Add incremental Automerge field changes

test/crdt-automerge.test.ts

@@ -2,7 +2,10 @@ import assert from "node:assert/strict";
 import test from "node:test";
 import * as Automerge from "@automerge/automerge";
 import {
+  AUTOMERGE_CHANGES_ENCODING,
+  AUTOMERGE_SNAPSHOT_ENCODING,
   createAutomergeFieldValue,
+  createAutomergeFieldChanges,
   encodeAutomergeFieldWrite,
   isAutomergeFieldDoc,
   loadAutomergeFieldDoc,
@@ -17,7 +20,7 @@ test("Automerge CRDT fields explicitly create stored envelopes", () => {
   const stored = createAutomergeFieldValue({ title: "draft" }, type);
 
   assert.equal(stored.$caminoCrdtType, type);
-  assert.equal(stored.$caminoCrdtEncoding, "base64");
+  assert.equal(stored.$caminoCrdtEncoding, AUTOMERGE_SNAPSHOT_ENCODING);
   assert.deepEqual(materializeAutomergeFieldValue(stored, type), {
     title: "draft",
   });
@@ -72,3 +75,49 @@ test("Automerge CRDT fields merge divergent saved documents", () => {
     right: true,
   });
 });
+
+test("Automerge CRDT fields encode and apply incremental changes", () => {
+  const stored = createAutomergeFieldValue({ title: "draft" }, type);
+  const base = loadAutomergeFieldDoc(stored, type);
+  const changed = Automerge.change(base, (doc) => {
+    (doc.value as { title: string }).title = "edited";
+  });
+  const update = createAutomergeFieldChanges(base, changed, type);
+
+  assert.equal(update.$caminoCrdtEncoding, AUTOMERGE_CHANGES_ENCODING);
+  assert.ok(update.$caminoCrdtPayload.length < saveAutomergeFieldDoc(changed, type).$caminoCrdtPayload.length);
+
+  const result = mergeAutomergeFieldValues({ existing: stored, incoming: update, type });
+  assert.deepEqual(result.materialized, { title: "edited" });
+  assert.equal(result.stored.$caminoCrdtEncoding, AUTOMERGE_SNAPSHOT_ENCODING);
+});
+
+test("Automerge change application is idempotent", () => {
+  const stored = createAutomergeFieldValue({ count: 0 }, type);
+  const base = loadAutomergeFieldDoc(stored, type);
+  const changed = Automerge.change(base, (doc) => {
+    (doc.value as { count: number }).count = 1;
+  });
+  const update = createAutomergeFieldChanges(base, changed, type);
+
+  const once = mergeAutomergeFieldValues({ existing: stored, incoming: update, type });
+  const twice = mergeAutomergeFieldValues({ existing: once.stored, incoming: update, type });
+  assert.deepEqual(twice.materialized, { count: 1 });
+});
+
+test("Automerge change batches reject malformed framing", () => {
+  const stored = createAutomergeFieldValue({ count: 0 }, type);
+  assert.throws(
+    () =>
+      mergeAutomergeFieldValues({
+        existing: stored,
+        incoming: {
+          $caminoCrdtType: type,
+          $caminoCrdtEncoding: AUTOMERGE_CHANGES_ENCODING,
+          $caminoCrdtPayload: Buffer.from([0, 0, 0, 1]).toString("base64"),
+        },
+        type,
+      }),
+    /missing change length/,
+  );
+});