feat: LWW-Register impl & Tests

packages/crdt/src/builtins/LWWRegister/index.ts

@@ -0,0 +1,47 @@
+export class LWWRegister<T> {
+    private _element: T;
+    private _timestamp: number;
+    private _nodeId: string;
+
+    constructor(element: T, nodeId: string) {
+        this._element = element;
+        this._timestamp = Date.now();
+        this._nodeId = nodeId;
+    }
+
+    assign(element: T, nodeId: string): void {
+        this._element = element;
+        this._timestamp = Date.now();
+        this._nodeId = nodeId;
+    }
+
+    getElement(): T {
+        return this._element;
+    }
+
+    getTimestamp(): number {
+        return this._timestamp;
+    }
+
+    getNodeId(): string {
+        return this._nodeId;
+    }
+
+    compare(register: LWWRegister<T>): boolean {
+        return (this._timestamp <= register.getTimestamp());
+    }
+
+    merge(register: LWWRegister<T>): void {
+        const otherTimestamp = register.getTimestamp();
+        const otherNodeId = register.getNodeId();
+        if (otherTimestamp < this._timestamp) {
+            return;
+        }
+        if (otherTimestamp === this._timestamp && otherNodeId <= this._nodeId) {
+            return;
+        }
+        this._element = register.getElement();
+        this._timestamp = otherTimestamp;
+        this._nodeId = otherNodeId;
+    }
+}

packages/crdt/tests/LWWRegister.test.ts

@@ -0,0 +1,64 @@
+import { describe, test, expect, beforeEach, vi } from "vitest";
+import { LWWRegister } from "../src/builtins/LWWRegister/index.ts";
+
+describe('LWW-Register Tests', () => {
+    test('Test Assign', () => {
+        let register1 = new LWWRegister<string>("alice", "node1");
+
+        expect(register1.getElement()).toBe("alice");
+        expect(register1.getNodeId()).toEqual("node1");
+        register1.assign("bob", "node2");
+        expect(register1.getElement()).toBe("bob");
+        expect(register1.getNodeId()).toEqual("node2");
+    });
+
+    test('Test Compare', () => {
+        vi.useFakeTimers();
+        const date = new Date(2000,1,1,13);
+        vi.setSystemTime(date);
+
+        let register1 = new LWWRegister<string>("alice", "node1");
+
+        vi.useRealTimers();
+
+        let register2 = new LWWRegister<string>("alice", "node2");
+
+        expect(register1.compare(register2)).toEqual(true);
+        expect(register2.compare(register1)).toEqual(false);
+    });
+
+    test('Test Merge', () => {
+        let register1 = new LWWRegister<string>("alice", "node1");
+        let register2 = new LWWRegister<string>("bob", "node2");
+
+        register1.merge(register2);
+        expect(register1.getElement()).toEqual("bob");
+        expect(register2.getNodeId()).toEqual("node2");
+
+        register2.merge(register1);
+        expect(register1.getElement()).toEqual("bob");
+        expect(register2.getNodeId()).toEqual("node2");
+    });
+
+    test('Test Merge w/same timestamp', () => {
+        vi.useFakeTimers();
+        const date = new Date(2000,1,1,13);
+        vi.setSystemTime(date);
+
+        let register1 = new LWWRegister<string>("alice", "node1");
+        let register2 = new LWWRegister<string>("bob", "node2");
+
+        expect(register1.getElement()).toBe("alice");
+        expect(register1.getNodeId()).toEqual("node1");
+
+        register1.merge(register2);
+        expect(register1.getElement()).toBe("bob");
+        expect(register1.getNodeId()).toEqual("node2");
+
+        register2.merge(register1);
+        expect(register1.getElement()).toBe("bob");
+        expect(register1.getNodeId()).toEqual("node2");
+
+        vi.useRealTimers();
+    });
+});