Undoable Database

Requirements

• Export UndoableDatabase as named and default. new UndoableDatabase() starts empty. Expose create({ name, email }), read(id), list(), update(id, patch), delete(id), undo(), and redo(). User records have only id, name, and email. create/update/delete return copies; read returns a copy or null, and list returns copies in insertion order.
• Generate positive integer IDs starting at 1. Each committed state includes the next-ID counter. Deleting a user does not recycle its ID, but undoing a creation restores its prior counter. A new branch after undo can therefore reuse an ID from a discarded future.
• Data and patches must be plain objects. create requires own nonempty string name and email fields; patches allow either or both of those fields. Validate using trimmed emptiness but preserve supplied string text. Reject unknown fields, id changes, and invalid values with TypeError. IDs must be positive safe integers; invalid IDs throw TypeError.
• update/delete of a missing user throws Error. Invalid writes leave records, history, and redo availability unchanged. update shallowly replaces supplied fields without changing insertion order. An empty patch or update with identical values is a no-op and does not create history or discard redo.
• Each successful create, changed update, or delete commits one history state. undo restores the previous complete state and returns true, or false at the beginning. redo restores the next state and returns true, or false at the end. Undo/redo do not themselves add history entries.
• A changed write after undo discards the redo branch. Read operations and no-op/invalid writes preserve it. Input objects and returned records must never expose internal state or history to mutation. Instances are independent. No persistent database, nested data, email-format validation, unique-email rules, transactions, or UI is required.

Examples

Input: const db = new UndoableDatabase(); const user = db.create({name:"Ada",email:"ada@example.com"}); db.update(user.id,{name:"Lin"}); db.undo(); db.read(user.id);
Output: { id: 1, name: "Ada", email: "ada@example.com" }

Input: db.redo(); db.delete(1); db.undo(); db.list();
Output: The user returns in its original order, with name Lin.