diff --git a/packages/better-search/model.ts b/packages/better-search/model.ts
index 350211cb8..5aa802130 100644
--- a/packages/better-search/model.ts
+++ b/packages/better-search/model.ts
@@ -1,6 +1,4 @@
 import nodejieba from 'nodejieba';
-import { Pdoc } from 'hydrooj';
-import * as document from 'hydrooj/dist/model/document';
 import * as bus from 'hydrooj/dist/service/bus';
 
 declare module 'hydrooj' {
@@ -9,15 +7,11 @@ declare module 'hydrooj' {
     }
 }
 
-bus.on('document/add', async (doc) => {
-    if (doc.type !== document.TYPE_PROBLEM) return;
-    const pdoc = doc as Pdoc;
+const jiebaHook = async (pdoc) => {
+    if (!pdoc.title) return;
     const segments = nodejieba.cutForSearch(pdoc.title);
     pdoc.search = segments.join(' ');
-});
+};
 
-bus.on('document/set', async (domainId, docType, docId, $set) => {
-    if (docType !== document.TYPE_PROBLEM || !$set.title) return;
-    const segments = nodejieba.cutForSearch($set.title);
-    $set.search = segments.join(' ');
-});
+bus.on('problem/before-add', jiebaHook);
+bus.on('problem/before-edit', jiebaHook);
diff --git a/packages/better-search/package.json b/packages/better-search/package.json
index 26289f553..b76318c68 100644
--- a/packages/better-search/package.json
+++ b/packages/better-search/package.json
@@ -1,6 +1,6 @@
 {
     "name": "@hydrooj/better-search",
-    "version": "1.0.2",
+    "version": "1.0.3",
     "description": "Enhance Problem Search",
     "main": "package.json",
     "repository": "https://github.com/hydro-dev/Hydro.git",
@@ -8,13 +8,5 @@
     "license": "AGPL-3.0-only",
     "dependencies": {
         "nodejieba": "^2.5.1"
-    },
-    "devDependencies": {},
-    "peerDependencies": {
-        "hydrooj": "^2.13.2"
-    },
-    "scripts": {
-        "build": "tsc",
-        "lint": "eslint . --ext ts --fix"
     }
 }
\ No newline at end of file
diff --git a/packages/hydrojudge/package.json b/packages/hydrojudge/package.json
index 21814e04c..a9dcd5a0e 100644
--- a/packages/hydrojudge/package.json
+++ b/packages/hydrojudge/package.json
@@ -1,7 +1,7 @@
 {
     "name": "@hydrooj/hydrojudge",
     "bin": "bin/hydrojudge.js",
-    "version": "2.4.15",
+    "version": "2.4.16",
     "os": [
         "linux"
     ],
diff --git a/packages/hydrojudge/src/service.ts b/packages/hydrojudge/src/service.ts
index bbc4fc5b5..e06372b56 100644
--- a/packages/hydrojudge/src/service.ts
+++ b/packages/hydrojudge/src/service.ts
@@ -44,10 +44,10 @@ async function postInit() {
 
     if (system.get('hydrojudge.disable')) return;
     const info = await sysinfo.get();
-    monitor.updateJudger(info);
+    monitor.updateJudge(info);
     setInterval(async () => {
         const [mid, inf] = await sysinfo.update();
-        monitor.updateJudger({ mid, ...inf });
+        monitor.updateJudge({ mid, ...inf });
     }, 1200000);
 
     async function processData(folder: string) {
diff --git a/packages/hydrooj/src/entry/common.ts b/packages/hydrooj/src/entry/common.ts
index 857e1972d..fb088dfe0 100644
--- a/packages/hydrooj/src/entry/common.ts
+++ b/packages/hydrooj/src/entry/common.ts
@@ -206,6 +206,10 @@ export async function service(pending: string[], fail: string[]) {
             }
         }
     }
+    for (const key in global.Hydro.service) {
+        const srv = global.Hydro.service[key];
+        if (!srv.started && srv.start) await srv.start();
+    }
     await bus.serial('app/load/service');
 }
 
diff --git a/packages/hydrooj/src/handler/contest.ts b/packages/hydrooj/src/handler/contest.ts
index a68338965..9c23094a7 100644
--- a/packages/hydrooj/src/handler/contest.ts
+++ b/packages/hydrooj/src/handler/contest.ts
@@ -12,7 +12,7 @@ import { PERM, PRIV } from '../model/builtin';
 import * as contest from '../model/contest';
 import * as system from '../model/system';
 import * as document from '../model/document';
-import * as problem from '../model/problem';
+import problem from '../model/problem';
 import domain from '../model/domain';
 import record from '../model/record';
 import user from '../model/user';
diff --git a/packages/hydrooj/src/handler/domain.ts b/packages/hydrooj/src/handler/domain.ts
index 641f53b01..60714dc12 100644
--- a/packages/hydrooj/src/handler/domain.ts
+++ b/packages/hydrooj/src/handler/domain.ts
@@ -17,11 +17,11 @@ import {
 import { gravatar } from '../lib/misc';
 import paginate from '../lib/paginate';
 import {
-    Route, Handler, Types, param,
+    Route, Handler, Types, param, query, post,
 } from '../service/server';
 
 class DomainRankHandler extends Handler {
-    @param('page', Types.PositiveInt, true)
+    @query('page', Types.PositiveInt, true)
     async get(domainId: string, page = 1) {
         const [dudocs, upcount, ucount] = await paginate(
             domain.getMultiUserInDomain(domainId).sort({ rp: -1 }),
@@ -129,8 +129,8 @@ class DomainUserHandler extends ManageHandler {
         };
     }
 
-    @param('uid', Types.Int)
-    @param('role', Types.String)
+    @post('uid', Types.Int)
+    @post('role', Types.String)
     async postSetUser(domainId: string, uid: number, role: string) {
         await domain.setUserRole(domainId, uid, role);
         this.back();
@@ -228,10 +228,10 @@ class DomainJoinApplicationsHandler extends ManageHandler {
         this.response.template = 'domain_join_applications.html';
     }
 
-    @param('method', Types.Range([domain.JOIN_METHOD_NONE, domain.JOIN_METHOD_ALL, domain.JOIN_METHOD_CODE]))
-    @param('role', Types.String, true)
-    @param('expire', Types.Int, true)
-    @param('invitationCode', Types.String, true)
+    @post('method', Types.Range([domain.JOIN_METHOD_NONE, domain.JOIN_METHOD_ALL, domain.JOIN_METHOD_CODE]))
+    @post('role', Types.String, true)
+    @post('expire', Types.Int, true)
+    @post('invitationCode', Types.String, true)
     async post(domainId: string, method: number, role: string, expire: number, invitationCode = '') {
         const r = await domain.getRoles(this.domain);
         const roles = r.map((rl) => rl._id);
diff --git a/packages/hydrooj/src/handler/homework.ts b/packages/hydrooj/src/handler/homework.ts
index c7fb50c00..6763fd8a3 100644
--- a/packages/hydrooj/src/handler/homework.ts
+++ b/packages/hydrooj/src/handler/homework.ts
@@ -18,7 +18,7 @@ import user from '../model/user';
 import * as system from '../model/system';
 import * as contest from '../model/contest';
 import * as discussion from '../model/discussion';
-import * as problem from '../model/problem';
+import problem from '../model/problem';
 import record from '../model/record';
 import * as document from '../model/document';
 import paginate from '../lib/paginate';
diff --git a/packages/hydrooj/src/handler/import.syzoj.ts b/packages/hydrooj/src/handler/import.syzoj.ts
index e55122f2b..99742b0a0 100644
--- a/packages/hydrooj/src/handler/import.syzoj.ts
+++ b/packages/hydrooj/src/handler/import.syzoj.ts
@@ -10,7 +10,7 @@ import yaml from 'js-yaml';
 import { ValidationError, RemoteOnlineJudgeError } from '../error';
 import { Logger } from '../logger';
 import type { ContentNode } from '../interface';
-import * as problem from '../model/problem';
+import problem from '../model/problem';
 import { PERM } from '../model/builtin';
 import {
     Route, Handler, Types, post,
diff --git a/packages/hydrooj/src/handler/judge.ts b/packages/hydrooj/src/handler/judge.ts
index 139c21133..503533f30 100644
--- a/packages/hydrooj/src/handler/judge.ts
+++ b/packages/hydrooj/src/handler/judge.ts
@@ -4,7 +4,7 @@ import { sleep } from '../utils';
 import { Logger } from '../logger';
 import difficultyAlgorithm from '../lib/difficulty';
 import record from '../model/record';
-import * as problem from '../model/problem';
+import problem from '../model/problem';
 import * as builtin from '../model/builtin';
 import * as contest from '../model/contest';
 import domain from '../model/domain';
@@ -14,7 +14,7 @@ import {
     Route, Handler, Connection, ConnectionHandler, post, Types,
 } from '../service/server';
 import storage from '../service/storage';
-import { updateJudger } from '../service/monitor';
+import { updateJudge } from '../service/monitor';
 
 const logger = new Logger('judge');
 
