Merge pull request #535 from streamich/gcnt

G-Counter (Grow-only counter) CRDT extension

src/json-crdt-extensions/constants.ts

@@ -1,5 +1,7 @@
 export const enum ExtensionId {
   mval = 0,
-  Peritext = 1,
-  QuillDelta = 2,
+  gcnt = 1,
+  pncnt = 2,
+  peritext = 3,
+  quill = 4,
 }

src/json-crdt-extensions/gcnt/__tests__/GcntExt.spec.ts

@@ -0,0 +1,35 @@
+import {GcntExt} from '..';
+import {Model} from '../../../json-crdt/model';
+
+test('can set new values in single fork', () => {
+  const model = Model.withLogicalClock();
+  model.ext.register(GcntExt);
+  model.api.root({
+    counter: GcntExt.new(24),
+  });
+  expect(model.view()).toEqual({counter: 24});
+  const counter = model.api.in(['counter']).asExt(GcntExt);
+  expect(counter.view()).toBe(24);
+  counter.inc(2);
+  expect(model.view()).toEqual({counter: 26});
+  counter.inc(-10);
+  expect(counter.view()).toBe(16);
+});
+
+test('two concurrent users can increment the counter', () => {
+  const model = Model.withLogicalClock();
+  model.ext.register(GcntExt);
+  model.api.root({
+    counter: GcntExt.new(),
+  });
+  expect(model.view()).toEqual({counter: 0});
+  const counter = model.api.in(['counter']).asExt(GcntExt);
+  expect(counter.view()).toBe(0);
+  const model2 = model.fork();
+  const counter2 = model2.api.in(['counter']).asExt(GcntExt);
+  counter.inc(2);
+  counter2.inc(3);
+  model.applyPatch(model2.api.flush());
+  expect(model.view()).toEqual({counter: 5});
+  expect(counter.view()).toBe(5);
+});

src/json-crdt-extensions/gcnt/index.ts

@@ -0,0 +1,78 @@
+import {delayed} from '../../json-crdt-patch/builder/DelayedValueBuilder';
+import {ext} from '../../json-crdt/extensions';
+import {ExtensionId} from '../constants';
+import {printTree} from '../../util/print/printTree';
+import {NodeApi} from '../../json-crdt/model/api/nodes';
+import type {ExtensionDefinition, ObjNode} from '../../json-crdt';
+import type {ITimestampStruct} from '../../json-crdt-patch/clock';
+import type {ExtensionJsonNode, JsonNode} from '../../json-crdt';
+import type {Printable} from '../../util/print/types';
+import type {ExtensionApi} from '../../json-crdt';
+
+const name = 'gcnt';
+
+class GcntNode implements ExtensionJsonNode, Printable {
+  public readonly id: ITimestampStruct;
+
+  constructor(public readonly data: ObjNode) {
+    this.id = data.id;
+  }
+
+  // -------------------------------------------------------- ExtensionJsonNode
+
+  public name(): string {
+    return name;
+  }
+
+  public view(): number {
+    const obj = this.data.view();
+    let sum: number = 0;
+    for (const key in obj) sum += Number(obj[key]);
+    return sum;
+  }
+
+  public children(callback: (node: JsonNode) => void): void {}
+
+  public child?(): JsonNode | undefined {
+    return this.data;
+  }
+
+  public container(): JsonNode | undefined {
+    return this.data.container();
+  }
+
+  public api: undefined | unknown = undefined;
+
+  // ---------------------------------------------------------------- Printable
+
+  public toString(tab?: string): string {
+    return `${this.name()} (${this.view()})` + printTree(tab, [(tab) => this.data.toString(tab)]);
+  }
+}
+
+class GcntApi extends NodeApi<GcntNode> implements ExtensionApi<GcntNode> {
+  public inc(increment: number): this {
+    const {api, node} = this;
+    const sid = api.model.clock.sid;
+    const sidStr = sid.toString(36);
+    const value = Number(node.data.get(sidStr)?.view() ?? 0);
+    const newValue = value + increment;
+    const obj = api.wrap(node.data);
+    obj.set({
+      [sidStr]: newValue,
+    });
+    return this;
+  }
+}
+
+export const GcntExt: ExtensionDefinition<ObjNode, GcntNode, GcntApi> = {
+  id: ExtensionId.gcnt,
+  name,
+  new: (value?: number, sid: number = 0) =>
+    ext(
+      ExtensionId.gcnt,
+      delayed((builder) => builder.constOrJson(value ? {[sid]: value} : {})),
+    ),
+  Node: GcntNode,
+  Api: GcntApi,
+};