Merge pull request #303 from boostcampwm2023/BE-feature/prevent-cycle

트리 순환 막기

nestjs-BE/server/src/crdt/crdt-tree.spec.ts

@@ -59,3 +59,18 @@ it('crdt tree 역직렬화', () => {
 
   expect(JSON.stringify(tree)).toEqual(JSON.stringify(parsedTree));
 });
+
+it('crdt tree 순환', () => {
+  const tree = new CrdtTree<string>('1');
+
+  const op1 = tree.generateOperationAdd('a', 'root', 'hello');
+  const op2 = tree.generateOperationAdd('b', 'root', 'hi');
+  const op3 = tree.generateOperationAdd('c', 'a', 'good');
+  const op4 = tree.generateOperationAdd('d', 'b', 'bad');
+  const op5 = tree.generateOperationMove('a', 'b');
+  const op6 = tree.generateOperationMove('b', 'a');
+
+  tree.applyOperations([op1, op2, op3, op4, op5, op6]);
+
+  expect(tree.tree.get('b').parentId).toEqual('root');
+});

nestjs-BE/server/src/crdt/operation.ts

@@ -141,6 +141,10 @@ export class OperationMove<T> extends Operation<T> {
     const node = tree.get(this.id);
     const oldParentId = node.parentId;
 
+    if (tree.isAncestor(this.parentId, this.id)) {
+      return { operation: this, oldParentId };
+    }
+
     tree.removeNode(this.id);
     tree.attachNode(this.id, this.parentId);
     return { operation: this, oldParentId };

nestjs-BE/server/src/crdt/tree.spec.ts

@@ -0,0 +1,19 @@
+import { Tree } from './tree';
+
+it('isAncestor', () => {
+  const tree = new Tree<string>();
+
+  tree.addNode('a', 'root', 'test');
+  tree.addNode('b', 'a', 'test');
+  tree.addNode('c', 'b', 'test');
+  tree.addNode('d', 'a', 'test');
+  tree.addNode('e', 'b', 'test');
+
+  expect(tree.isAncestor('c', 'a')).toBeTruthy();
+  expect(tree.isAncestor('c', 'root')).toBeTruthy();
+  expect(tree.isAncestor('d', 'root')).toBeTruthy();
+  expect(tree.isAncestor('d', 'a')).toBeTruthy();
+  expect(tree.isAncestor('c', 'e')).toBeFalsy();
+  expect(tree.isAncestor('e', 'c')).toBeFalsy();
+  expect(tree.isAncestor('c', 'd')).toBeFalsy();
+});

nestjs-BE/server/src/crdt/tree.ts

@@ -41,6 +41,7 @@ export class Tree<T> {
 
     const targetIndex = parentNode.children.indexOf(targetId);
     if (targetIndex !== -1) parentNode.children.splice(targetIndex, 1);
+    targetNode.parentId = '0';
 
     return this.nodes.get(targetId);
   }
@@ -56,6 +57,15 @@ export class Tree<T> {
     return { nodes: Array.from(this.nodes.values()) };
   }
 
+  isAncestor(targetId: string, ancestorId: string) {
+    let curNode = this.nodes.get(targetId);
+    while (curNode) {
+      if (curNode.parentId === ancestorId) return true;
+      curNode = this.nodes.get(curNode.parentId);
+    }
+    return false;
+  }
+
   static parse<T>(json: string) {
     const { nodes } = JSON.parse(json);
     const tree = new Tree<T>();