@@ -145,7 +145,7 @@ class JudgeConnectionHandler extends ConnectionHandler {
             this.processing = null;
             await this.newTask();
         } else if (msg.key === 'status') {
-            await updateJudger(msg.info);
+            await updateJudge(msg.info);
         }
     }
 
diff --git a/packages/hydrooj/src/handler/manage.ts b/packages/hydrooj/src/handler/manage.ts
index cdddb0cee..6c23807cc 100644
--- a/packages/hydrooj/src/handler/manage.ts
+++ b/packages/hydrooj/src/handler/manage.ts
@@ -3,6 +3,7 @@ import * as yaml from 'js-yaml';
 import * as judge from './judge';
 import { ValidationError } from '../error';
 import * as check from '../check';
+import { Logger } from '../logger';
 import * as setting from '../model/setting';
 import * as system from '../model/system';
 import user from '../model/user';
@@ -17,6 +18,8 @@ import {
     validate, isEmail, isUname, isPassword,
 } from '../lib/validator';
 
+const logger = new Logger('manage');
+
 function set(key: string, value: any) {
     if (setting.SYSTEM_SETTINGS_BY_KEY[key]) {
         const s = setting.SYSTEM_SETTINGS_BY_KEY[key];
@@ -125,11 +128,12 @@ class SystemScriptHandler extends SystemHandler {
             })
             .catch((err: Error) => {
                 const time = new Date().getTime() - start;
+                logger.error(err);
                 judge.end({
                     domainId,
                     rid,
                     status: STATUS.STATUS_SYSTEM_ERROR,
-                    message: `${err} \n${err.stack} `,
+                    message: `${err.message} \n${err.stack} `,
                     judger: 1,
                     time,
                     memory: 0,
diff --git a/packages/hydrooj/src/handler/misc.ts b/packages/hydrooj/src/handler/misc.ts
index 9dc24b734..af8c138b7 100644
--- a/packages/hydrooj/src/handler/misc.ts
+++ b/packages/hydrooj/src/handler/misc.ts
@@ -32,9 +32,9 @@ class StatusHandler extends Handler {
 class StatusUpdateHandler extends Handler {
     async post(args) {
         this.checkPriv(PRIV.PRIV_JUDGE);
-        args.type = 'judger';
+        args.type = 'judge';
         return coll.updateOne(
-            { mid: args.mid, type: 'judger' },
+            { mid: args.mid, type: 'judge' },
             { $set: args },
             { upsert: true },
         );
diff --git a/packages/hydrooj/src/handler/problem.ts b/packages/hydrooj/src/handler/problem.ts
index 8f926362d..84fd75322 100644
--- a/packages/hydrooj/src/handler/problem.ts
+++ b/packages/hydrooj/src/handler/problem.ts
@@ -12,7 +12,7 @@ import paginate from '../lib/paginate';
 import { isTitle, isContent, isPid } from '../lib/validator';
 import difficultyAlgorithm from '../lib/difficulty';
 import * as system from '../model/system';
-import * as problem from '../model/problem';
+import problem from '../model/problem';
 import record from '../model/record';
 import domain from '../model/domain';
 import user from '../model/user';
@@ -62,18 +62,26 @@ export class ProblemMainHandler extends ProblemHandler {
             ['Hydro', 'homepage'],
             ['problem_main', null],
         ];
+        const search = global.Hydro.lib.problemSearch;
+        let sort: number[];
         if (q) {
-            query.$text = { $search: q };
             path[1][1] = 'problem_main';
             path.push([q, null, null, true]);
+            if (search) {
+                const result = await search(domainId, q);
+                query.docId = { $in: result };
+                sort = result;
+            } else query.$text = { $search: q };
         }
         if (!this.user.hasPerm(PERM.PERM_VIEW_PROBLEM_HIDDEN)) query.hidden = false;
         await bus.serial('problem/list', query, this);
-        const [pdocs, ppcount, pcount] = await paginate(
+        // eslint-disable-next-line prefer-const
+        let [pdocs, ppcount, pcount] = await paginate(
             problem.getMulti(domainId, query).sort({ pid: 1, docId: 1 }),
             page,
             system.get('pagination.problem'),
         );
+        if (sort) pdocs = pdocs.sort((a, b) => sort.indexOf(a.docId) - sort.indexOf(b.docId));
         if (q && +q) {
             const pdoc = await problem.get(domainId, +q, this.user._id, problem.PROJECTION_LIST);
             if (pdoc) pdocs.unshift(pdoc);
@@ -341,9 +349,7 @@ export class ProblemEditHandler extends ProblemManageHandler {
         };
         let pdoc = await problem.get(domainId, pid);
         $update.difficulty = difficultyAlgorithm(pdoc.nSubmit, pdoc.nAccept);
-        await bus.serial('problem/before-edit', $update);
         pdoc = await problem.edit(domainId, pdoc.docId, $update);
-        await bus.emit('problem/edit', pdoc);
         this.response.redirect = this.url('problem_detail', { pid: newPid || pdoc.docId });
     }
 }
diff --git a/packages/hydrooj/src/handler/record.ts b/packages/hydrooj/src/handler/record.ts
index de126787f..5465c8d08 100644
--- a/packages/hydrooj/src/handler/record.ts
+++ b/packages/hydrooj/src/handler/record.ts
@@ -3,7 +3,7 @@ import { PermissionError, RecordNotFoundError } from '../error';
 import { Rdoc } from '../interface';
 import { PERM, STATUS, PRIV } from '../model/builtin';
 import * as system from '../model/system';
-import * as problem from '../model/problem';
+import problem from '../model/problem';
 import record from '../model/record';
 import * as contest from '../model/contest';
 import user from '../model/user';
@@ -49,7 +49,7 @@ class RecordListHandler extends RecordHandler {
             user.getList(domainId, rdocs.map((rdoc) => rdoc.uid)),
             canViewProblem
                 ? problem.getList(domainId, rdocs.map((rdoc) => rdoc.pid), canViewProblemHidden, false)
-                : Object.fromEntries([rdocs.map((rdoc) => [rdoc.pid, problem.Pdoc.create(rdoc.pid, rdoc.pid)])]),
+                : Object.fromEntries([rdocs.map((rdoc) => [rdoc.pid, problem.create(rdoc.pid, rdoc.pid)])]),
         ]);
         const path = [
             ['Hydro', 'homepage'],
@@ -88,11 +88,11 @@ class RecordDetailHandler extends RecordHandler {
             user.getById(domainId, rdoc.uid),
         ]);
         if (!(pdoc && this.user.hasPerm(PERM.PERM_VIEW_PROBLEM))) {
-            pdoc = problem.Pdoc.create(pdoc?.docId || 0, pdoc?.pid || '*');
+            pdoc = problem.create(pdoc?.docId || 0, pdoc?.pid || '*');
         }
         if (!rdoc.contest && pdoc.hidden && pdoc.owner !== this.user._id) {
             if (!this.user.hasPerm(PERM.PERM_VIEW_PROBLEM_HIDDEN)) {
-                pdoc = problem.Pdoc.create(pdoc.docId, pdoc.pid);
+                pdoc = problem.create(pdoc.docId, pdoc.pid);
             }
         }
         this.response.body = {
diff --git a/packages/hydrooj/src/handler/remote.ts b/packages/hydrooj/src/handler/remote.ts
index 35252a961..c147b4eae 100644
--- a/packages/hydrooj/src/handler/remote.ts
+++ b/packages/hydrooj/src/handler/remote.ts
@@ -6,7 +6,7 @@ import { Logger } from '../logger';
 import { ProblemAdd } from '../lib/ui';
 import { PERM } from '../model/builtin';
 import token from '../model/token';
-import * as problem from '../model/problem';
+import problem from '../model/problem';
 import * as system from '../model/system';
 import {
     Handler, Types, Route, post,
@@ -24,9 +24,10 @@ export class ProblemSendHandler extends Handler {
 
