler init: ${i}`);
-                console.time(`Handler init: ${i}`);
+                logger.info('Handler init: %s', i);
                 eval('require')(p);
-                console.timeEnd(`Handler init: ${i}`);
             } catch (e) {
                 fail.push(i);
-                console.error(`Handler Load Fail: ${i}`);
-                if (argv.debug) console.error(e);
+                logger.error('Handler Load Fail: %s', i);
+                logger.error('%o', e);
             }
         }
     }
@@ -72,11 +72,11 @@ export async function locale(pending: string[], fail: string[]) {
                     locales[file.split('.')[0]] = yaml.safeLoad(content);
                 }
                 global.Hydro.lib.i18n(locales);
-                console.log(`Locale init: ${i}`);
+                logger.info('Locale init: %s', i);
             } catch (e) {
                 fail.push(i);
-                console.error(`Locale Load Fail: ${i}`);
-                if (argv.debug) console.error(e);
+                logger.error('Locale Load Fail: %s', i);
+                logger.error('%o', e);
             }
         }
     }
@@ -105,8 +105,8 @@ export async function setting(pending: string[], fail: string[], modelSetting: t
                     );
                 }
             } catch (e) {
-                console.error(`Config Load Fail: ${i}`);
-                if (argv.debug) console.error(e);
+                logger.error('Config Load Fail: %s', i);
+                logger.error(e);
             }
         }
     }
@@ -124,11 +124,11 @@ export async function template(pending: string[], fail: string[]) {
                         path.resolve(p, file),
                     ).toString();
                 }
-                console.log(`Template init: ${i}`);
+                logger.info('Template init: %s', i);
             } catch (e) {
                 fail.push(i);
-                console.error(`Template Load Fail: ${i}`);
-                if (argv.debug) console.error(e);
+                logger.error('Template Load Fail: %s', i);
+                logger.error(e);
             }
         }
     }
@@ -152,14 +152,12 @@ export async function model(pending: string[], fail: string[]) {
         const p = path.resolve(i, 'model.js');
         if (fs.existsSync(p) && !fail.includes(i)) {
             try {
-                console.log(`Model init: ${i}`);
-                console.time(`Model init: ${i}`);
+                logger.info('Model init: %s', i);
                 eval('require')(p);
-                console.timeEnd(`Model init: ${i}`);
             } catch (e) {
                 fail.push(i);
-                console.error(`Model Load Fail: ${i}`);
-                if (argv.debug) console.error(e);
+                logger.error('Model Load Fail: %s', i);
+                logger.error(e);
             }
         }
     }
@@ -170,14 +168,12 @@ export async function lib(pending: string[], fail: string[]) {
         const p = path.resolve(i, 'lib.js');
         if (fs.existsSync(p) && !fail.includes(i)) {
             try {
-                console.log(`Lib init: ${i}`);
-                console.time(`Lib init: ${i}`);
+                logger.info('Lib init: %s', i);
                 eval('require')(p);
-                console.timeEnd(`Lib init: ${i}`);
             } catch (e) {
                 fail.push(i);
-                console.error(`Lib Load Fail: ${i}`);
-                if (argv.debug) console.error(e);
+                logger.error('Lib Load Fail: %s', i);
+                logger.error(e);
             }
         }
     }
@@ -188,14 +184,12 @@ export async function service(pending: string[], fail: string[]) {
         const p = path.resolve(i, 'service.js');
         if (fs.existsSync(p) && !fail.includes(i)) {
             try {
-                console.log(`Service init: ${i}`);
-                console.time(`Service init: ${i}`);
+                logger.info('Service init: %s', i);
                 eval('require')(p);
-                console.timeEnd(`Service init: ${i}`);
             } catch (e) {
                 fail.push(i);
-                console.error(`Service Load Fail: ${i}`);
-                if (argv.debug) console.error(e);
+                logger.error('Service Load Fail: %s', i);
+                logger.error(e);
             }
         }
     }
@@ -206,13 +200,12 @@ export async function script(pending: string[], fail: string[], active: string[]
         const p = path.resolve(i, 'script.js');
         if (fs.existsSync(p) && !fail.includes(i)) {
             try {
-                console.time(`Script init: ${i}`);
+                logger.info('Script init: %s', i);
                 eval('require')(p);
-                console.timeEnd(`Script init: ${i}`);
             } catch (e) {
                 fail.push(i);
-                console.error(`Script Load Fail: ${i}`);
-                if (argv.debug) console.error(e);
+                logger.error('Script Load Fail: %s', i);
+                logger.error(e);
             }
         }
         active.push(i);
diff --git a/packages/hydrooj/src/entry/master.ts b/packages/hydrooj/src/entry/master.ts
index 25060e6a6..ae5c61cae 100644
--- a/packages/hydrooj/src/entry/master.ts
+++ b/packages/hydrooj/src/entry/master.ts
@@ -47,11 +47,7 @@ export async function load(call: Entry) {
         fs.removeSync(lockfile);
     });
     await new Promise((resolve) => {
-        const h = () => {
-            console.log('Database connected');
-            resolve();
-        };
-        bus.once('database/connect', h);
+        bus.once('database/connect', resolve);
         require('../service/db');
     });
     require('../service/monitor');
diff --git a/packages/hydrooj/src/entry/setup.ts b/packages/hydrooj/src/entry/setup.ts
index 088c769e7..89b313072 100644
--- a/packages/hydrooj/src/entry/setup.ts
+++ b/packages/hydrooj/src/entry/setup.ts
@@ -7,6 +7,9 @@ import Body from 'koa-body';
 import cache from 'koa-static-cache';
 import mongodb from 'mongodb';
 import { argv } from 'yargs';
+import { Logger } from '../logger';
+
+const logger = new Logger('setup');
 
