feat(json-crdt): 🎸 add ability to replay to specific patch

Author: streamich

src/json-crdt/file/PatchLog.ts

@@ -3,6 +3,7 @@ import {printTree} from '../../util/print/printTree';
 import {AvlMap} from '../../util/trees/avl/AvlMap';
 import {Model} from '../model';
 import type {Printable} from '../../util/print/types';
+import {first, next} from '../../util/trees/util';
 
 export class PatchLog implements Printable {
   public static fromModel(model: Model<any>): PatchLog {
@@ -26,9 +27,17 @@ export class PatchLog implements Printable {
   }
 
   public replayToEnd(): Model {
-    const model = this.start.clone();
-    this.patches.forEach(({v}) => model.applyPatch(v));
-    return model;
+    const clone = this.start.clone();
+    for (let node = first(this.patches.root); node; node = next(node))
+      clone.applyPatch(node.v);
+    return clone;
+  }
+
+  public replayTo(ts: ITimestampStruct): Model {
+    const clone = this.start.clone();
+    for (let node = first(this.patches.root); node && (compare(ts, node.k) >= 0); node = next(node))
+      clone.applyPatch(node.v);
+    return clone;
   }
 
   // ---------------------------------------------------------------- Printable

src/json-crdt/file/__tests__/PatchLog.spec.ts

@@ -0,0 +1,27 @@
+import {Model} from '../../model';
+import {File} from '../File';
+
+const setup = (view: unknown) => {
+  const model = Model.withServerClock();
+  model.api.root(view);
+  const file = File.fromModel(model);
+  return {model, file};
+};
+
+test('can replay to specific patch', () => {
+  const {model, file} = setup({foo: 'bar'});
+  model.api.obj([]).set({x: 1});
+  const patch1 = model.api.flush();
+  model.api.obj([]).set({y: 2});
+  const patch2 = model.api.flush();
+  file.log.push(patch1);
+  file.log.push(patch2);
+  const model2 = file.log.replayToEnd();
+  const model3 = file.log.replayTo(patch1.getId()!);
+  const model4 = file.log.replayTo(patch2.getId()!);
+  expect(model.view()).toEqual({foo: 'bar', x: 1, y: 2});
+  expect(file.log.start.view()).toEqual({foo: 'bar'});
+  expect(model2.view()).toEqual({foo: 'bar', x: 1, y: 2});
+  expect(model3.view()).toEqual({foo: 'bar', x: 1});
+  expect(model4.view()).toEqual({foo: 'bar', x: 1, y: 2});
+});