     @post('target', Types.String)
     @post('pids', Types.Array)
-    async postSend(domainId: string, target: any, _pids: (number | string)[]) {
+    async postSend(domainId: string, _target: string, _pids: (number | string)[]) {
         this.checkPerm(PERM.PERM_VIEW_PROBLEM);
-        target = target.split('@');
+        const target = _target.split('@');
+        if (target[1].endsWith('/')) target[1] = target[1].substr(0, target[1].length - 1);
         const getHidden = this.user.hasPerm(PERM.PERM_VIEW_PROBLEM_HIDDEN);
         const getData = this.user.hasPerm(PERM.PERM_READ_PROBLEM_DATA);
         const pdocs = await problem.getList(domainId, _pids, true, true, ['docId', 'owner', 'hidden']);
diff --git a/packages/hydrooj/src/handler/training.ts b/packages/hydrooj/src/handler/training.ts
index 231192fc5..443cfa279 100644
--- a/packages/hydrooj/src/handler/training.ts
+++ b/packages/hydrooj/src/handler/training.ts
@@ -6,7 +6,7 @@ import { isTitle, isContent, isDescription } from '../lib/validator';
 import paginate from '../lib/paginate';
 import * as system from '../model/system';
 import { PERM, PRIV } from '../model/builtin';
-import * as problem from '../model/problem';
+import problem from '../model/problem';
 import * as builtin from '../model/builtin';
 import * as training from '../model/training';
 import user from '../model/user';
diff --git a/packages/hydrooj/src/handler/user.ts b/packages/hydrooj/src/handler/user.ts
index 8d2028171..d4267e638 100644
--- a/packages/hydrooj/src/handler/user.ts
+++ b/packages/hydrooj/src/handler/user.ts
@@ -11,7 +11,7 @@ import user from '../model/user';
 import oauth from '../model/oauth';
 import token from '../model/token';
 import record from '../model/record';
-import * as problem from '../model/problem';
+import problem, { Pdoc } from '../model/problem';
 import task from '../model/task';
 import * as system from '../model/system';
 import { PERM, PRIV } from '../model/builtin';
@@ -183,7 +183,7 @@ class UserDetailHandler extends Handler {
                     1,
                     100,
                 )
-                : [[], 0, 0] as [problem.Pdoc[], number, number],
+                : [[], 0, 0] as [Pdoc[], number, number],
         ]);
         const pdict = this.user.hasPerm(PERM.PERM_VIEW_PROBLEM)
             ? await problem.getList(
@@ -191,7 +191,7 @@ class UserDetailHandler extends Handler {
                 this.user.hasPerm(PERM.PERM_VIEW_PROBLEM_HIDDEN), false,
             )
             : Object.fromEntries(rdocs.map(
-                (rdoc) => [rdoc.pid, problem.Pdoc.create(undefined, rdoc.pid.toString())],
+                (rdoc) => [rdoc.pid, problem.create(undefined, rdoc.pid.toString())],
             ));
         // Remove sensitive data
         if (!isSelfProfile && sdoc) {
diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index 7392356c2..763b468ec 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -458,6 +458,13 @@ export interface HydroFileSystem {
 
 export type PathComponent = [string, string, Dictionary<any>?, boolean?];
 
+export interface BaseService {
+    started: boolean;
+    error?: Error | string;
+    start: Function;
+    stop?: Function;
+}
+
 export interface Collections {
     'blacklist': Bdoc,
     'contest': Tdoc,
@@ -483,25 +490,25 @@ export interface Collections {
 }
 
 export interface Model {
-    blacklist: typeof import('./model/blacklist'),
+    blacklist: typeof import('./model/blacklist').default,
     builtin: typeof import('./model/builtin'),
     contest: typeof import('./model/contest'),
     discussion: typeof import('./model/discussion'),
     document: typeof import('./model/document'),
-    domain: typeof import('./model/domain'),
-    message: typeof import('./model/message'),
+    domain: typeof import('./model/domain').default,
+    message: typeof import('./model/message').default,
     opcount: typeof import('./model/opcount'),
-    problem: typeof import('./model/problem'),
-    record: typeof import('./model/record'),
+    problem: typeof import('./model/problem').default,
+    record: typeof import('./model/record').default,
     setting: typeof import('./model/setting'),
-    solution: typeof import('./model/solution'),
+    solution: typeof import('./model/solution').default,
     system: typeof import('./model/system'),
-    task: typeof import('./model/task'),
+    task: typeof import('./model/task').default,
     oplog: typeof import('./model/oplog'),
-    token: typeof import('./model/token'),
+    token: typeof import('./model/token').default,
     training: typeof import('./model/training'),
-    user: typeof import('./model/user'),
-    oauth: typeof import('./model/oauth'),
+    user: typeof import('./model/user').default,
+    oauth: typeof import('./model/oauth').default,
 }
 
 export interface Service {
diff --git a/packages/hydrooj/src/model/blacklist.ts b/packages/hydrooj/src/model/blacklist.ts
index a1e7bf32a..d6bb0cd93 100644
--- a/packages/hydrooj/src/model/blacklist.ts
+++ b/packages/hydrooj/src/model/blacklist.ts
@@ -32,5 +32,5 @@ async function ensureIndexes() {
 }
 
 bus.once('app/started', ensureIndexes);
-export = BlackListModel;
+export default BlackListModel;
 global.Hydro.model.blacklist = BlackListModel;
diff --git a/packages/hydrooj/src/model/contest.ts b/packages/hydrooj/src/model/contest.ts
index 185c9d404..85da111a7 100644
--- a/packages/hydrooj/src/model/contest.ts
+++ b/packages/hydrooj/src/model/contest.ts
@@ -1,6 +1,6 @@
 import { ObjectID, FilterQuery } from 'mongodb';
 import user from './user';
-import * as problem from './problem';
+import problem from './problem';
 import * as document from './document';
 import { PERM } from './builtin';
 import {
diff --git a/packages/hydrooj/src/model/discussion.ts b/packages/hydrooj/src/model/discussion.ts
index 643232cdd..8ce83d393 100644
--- a/packages/hydrooj/src/model/discussion.ts
+++ b/packages/hydrooj/src/model/discussion.ts
@@ -1,5 +1,5 @@
 import { FilterQuery, ObjectID } from 'mongodb';
-import * as problem from './problem';
+import problem from './problem';
 import * as contest from './contest';
 import * as training from './training';
 import * as document from './document';
diff --git a/packages/hydrooj/src/model/domain.ts b/packages/hydrooj/src/model/domain.ts
index cf84581cf..f246dd2df 100644
--- a/packages/hydrooj/src/model/domain.ts
+++ b/packages/hydrooj/src/model/domain.ts
@@ -235,5 +235,5 @@ class DomainModel {
     }
 }
 
-export = DomainModel;
+export default DomainModel;
 global.Hydro.model.domain = DomainModel;
diff --git a/packages/hydrooj/src/model/message.ts b/packages/hydrooj/src/model/message.ts
index 76df8fc42..8794fede2 100644
--- a/packages/hydrooj/src/model/message.ts
+++ b/packages/hydrooj/src/model/message.ts
@@ -76,5 +76,5 @@ function ensureIndexes() {
 }
 
 bus.once('app/started', ensureIndexes);
-export = MessageModel;
+export default MessageModel;
 global.Hydro.model.message = MessageModel;
diff --git a/packages/hydrooj/src/model/oauth.ts b/packages/hydrooj/src/model/oauth.ts
index 216f13fef..167dce7e5 100644
--- a/packages/hydrooj/src/model/oauth.ts
+++ b/packages/hydrooj/src/model/oauth.ts
@@ -25,5 +25,5 @@ class OauthModel {
     }
 }
 