 const listenPort = argv.port || 8888;
 
@@ -141,5 +144,5 @@ export function load() {
             return get(ctx);
         });
     server.listen(listenPort);
-    console.log('Server listening at:', listenPort);
+    logger.success('Server listening at: %d', listenPort);
 }
diff --git a/packages/hydrooj/src/entry/worker.ts b/packages/hydrooj/src/entry/worker.ts
index c1d757409..5e8c3ca04 100644
--- a/packages/hydrooj/src/entry/worker.ts
+++ b/packages/hydrooj/src/entry/worker.ts
@@ -20,11 +20,7 @@ export async function load() {
         uistatic(pending, fail),
     ]);
     await new Promise((resolve) => {
-        const h = () => {
-            console.log('Database connected');
-            resolve();
-        };
-        bus.once('database/connect', h);
+        bus.once('database/connect', resolve);
         require('../service/db');
     });
     for (const i of builtinLib) require(`../lib/${i}`);
diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index 393ea97c5..8942513d1 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -510,6 +510,7 @@ declare global {
                 stat: any,
                 ui: UI,
                 error: typeof import('./error'),
+                Logger: typeof import('./logger'),
                 locales: Dict<Dict<string>>,
             },
             addons: string[],
diff --git a/packages/hydrooj/src/loader.ts b/packages/hydrooj/src/loader.ts
index f959bd597..f1fa1a35c 100644
--- a/packages/hydrooj/src/loader.ts
+++ b/packages/hydrooj/src/loader.ts
@@ -40,14 +40,14 @@ if (!global.Hydro) {
     global.addons = [];
 }
 
-if (argv.debug) {
-    console.log(process.argv);
-    console.log(argv);
-}
-
+// eslint-disable-next-line import/first
+import { Logger } from './logger';
 // eslint-disable-next-line import/first
 import * as bus from './service/bus';
 
+const logger = new Logger('loader');
+logger.debug('%o', argv);
+
 async function terminate() {
     try {
         await bus.parallel('app/exit');
@@ -113,9 +113,9 @@ async function executeCommand(input: string) {
 }
 
 async function reload(count = 1) {
-    console.log('Reloading');
+    logger.info('Reloading');
     await stopWorker();
-    console.log('Worker stopped');
+    logger.info('Worker stopped');
     await startWorker(count);
 }
 
