Struct SnapshotStore 

pub struct SnapshotStore<T> { /* private fields */ }

A snapshot-based undo/redo store using Arc<T> for structural sharing.

T should ideally use persistent data structures internally (e.g., im::HashMap) so that cloning is O(1) and snapshots share memory.

Invariants

1. undo_stack is never empty after the first push.
2. undo_stack.len() <= config.max_depth (after any operation).
3. Redo stack is cleared on every push.
4. current() always returns the most recently pushed or restored snapshot.

Implementations

impl<T> SnapshotStore<T>

pub fn new(config: SnapshotConfig) -> Self

Create a new snapshot store with the given configuration.

pub fn with_default_config() -> Self

Create a new snapshot store with default configuration.

pub fn push(&mut self, state: T)

Push a new snapshot, clearing the redo stack (new branch).

The snapshot is wrapped in Arc for structural sharing. If the undo stack exceeds max_depth, the oldest snapshot is evicted.

pub fn push_arc(&mut self, state: Arc<T>)

Push a pre-wrapped Arc<T> snapshot.

Use this when you already have an Arc<T> and want to avoid double-wrapping.

pub fn undo(&mut self) -> Option<Arc<T>>

Undo: move the current snapshot to the redo stack and return the previous snapshot.

Returns None if there is only one snapshot (the initial state) or the store is empty.

pub fn redo(&mut self) -> Option<Arc<T>>

Redo: move the most recently undone snapshot back to the undo stack.

Returns None if there is nothing to redo.

pub fn current(&self) -> Option<&Arc<T>>

Get the current snapshot (the most recent on the undo stack).

Returns None if the store is empty.

pub fn can_undo(&self) -> bool

Check if undo is available.

pub fn can_redo(&self) -> bool

Check if redo is available.

pub fn undo_depth(&self) -> usize

Number of snapshots on the undo stack (including current).

pub fn redo_depth(&self) -> usize

Number of snapshots on the redo stack.

pub fn total_snapshots(&self) -> usize

Total number of snapshots across both stacks.

pub fn config(&self) -> &SnapshotConfig

Get the configuration.

pub fn is_empty(&self) -> bool

Check if the store is empty (no snapshots at all).

pub fn clear(&mut self)

Clear all snapshots.

Trait Implementations

impl<T: Debug> Debug for SnapshotStore<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.