-export = OauthModel;
+export default OauthModel;
 global.Hydro.model.oauth = OauthModel;
diff --git a/packages/hydrooj/src/model/problem.ts b/packages/hydrooj/src/model/problem.ts
index 1e268c7f3..651024478 100644
--- a/packages/hydrooj/src/model/problem.ts
+++ b/packages/hydrooj/src/model/problem.ts
@@ -13,245 +13,231 @@ import storage from '../service/storage';
 import * as bus from '../service/bus';
 
 export interface Pdoc extends Document { }
-export namespace Pdoc {
-    export type Field = keyof Pdoc;
-    export const fields: Field[] = [];
-    type Getter = (docId?: number, pid?: string) => Partial<Pdoc>;
-    const getters: Getter[] = [];
-    export function extend(getter: Getter) {
+export type Field = keyof Pdoc;
+const fields: Field[] = [];
+export type Getter = (docId?: number, pid?: string) => Partial<Pdoc>;
+const getters: Getter[] = [];
+
+export class ProblemModel {
+    static PROJECTION_LIST: Field[] = [
+        '_id', 'domainId', 'docType', 'docId', 'pid',
+        'owner', 'title', 'nSubmit', 'nAccept', 'difficulty',
+        'tag', 'hidden',
+    ];
+
+    static PROJECTION_PUBLIC: Field[] = [
+        ...ProblemModel.PROJECTION_LIST,
+        'content', 'html', 'data', 'config', 'acMsg',
+        'additional_file',
+    ];
+
+    static extend(getter: Getter) {
         getters.push(getter);
         fields.push(...Object.keys(getter(0, '0')) as any);
     }
 
-    extend((docId, pid) => ({
-        _id: new ObjectID(),
-        domainId: 'system',
-        docType: document.TYPE_PROBLEM,
-        docId: docId || -1,
-        pid: pid || docId.toString(),
-        owner: 1,
-        title: '*',
-        content: '',
-        html: false,
-        nSubmit: 0,
-        nAccept: 0,
-        tag: [],
-        data: [],
-        additional_file: [],
-        hidden: true,
-        config: {},
-        acMsg: '',
-        difficulty: 0,
-    }));
-
-    export function create(docId?: number, pid?: string) {
+    static create(docId?: number, pid?: string) {
         const result = {} as Pdoc;
         for (const getter of getters) {
             Object.assign(result, getter(docId, pid));
         }
         return result;
     }
-}
 
-export const PROJECTION_LIST: Pdoc.Field[] = [
-    '_id', 'domainId', 'docType', 'docId', 'pid',
-    'owner', 'title', 'nSubmit', 'nAccept', 'difficulty',
-    'tag', 'hidden',
-];
-
-export const PROJECTION_PUBLIC: Pdoc.Field[] = [
-    ...PROJECTION_LIST,
-    'content', 'html', 'data', 'config', 'acMsg',
-    'additional_file',
-];
-
-export async function add(
-    domainId: string, pid: string = null, title: string, content: Content, owner: number,
-    tag: string[] = [], hidden = false,
-) {
-    const pidCounter = await domain.inc(domainId, 'pidCounter', 1);
-    const args: Partial<Pdoc> = {
-        title, tag, hidden, nSubmit: 0, nAccept: 0,
-    };
-    if (pid) args.pid = pid;
-    return await document.add(domainId, content, owner, document.TYPE_PROBLEM, pidCounter, null, null, args);
-}
-
-export async function get(
-    domainId: string, pid: string | number,
-    uid: number = null, projection: Projection<Pdoc> = PROJECTION_PUBLIC,
-): Promise<Pdoc> {
-    if (typeof pid !== 'number') {
-        if (Number.isSafeInteger(parseInt(pid, 10))) pid = parseInt(pid, 10);
+    static async add(
+        domainId: string, pid: string = null, title: string, content: Content, owner: number,
+        tag: string[] = [], hidden = false,
+    ) {
+        const pidCounter = await domain.inc(domainId, 'pidCounter', 1);
+        const args: Partial<Pdoc> = {
+            title, tag, hidden, nSubmit: 0, nAccept: 0,
+        };
+        if (pid) args.pid = pid;
+        await bus.serial('problem/before-add', args);
+        const result = await document.add(domainId, content, owner, document.TYPE_PROBLEM, pidCounter, null, null, args);
+        await bus.emit('problem/add', args, result);
+        return result;
     }
-    const pdoc = typeof pid === 'number'
-        ? await document.get(domainId, document.TYPE_PROBLEM, pid, projection)
-        : (await document.getMulti(domainId, document.TYPE_PROBLEM, { pid }).toArray())[0];
-    if (!pdoc) return null;
-    if (uid) {
-        pdoc.psdoc = await document.getStatus(domainId, document.TYPE_PROBLEM, pdoc.docId, uid);
+
+    static async get(
+        domainId: string, pid: string | number,
+        uid: number = null, projection: Projection<Pdoc> = ProblemModel.PROJECTION_PUBLIC,
+    ): Promise<Pdoc> {
+        if (typeof pid !== 'number') {
+            if (Number.isSafeInteger(parseInt(pid, 10))) pid = parseInt(pid, 10);
+        }
+        const pdoc = typeof pid === 'number'
+            ? await document.get(domainId, document.TYPE_PROBLEM, pid, projection)
+            : (await document.getMulti(domainId, document.TYPE_PROBLEM, { pid }).toArray())[0];
+        if (!pdoc) return null;
+        if (uid) {
+            pdoc.psdoc = await document.getStatus(domainId, document.TYPE_PROBLEM, pdoc.docId, uid);
+        }
+        return pdoc;
     }
-    return pdoc;
-}
 