@@ -176,13 +176,13 @@ export function addon(addonPath: string) {
             if (fs.existsSync(publicPath)) fs.copySync(publicPath, publicTemp);
             global.addons.push(targetPath);
         } catch (e) {
-            console.error('Addon load fail: ', e);
+            logger.error('Addon load fail: ', e);
             throw e;
         }
     } else throw new Error(`Addon not found: ${addonPath}`);
 }
 
-process.on('unhandledRejection', (e) => console.error(e));
+process.on('unhandledRejection', logger.error);
 process.on('SIGINT', terminate);
 
 export async function load() {
@@ -191,7 +191,7 @@ export async function load() {
     process.on('message', messageHandler);
     cluster.on('message', messageHandler);
     if (cluster.isMaster || argv.startAsMaster) {
-        console.log(`Master ${process.pid} Starting`);
+        logger.info(`Master ${process.pid} Starting`);
         process.stdin.setEncoding('utf8');
         process.stdin.on('data', (buf) => {
             const input = buf.toString();
@@ -205,33 +205,33 @@ export async function load() {
             }
         });
         const cnt = await entry({ entry: 'master' });
-        console.log('Master started');
+        logger.info('Master started');
         cluster.on('exit', (worker, code, signal) => {
-            console.log(`Worker ${worker.process.pid} ${worker.id} exit: ${code} ${signal}`);
+            logger.info(`Worker ${worker.process.pid} ${worker.id} exit: ${code} ${signal}`);
         });
         cluster.on('disconnect', (worker) => {
-            console.log(`Worker ${worker.process.pid} ${worker.id} disconnected`);
+            logger.info(`Worker ${worker.process.pid} ${worker.id} disconnected`);
         });
         cluster.on('listening', (worker, address) => {
-            console.log(`Worker ${worker.process.pid} ${worker.id} listening at `, address);
+            logger.info(`Worker ${worker.process.pid} ${worker.id} listening at `, address);
         });
         cluster.on('online', (worker) => {
-            console.log(`Worker ${worker.process.pid} ${worker.id} is online`);
+            logger.success(`Worker ${worker.process.pid} ${worker.id} is online`);
         });
         await startWorker(cnt);
     } else {
         global.addons = JSON.parse(Buffer.from(argv.addons as string, 'base64').toString());
-        console.log(global.addons);
+        logger.info('%o', global.addons);
         if (argv.entry) {
-            console.log(`Worker ${process.pid} Starting as ${argv.entry}`);
+            logger.info(`Worker ${process.pid} Starting as ${argv.entry}`);
             await entry({ entry: argv.entry as string });
-            console.log(`Worker ${process.pid} Started as ${argv.entry}`);
+            logger.success(`Worker ${process.pid} Started as ${argv.entry}`);
         } else {
             if (argv.firstWorker) cluster.isFirstWorker = true;
             else cluster.isFirstWorker = false;
-            console.log(`Worker ${process.pid} Starting`);
+            logger.info(`Worker ${process.pid} Starting`);
             await entry({ entry: 'worker' });
-            console.log(`Worker ${process.pid} Started`);
+            logger.success(`Worker ${process.pid} Started`);
         }
     }
     if (global.gc) global.gc();
@@ -245,7 +245,7 @@ export async function loadCli() {
 if (argv.pandora || !module.parent) {
     const func = argv._[0] === 'cli' ? load : loadCli;
     func().catch((e) => {
-        console.error(e);
+        logger.error(e);
         process.exit(1);
     });
 }
diff --git a/packages/hydrooj/src/logger.ts b/packages/hydrooj/src/logger.ts
new file mode 100644
index 000000000..063f8118f
--- /dev/null
+++ b/packages/hydrooj/src/logger.ts
@@ -0,0 +1,142 @@
+import { inspect, InspectOptions, format } from 'util';
+import { argv } from 'yargs';
+import { stderr } from 'supports-color';
+
+namespace Time {
+    export const second = 1000;
+    export const minute = second * 60;
+    export const hour = minute * 60;
+    export const day = hour * 24;
+    export const week = day * 7;
+    export function formatTimeShort(ms: number) {
+        const abs = Math.abs(ms);
+        if (abs >= day - hour / 2) {
+            return `${Math.round(ms / day)}d`;
+        } if (abs >= hour - minute / 2) {
+            return `${Math.round(ms / hour)}h`;
+        } if (abs >= minute - second / 2) {
+            return `${Math.round(ms / minute)}m`;
+        } if (abs >= second) {
+            return `${Math.round(ms / second)}s`;
+        }
