feat(json-crdt): 🎸 add JSON Patch+ str_del operation support

Author: streamich

src/json-crdt/json-patch/JsonPatchDraft.ts

@@ -6,7 +6,7 @@ import {ObjectType} from '../types/lww-object/ObjectType';
 import {UNDEFINED_ID} from '../../json-crdt-patch/constants';
 import {toPath} from '../../json-pointer/util';
 import type {Model} from '../model';
-import type {Operation, OperationAdd, OperationRemove, OperationReplace, OperationMove, OperationCopy, OperationTest, OperationStrIns} from '../../json-patch';
+import type {Operation, OperationAdd, OperationRemove, OperationReplace, OperationMove, OperationCopy, OperationTest, OperationStrIns, OperationStrDel} from '../../json-patch';
 
 export class JsonPatchDraft {
   public readonly draft = new Draft();
@@ -26,6 +26,7 @@ export class JsonPatchDraft {
       case 'copy': this.applyCopy(op); break;
       case 'test': this.applyTest(op); break;
       case 'str_ins': this.applyStrIns(op); break;
+      case 'str_del': this.applyStrDel(op); break;
     }
   }
 
@@ -117,6 +118,17 @@ export class JsonPatchDraft {
     builder.insStr(node.id, after, op.str);
   }
 
+  public applyStrDel(op: OperationStrDel): void {
+    const path = toPath(op.path);
+    const {node} = this.model.api.str(path);
+    const {builder} = this.draft;
+    const length = node.length();
+    if (length <= op.pos) return;
+    const after = node.findId(op.pos);
+    const deletionLength = Math.min(op.len ?? op.str!.length, length - op.pos);
+    builder.del(node.id, after, deletionLength);
+  }
+
   private get(steps: Path): unknown {
     if (!steps.length) return this.model.toView();
     else {

src/json-crdt/json-patch/__tests__/JsonPatch.str.spec.ts

@@ -66,6 +66,71 @@ const testCases: TestCase[] = [
     ],
     doc2: {foo: [{bar: 'baz!'}]},
   },
+  {
+    name: 'can delete a single char',
+    doc1: 'a',
+    patches: [
+      [{op: 'str_del', path: [], pos: 0, len: 1}]
+    ],
+    doc2: '',
+  },
+  {
+    name: 'can delete from already empty string',
+    doc1: '',
+    patches: [
+      [{op: 'str_del', path: [], pos: 0, len: 1}]
+    ],
+    doc2: '',
+  },
+  {
+    name: 'can delete at the end of string',
+    doc1: 'ab',
+    patches: [
+      [{op: 'str_del', path: [], pos: 1, len: 1}]
+    ],
+    doc2: 'a',
+  },
+  {
+    name: 'can delete at the beginning of string',
+    doc1: 'ab',
+    patches: [
+      [{op: 'str_del', path: [], pos: 0, len: 1}]
+    ],
+    doc2: 'b',
+  },
+  {
+    name: 'can delete in the middle of string',
+    doc1: 'abc',
+    patches: [
+      [{op: 'str_del', path: [], pos: 1, len: 1}]
+    ],
+    doc2: 'ac',
+  },
+  {
+    name: 'can delete multiple chars',
+    doc1: '1234',
+    patches: [
+      [{op: 'str_del', path: [], pos: 1, len: 2}],
+      [{op: 'str_del', path: [], pos: 1, len: 5}],
+    ],
+    doc2: '1',
+  },
+  {
+    name: 'handles deletion beyond end of string',
+    doc1: '1234',
+    patches: [
+      [{op: 'str_del', path: [], pos: 1111, len: 2}],
+    ],
+    doc2: '1234',
+  },
+  {
+    name: 'can delete a string in object',
+    doc1: {foo: '123'},
+    patches: [
+      [{op: 'str_del', path: '/foo', pos: 1, len: 2}],
+    ],
+    doc2: {foo: '1'},
+  },
 ];
 
 for (const {only, name, doc1, doc2, patches, throws} of testCases) {