feat: 🎸 add ability to write at offset and append in FSA CRUD

src/crud/__tests__/testCrudfs.ts

@@ -71,6 +71,44 @@ export const testCrudfs = (setup: Setup) => {
         '/a/b/bar': '3',
       });
     });
+
+    test('overwrites existing data', async () => {
+      const { crud, snapshot } = setup();
+      await crud.put(['a', 'b'], 'bar', b('abc'));
+      await crud.put(['a', 'b'], 'bar', b('.'));
+      expect(snapshot()).toStrictEqual({
+        '/a/b/bar': '.',
+      });
+    });
+
+    test('can write at offset', async () => {
+      const { crud, snapshot } = setup();
+      await crud.put(['a', 'b'], 'bar', b('abc'));
+      await crud.put(['a', 'b'], 'bar', b('.'), {pos: 1});
+      expect(snapshot()).toStrictEqual({
+        '/a/b/bar': 'a.c',
+      });
+    });
+
+    test('can write at the beginning of file', async () => {
+      const { crud, snapshot } = setup();
+      await crud.put(['a', 'b'], 'bar', b('abc'));
+      await crud.put(['a', 'b'], 'bar', b('.'), {pos: 0});
+      expect(snapshot()).toStrictEqual({
+        '/a/b/bar': '.bc',
+      });
+    });
+
+    test('can append to the file', async () => {
+      const { crud, snapshot } = setup();
+      await crud.put(['a', 'b'], 'bar', b('abc'));
+      await crud.put(['a', 'b'], 'bar', b('1'), {pos: -1});
+      await crud.put(['a', 'b'], 'bar', b('2'), {pos: -1});
+      await crud.put(['a', 'b'], 'bar', b('3'), {pos: -1});
+      expect(snapshot()).toStrictEqual({
+        '/a/b/bar': 'abc123',
+      });
+    });
   });
 
   describe('.get()', () => {

src/crud/types.ts

@@ -74,7 +74,18 @@ export interface CrudApi {
 export type CrudCollection = string[];
 
 export interface CrudPutOptions {
+  /**
+   * Specifies conditions for throwing an error.
+   */
   throwIf?: 'exists' | 'missing';
+
+  /**
+   * Specifies the position where to write the data. If not set, or set to
+   * `undefined` the existing resource is discarded and the new data replaces
+   * it. If set, the new data will be inserted at the specified position. If
+   * set, to `-1` the new data will be appended to the existing resource.
+   */
+  pos?: undefined | number | -1;
 }
 
 export interface CrudCollectionEntry {

src/fsa-to-crud/FsaCrud.ts

@@ -76,8 +76,25 @@ export class FsaCrud implements crud.CrudApi {
         file = await dir.getFileHandle(id, { create: true });
       }
     }
-    const writable = await file!.createWritable();
-    await writable.write(data);
+    let pos = options?.pos;
+    const writable = await file!.createWritable({keepExistingData: typeof pos !== 'undefined'});
+    switch (typeof pos) {
+      case 'undefined': {
+        await writable.write(data);
+        break;
+      }
+      case 'number': {
+        if (pos === -1) {
+          const blob = await file.getFile();
+          pos = blob.size;
+        }
+        await writable.write({type: 'write', data, position: pos});
+        break;
+      }
+      default: {
+        throw new Error(`Invalid position: ${pos}`);
+      }
+    } 
     await writable.close();
   };