+        return `${ms}ms`;
+    }
+}
+
+const colors = stderr.level < 2 ? [6, 2, 3, 4, 5, 1] : [
+    20, 21, 26, 27, 32, 33, 38, 39, 40, 41, 42, 43, 44, 45, 56, 57, 62,
+    63, 68, 69, 74, 75, 76, 77, 78, 79, 80, 81, 92, 93, 98, 99, 112, 113,
+    129, 134, 135, 148, 149, 160, 161, 162, 163, 164, 165, 166, 167, 168,
+    169, 170, 171, 172, 173, 178, 179, 184, 185, 196, 197, 198, 199, 200,
+    201, 202, 203, 204, 205, 206, 207, 208, 209, 214, 215, 220, 221,
+];
+
+const instances: Record<string, Logger> = {};
+
+type LogFunction = (format: any, ...param: any[]) => void
+
+type LogType = 'success' | 'error' | 'info' | 'warn' | 'debug'
+
+export interface Logger extends Record<LogType, LogFunction> { }
+
+export class Logger {
+    static readonly SUCCESS = 1
+
+    static readonly ERROR = 1
+
+    static readonly INFO = 2
+
+    static readonly WARN = 2
+
+    static readonly DEBUG = 3
+
+    static baseLevel = argv.debug ? 3 : 2
+
+    static showDiff = false
+
+    static levels: Record<string, number> = {}
+
+    static lastTime = 0
+
+    static options: InspectOptions = {
+        colors: stderr.hasBasic,
+    }
+
+    static formatters: Record<string, (this: Logger, value: any) => string> = {
+        c: Logger.prototype.color,
+        C: (value) => Logger.color(15, value, ';1'),
+        o: (value) => inspect(value, Logger.options).replace(/\s*\n\s*/g, ' '),
+    }
+
+    static color(code: number, value: any, decoration = '') {
+        if (!Logger.options.colors) return `${value}`;
+        return `\u001B[3${code < 8 ? code : `8;5;${code}`}${decoration}m${value}\u001B[0m`;
+    }
+
+    private code: number
+
+    private displayName: string
+
+    public stream: NodeJS.WritableStream = process.stderr
+
+    constructor(public name: string, private showDiff = false) {
+        if (name in instances) return instances[name];
+        let hash = 0;
+        for (let i = 0; i < name.length; i++) {
+            hash = ((hash << 3) - hash) + name.charCodeAt(i);
+            hash |= 0;
+        }
+        instances[name] = this;
+        this.code = colors[Math.abs(hash) % colors.length];
+        this.displayName = name ? this.color(`${name} `, ';1') : '';
+        this.createMethod('success', '[S] ', Logger.SUCCESS);
+        this.createMethod('error', '[E] ', Logger.ERROR);
+        this.createMethod('info', '[I] ', Logger.INFO);
+        this.createMethod('warn', '[W] ', Logger.WARN);
+        this.createMethod('debug', '[D] ', Logger.DEBUG);
+    }
+
+    private color(value: any, decoration = '') {
+        return Logger.color(this.code, value, decoration);
+    }
+
+    private createMethod(name: LogType, prefix: string, minLevel: number) {
+        this[name] = (...args: [any, ...any[]]) => {
+            if (this.level < minLevel) return;
+            this.stream.write(`${prefix + this.displayName + this.format(...args)}\n`);
+        };
+    }
+
+    get level() {
+        return Logger.levels[this.name] ?? Logger.baseLevel;
+    }
+
+    extend = (namespace: string, showDiff = this.showDiff) => new Logger(`${this.name}:${namespace}`, showDiff)
+
+    format: (format: any, ...param: any[]) => string = (...args) => {
+        if (args[0] instanceof Error) args[0] = args[0].stack || args[0].message;
+        else if (typeof args[0] !== 'string') args.unshift('%O');
+        let index = 0;
+        args[0] = (args[0] as string).replace(/%([a-zA-Z%])/g, (match, fmt) => {
+            if (match === '%%') return '%';
+            index += 1;
+            const formatter = Logger.formatters[fmt];
+            if (typeof formatter === 'function') {
+                match = formatter.call(this, args[index]);
+                args.splice(index, 1);
+                index -= 1;
+            }
+            return match;
+        }).split('\n').join('\n    ');
+        if (Logger.showDiff || this.showDiff) {
+            const now = Date.now();
+            if (Logger.lastTime) {
+                args.push(this.color(`+${Time.formatTimeShort(now - Logger.lastTime)}`));
+            }
+            Logger.lastTime = now;
+        }
+        return format(...args);
+    }
+}
+
+global.Hydro.Logger = { Logger };
diff --git a/packages/hydrooj/src/model/contest.ts b/packages/hydrooj/src/model/contest.ts
index 01b04d144..2ae1e4c18 100644
--- a/packages/hydrooj/src/model/contest.ts
+++ b/packages/hydrooj/src/model/contest.ts
@@ -528,8 +528,8 @@ export function count(domainId: string, query: any, type: Type = document.TYPE_C
     return document.count(domainId, type, query);
 }
 
