nami 0.11.2

//! Reactive collections with watcher support.
//!
//! This module provides a trait-based approach for creating observable collections
//! that can notify watchers when their contents change. It supports both reactive
//! collections that emit change notifications and static collections that provide
//! one-time snapshots.
//!
//! # Core Components
//!
//! - [`Collection`]: A trait defining the interface for observable collections
//! - [`List<T>`]: A reactive list implementation using `Rc<RefCell<Vec<T>>>`
//! - [`AnyCollection<T>`]: A type-erased wrapper for storing different collection types
//!
//! # Collection Types
//!
//! The module provides `Collection` implementations for:
//! - `List<T>`: Fully reactive with ongoing change notifications
//! - `Vec<T>`: Static collection with one-time watcher notifications
//! - `[T; N]`: Static array with one-time watcher notifications
//!
//! # Usage Example
//!
//! ```rust
//! use nami::collection::{Collection, List};
//!
//! // Create a reactive list
//! let mut list = List::new();
//! list.push(1);
//! list.push(2);
//!
//! // Watch for changes in a specific range
//! let _guard = list.watch(0..2, |ctx| {
//!     println!("Items changed: {:?}", ctx.into_value());
//! });
//!
//! // Modifications will trigger the watcher
//! list.push(3);
//! ```
//!
//! # Range-based Watching
//!
//! All collections support range-based watching using standard Rust range syntax:
//! - `collection.watch(.., watcher)` - Watch entire collection
//! - `collection.watch(1..5, watcher)` - Watch indices 1 through 4
//! - `collection.watch(2.., watcher)` - Watch from index 2 to end
//! - `collection.watch(..3, watcher)` - Watch from start to index 2
//!
//! # Type Erasure
//!
//! The `AnyCollection` wrapper allows storing different collection types
//! in the same container while preserving the ability to observe them:
//!
//! ```rust
//! use nami::collection::{AnyCollection, List};
//!
//! let list = List::from(vec![1, 2, 3]);
//! let any_collection = AnyCollection::new(list);
//!
//! // Still supports watching despite type erasure
//! let _guard = any_collection.watch(.., |ctx| {
//!     // Handle change notifications
//! });
//! ```

use core::{
    cell::{Cell, RefCell},
    ops::{Bound, RangeBounds},
};
pub use nami_core::collection::*;

use alloc::{rc::Rc, vec::Vec};
use nami_core::{
    SignalIdentity,
    observe::Origin,
    watcher::{Context, Metadata},
};

use crate::{
    Signal,
    watcher::{WatcherManager, WatcherManagerGuard},
};

/// Adapts a signal of vector snapshots into a reactive collection.
///
/// Collection consumers reconcile snapshots by item identity, so membership
/// changes update only inserted, removed, moved, or replaced items instead of
/// rebuilding the containing view subtree.
#[derive(Debug, Clone)]
pub struct SignalCollection<S> {
    signal: S,
}

impl<S> SignalCollection<S> {
    /// Creates a collection backed by vector snapshots from `signal`.
    pub const fn new(signal: S) -> Self {
        Self { signal }
    }
}

/// A reactive list that can be observed for changes.
///
/// Notifications use `Rc<[T]>` snapshots so that cloning a `Context` across
/// multiple watchers is O(1) (reference-count bump) instead of O(n).
#[derive(Debug)]
pub struct List<T> {
    vec: Rc<RefCell<Vec<T>>>,
    watchers: WatcherManager<Rc<[T]>>,
}

impl<T: 'static> From<Vec<T>> for List<T> {
    #[track_caller]
    fn from(value: Vec<T>) -> Self {
        Self::from_vec(value)
    }
}

impl<T: 'static> List<T> {
    /// Creates a new empty reactive list.
    #[must_use]
    #[track_caller]
    pub fn new() -> Self {
        Self::from_vec(Vec::new())
    }

    /// Builds a list around `value`, attributing the node to the caller.
    #[track_caller]
    fn from_vec(value: Vec<T>) -> Self {
        let vec = Rc::new(RefCell::new(value));
        let origin = Origin::capture::<Self>(SignalIdentity::from_rc(&vec));
        Self {
            vec,
            watchers: WatcherManager::with_origin(origin),
        }
    }

