feat(json-crdt): 🎸 implement deep schema equality check

Author: streamich

src/json-crdt/equal/__tests__/index.spec.ts

@@ -0,0 +1,73 @@
+import {Model} from '../../model';
+import {equalSchema} from '..';
+import {s} from '../../../json-crdt-patch';
+
+describe('equalSchema()', () => {
+  const assertSchemasEqual = (a: unknown): void => {
+    const model1 = Model.create(a);
+    const model2 = Model.create(a);
+    const result = equalSchema(model1.root, model2.root);
+    expect(result).toBe(true);
+  };
+
+  const assertSchemasDifferent = (a: unknown, b: unknown): void => {
+    const model1 = Model.create(a);
+    const model2 = Model.create(b);
+    const result = equalSchema(model1.root, model2.root);
+    expect(result).toBe(false);
+  };
+
+  test('returns true for identical nodes', () => {
+    assertSchemasEqual(new Uint8Array([1, 2, 3]));
+    assertSchemasEqual({foo: new Uint8Array([1, 2, 3])});
+    assertSchemasEqual([[[{a: [1, [2, 3]]}]]]);
+    assertSchemasEqual([[[{a: [1, s.vec(s.con(2), s.json(3))]}]]]);
+    assertSchemasEqual({
+      foo: 'bar',
+      num: 123,
+      obj: {key: 'value'},
+      arr: [1, 2, 3, false],
+      bool: true,
+    });
+  });
+
+  test('returns false for slightly different nodes', () => {
+    assertSchemasDifferent({
+      foo: 'bar',
+      num: 123,
+      obj: {key: 'value'},
+      arr: [1, 2, 3],
+      bool: true,
+    }, {
+      foo: 'bar',
+      num: 124,
+      obj: {key: 'value'},
+      arr: [1, 2, 3],
+      bool: true,
+    });
+  });
+
+  test('returns false for slightly different nodes - 2', () => {
+    assertSchemasDifferent({
+      foo: 'baz',
+      num: 123,
+      obj: {key: 'value'},
+      arr: [1, 2, 3],
+      bool: true,
+    }, {
+      foo: 'baz',
+      num: 123,
+      obj: {key: 'valee'},
+      arr: [1, 2, 3],
+      bool: true,
+    });
+  });
+
+  test('returns false for slightly different nodes - 3', () => {
+    assertSchemasDifferent({
+      bin: new Uint8Array([1, 2, 3]),
+    }, {
+      bin: new Uint8Array([1, 0, 3]),
+    });
+  });
+});

src/json-crdt/equal/index.ts

@@ -0,0 +1,45 @@
+import {deepEqual} from '@jsonjoy.com/util/lib/json-equal/deepEqual';
+import {ArrNode, BinNode, ConNode, JsonNode, ObjNode, StrNode, ValNode, VecNode} from '../nodes';
+
+/**
+ * Deeply checks if two JSON nodes have the same schema and values. Does not
+ * verify that the CRDT metadata (like timestamps) are the same, only that
+ * the structure and values are equal.
+ *
+ * @param a The first JSON CRDT node.
+ * @param b The second JSON CRDT node.
+ * @returns True if the schemas and values are equal, false otherwise.
+ */
+export const equalSchema = <A extends JsonNode<any>>(a: A, b: unknown): b is A => {
+  if (a === b) return true;
+  if (a instanceof ConNode) return b instanceof ConNode && deepEqual(a.val, b.val);
+  else if (a instanceof ValNode) return b instanceof ValNode && equalSchema(a.node(), b.node());
+  else if (a instanceof StrNode) return b instanceof StrNode && a.length() === b.length() && a.view() === b.view();
+  else if (a instanceof ObjNode) {
+    if (!(b instanceof ObjNode)) return false;
+    const keys1 = a.keys;
+    const keys2 = b.keys;
+    const length1 = keys1.size;
+    const length2 = keys2.size;
+    if (length1 !== length2) return false;
+    for (const key of keys1.keys()) {
+      if (!keys2.has(key)) return false;
+      if (!equalSchema(a.get(key), b.get(key))) return false;
+    }
+    return true;
+  } else if (a instanceof ArrNode) {
+    if (!(b instanceof ArrNode)) return false;
+    const length = a.length();
+    if (length !== b.length()) return false;
+    for (let i = 0; i < length; i++) if (!equalSchema(a.getNode(i)!, b.getNode(i))) return false;
+    return true;
+  } else if (a instanceof VecNode) {
+    if (!(b instanceof VecNode)) return false;
+    const length = a.length();
+    if (length !== b.length()) return false;
+    for (let i = 0; i < length; i++) if (!equalSchema(a.get(i), b.get(i))) return false;
+    return true;
+  } else if (a instanceof BinNode)
+    return b instanceof BinNode && a.length() === b.length() && deepEqual(a.view(), b.view());
+  return false;
+};

src/json-crdt/nodes/vec/VecNode.ts

@@ -31,13 +31,17 @@ export class VecNode<Value extends JsonNode[] = JsonNode[]> implements JsonNode<
     public readonly id: ITimestampStruct,
   ) {}
 
+  public length(): number {
+    return this.elements.length;
+  }
+
   /**
    * Retrieves the ID of an element at the given index.
    *
    * @param index Index of the element to get.
    * @returns ID of the element at the given index, if any.
    */
-  public val(index: number): undefined | ITimestampStruct {
+  public val(index: number): ITimestampStruct | undefined {
     return this.elements[index] as ITimestampStruct | undefined;
   }
 
@@ -47,7 +51,7 @@ export class VecNode<Value extends JsonNode[] = JsonNode[]> implements JsonNode<
    * @param index Index of the element to get.
    * @returns JSON CRDT node at the given index, if any.
    */
-  public get<Index extends number>(index: Index): undefined | Value[Index] {
+  public get<Index extends number>(index: Index): Value[Index] | undefined {
     const id = this.elements[index] as ITimestampStruct | undefined;
     if (!id) return undefined;
     return this.doc.index.get(id);
@@ -56,7 +60,7 @@ export class VecNode<Value extends JsonNode[] = JsonNode[]> implements JsonNode<
   /**
    * @ignore
    */
-  public put(index: number, id: ITimestampStruct): undefined | ITimestampStruct {
+  public put(index: number, id: ITimestampStruct): ITimestampStruct | undefined {
     if (index > CRDT_CONSTANTS.MAX_TUPLE_LENGTH) throw new Error('OUT_OF_BOUNDS');
     const currentId = this.val(index);
     if (currentId && compare(currentId, id) >= 0) return;