-export function getMulti<K extends Type & keyof document.DocumentType>(
-    domainId: string, query: FilterQuery<document.DocumentType[K]> = {}, type?: K,
+export function getMulti<K extends Type & keyof document.DocType>(
+    domainId: string, query: FilterQuery<document.DocType[K]> = {}, type?: K,
 ) {
     return document.getMulti(domainId, type || document.TYPE_CONTEST, query);
 }
diff --git a/packages/hydrooj/src/model/document.ts b/packages/hydrooj/src/model/document.ts
index bcc113e9c..97a8f5d70 100644
--- a/packages/hydrooj/src/model/document.ts
+++ b/packages/hydrooj/src/model/document.ts
@@ -22,7 +22,7 @@ export const TYPE_TRAINING = 40;
 export const TYPE_FILE = 50;
 export const TYPE_HOMEWORK = 60;
 
-export interface DocumentType {
+export interface DocType {
     [TYPE_PROBLEM]: Pdoc,
     [TYPE_PROBLEM_SOLUTION]: any,
     [TYPE_PROBLEM_LIST]: any,
@@ -35,13 +35,13 @@ export interface DocumentType {
     [TYPE_HOMEWORK]: Tdoc,
 }
 
-export async function add<T extends DocID, K extends keyof DocumentType>(
+export async function add<T extends DocID, K extends keyof DocType>(
     domainId: string, content: string, owner: number,
-    docType: K, docId: DocumentType[K]['docId'],
+    docType: K, docId: DocType[K]['docId'],
     parentType?: number | null, parentId?: DocID,
     args?: any,
 ): Promise<T>
-export async function add<K extends keyof DocumentType>(
+export async function add<K extends keyof DocType>(
     domainId: string, content: string, owner: number,
     docType: K, docId: null,
     parentType?: number, parentId?: DocID,
@@ -73,13 +73,13 @@ export async function add(
     return docId || res.insertedId;
 }
 