    /// Takes an `Rc<[T]>` snapshot of the current contents and notifies all
    /// watchers.  The snapshot is shared (O(1) clone) across watchers so each
    /// notification cycle only pays for one allocation.
    fn notify(&self)
    where
        T: Clone,
    {
        self.notify_with_metadata(Metadata::new());
    }

    fn notify_with_metadata(&self, metadata: Metadata)
    where
        T: Clone,
    {
        if self.watchers.is_empty() {
            return;
        }
        let snapshot: Rc<[T]> = Rc::from(self.vec.borrow().as_slice());
        self.watchers.notify(&Context::new(snapshot, metadata));
    }

    /// Adds an element to the end of the list.
    pub fn push(&self, value: T)
    where
        T: Clone,
    {
        self.vec.borrow_mut().push(value);
        self.notify();
    }

    /// Sorts the list in place.
    pub fn sort(&self)
    where
        T: Ord + Clone,
    {
        self.vec.borrow_mut().sort();
        self.notify();
    }

    /// Removes and returns the last element of the list.
    #[must_use]
    pub fn pop(&self) -> Option<T>
    where
        T: Clone,
    {
        let result = self.vec.borrow_mut().pop();
        if result.is_some() {
            self.notify();
        }
        result
    }

    /// Inserts an element at the specified index.
    pub fn insert(&self, index: usize, value: T)
    where
        T: Clone,
    {
        self.vec.borrow_mut().insert(index, value);
        self.notify();
    }

    /// Removes and returns the element at the specified index.
    #[must_use]
    pub fn remove(&self, index: usize) -> T
    where
        T: Clone,
    {
        let result = self.vec.borrow_mut().remove(index);
        self.notify();
        result
    }

    /// Clears all elements from the list.
    pub fn clear(&self)
    where
        T: Clone,
    {
        let was_empty = self.vec.borrow().is_empty();
        self.vec.borrow_mut().clear();
        if !was_empty {
            self.notify();
        }
    }

    /// Atomically replaces the complete list and returns the previous contents.
    ///
    /// Watchers observe only the final replacement snapshot, regardless of how
    /// many items differ between the old and new collections.
    #[must_use]
    pub fn replace(&self, value: Vec<T>) -> Vec<T>
    where
        T: Clone,
    {
        let previous = core::mem::replace(&mut *self.vec.borrow_mut(), value);
        self.notify();
        previous
    }

    /// Atomically replaces the complete list and propagates watcher metadata.
    #[must_use]
    pub fn replace_with_metadata(&self, value: Vec<T>, metadata: Metadata) -> Vec<T>
    where
        T: Clone,
    {
        let previous = core::mem::replace(&mut *self.vec.borrow_mut(), value);
        self.notify_with_metadata(metadata);
        previous
    }

    /// Takes a snapshot of the current list contents.
    #[must_use]
    pub fn snapshot(&self) -> Vec<T>
    where
        T: Clone,
    {
        self.vec.borrow().clone()
    }

    /// Returns an iterator over the list's items.
    ///
    /// Warning: This will clone the entire list, ensuring that modifications during iteration do not affect the iterator.
    #[must_use]
    pub fn iter(&self) -> <&Self as IntoIterator>::IntoIter
    where
        T: Clone,
    {
        self.snapshot().into_iter()
    }
}

/// Iterator implementation for `List<T>`
/// Tip: This method will attempt to avoid cloning the internal Vec if possible. However, if there are multiple references to the List, it will clone the Vec to ensure safety.
impl<T: Clone + 'static> IntoIterator for List<T> {
    type Item = T;
    type IntoIter = alloc::vec::IntoIter<T>;

    fn into_iter(self) -> Self::IntoIter {
        // if we can unwrap the Rc, we can avoid cloning
        match Rc::try_unwrap(self.vec) {
            Ok(vec) => vec.into_inner().into_iter(),
            Err(rc) => rc.borrow().clone().into_iter(),
        }
    }
}

/// Iterator implementation for references to `List<T>`
/// Warning: This will clone the entire list, ensuring that modifications during iteration do not affect the iterator.
impl<T: Clone + 'static> IntoIterator for &List<T> {
    type Item = T;
    type IntoIter = alloc::vec::IntoIter<T>;

    fn into_iter(self) -> Self::IntoIter {
        self.snapshot().into_iter()
    }
}

impl<T> Clone for List<T> {
    fn clone(&self) -> Self {
        Self {
            vec: self.vec.clone(),
            watchers: self.watchers.clone(),
        }
    }
}

impl<T: 'static> Default for List<T> {
    fn default() -> Self {
        Self::new()
    }
}

