feat(#21, #22): 간단한 crdt 기능 구현

state를 보낸 id, timestamp를 비교해서 merge 처리

Co-authored-by: Yong <[email protected]>

nestjs-BE/crdt/lww-map.ts

@@ -0,0 +1,66 @@
+import { LWWRegister, lwwRegisterState } from './lww-register';
+
+export type lwwMapState<T> = {
+  [key: string]: lwwRegisterState<T>;
+};
+
+export class LWWMap<T> {
+  readonly id: string;
+  private data = new Map<string, LWWRegister<T | null>>();
+
+  constructor(id: string, state: lwwMapState<T> = {}) {
+    this.id = id;
+    this.initializeData(state);
+  }
+
+  private initializeData(state: lwwMapState<T>): void {
+    for (const [key, register] of Object.entries(state))
+      this.data.set(key, new LWWRegister(this.id, register));
+  }
+
+  getState(): lwwMapState<T> {
+    const state: lwwMapState<T> = {};
+    for (const [key, register] of this.data.entries())
+      if (register) state[key] = register.state;
+    return state;
+  }
+
+  get(key: string): T | null | undefined {
+    return this.data.get(key)?.getValue();
+  }
+
+  set(key: string, value: T): void {
+    const register = this.data.get(key);
+    if (register) register.setValue(value);
+    else
+      this.data.set(
+        key,
+        new LWWRegister(this.id, {
+          id: this.id,
+          timestamp: Date.now(),
+          value,
+        }),
+      );
+  }
+
+  delete(key: string): void {
+    this.data.get(key)?.setValue(null);
+  }
+
+  has(key: string): boolean {
+    return !!this.data.get(key)?.getValue();
+  }
+
+  clear(): void {
+    for (const [key, register] of this.data.entries())
+      if (register) this.delete(key);
+  }
+
+  merge(state: lwwMapState<T>): void {
+    for (const [key, remoteRegister] of Object.entries(state)) {
+      const local = this.data.get(key);
+      if (local) local.merge(remoteRegister);
+      else this.data.set(key, new LWWRegister(this.id, remoteRegister));
+    }
+  }
+}

nestjs-BE/crdt/lww-register.ts

@@ -0,0 +1,31 @@
+export interface lwwRegisterState<T> {
+  id: string;
+  timestamp: number;
+  value: T;
+}
+
+export class LWWRegister<T> {
+  readonly id: string;
+  state: lwwRegisterState<T>;
+
+  constructor(id: string, state: lwwRegisterState<T>) {
+    this.id = id;
+    this.state = state;
+  }
+
+  getValue(): T {
+    return this.state.value;
+  }
+
+  setValue(value: T): void {
+    this.state = { id: this.id, timestamp: Date.now(), value };
+  }
+
+  merge(state: lwwRegisterState<T>): void {
+    const { id: remoteId, timestamp: remoteTimestamp } = state;
+    const { id: localId, timestamp: localTimestamp } = this.state;
+    if (localTimestamp > remoteTimestamp) return;
+    if (localTimestamp === remoteTimestamp && localId > remoteId) return;
+    this.state = state;
+  }
+}

nestjs-BE/package.json

@@ -26,8 +26,7 @@
     "@nestjs/platform-socket.io": "^10.2.8",
     "@nestjs/websockets": "^10.2.8",
     "reflect-metadata": "^0.1.13",
-    "rxjs": "^7.8.1",
-    "yjs": "^13.6.8"
+    "rxjs": "^7.8.1"
   },
   "devDependencies": {
     "@nestjs/cli": "^10.0.0",

nestjs-BE/src/mindmap/mindmap.service.ts

@@ -1,26 +1,26 @@
 import { Injectable } from '@nestjs/common';
-import * as Y from 'yjs';
+import { LWWMap, lwwMapState } from 'crdt/lww-map';
 
 @Injectable()
 export class MindmapService {
-  private ydocs = new Map<string, Y.Doc>();
+  private boards = new Map<string, LWWMap<string>>();
 
-  updateMindmap(boardId: string, message: any) {
-    const ydoc = this.getMindmap(boardId);
-    Y.applyUpdate(ydoc, message);
+  updateMindmap(boardId: string, message: any): void {
+    const board = this.getMindmap(boardId);
+    board.merge(message);
   }
 
-  getEncodedState(boardId: string) {
-    const ydoc = this.getMindmap(boardId);
-    return Y.encodeStateAsUpdate(ydoc);
+  getEncodedState(boardId: string): lwwMapState<string> {
+    const board = this.getMindmap(boardId);
+    return board.getState();
   }
 
   private getMindmap(boardId: string) {
-    let ydoc = this.ydocs.get(boardId);
-    if (!ydoc) {
-      ydoc = new Y.Doc();
-      this.ydocs.set(boardId, ydoc);
+    let board = this.boards.get(boardId);
+    if (!board) {
+      board = new LWWMap<string>(boardId); // boardId 대신에 서버 아이디???
+      this.boards.set(boardId, board);
     }
-    return ydoc;
+    return board;
   }
 }