-export function get<K extends keyof DocumentType>(domainId: string, docType: K, docId: DocumentType[K]['docId']) {
+export function get<K extends keyof DocType>(domainId: string, docType: K, docId: DocType[K]['docId']) {
     return coll.findOne({ domainId, docType, docId });
 }
 
-export async function set<K extends keyof DocumentType>(
-    domainId: string, docType: K, docId: DocumentType[K]['docId'], $set: Partial<DocumentType[K]>,
-): Promise<DocumentType[K]> {
+export async function set<K extends keyof DocType>(
+    domainId: string, docType: K, docId: DocType[K]['docId'], $set: Partial<DocType[K]>,
+): Promise<DocType[K]> {
     await bus.parallel('document/set', domainId, docType, docId, $set);
     const res = await coll.findOneAndUpdate(
         { domainId, docType, docId },
@@ -89,8 +89,8 @@ export async function set<K extends keyof DocumentType>(
     return res.value;
 }
 
-export function deleteOne<K extends keyof DocumentType>(
-    domainId: string, docType: K, docId: DocumentType[K]['docId'],
+export function deleteOne<K extends keyof DocType>(
+    domainId: string, docType: K, docId: DocType[K]['docId'],
 ) {
     return Promise.all([
         collStatus.deleteMany({ domainId, docType, docId }),
@@ -98,27 +98,27 @@ export function deleteOne<K extends keyof DocumentType>(
     ]);
 }
 
-export function deleteMulti<K extends keyof DocumentType>(
-    domainId: string, docType: K, query?: FilterQuery<DocumentType[K]>,
+export function deleteMulti<K extends keyof DocType>(
+    domainId: string, docType: K, query?: FilterQuery<DocType[K]>,
 ) {
     return coll.deleteMany({ ...query, domainId, docType });
 }
 
-export function deleteMultiStatus<K extends keyof DocumentType>(
-    domainId: string, docType: K, query?: FilterQuery<DocumentType[K]>,
+export function deleteMultiStatus<K extends keyof DocType>(
+    domainId: string, docType: K, query?: FilterQuery<DocType[K]>,
 ) {
     return collStatus.deleteMany({ ...query, domainId, docType });
 }
 
-export function getMulti<K extends keyof DocumentType>(
-    domainId: string, docType: K, query?: FilterQuery<DocumentType[K]>,
-): Cursor<DocumentType[K]> {
+export function getMulti<K extends keyof DocType>(
+    domainId: string, docType: K, query?: FilterQuery<DocType[K]>,
+): Cursor<DocType[K]> {
     return coll.find({ ...query, docType, domainId });
 }
 
-export async function inc<K extends keyof DocumentType>(
-    domainId: string, docType: K, docId: DocumentType[K]['docId'],
-    key: NumberKeys<DocumentType[K]>, value: number,
+export async function inc<K extends keyof DocType>(
+    domainId: string, docType: K, docId: DocType[K]['docId'],
+    key: NumberKeys<DocType[K]>, value: number,
 ) {
     const res = await coll.findOneAndUpdate(
         { domainId, docType, docId },
@@ -128,11 +128,11 @@ export async function inc<K extends keyof DocumentType>(
     return res.value;
 }
 
-type Q = NumberKeys<DocumentType[10]>
+type Q = NumberKeys<DocType[10]>
 
-export async function incAndSet<K extends keyof DocumentType>(
-    domainId: string, docType: K, docId: DocumentType[K]['docId'],
-    key: NumberKeys<DocumentType[K]>, value: number, args: Partial<DocumentType[K]>,
+export async function incAndSet<K extends keyof DocType>(
+    domainId: string, docType: K, docId: DocType[K]['docId'],
+    key: NumberKeys<DocType[K]>, value: number, args: Partial<DocType[K]>,
 ) {
     const res = await coll.findOneAndUpdate(
         { domainId, docType, docId },
@@ -142,15 +142,15 @@ export async function incAndSet<K extends keyof DocumentType>(
     return res.value;
 }
 