-export function getMulti(domainId: string, query: FilterQuery<Pdoc>, projection = PROJECTION_LIST) {
-    return document.getMulti(domainId, document.TYPE_PROBLEM, query, projection);
-}
-
-export function getMultiStatus(domainId: string, query: FilterQuery<Pdoc>) {
-    return document.getMultiStatus(domainId, document.TYPE_PROBLEM, query);
-}
-
-export function edit(domainId: string, _id: number, $set: Partial<Pdoc>): Promise<Pdoc> {
-    const delpid = $set.pid === '';
-    if (delpid) delete $set.pid;
-    return document.set(domainId, document.TYPE_PROBLEM, _id, $set, delpid ? { pid: '' } : undefined);
-}
-
-export function push<T extends ArrayKeys<Pdoc>>(domainId: string, _id: number, key: ArrayKeys<Pdoc>, value: Pdoc[T][0]) {
-    return document.push(domainId, document.TYPE_PROBLEM, _id, key, value);
-}
-
-export function pull<T extends ArrayKeys<Pdoc>>(domainId: string, pid: number, key: ArrayKeys<Pdoc>, values: Pdoc[T][0][]) {
-    return document.deleteSub(domainId, document.TYPE_PROBLEM, pid, key, values);
-}
-
-export function inc(domainId: string, _id: number, field: NumberKeys<Pdoc>, n: number): Promise<Pdoc> {
-    return document.inc(domainId, document.TYPE_PROBLEM, _id, field, n);
-}
-
-export function count(domainId: string, query: FilterQuery<Pdoc>) {
-    return document.count(domainId, document.TYPE_PROBLEM, query);
-}
-
-export function del(domainId: string, docId: number) {
-    return Promise.all([
-        document.deleteOne(domainId, document.TYPE_PROBLEM, docId),
-        document.deleteMultiStatus(domainId, document.TYPE_PROBLEM, { docId }),
-        storage.list(`problem/${domainId}/${docId}/`).then((items) => storage.del(items.map((item) => item.prefix + item.name))),
-        bus.parallel('problem/delete', domainId, docId),
-    ]);
-}
-
-export async function addTestdata(domainId: string, pid: number, name: string, f: Readable | Buffer | string) {
-    if (!name) throw new ValidationError('name');
-    const [[, fileinfo]] = await Promise.all([
-        document.getSub(domainId, document.TYPE_PROBLEM, pid, 'data', name),
-        storage.put(`problem/${domainId}/${pid}/testdata/${name}`, f),
-    ]);
-    const meta = await storage.getMeta(`problem/${domainId}/${pid}/testdata/${name}`);
-    if (!meta) throw new Error('Upload failed');
-    const payload = { name, ...pick(meta, ['size', 'lastModified', 'etag']) };
-    if (!fileinfo) await push(domainId, pid, 'data', { _id: name, ...payload });
-    else await document.setSub(domainId, document.TYPE_PROBLEM, pid, 'data', name, payload);
-}
-
-export async function delTestdata(domainId: string, pid: number, name: string | string[]) {
-    const names = (name instanceof Array) ? name : [name];
-    await storage.del(names.map((t) => `problem/${domainId}/${pid}/testdata/${t}`));
-    await pull(domainId, pid, 'data', names);
-}
-
-export async function addAdditionalFile(domainId: string, pid: number, name: string, f: Readable | Buffer | string) {
-    const [[, fileinfo]] = await Promise.all([
-        document.getSub(domainId, document.TYPE_PROBLEM, pid, 'additional_file', name),
-        storage.put(`problem/${domainId}/${pid}/additional_file/${name}`, f),
-    ]);
-    const meta = await storage.getMeta(`problem/${domainId}/${pid}/additional_file/${name}`);
-    const payload = { name, ...pick(meta, ['size', 'lastModified', 'etag']) };
-    if (!fileinfo) await push(domainId, pid, 'additional_file', { _id: name, ...payload });
-    else await document.setSub(domainId, document.TYPE_PROBLEM, pid, 'additional_file', name, payload);
-}
-
-export async function delAdditionalFile(domainId: string, pid: number, name: string | string[]) {
-    const names = (name instanceof Array) ? name : [name];
-    await storage.del(names.map((t) => `problem/${domainId}/${pid}/additional_file/${t}`));
-    await pull(domainId, pid, 'additional_file', names);
-}
-
-export async function random(domainId: string, query: FilterQuery<Pdoc>): Promise<string | null> {
-    const cursor = document.getMulti(domainId, document.TYPE_PROBLEM, query);
-    const pcount = await cursor.count();
-    if (pcount) {
-        const pdoc = await cursor.skip(Math.floor(Math.random() * pcount)).limit(1).toArray();
-        return pdoc[0].pid;
-    } return null;
-}
-
-export async function getList(
-    domainId: string, pids: Array<number | string>,
-    getHidden = false, doThrow = true, projection = PROJECTION_PUBLIC,
-): Promise<Pdict> {
-    pids = Array.from(new Set(pids)).map((i) => (+i ? +i : i));
-    const r = {};
-    const l = {};
-    const q: any = { $or: [{ docId: { $in: pids } }, { pid: { $in: pids } }] };
-    if (!getHidden) q.hidden = false;
-    const pdocs = await document.getMulti(domainId, document.TYPE_PROBLEM, q)
-        .project(buildProjection(projection)).toArray();
-    for (const pdoc of pdocs) {
-        r[pdoc.docId] = pdoc;
-        l[pdoc.pid] = pdoc;
+    static getMulti(domainId: string, query: FilterQuery<Pdoc>, projection = ProblemModel.PROJECTION_LIST) {
+        return document.getMulti(domainId, document.TYPE_PROBLEM, query, projection);
     }
-    // TODO enhance
-    if (pdocs.length !== pids.length) {
-        for (const pid of pids) {
-            if (!(r[pid] || l[pid])) {
-                if (doThrow) throw new ProblemNotFoundError(domainId, pid);
-                else r[pid] = Pdoc.create(undefined, pid.toString());
+
+    static getMultiStatus(domainId: string, query: FilterQuery<Pdoc>) {
+        return document.getMultiStatus(domainId, document.TYPE_PROBLEM, query);
+    }
+
+    static async edit(domainId: string, _id: number, $set: Partial<Pdoc>): Promise<Pdoc> {
+        const delpid = $set.pid === '';
+        if (delpid) delete $set.pid;
+        await bus.serial('problem/before-edit', $set);
+        const result = await document.set(domainId, document.TYPE_PROBLEM, _id, $set, delpid ? { pid: '' } : undefined);
+        await bus.emit('problem/edit', result);
+        return result;
+    }
+
+    static push<T extends ArrayKeys<Pdoc>>(domainId: string, _id: number, key: ArrayKeys<Pdoc>, value: Pdoc[T][0]) {
+        return document.push(domainId, document.TYPE_PROBLEM, _id, key, value);
+    }
+
+    static pull<T extends ArrayKeys<Pdoc>>(domainId: string, pid: number, key: ArrayKeys<Pdoc>, values: Pdoc[T][0][]) {
+        return document.deleteSub(domainId, document.TYPE_PROBLEM, pid, key, values);
+    }
+
+    static inc(domainId: string, _id: number, field: NumberKeys<Pdoc>, n: number): Promise<Pdoc> {
+        return document.inc(domainId, document.TYPE_PROBLEM, _id, field, n);
+    }
+
+    static count(domainId: string, query: FilterQuery<Pdoc>) {
+        return document.count(domainId, document.TYPE_PROBLEM, query);
+    }
+
+    static async del(domainId: string, docId: number) {
+        await bus.serial('problem/before-del', domainId, docId);
+        const res = await Promise.all([
+            document.deleteOne(domainId, document.TYPE_PROBLEM, docId),
+            document.deleteMultiStatus(domainId, document.TYPE_PROBLEM, { docId }),
+            storage.list(`problem/${domainId}/${docId}/`).then((items) => storage.del(items.map((item) => item.prefix + item.name))),
+            bus.parallel('problem/delete', domainId, docId),
+        ]);
+        await bus.emit('problem/del', domainId, docId);
+        return res;
+    }
+
+    static async addTestdata(domainId: string, pid: number, name: string, f: Readable | Buffer | string) {
+        if (!name) throw new ValidationError('name');
+        const [[, fileinfo]] = await Promise.all([
+            document.getSub(domainId, document.TYPE_PROBLEM, pid, 'data', name),
+            storage.put(`problem/${domainId}/${pid}/testdata/${name}`, f),
+        ]);
+        const meta = await storage.getMeta(`problem/${domainId}/${pid}/testdata/${name}`);
+        if (!meta) throw new Error('Upload failed');
+        const payload = { name, ...pick(meta, ['size', 'lastModified', 'etag']) };
+        if (!fileinfo) await ProblemModel.push(domainId, pid, 'data', { _id: name, ...payload });
+        else await document.setSub(domainId, document.TYPE_PROBLEM, pid, 'data', name, payload);
+    }
+
+    static async delTestdata(domainId: string, pid: number, name: string | string[]) {
+        const names = (name instanceof Array) ? name : [name];
+        await storage.del(names.map((t) => `problem/${domainId}/${pid}/testdata/${t}`));
+        await ProblemModel.pull(domainId, pid, 'data', names);
+    }
+
+    static async addAdditionalFile(domainId: string, pid: number, name: string, f: Readable | Buffer | string) {
+        const [[, fileinfo]] = await Promise.all([
+            document.getSub(domainId, document.TYPE_PROBLEM, pid, 'additional_file', name),
+            storage.put(`problem/${domainId}/${pid}/additional_file/${name}`, f),
+        ]);
+        const meta = await storage.getMeta(`problem/${domainId}/${pid}/additional_file/${name}`);
+        const payload = { name, ...pick(meta, ['size', 'lastModified', 'etag']) };
+        if (!fileinfo) await ProblemModel.push(domainId, pid, 'additional_file', { _id: name, ...payload });
+        else await document.setSub(domainId, document.TYPE_PROBLEM, pid, 'additional_file', name, payload);
+    }
+
+    static async delAdditionalFile(domainId: string, pid: number, name: string | string[]) {
+        const names = (name instanceof Array) ? name : [name];
+        await storage.del(names.map((t) => `problem/${domainId}/${pid}/additional_file/${t}`));
+        await ProblemModel.pull(domainId, pid, 'additional_file', names);
+    }
+
+    static async random(domainId: string, query: FilterQuery<Pdoc>): Promise<string | null> {
+        const cursor = document.getMulti(domainId, document.TYPE_PROBLEM, query);
+        const pcount = await cursor.count();
+        if (pcount) {
+            const pdoc = await cursor.skip(Math.floor(Math.random() * pcount)).limit(1).toArray();
+            return pdoc[0].pid;
+        } return null;
+    }
+
+    static async getList(
+        domainId: string, pids: Array<number | string>,
+        getHidden = false, doThrow = true, projection = ProblemModel.PROJECTION_PUBLIC,
+    ): Promise<Pdict> {
+        pids = Array.from(new Set(pids)).map((i) => (+i ? +i : i));
+        const r = {};
+        const l = {};
+        const q: any = { $or: [{ docId: { $in: pids } }, { pid: { $in: pids } }] };
+        if (!getHidden) q.hidden = false;
+        const pdocs = await document.getMulti(domainId, document.TYPE_PROBLEM, q)
+            .project(buildProjection(projection)).toArray();
+        for (const pdoc of pdocs) {
+            r[pdoc.docId] = pdoc;
+            l[pdoc.pid] = pdoc;
+        }
+        // TODO enhance
+        if (pdocs.length !== pids.length) {
+            for (const pid of pids) {
+                if (!(r[pid] || l[pid])) {
+                    if (doThrow) throw new ProblemNotFoundError(domainId, pid);
+                    else r[pid] = ProblemModel.create(undefined, pid.toString());
+                }
             }
         }
+        return Object.assign(r, l);
+    }
+
+    static async getListStatus(domainId: string, uid: number, pids: number[]) {
+        const psdocs = await ProblemModel.getMultiStatus(
+            domainId, { uid, docId: { $in: Array.from(new Set(pids)) } },
+        ).toArray();
+        const r: Dictionary<ProblemStatusDoc> = {};
+        for (const psdoc of psdocs) r[psdoc.docId] = psdoc;
+        return r;
+    }
+
+    static async updateStatus(
+        domainId: string, pid: number, uid: number,
+        rid: ObjectID, status: number,
+    ) {
+        const res = await document.setIfNotStatus(
+            domainId, document.TYPE_PROBLEM, pid, uid,
+            'status', status, STATUS.STATUS_ACCEPTED, { rid },
+        );
+        return !!res;
+    }
+
+    static setStar(domainId: string, pid: number, uid: number, star: boolean) {
+        return document.setStatus(domainId, document.TYPE_PROBLEM, pid, uid, { star });
     }
-    return Object.assign(r, l);
 }
 
