diff --git a/packages/customize b/packages/customize
new file mode 160000
index 000000000..88b1f57a8
--- /dev/null
+++ b/packages/customize
@@ -0,0 +1 @@
+Subproject commit 88b1f57a84f4db58489fec74897cdd961d35c1a5
diff --git a/packages/hydrooj/TODO b/packages/hydrooj/TODO
index 28a6cf6fe..7927f9f1f 100644
--- a/packages/hydrooj/TODO
+++ b/packages/hydrooj/TODO
@@ -12,4 +12,6 @@ message.markAsRead
 存储系统抽象化
 extend problem settings
 +oplog
-将系统设置存于本地而非数据库
\ No newline at end of file
+将系统设置存于本地而非数据库
+添加nav排序功能
+自动拓扑组件加载顺序？
\ No newline at end of file
diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index 7c2b3175a..fdcd54bbe 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -1,4 +1,5 @@
 // eslint-disable-next-line @typescript-eslint/no-unused-vars
+import { Readable, Writable } from 'stream';
 import { ObjectID, GridFSBucket } from 'mongodb';
 import fs from 'fs';
 import { Dictionary, NumericDictionary } from 'lodash';
@@ -433,6 +434,17 @@ export interface Task {
     [key: string]: any
 }
 
+export interface UploadStream extends Writable {
+    id: ObjectID
+}
+
+export interface HydroFileSystem {
+    openUploadStream: (filename: string) => UploadStream
+    openDownloadStream: (_id: ObjectID) => Readable
+    // TODO
+    find: (...args: any[]) => any
+}
+
 export type PathComponent = [string, string, Dictionary<any>?, boolean?];
 
 export interface Collections {
@@ -483,7 +495,7 @@ export interface Model {
 export interface Service {
     bus: typeof import('./service/bus'),
     db: typeof import('./service/db'),
-    gridfs: GridFSBucket,
+    fs: HydroFileSystem,
     monitor: typeof import('./service/monitor'),
     server: typeof import('./service/server'),
 }
diff --git a/packages/hydrooj/src/model/file.ts b/packages/hydrooj/src/model/file.ts
index f5c05e28a..5ab8eee1f 100644
--- a/packages/hydrooj/src/model/file.ts
+++ b/packages/hydrooj/src/model/file.ts
@@ -26,7 +26,7 @@ export async function add(
     const w = gridfs.openUploadStream(filename);
     await coll.insertOne({
         ...meta,
-        _id: w.id as ObjectID,
+        _id: w.id,
         secret: String.random(32),
         owner,
         filename,
@@ -37,8 +37,8 @@ export async function add(
         stream.pipe(w);
     });
     const c = await gridfs.find({ _id: w.id }).toArray();
-    await coll.updateOne({ _id: w.id as ObjectID }, { $set: { md5: c[0].md5, size: c[0].length } });
-    return w.id as ObjectID;
+    await coll.updateOne({ _id: w.id }, { $set: { md5: c[0].md5, size: c[0].length } });
+    return w.id;
 }
 
 export function del(_id: ObjectID) {
diff --git a/packages/hydrooj/src/service/gridfs.ts b/packages/hydrooj/src/service/gridfs.ts
index b75bb0001..b0779045d 100644
--- a/packages/hydrooj/src/service/gridfs.ts
+++ b/packages/hydrooj/src/service/gridfs.ts
@@ -1,8 +1,10 @@
 import { GridFSBucket } from 'mongodb';
 import { db2 } from './db';
+import { HydroFileSystem } from '../interface';
 
 const fs = new GridFSBucket(db2);
 
-global.Hydro.service.gridfs = fs;
+// @ts-ignore
+global.Hydro.service.fs = fs;
 
-export = fs;
+export = fs as HydroFileSystem;