/// Resolve concrete `(start, end)` offsets from captured `Bound` values and
/// the current snapshot length, clamping to valid indices.
fn resolve_range(start_bound: Bound<usize>, end_bound: Bound<usize>, len: usize) -> (usize, usize) {
    let mut start = match start_bound {
        Bound::Included(n) => n,
        Bound::Excluded(n) => n.saturating_add(1),
        Bound::Unbounded => 0,
    };
    let mut end = match end_bound {
        Bound::Included(n) => n.saturating_add(1),
        Bound::Excluded(n) => n,
        Bound::Unbounded => len,
    };
    start = start.min(len);
    end = end.min(len);
    if start > end {
        start = end;
    }
    (start, end)
}

fn notify_signal_collection<T>(
    watcher: &dyn for<'a> Fn(Context<&'a [T]>),
    context: Context<Vec<T>>,
    start_bound: Bound<usize>,
    end_bound: Bound<usize>,
) {
    let metadata = context.metadata().clone();
    let snapshot = context.into_value();
    let (start, end) = resolve_range(start_bound, end_bound, snapshot.len());
    watcher(Context::new(&snapshot[start..end], metadata));
}

impl<S, T> Collection for SignalCollection<S>
where
    S: Signal<Output = Vec<T>> + Clone,
    T: Clone + 'static,
{
    type Item = T;
    type Guard = S::Guard;

    fn get(&self, index: usize) -> Option<Self::Item> {
        self.signal.get().as_slice().get(index).cloned()
    }

    fn len(&self) -> usize {
        self.signal.get().len()
    }

    fn watch(
        &self,
        range: impl RangeBounds<usize>,
        watcher: impl for<'a> Fn(Context<&'a [Self::Item]>) + 'static,
    ) -> Self::Guard {
        let start_bound = range.start_bound().cloned();
        let end_bound = range.end_bound().cloned();
        let watcher = Rc::new(watcher);
        let pending = Rc::new(RefCell::new(None));
        let subscribed = Rc::new(Cell::new(false));

        let guard = self.signal.watch({
            let watcher = Rc::clone(&watcher);
            let pending = Rc::clone(&pending);
            let subscribed = Rc::clone(&subscribed);
            move |context| {
                if subscribed.get() {
                    notify_signal_collection(watcher.as_ref(), context, start_bound, end_bound);
                } else {
                    *pending.borrow_mut() = Some(context);
                }
            }
        });

        let initial = pending
            .borrow_mut()
            .take()
            .unwrap_or_else(|| Context::from(self.signal.get()));
        subscribed.set(true);
        notify_signal_collection(watcher.as_ref(), initial, start_bound, end_bound);

        guard
    }
}

impl<T: Clone + 'static> Collection for List<T> {
    type Item = T;
    type Guard = WatcherManagerGuard<Rc<[T]>>;

    fn get(&self, index: usize) -> Option<Self::Item> {
        self.vec.borrow().as_slice().get(index).cloned()
    }
    fn len(&self) -> usize {
        self.vec.borrow().len()
    }
    fn watch(
        &self,
        range: impl RangeBounds<usize>,
        watcher: impl for<'a> Fn(Context<&'a [Self::Item]>) + 'static,
    ) -> Self::Guard {
        // Convert range bounds to concrete values for capture
        let start_bound = match range.start_bound() {
            Bound::Included(&n) => Bound::Included(n),
            Bound::Excluded(&n) => Bound::Excluded(n),
            Bound::Unbounded => Bound::Unbounded,
        };
        let end_bound = match range.end_bound() {
            Bound::Included(&n) => Bound::Included(n),
            Bound::Excluded(&n) => Bound::Excluded(n),
            Bound::Unbounded => Bound::Unbounded,
        };

        // Call watcher immediately with current data
        {
            let snapshot: Rc<[T]> = Rc::from(self.vec.borrow().as_slice());
            let (start, end) = resolve_range(start_bound, end_bound, snapshot.len());
            watcher(Context::from(&snapshot[start..end]));
        }

        // Subsequent notifications: slice the Rc<[T]> snapshot carried inside
        // the Context.  Cloning an Rc is O(1), so this avoids the previous
        // O(n) re-borrow + range clone per watcher.
        self.watchers.register_as_guard(move |ctx| {
            let snapshot: Rc<[T]> = ctx.value().clone(); // O(1) ref-count bump
            let metadata = ctx.metadata().clone();
            let (start, end) = resolve_range(start_bound, end_bound, snapshot.len());
            watcher(Context::new(&snapshot[start..end], metadata));
        })
    }
}

impl<T: 'static> FromIterator<T> for List<T> {
    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
        Self::from(iter.into_iter().collect::<Vec<_>>())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use alloc::{rc::Rc, vec};
    use core::cell::{Cell, RefCell};