-export async function getListStatus(domainId: string, uid: number, pids: number[]) {
-    const psdocs = await getMultiStatus(
-        domainId, { uid, docId: { $in: Array.from(new Set(pids)) } },
-    ).toArray();
-    const r: Dictionary<ProblemStatusDoc> = {};
-    for (const psdoc of psdocs) r[psdoc.docId] = psdoc;
-    return r;
-}
+ProblemModel.extend((docId, pid) => ({
+    _id: new ObjectID(),
+    domainId: 'system',
+    docType: document.TYPE_PROBLEM,
+    docId: docId || -1,
+    pid: pid || docId.toString(),
+    owner: 1,
+    title: '*',
+    content: '',
+    html: false,
+    nSubmit: 0,
+    nAccept: 0,
+    tag: [],
+    data: [],
+    additional_file: [],
+    hidden: true,
+    config: {},
+    acMsg: '',
+    difficulty: 0,
+}));
 
-export async function updateStatus(
-    domainId: string, pid: number, uid: number,
-    rid: ObjectID, status: number,
-) {
-    const res = await document.setIfNotStatus(
-        domainId, document.TYPE_PROBLEM, pid, uid,
-        'status', status, STATUS.STATUS_ACCEPTED, { rid },
-    );
-    return !!res;
-}
-
-export function setStar(domainId: string, pid: number, uid: number, star: boolean) {
-    return document.setStatus(domainId, document.TYPE_PROBLEM, pid, uid, { star });
-}
-
-global.Hydro.model.problem = {
-    Pdoc,
-
-    PROJECTION_LIST,
-    PROJECTION_PUBLIC,
-
-    add,
-    inc,
-    get,
-    del,
-    edit,
-    count,
-    push,
-    pull,
-    random,
-    addTestdata,
-    delTestdata,
-    addAdditionalFile,
-    delAdditionalFile,
-    getMulti,
-    getList,
-    getListStatus,
-    getMultiStatus,
-    setStar,
-    updateStatus,
-};
+global.Hydro.model.problem = ProblemModel;
+export default ProblemModel;
diff --git a/packages/hydrooj/src/model/record.ts b/packages/hydrooj/src/model/record.ts
index 35a6d6c0e..81f1aad13 100644
--- a/packages/hydrooj/src/model/record.ts
+++ b/packages/hydrooj/src/model/record.ts
@@ -5,7 +5,7 @@ import { Dictionary } from 'lodash';
 import moment from 'moment';
 import { STATUS } from './builtin';
 import task from './task';
-import * as problem from './problem';
+import problem from './problem';
 import { Rdoc, ContestInfo, ProblemConfig } from '../interface';
 import { ArgMethod, Time } from '../utils';
 import * as bus from '../service/bus';
@@ -166,5 +166,5 @@ class RecordModel {
 }
 
 bus.on('problem/delete', (domainId, docId) => RecordModel.coll.deleteMany({ domainId, pid: docId }));
-export = RecordModel;
+export default RecordModel;
 global.Hydro.model.record = RecordModel;
diff --git a/packages/hydrooj/src/model/solution.ts b/packages/hydrooj/src/model/solution.ts
index a4fc516c6..c29178c6e 100644
--- a/packages/hydrooj/src/model/solution.ts
+++ b/packages/hydrooj/src/model/solution.ts
@@ -92,5 +92,5 @@ bus.on('problem/delete', async (domainId, docId) => {
     ]);
 });
 
-export = SolutionModel;
+export default SolutionModel;
 global.Hydro.model.solution = SolutionModel;
diff --git a/packages/hydrooj/src/model/task.ts b/packages/hydrooj/src/model/task.ts
index eecefeed6..a47402880 100644
--- a/packages/hydrooj/src/model/task.ts
+++ b/packages/hydrooj/src/model/task.ts
@@ -97,5 +97,5 @@ class TaskModel {
     };
 }
 
-export = TaskModel;
+export default TaskModel;
 global.Hydro.model.task = TaskModel;
diff --git a/packages/hydrooj/src/model/token.ts b/packages/hydrooj/src/model/token.ts
index 7689b9d61..9de14eea1 100644
--- a/packages/hydrooj/src/model/token.ts
+++ b/packages/hydrooj/src/model/token.ts
@@ -101,5 +101,5 @@ function ensureIndexes() {
 }
 
 bus.once('app/started', ensureIndexes);
-export = TokenModel;
+export default TokenModel;
 global.Hydro.model.token = TokenModel;
diff --git a/packages/hydrooj/src/model/user.ts b/packages/hydrooj/src/model/user.ts
index 593200963..407a2cc72 100644
--- a/packages/hydrooj/src/model/user.ts
+++ b/packages/hydrooj/src/model/user.ts
@@ -271,5 +271,5 @@ function ensureIndexes() {
 }
 
 bus.once('app/started', ensureIndexes);
-export = UserModel;
+export default UserModel;
 global.Hydro.model.user = UserModel;
diff --git a/packages/hydrooj/src/script/rating.ts b/packages/hydrooj/src/script/rating.ts
index 8c3f46c0e..4127b9a7e 100644
--- a/packages/hydrooj/src/script/rating.ts
+++ b/packages/hydrooj/src/script/rating.ts
@@ -4,7 +4,7 @@ import { ObjectID, FilterQuery } from 'mongodb';
 import { Tdoc, Pdoc, Udoc } from '../interface';
 import domain from '../model/domain';
 import * as contest from '../model/contest';
-import * as problem from '../model/problem';
+import problem from '../model/problem';
 import record from '../model/record';
 import { STATUS } from '../model/builtin';
 import rating from '../lib/rating';
diff --git a/packages/hydrooj/src/service/bus.ts b/packages/hydrooj/src/service/bus.ts
index c5f28f3f8..d96d2c2df 100644
--- a/packages/hydrooj/src/service/bus.ts
+++ b/packages/hydrooj/src/service/bus.ts
@@ -45,7 +45,7 @@ export interface EventMap extends Record<string, any> {
 
     'system/setting': (args: Record<string, any>) => VoidReturn
 
-    'monitor/update': (type: 'server' | 'judger', $set: any) => VoidReturn
+    'monitor/update': (type: 'server' | 'judge', $set: any) => VoidReturn
 
     'user/message': (uid: number, mdoc: Mdoc, udoc: User) => void
     'user/get': (udoc: User) => void
@@ -76,10 +76,13 @@ export interface EventMap extends Record<string, any> {
         ip: string | null, highlight: boolean, pin: boolean
     ) => VoidReturn
 
