feat: 🎸 add .findMax() utility

Author: streamich

src/json-crdt/log/Log.ts

@@ -1,5 +1,5 @@
 import {AvlMap} from 'sonic-forest/lib/avl/AvlMap';
-import {first, next} from 'sonic-forest/lib/util';
+import {first, next, prev} from 'sonic-forest/lib/util';
 import {printTree} from 'tree-dump/lib/printTree';
 import {listToUint8} from '@jsonjoy.com/util/lib/buffers/concat';
 import {Model} from '../model';
@@ -160,6 +160,22 @@ export class Log<N extends JsonNode = JsonNode<any>, Metadata extends Record<str
     return clone;
   }
 
+  /**
+   * Finds the latest patch for a given session ID.
+   *
+   * @param sid Session ID to find the latest patch for.
+   * @return The latest patch for the given session ID, or `undefined` if no
+   *     such patch exists.
+   */
+  public findMax(sid: number): Patch | undefined {
+    let curr = this.patches.max;
+    while (curr) {
+      if (curr.k.sid === sid) return curr.v;
+      curr = prev(curr);
+    }
+    return;
+  }
+
   /**
    * Advance the start of the log to a specified timestamp, excluding the patch
    * at the given timestamp. This method removes all patches from the log that

src/json-crdt/log/__tests__/Log.spec.ts

@@ -119,6 +119,30 @@ describe('.advanceTo()', () => {
   });
 });
 
+describe('.findMax()', () => {
+  test('can advance the log from start', () => {
+    const model = Model.create();
+    const sid0 = model.clock.sid;
+    const sid1 = Model.sid();
+    model.api.set({foo: 'bar'});
+    const log = Log.fromNewModel(model);
+    log.end.api.obj([]).set({x: 1});
+    const patch1 = log.end.api.flush();
+    log.end.setSid(sid1);
+    log.end.api.obj([]).set({y: 2});
+    const patch2 = log.end.api.flush();
+    log.end.setSid(sid0);
+    log.end.api.obj([]).set({foo: 'baz'});
+    const patch3 = log.end.api.flush();
+    const found0 = log.findMax(sid0);
+    const found1 = log.findMax(sid1);
+    const found2 = log.findMax(12345);
+    expect(found0).toBe(patch3);
+    expect(found1).toBe(patch2);
+    expect(found2).toBe(void 0);
+  });
+});
+
 describe('.undo()', () => {
   describe('RGA', () => {
     describe('str', () => {