    #[test]
    fn test_collection_trait_basic_operations() {
        let list = List::from(vec![1, 2, 3]);

        assert_eq!(Collection::len(&list), 3);
        assert!(!Collection::is_empty(&list));
        assert_eq!(Collection::get(&list, 0), Some(1));
        assert_eq!(Collection::get(&list, 1), Some(2));
        assert_eq!(Collection::get(&list, 2), Some(3));
        assert_eq!(Collection::get(&list, 3), None);
    }

    #[test]
    fn replace_notifies_only_the_final_snapshot() {
        let list = List::from(vec![1, 2]);
        let observed = Rc::new(RefCell::new(Vec::<Vec<i32>>::new()));
        let observed_for_watcher = Rc::clone(&observed);
        let _guard = list.watch(.., move |context| {
            observed_for_watcher
                .borrow_mut()
                .push(context.into_value().to_vec());
        });

        let previous = list.replace(vec![3, 4, 5]);

        assert_eq!(previous, vec![1, 2]);
        assert_eq!(*observed.borrow(), vec![vec![1, 2], vec![3, 4, 5]]);
    }

    #[test]
    fn signal_collection_emits_initial_and_updated_snapshots() {
        let values = crate::binding(vec![1, 2]);
        let collection = SignalCollection::new(values.clone());
        let observed = Rc::new(RefCell::new(Vec::<Vec<i32>>::new()));
        let observed_for_watcher = Rc::clone(&observed);
        let _guard = collection.watch(.., move |context| {
            observed_for_watcher
                .borrow_mut()
                .push(context.into_value().to_vec());
        });

        values.set(vec![2, 3, 4]);

        assert_eq!(*observed.borrow(), vec![vec![1, 2], vec![2, 3, 4]]);
    }

    #[test]
    fn test_list_new_and_default() {
        let list1: List<i32> = List::new();
        let list2: List<i32> = List::default();

        assert_eq!(Collection::len(&list1), 0);
        assert!(Collection::is_empty(&list1));
        assert_eq!(Collection::len(&list2), 0);
        assert!(Collection::is_empty(&list2));
    }

    #[test]
    fn test_list_from_vec() {
        let vec = vec![1, 2, 3, 4, 5];
        let list = List::from(vec);

        assert_eq!(Collection::len(&list), 5);
        for i in 0..5 {
            assert_eq!(Collection::get(&list, i), Some(i + 1));
        }
    }

    #[test]
    fn test_list_push_and_pop() {
        let list = List::new();

        list.push(1);
        list.push(2);
        list.push(3);

        assert_eq!(Collection::len(&list), 3);
        assert_eq!(Collection::get(&list, 0), Some(1));
        assert_eq!(Collection::get(&list, 1), Some(2));
        assert_eq!(Collection::get(&list, 2), Some(3));

        assert_eq!(list.pop(), Some(3));
        assert_eq!(Collection::len(&list), 2);
        assert_eq!(list.pop(), Some(2));
        assert_eq!(list.pop(), Some(1));
        assert_eq!(list.pop(), None);
        assert!(Collection::is_empty(&list));
    }

    #[test]
    fn test_list_insert_and_remove() {
        let list = List::from(vec![1, 3, 5]);

        list.insert(1, 2);
        list.insert(3, 4);

        assert_eq!(Collection::len(&list), 5);
        assert_eq!(Collection::get(&list, 0), Some(1));
        assert_eq!(Collection::get(&list, 1), Some(2));
        assert_eq!(Collection::get(&list, 2), Some(3));
        assert_eq!(Collection::get(&list, 3), Some(4));
        assert_eq!(Collection::get(&list, 4), Some(5));

        assert_eq!(list.remove(1), 2);
        assert_eq!(list.remove(2), 4);
        assert_eq!(Collection::len(&list), 3);
        assert_eq!(Collection::get(&list, 0), Some(1));
        assert_eq!(Collection::get(&list, 1), Some(3));
        assert_eq!(Collection::get(&list, 2), Some(5));
    }

    #[test]
    fn test_list_clear() {
        let list = List::from(vec![1, 2, 3, 4, 5]);
        assert_eq!(Collection::len(&list), 5);

        list.clear();
        assert_eq!(Collection::len(&list), 0);
        assert!(Collection::is_empty(&list));

