Vue State Snapshotter

Imagine you're building a complex Vue application with many interactive elements and nested components. Frequently, you'll need to save the current state of your application to be able to revert to it later, perhaps for debugging, undo functionality, or even creating "save points" in a game. This challenge focuses on creating a robust mechanism to capture and restore the state of a Vue component.

Problem Description

Your task is to implement a Vue composable function in TypeScript that allows you to take a snapshot of a reactive state and later restore the component's state to that snapshot. This is crucial for features like undo/redo functionality, debugging tools, or complex form management where reverting to a previous valid state is essential.

Key Requirements:

• Snapshot Creation: The composable should provide a function to capture the current value of a reactive state (e.g., a ref or a reactive object).
• State Restoration: The composable should provide a function to restore the reactive state to a previously captured snapshot.
• Deep Copy: The snapshot must be a deep copy of the original state. Modifying the original state after taking a snapshot should not affect the snapshot, and vice versa.
• Multiple Snapshots: The system should be capable of storing and restoring multiple snapshots.
• TypeScript Support: The solution must be implemented in TypeScript, leveraging its type-safety features.

Expected Behavior:

1. Initialize a reactive state within a Vue component.
2. Use the composable to create a snapshot of this state.
3. Modify the reactive state.
4. Use the composable to restore the state from the previously created snapshot. The state should revert to its exact value at the time the snapshot was taken.

Edge Cases:

• Restoring from an empty list of snapshots.
• Handling complex nested objects and arrays within the reactive state.
• Ensuring that circular references (if any) are handled gracefully, though for this challenge, we will assume no circular references.

Examples

Example 1:

// Initial state in a Vue component
const count = ref(0);
const user = reactive({ name: 'Alice', address: { city: 'Wonderland' } });

// In a composable function:
const { takeSnapshot, restoreState } = useStateSnapshotter();

// ... later in component logic ...
takeSnapshot([count, user]); // Capture the current state

// Modify the state
count.value = 10;
user.name = 'Bob';
user.address.city = 'New York';

// Restore the state
restoreState();

// Expected state after restoration:
// count.value should be 0
// user.name should be 'Alice'
// user.address.city should be 'Wonderland'

Explanation: The takeSnapshot function stores a deep copy of the count and user reactive objects. When restoreState is called, the count and user objects are reset to their values from before the modification.

Example 2:

// Initial state
const items = ref<string[]>(['apple', 'banana']);

// In a composable function:
const { takeSnapshot, restoreState, getSnapshots } = useStateSnapshotter();

takeSnapshot([items]); // Snapshot 1

items.value.push('cherry');
takeSnapshot([items]); // Snapshot 2

items.value.pop(); // Remove 'cherry'

// Restore to Snapshot 1
restoreState(0); // Restore to the first snapshot (index 0)

// Expected state after restoration:
// items.value should be ['apple', 'banana', 'cherry']

// Get all stored snapshots
const allSnapshots = getSnapshots();
// allSnapshots[0] should represent ['apple', 'banana']
// allSnapshots[1] should represent ['apple', 'banana', 'cherry']

Explanation: This example shows how to manage multiple snapshots. Restoring to index 0 brings the state back to the point after the first takeSnapshot call.

Example 3: Restoring from no snapshots

// Initial state
const isActive = ref(true);

// In a composable function:
const { takeSnapshot, restoreState } = useStateSnapshotter();

// Attempt to restore without taking any snapshots
restoreState();

// Expected behavior:
// The state should remain unchanged. The composable should handle this gracefully.

Explanation: Calling restoreState when no snapshots have been taken should not cause an error and should leave the state as is.

Constraints

• The composable should work with any combination of Vue's built-in reactive primitives: ref, reactive.
• The deep copy mechanism should be efficient enough for typical application states.
• The number of snapshots stored should not be limited by the implementation, but it's good practice to manage memory if many are stored.

Notes

• Consider how to handle different types of reactive references (e.g., ref vs. reactive objects).
• Think about the best way to store and access multiple snapshots.
• The deep copying of state is a critical part of this challenge. Libraries like Lodash's cloneDeep can be helpful, or you might implement your own.
• The composable should be designed to be reusable across different components.
• The return type of takeSnapshot is not strictly defined, but it should allow for later restoration. The restoreState function should accept an identifier (like an index) for which snapshot to restore.