v1.59.0-rc.2: make plan editing predictable

src/command-stack.ts

@@ -0,0 +1,55 @@
+/**
+ * Session-local, named undo/redo history.
+ *
+ * The stack deliberately knows nothing about Houseplan geometry. Callers own
+ * immutable before/after values and decide how to apply them. Keeping the
+ * history generic gives every geometry tool one transaction model instead of
+ * another private undo implementation.
+ */
+export interface NamedCommand<T> {
+  name: string;
+  before: T;
+  after: T;
+}
+
+export class CommandStack<T> {
+  private readonly _limit: number;
+  private _undo: NamedCommand<T>[] = [];
+  private _redo: NamedCommand<T>[] = [];
+
+  public constructor(limit = 50) {
+    // UX-04 promises a useful 30–50-step history. Fifty is the product
+    // default; the floor prevents a future caller from silently weakening it.
+    this._limit = Math.max(30, Math.floor(limit));
+  }
+
+  public get canUndo(): boolean { return this._undo.length > 0; }
+  public get canRedo(): boolean { return this._redo.length > 0; }
+  public get undoName(): string | null { return this._undo[this._undo.length - 1]?.name ?? null; }
+  public get redoName(): string | null { return this._redo[this._redo.length - 1]?.name ?? null; }
+  public get size(): number { return this._undo.length; }
+
+  public push(command: NamedCommand<T>): void {
+    this._undo.push(command);
+    if (this._undo.length > this._limit) this._undo.splice(0, this._undo.length - this._limit);
+    // A new branch makes every previously redoable command stale.
+    this._redo = [];
+  }
+
+  public undo(): NamedCommand<T> | null {
+    const command = this._undo.pop() ?? null;
+    if (command) this._redo.push(command);
+    return command;
+  }
+
+  public redo(): NamedCommand<T> | null {
+    const command = this._redo.pop() ?? null;
+    if (command) this._undo.push(command);
+    return command;
+  }
+
+  public clear(): void {
+    this._undo = [];
+    this._redo = [];
+  }
+}