        // Clearing an empty list should not panic
        list.clear();
        assert!(Collection::is_empty(&list));
    }

    #[test]
    fn test_list_clone() {
        let list1 = List::from(vec![1, 2, 3]);
        let list2 = Clone::clone(&list1);

        assert_eq!(Collection::len(&list1), Collection::len(&list2));
        for i in 0..3 {
            assert_eq!(Collection::get(&list1, i), Collection::get(&list2, i));
        }

        // Modifications to one should affect the other (shared ownership)
        list1.push(4);
        assert_eq!(Collection::len(&list2), 4);
        assert_eq!(Collection::get(&list2, 3), Some(4));
    }

    #[test]
    fn test_list_watcher_notifications() {
        let list = List::new();
        let notification_count = Rc::new(RefCell::new(0));

        let count = notification_count.clone();
        let _guard = Collection::watch(&list, .., move |_ctx| {
            *count.borrow_mut() += 1;
        });

        // Initial snapshot should fire once with empty data.
        assert_eq!(*notification_count.borrow(), 1);
        {
            let mut count_mut = notification_count.borrow_mut();
            *count_mut = 0;
        }

        // Push operations should trigger notifications
        list.push(1);
        assert_eq!(*notification_count.borrow(), 1);

        list.push(2);
        assert_eq!(*notification_count.borrow(), 2);

        let _ = list.pop();
        assert_eq!(*notification_count.borrow(), 3);
    }

    #[test]
    fn test_list_watcher_range() {
        let list = List::from(vec![1, 2, 3, 4, 5]);
        let notification_count = Rc::new(RefCell::new(0));

        let count = notification_count.clone();
        let _guard = Collection::watch(&list, 1..4, move |ctx| {
            *count.borrow_mut() += 1;
            assert_eq!(ctx.into_value(), vec![2, 3, 4]);
        });

        list.push(6);
        assert_eq!(*notification_count.borrow(), 2);
    }

    #[test]
    fn test_vec_collection_implementation() {
        let vec = vec![1, 2, 3, 4, 5];

        assert_eq!(Collection::len(&vec), 5);
        assert!(!Collection::is_empty(&vec));
        assert_eq!(Collection::get(&vec, 2), Some(3));
        assert_eq!(Collection::get(&vec, 10), None);

        // Vec is static - watch should be a no-op and not call the watcher
        let called = Rc::new(Cell::new(false));
        let c = called.clone();
        Collection::watch(&vec, 1..3, move |_ctx| {
            c.set(true);
        });

        assert!(!called.get()); // Watcher should not be called for static Vec
    }

    #[test]
    fn test_array_collection_implementation() {
        let arr = [1, 2, 3, 4, 5];

        assert_eq!(Collection::len(&arr), 5);
        assert!(!Collection::is_empty(&arr));
        assert_eq!(Collection::get(&arr, 2), Some(3));
        assert_eq!(Collection::get(&arr, 10), None);

        // Arrays are static - watch should be a no-op and not call the watcher
        let called = Rc::new(Cell::new(false));
        let c = called.clone();
        Collection::watch(&arr, 0..2, move |_ctx| {
            c.set(true);
        });

        assert!(!called.get()); // Watcher should not be called for static array
    }

    #[test]
    fn test_empty_array_collection() {
        let arr: [i32; 0] = [];

        assert_eq!(Collection::len(&arr), 0);
        assert!(Collection::is_empty(&arr));
        assert_eq!(Collection::get(&arr, 0), None);

        // Empty arrays are static - watch should be a no-op
        let called = Rc::new(Cell::new(false));
        let c = called.clone();
        Collection::watch(&arr, .., move |_ctx| {
            c.set(true);
        });

        assert!(!called.get()); // Watcher should not be called for static empty array
    }

    #[test]
    fn test_any_collection_basic_operations() {
        let list = List::from(vec![1, 2, 3]);
        let any_collection = AnyCollection::new(list);

        assert_eq!(any_collection.len(), 3);
        assert!(!any_collection.is_empty());
        assert_eq!(any_collection.get(0), Some(1));
        assert_eq!(any_collection.get(1), Some(2));
        assert_eq!(any_collection.get(2), Some(3));
        assert_eq!(any_collection.get(3), None);
    }