-export function count<K extends keyof DocumentType>(
-    domainId: string, docType: K, query?: FilterQuery<DocumentType[K]>,
+export function count<K extends keyof DocType>(
+    domainId: string, docType: K, query?: FilterQuery<DocType[K]>,
 ) {
     return coll.find({ ...query, docType, domainId }).count();
 }
 
-export async function push<K extends keyof DocumentType, T extends keyof DocumentType[K]>(
-    domainId: string, docType: K, docId: DocumentType[K]['docId'],
-    key: keyof DocumentType[K], content: string, owner: number, args: DocumentType[K][T][0] = {},
+export async function push<K extends keyof DocType, T extends keyof DocType[K]>(
+    domainId: string, docType: K, docId: DocType[K]['docId'],
+    key: keyof DocType[K], content: string, owner: number, args: DocType[K][T][0] = {},
 ) {
     const _id = new ObjectID();
     const doc = await coll.findOneAndUpdate(
@@ -167,10 +167,10 @@ export async function push<K extends keyof DocumentType, T extends keyof Documen
     return [doc.value, _id];
 }
 
-export async function pull<K extends keyof DocumentType>(
-    domainId: string, docType: K, docId: DocumentType[K]['docId'],
+export async function pull<K extends keyof DocType>(
+    domainId: string, docType: K, docId: DocType[K]['docId'],
     setKey: string, contents: string[],
-): Promise<DocumentType[K]> {
+): Promise<DocType[K]> {
     const res = await coll.findOneAndUpdate(
         { domainId, docType, docId },
         { $pull: { [setKey]: { $in: contents } } },
diff --git a/packages/hydrooj/src/service/bus.ts b/packages/hydrooj/src/service/bus.ts
index 241e9e2d0..315308381 100644
--- a/packages/hydrooj/src/service/bus.ts
+++ b/packages/hydrooj/src/service/bus.ts
@@ -1,10 +1,14 @@
 /* eslint-disable no-await-in-loop */
 import cluster from 'cluster';
-import { Db, ObjectID } from 'mongodb';
+import { Db, UpdateQuery } from 'mongodb';
+import { Logger } from '../logger';
 import { Mdoc, Rdoc, User } from '../interface';
+// only typings.
+// eslint-disable-next-line import/no-cycle
+import { DocType } from '../model/document';
 
 const _hooks: Record<keyof any, Array<(...args: any[]) => any>> = {};
-const _disposables = [];
+const logger = new Logger('bus', true);
 
 function isBailed(value: any) {
     return value !== null && value !== false && value !== undefined;
@@ -12,7 +16,7 @@ function isBailed(value: any) {
 
 export type Disposable = () => void
 
-interface EventMap {
+export interface EventMap {
     'app/started': () => void
     'app/exit': () => Promise<void> | void
     'dispose': () => void
@@ -22,15 +26,16 @@ interface EventMap {
     'user/message': (uid: number, mdoc: Mdoc, udoc: User) => void
 
     'document/add': (doc: any) => Promise<void> | void
-    'document/set': (domainId: string, docType: number, docId: ObjectID | string | number, $set: any) => Promise<void> | void
+    'document/set': <T extends keyof DocType>
+        (domainId: string, docType: T, docId: DocType[T], $set: UpdateQuery<DocType[T]>['$set']) => Promise<void> | void
 
-    'record/change': (rdoc: Rdoc, $set?: any, $push?: any) => void
+    'record/change': (rdoc: Rdoc, $set?: UpdateQuery<Rdoc>['$set'], $push?: UpdateQuery<Rdoc>['$push']) => void
 }
 
 function getHooks<K extends keyof EventMap>(name: K) {
     const hooks = _hooks[name] || (_hooks[name] = []);
     if (hooks.length >= 128) {
-        console.warn(
+        logger.warn(
             'max listener count (128) for event "%s" exceeded, which may be caused by a memory leak',
             name,
         );
@@ -49,23 +54,17 @@ export function removeListener<K extends keyof EventMap>(name: K, listener: Even
 