+    'problem/before-add': (doc: Partial<Pdoc>) => VoidReturn
+    'problem/add': (doc: Partial<Pdoc>, docId: number) => VoidReturn
     'problem/before-edit': (doc: Partial<Pdoc>) => VoidReturn
     'problem/edit': (doc: Pdoc) => VoidReturn
+    'problem/before-del': (domainId: string, docId: number) => VoidReturn
+    'problem/del': (domainId: string, docId: number) => VoidReturn
     'problem/list': (query: FilterQuery<Pdoc>, handler: any) => VoidReturn
-    'problem/setting': (update: Partial<Pdoc>, handler: any) => VoidReturn
     'problem/get': (doc: Pdoc, handler: any) => VoidReturn
     'problem/delete': (domainId: string, docId: number) => VoidReturn
 
diff --git a/packages/hydrooj/src/service/db.ts b/packages/hydrooj/src/service/db.ts
index f8782e715..fb4fd2689 100644
--- a/packages/hydrooj/src/service/db.ts
+++ b/packages/hydrooj/src/service/db.ts
@@ -1,6 +1,6 @@
 import { Collection, Db, MongoClient } from 'mongodb';
 import * as bus from './bus';
-import { Collections } from '../interface';
+import { Collections, BaseService } from '../interface';
 
 interface MongoConfig {
     protocol?: string,
@@ -13,11 +13,12 @@ interface MongoConfig {
     prefix?: string,
 }
 
-class MongoService {
+class MongoService implements BaseService {
     public client: MongoClient;
     public client2: MongoClient;
     public db: Db;
     public db2: Db;
+    public started = false;
     private opts: MongoConfig;
 
     static buildUrl(opts: MongoConfig) {
@@ -35,7 +36,8 @@ class MongoService {
         this.db = this.client.db(opts.name);
         this.client2 = await MongoClient.connect(mongourl, { useNewUrlParser: true, useUnifiedTopology: true });
         this.db2 = this.client2.db(opts.name);
-        bus.parallel('database/connect', this.db);
+        await bus.parallel('database/connect', this.db);
+        this.started = true;
     }
 
     public collection<K extends keyof Collections>(c: K): Collection<Collections[K]> {
diff --git a/packages/hydrooj/src/service/monitor.ts b/packages/hydrooj/src/service/monitor.ts
index f892f210c..9aca31fe5 100644
--- a/packages/hydrooj/src/service/monitor.ts
+++ b/packages/hydrooj/src/service/monitor.ts
@@ -70,11 +70,11 @@ export async function update() {
     global.Hydro.stat.reqCount = 0;
 }
 
-export async function updateJudger(args) {
+export async function updateJudge(args) {
     const $set = { ...args, updateAt: new Date() };
-    await bus.serial('monitor/update', 'judger', $set);
+    await bus.serial('monitor/update', 'judge', $set);
     return await coll.updateOne(
-        { mid: args.mid, type: 'judger' },
+        { mid: args.mid, type: 'judge' },
         { $set },
         { upsert: true },
     );
@@ -93,4 +93,4 @@ if (cluster.isMaster) {
     });
 }
 
-global.Hydro.service.monitor = { feedback, update, updateJudger };
+global.Hydro.service.monitor = { feedback, update, updateJudge };
diff --git a/packages/hydrooj/src/service/server.ts b/packages/hydrooj/src/service/server.ts
index 9a6e70250..0a7ff8bac 100644
--- a/packages/hydrooj/src/service/server.ts
+++ b/packages/hydrooj/src/service/server.ts
@@ -210,6 +210,7 @@ type DescriptorBuilder =
     & ((name: string, ...args: Array<Type | boolean | Validator | Converter>) => MethodDecorator);
 
 export const get: DescriptorBuilder = (name, ...args) => _descriptor(_buildParam(name, 'get', ...args));
+export const query: DescriptorBuilder = (name, ...args) => _descriptor(_buildParam(name, 'get', ...args));
 export const post: DescriptorBuilder = (name, ...args) => _descriptor(_buildParam(name, 'post', ...args));
 export const route: DescriptorBuilder = (name, ...args) => _descriptor(_buildParam(name, 'route', ...args));
 export const param: DescriptorBuilder = (name, ...args) => _descriptor(_buildParam(name, 'all', ...args));
@@ -319,6 +320,7 @@ export class HandlerCommon {
     url(name: string, kwargs: any = {}) {
         let res = '#';
         const args: any = {};
+        // eslint-disable-next-line @typescript-eslint/no-shadow
         const query: any = {};
         for (const key in kwargs) {
             if (kwargs[key] instanceof ObjectID) args[key] = kwargs[key].toHexString();
@@ -803,12 +805,16 @@ export function Connection(
     sock.installHandlers(server);
 }
 
+let started = false;
+
 // TODO use postInit?
 export function start() {
+    if (started) return;
     const port = system.get('server.port');
     app.use(router.routes()).use(router.allowedMethods());
     server.listen(argv.port || port);
     logger.success('Server listening at: %d', argv.port || port);
+    started = true;
 }
 
 global.Hydro.service.server = {
@@ -818,6 +824,7 @@ global.Hydro.service.server = {
     router,
     UiContextBase,
     get,
+    query,
     post,
     route,
     param,
diff --git a/packages/hydrooj/src/upgrade.ts b/packages/hydrooj/src/upgrade.ts
index 4db735d32..72d55cec3 100644
--- a/packages/hydrooj/src/upgrade.ts
+++ b/packages/hydrooj/src/upgrade.ts
@@ -11,7 +11,7 @@ import { streamToBuffer } from './utils';
 import gridfs from './service/gridfs';
 import storage from './service/storage';
 import db from './service/db';
-import * as problem from './model/problem';
+import problem, { Field, Pdoc } from './model/problem';
 import domain from './model/domain';
 import * as document from './model/document';
 import * as system from './model/system';
@@ -25,13 +25,13 @@ export async function iterateAllDomain(cb: (ddoc: DomainDoc, current?: number, t
     for (const i in ddocs) await cb(ddocs[i], +i, ddocs.length);
 }
 
-interface PartialPdoc extends problem.Pdoc {
+interface PartialPdoc extends Pdoc {
     [key: string]: any,
 }
 
 export async function iterateAllProblemInDomain(
     domainId: string,
-    fields: (problem.Pdoc.Field | string)[],
+    fields: (Field | string)[],
     cb: (pdoc: PartialPdoc, current?: number, total?: number) => Promise<any>,
 ) {
     if (!fields.includes('domainId')) fields.push('domainId');
@@ -48,7 +48,7 @@ export async function iterateAllProblemInDomain(
 }
 
 export async function iterateAllProblem(
-    fields: (problem.Pdoc.Field | string)[],
+    fields: (Field | string)[],
     cb: (pdoc: PartialPdoc, current?: number, total?: number) => Promise<any>,
 ) {
     await iterateAllDomain(async (d) => {
@@ -171,7 +171,7 @@ const scripts: UpgradeScript[] = [
             logger.info('%s/%s', pdoc.domainId, pdoc.docId);
             const [data, additional_file] = await Promise.all([
                 storage.list(`problem/${pdoc.domainId}/${pdoc.docId}/testdata/`),
-                storage.list(`problem/${pdoc.domainId}/${pdoc.docId}/additional_files/`),
+                storage.list(`problem/${pdoc.domainId}/${pdoc.docId}/additional_file/`),
             ]);
             await problem.edit(pdoc.domainId, pdoc.docId, { data, additional_file });
             if (!pdoc.config) return;
@@ -187,7 +187,7 @@ const scripts: UpgradeScript[] = [
             logger.info('%s/%s', pdoc.domainId, pdoc.docId);
             const [data, additional_file] = await Promise.all([
                 storage.list(`problem/${pdoc.domainId}/${pdoc.docId}/testdata/`),
-                storage.list(`problem/${pdoc.domainId}/${pdoc.docId}/additional_files/`),
+                storage.list(`problem/${pdoc.domainId}/${pdoc.docId}/additional_file/`),
             ]) as any;
             for (let i = 0; i < data.length; i++) {
                 data[i]._id = data[i].name;
diff --git a/packages/import-qduoj/handler.ts b/packages/import-qduoj/handler.ts
index bbff3094c..2c440e530 100644
--- a/packages/import-qduoj/handler.ts
+++ b/packages/import-qduoj/handler.ts
@@ -8,7 +8,7 @@ import type { ContentNode, ProblemConfig } from 'hydrooj';
 import { Route, Handler } from 'hydrooj/dist/service/server';
 import { BadRequestError, ValidationError } from 'hydrooj/dist/error';
 import { ProblemAdd } from 'hydrooj/dist/lib/ui';
-import * as problem from 'hydrooj/dist/model/problem';
+import problem from 'hydrooj/dist/model/problem';
 import { PERM } from 'hydrooj/dist/model/builtin';
 
