feat(json-crdt-peritext-ui): 🎸 implement in-memory undo manager

Author: streamich

src/json-crdt-peritext-ui/dom/annals/MemoryUndo.ts

@@ -0,0 +1,40 @@
+import type {UndoManager, UndoItem} from '../../types';
+import type {UiLifeCycles} from '../types';
+
+/**
+ * A Memory-based undo manager.
+ */
+export class MemoryUndo implements UndoManager, UiLifeCycles {
+  /** Undo stack. */
+  public uStack: UndoItem[] = [];
+  /** Redo stack. */
+  public rStack: UndoItem[] = [];
+
+  // /** ------------------------------------------------------ {@link UndoRedo} */
+
+  public push<U, R>(undo: UndoItem<U, R>): void {
+    this.rStack = [];
+    this.uStack.push(undo as UndoItem);
+  }
+
+  undo(): void {
+    const undo = this.uStack.pop();
+    if (undo) {
+      const redo = undo[1](undo[0]);
+      this.rStack.push(redo);
+    }
+  }
+
+  redo(): void {
+    const redo = this.rStack.pop();
+    if (redo) {
+      const undo = redo[1](redo[0]);
+      this.uStack.push(undo);
+    }
+  }
+
+  /** -------------------------------------------------- {@link UiLifeCycles} */
+
+  public start(): void {}
+  public stop(): void {}
+}