 export function addListener<K extends keyof EventMap>(name: K, listener: EventMap[K]) {
     getHooks(name).push(listener);
-    const dispose = () => removeListener(name, listener);
-    _disposables.push(name === 'dispose' ? listener as Disposable : dispose);
-    return dispose;
+    return () => removeListener(name, listener);
 }
 
 export function prependListener<K extends keyof EventMap>(name: K, listener: EventMap[K]) {
     getHooks(name).unshift(listener);
-    const dispose = () => removeListener(name, listener);
-    _disposables.push(name === 'dispose' ? listener as Disposable : dispose);
-    return dispose;
+    return () => removeListener(name, listener);
 }
 
 export function once<K extends keyof EventMap>(name: K, listener: EventMap[K]) {
-    // @ts-ignore
-    const dispose = addListener(name, (...args: Parameters<EventMap[K]>) => {
+    const dispose = addListener(name, function _listener(...args: any[]) {
         dispose();
-        // @ts-ignore
         return listener.apply(this, args);
     });
     return dispose;
@@ -91,12 +90,12 @@ export function emit<K extends keyof EventMap>(name: K, ...args: Parameters<Even
     return parallel(name, ...args);
 }
 
-export async function serial<K extends keyof EventMap>(name: K, ...args: Parameters<EventMap[K]>): Promise<ReturnType<EventMap[K]>> {
-    for (const callback of _hooks[name] || []) {
-        const result = await callback.apply(this, args);
-        if (isBailed(result)) return result;
+export async function serial<K extends keyof EventMap>(name: K, ...args: Parameters<EventMap[K]>): Promise<void> {
+    logger.debug('serial: %s', name, args);
+    const hooks = Array.from(_hooks[name]);
+    for (const callback of hooks) {
+        await callback.apply(this, args);
     }
-    return null;
 }
 
 export function bail<K extends keyof EventMap>(name: K, ...args: Parameters<EventMap[K]>): ReturnType<EventMap[K]> {
diff --git a/packages/hydrooj/src/service/server.ts b/packages/hydrooj/src/service/server.ts
index 699034f8f..8b04bc581 100644
--- a/packages/hydrooj/src/service/server.ts
+++ b/packages/hydrooj/src/service/server.ts
@@ -18,6 +18,7 @@ import serialize, { SerializeJSOptions } from 'serialize-javascript';
 import { argv } from 'yargs';
 import { lrucache } from '../utils';
 import { User, DomainDoc } from '../interface';
+import { Logger } from '../logger';
 import {
     UserNotFoundError, BlacklistedError, PermissionError,
     UserFacingError, ValidationError, PrivilegeError,
@@ -33,6 +34,7 @@ import * as blacklist from '../model/blacklist';
 import * as token from '../model/token';
 import * as opcount from '../model/opcount';
 
+const logger = new Logger('server');
 export const app = new Koa();
 export const server = http.createServer(app.callback());
 export const router = new Router();
@@ -762,7 +764,7 @@ export function Connection(
     RouteConnHandler: any,
     ...permPrivChecker: Array<number | bigint | Function>
 ) {
-    const log = argv.debug ? console.log : () => { };
+    const log = (v: string, fmt: string, ...args: any[]) => logger.debug(fmt, ...args);
     const sock = sockjs.createServer({ prefix, log });
     const checker = Checker(permPrivChecker);
     sock.on('connection', async (conn) => {
@@ -792,7 +794,7 @@ export function Connection(
                 if (h.finish) await h.finish(args);
             });
         } catch (e) {
-            console.log(e);
+            logger.warn(e);
             await h.onerror(e);
         }
     });
@@ -820,7 +822,7 @@ export async function start() {
     });
     app.use(router.routes()).use(router.allowedMethods());
     server.listen(argv.port || port);
-    console.log('Server listening at: %s', argv.port || port);
+    logger.success('Server listening at: %d', argv.port || port);
 }
 
 global.Hydro.service.server = {