 fs.ensureDirSync('/tmp/hydro/import-qduoj');
diff --git a/packages/sonic/model.ts b/packages/sonic/model.ts
new file mode 100644
index 000000000..c23455344
--- /dev/null
+++ b/packages/sonic/model.ts
@@ -0,0 +1,27 @@
+import * as bus from 'hydrooj/dist/service/bus';
+import * as system from 'hydrooj/dist/model/system';
+import sonic from './service';
+
+bus.on('problem/add', async (doc, docId) => {
+    await sonic.push('problem', `${doc.domainId}@title`, docId.toString(), doc.title);
+    await sonic.push('problem', `${doc.domainId}@content`, docId.toString(), doc.content.toString());
+});
+
+bus.on('problem/edit', async (pdoc) => {
+    await sonic.flusho('problem', `${pdoc.domainId}@title`, pdoc.docId.toString());
+    await sonic.flusho('problem', `${pdoc.domainId}@content`, pdoc.docId.toString());
+    await sonic.push('problem', `${pdoc.domainId}@title`, pdoc.docId.toString(), pdoc.title);
+    await sonic.push('problem', `${pdoc.domainId}@content`, pdoc.docId.toString(), pdoc.content.toString());
+});
+
+bus.on('problem/del', async (domainId, docId) => {
+    await sonic.flusho('problem', `${domainId}@title`, docId.toString());
+    await sonic.flusho('problem', `${domainId}@content`, docId.toString());
+});
+
+global.Hydro.lib.problemSearch = async (domainId: string, query: string) => {
+    const c = system.get('pagination.problem');
+    const docIds = await sonic.query('problem', `${domainId}@title`, query, { limit: c });
+    docIds.push(...await sonic.query('problem', `${domainId}@content`, query, { limit: c - docIds.length }));
+    return docIds.map(Number);
+};
diff --git a/packages/sonic/package.json b/packages/sonic/package.json
new file mode 100644
index 000000000..593164582
--- /dev/null
+++ b/packages/sonic/package.json
@@ -0,0 +1,13 @@
+{
+    "name": "@hydrooj/sonic",
+    "version": "1.0.0",
+    "description": "Sonic search service",
+    "main": "service.js",
+    "typings": "service.d.ts",
+    "repository": "https://github.com/hydro-dev/Hydro.git",
+    "author": "undefined <i@undefined.moe>",
+    "license": "AGPL-3.0-only",
+    "dependencies": {
+        "sonic-channel": "^1.2.6"
+    }
+}
\ No newline at end of file
diff --git a/packages/sonic/script.ts b/packages/sonic/script.ts
new file mode 100644
index 000000000..0ddd4ebe4
--- /dev/null
+++ b/packages/sonic/script.ts
@@ -0,0 +1,25 @@
+import { iterateAllProblem, iterateAllProblemInDomain } from 'hydrooj/dist/upgrade';
+import sonic from './service';
+
+export const description = 'Sonic problem search re-index';
+
+export async function run({ domainId }) {
+    if (domainId) await sonic.flushb('problem', domainId);
+    else await sonic.flushc('problem');
+    const cb = async (pdoc) => {
+        await sonic.push('problem', `${pdoc.domainId}@title`, pdoc.docId.toString(), pdoc.title);
+        await sonic.push('problem', `${pdoc.domainId}@content`, pdoc.docId.toString(), pdoc.content.toString());
+    };
+    if (domainId) await iterateAllProblemInDomain(domainId, ['title', 'content'], cb);
+    else await iterateAllProblem(['title', 'content'], cb);
+    return true;
+}
+
+export const validate = {
+    $or: [
+        { domainId: 'string' },
+        { domainId: 'undefined' },
+    ],
+};
+
+global.Hydro.script.ensureSonicSearch = { run, description, validate };
diff --git a/packages/sonic/service.ts b/packages/sonic/service.ts
new file mode 100644
index 000000000..bce3d6a10
--- /dev/null
+++ b/packages/sonic/service.ts
@@ -0,0 +1,117 @@
+import { BaseService } from 'hydrooj';
+import * as system from 'hydrooj/dist/model/system';
+import {
+    Search, Ingest, QueryOptions, SuggestOptions, PushOptions,
+} from 'sonic-channel';
+import { Logger } from 'hydrooj/dist/logger';
+
+const logger = new Logger('sonic');
+
+declare module 'hydrooj/dist/interface' {
+    interface SystemKeys {
+        'sonic.host': string;
+        'sonic.port': number;
+        'sonic.auth': string;
+    }
+}
+
+function getHandler(type: string, that: any) {
+    return {
+        connected() {
+            that.started = true;
+            logger.info(`Sonic Channel succeeded to connect to host (${type}).`);
+        },
+        disconnected() {
+            that.started = false;
+            logger.error(`Sonic Channel is now disconnected (${type}).`);
+        },
+        timeout() {
+            logger.error(`Sonic Channel connection timed out (${type}).`);
+        },
+        retrying() {
+            logger.error(`Trying to reconnect to Sonic Channel (${type})...`);
+        },
+        error(error) {
+            that.error = error;
+            logger.error(`Sonic Channel failed to connect to host (${type}).`, error);
+        },
+    };
+}
+
+class SonicService implements BaseService {
+    public search: Search;
+    public ingest: Ingest;
+    public started = false;
+    public error = '';
+
+    async start() {
+        const [host, port, auth] = system.getMany(['sonic.host', 'sonic.port', 'sonic.auth']);
+        const cfg = {
+            host: host || '127.0.0.1',
+            port: port || 1491,
+            auth: auth || 'sonic-passwd',
+        };
+        this.search = new Search(cfg);
+        this.ingest = new Ingest(cfg);
+        await this.connect();
+    }
+
+    async connect() {
+        try {
+            this.search.connect(getHandler('search', this));
+            this.ingest.connect(getHandler('ingest', this));
+        } catch (e) {
+            logger.warn('Sonic init fail. will retry later.');
+            this.error = e.toString();
+            setTimeout(() => this.start(), 10000);
+        }
+    }
+
+    async query(collection: string, bucket: string, terms: string, options?: QueryOptions) {
+        return await this.search.query(collection, bucket, terms, options);
+    }
+
+    async suggest(collection: string, bucket: string, word: string, options?: SuggestOptions) {
+        return await this.search.suggest(collection, bucket, word, options);
+    }
+
+    async push(collection: string, bucket: string, object: string, text: string, options?: PushOptions) {
+        return await this.ingest.push(collection, bucket, object, text, options);
+    }
+
+    async pop(collection: string, bucket: string, object: string, text: string) {
+        return await this.ingest.pop(collection, bucket, object, text);
+    }
+
+    async count(collection: string, bucket?: string, object?: string) {
+        return await this.ingest.count(collection, bucket, object);
+    }
+
+    async flusho(collection: string, bucket: string, object: string) {
+        return await this.ingest.flusho(collection, bucket, object);
+    }
+
+    async flushb(collection: string, bucket: string) {
+        return await this.ingest.flushb(collection, bucket);
+    }
+
+    async flushc(collection: string) {
+        return await this.ingest.flushc(collection);
+    }
+
+    async stop() {
+        await Promise.all([
+            this.search.close(),
+            this.ingest.close(),
+        ]);
+    }
+}
+
+const service = new SonicService();
+global.Hydro.service.sonic = service;
+export = service;
+declare module 'hydrooj/dist/interface' {
+    interface Service {
+        sonic: typeof service
+    }
+}
diff --git a/packages/sonic/setting.yaml b/packages/sonic/setting.yaml
new file mode 100644
index 000000000..d9ae6043e
--- /dev/null
+++ b/packages/sonic/setting.yaml
@@ -0,0 +1,7 @@
+host:
+  value: localhost
+port:
+  type: number
+  value: 1491
+auth:
+  type: text
\ No newline at end of file
diff --git a/packages/syzoj-ng-api/handlers/problem.ts b/packages/syzoj-ng-api/handlers/problem.ts
index 566739f04..df20ed381 100644
--- a/packages/syzoj-ng-api/handlers/problem.ts
+++ b/packages/syzoj-ng-api/handlers/problem.ts
@@ -1,6 +1,6 @@
 import { FilterQuery } from 'mongodb';
 import { Pdoc } from 'hydrooj/dist/interface';
-import * as problem from 'hydrooj/dist/model/problem';
+import problem from 'hydrooj/dist/model/problem';
 import record from 'hydrooj/dist/model/record';
 import user from 'hydrooj/dist/model/user';
 import { PERM, PRIV } from 'hydrooj/dist/model/builtin';