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type BlockingDeque[T any] interface {
	Deque[T]

	// Close and empty the deque.
	Close()
}

type Deque[T any] interface {
	// Place an element at the leftmost end of the deque.
	// Returns true if the element was placed in the deque.
	PushLeft(T) bool
	// Place an element at the rightmost end of the deque.
	// Returns true if the element was placed in the deque.
	PushRight(T) bool
	// Remove and return the leftmost element of the deque.
	// Returns false if the deque is empty.
	PopLeft() (T, bool)
	// Remove and return the rightmost element of the deque.
	// Returns false if the deque is empty.
	PopRight() (T, bool)
	// Return the leftmost element of the deque without removing it.
	// Returns false if the deque is empty.
	PeekLeft() (T, bool)
	// Return the rightmost element of the deque without removing it.
	// Returns false if the deque is empty.
	PeekRight() (T, bool)
	// Returns the element at the given index.
	// Returns false if the index is out of bounds.
	// The leftmost element is at index 0.
	Index(int) (T, bool)
	// Returns the number of elements in the deque.
	Len() int
	// Returns the elements in the deque from left to right.
	List() []T
}

type Queue[T any] interface {
	// Pushes [elt] onto the queue.
	// If the queue is full, the oldest element is evicted to make space.
	Push(T)
	// Pops the oldest element from the queue.
	// Returns false if the queue is empty.
	Pop() (T, bool)
	// Returns the oldest element without removing it.
	// Returns false if the queue is empty.
	Peek() (T, bool)
	// Returns the element at the given index without removing it.
	// Index(0) returns the oldest element.
	// Index(Len() - 1) returns the newest element.
	// Returns false if there is no element at that index.
	Index(int) (T, bool)
	// Returns the number of elements in the queue.
	Len() int
	// Returns the queue elements from oldest to newest.
	// This is an O(n) operation and should be used sparingly.
	List() []T
}