    #[test]
    fn test_any_collection_from_vec() {
        let vec = vec![10, 20, 30];
        let any_collection = AnyCollection::new(vec);

        assert_eq!(any_collection.len(), 3);
        assert_eq!(any_collection.get(0), Some(10));
        assert_eq!(any_collection.get(1), Some(20));
        assert_eq!(any_collection.get(2), Some(30));
    }

    #[test]
    fn test_any_collection_from_array() {
        let arr = [100, 200, 300];
        let any_collection = AnyCollection::new(arr);

        assert_eq!(any_collection.len(), 3);
        assert_eq!(any_collection.get(0), Some(100));
        assert_eq!(any_collection.get(1), Some(200));
        assert_eq!(any_collection.get(2), Some(300));
    }

    #[test]
    fn test_any_collection_watcher() {
        let list = List::from(vec![1, 2, 3, 4, 5]);
        let any_collection = AnyCollection::new(list);

        let called = Rc::new(RefCell::new(false));
        let c = called.clone();
        let _guard = any_collection.watch(1..3, move |ctx| {
            *c.borrow_mut() = true;
            assert_eq!(ctx.into_value(), vec![2, 3]);
        });

        assert!(*called.borrow());
    }

    #[test]
    fn test_range_bounds_inclusive() {
        let list = List::from(vec![0, 1, 2, 3, 4]);
        let called = Rc::new(RefCell::new(false));

        let c = called.clone();
        let _guard = Collection::watch(&list, 1..=3, move |ctx| {
            *c.borrow_mut() = true;
            assert_eq!(ctx.into_value(), vec![1, 2, 3]);
        });

        assert!(*called.borrow());
    }

    #[test]
    fn test_range_bounds_from() {
        let list = List::from(vec![0, 1, 2, 3, 4]);
        let called = Rc::new(RefCell::new(false));

        let c = called.clone();
        let _guard = Collection::watch(&list, 2.., move |ctx| {
            *c.borrow_mut() = true;
            assert_eq!(ctx.into_value(), vec![2, 3, 4]);
        });

        assert!(*called.borrow());
    }

    #[test]
    fn test_range_bounds_to() {
        let list = List::from(vec![0, 1, 2, 3, 4]);
        let called = Rc::new(RefCell::new(false));

        let c = called.clone();
        let _guard = Collection::watch(&list, ..3, move |ctx| {
            *c.borrow_mut() = true;
            assert_eq!(ctx.into_value(), vec![0, 1, 2]);
        });

        assert!(*called.borrow());
    }

    #[test]
    fn test_range_bounds_full() {
        let list = List::from(vec![0, 1, 2, 3, 4]);
        let called = Rc::new(RefCell::new(false));

        let c = called.clone();
        let _guard = Collection::watch(&list, .., move |ctx| {
            *c.borrow_mut() = true;
            assert_eq!(ctx.into_value(), vec![0, 1, 2, 3, 4]);
        });

        assert!(*called.borrow());
    }

    #[test]
    fn test_out_of_bounds_range() {
        let list = List::from(vec![1, 2, 3]);
        let called = Rc::new(Cell::new(None::<bool>));

        let c = called.clone();
        let _guard = Collection::watch(&list, 10..20, move |ctx| {
            let is_empty = ctx.map(<[i32]>::is_empty).into_value();
            c.set(Some(is_empty));
        });

        // Out-of-bounds range should yield an empty snapshot
        assert_eq!(called.get(), Some(true));
    }

    #[test]
    fn test_empty_range() {
        let list = List::from(vec![1, 2, 3]);
        let called = Rc::new(Cell::new(None::<bool>));

        let c = called.clone();
        let _guard = Collection::watch(&list, 2..2, move |ctx| {
            let is_empty = ctx.map(<[i32]>::is_empty).into_value();
            c.set(Some(is_empty));
        });

        // Empty range should snapshot as an empty slice
        assert_eq!(called.get(), Some(true));
    }

    #[test]
    fn test_watcher_guard_cleanup() {
        let list = List::new();
        let notification_count = Rc::new(RefCell::new(0));

        {
            let count = notification_count.clone();
            let _guard = Collection::watch(&list, .., move |_ctx| {
                *count.borrow_mut() += 1;
            });

            // Initial snapshot
            assert_eq!(*notification_count.borrow(), 1);
            {
                let mut count_mut = notification_count.borrow_mut();
                *count_mut = 0;
            }

            list.push(1);
            assert_eq!(*notification_count.borrow(), 1);
        } // Guard is dropped here

        // After guard is dropped, no more notifications should occur
        list.push(2);
        assert_eq!(*notification_count.borrow(), 1);
    }
}