//#define ASTAR_NO_POOLING //@SHOWINEDITOR Disable pooling for some reason. Could be debugging or just for measuring the difference.

using System.Collections.Generic;

namespace Pathfinding.Util {
	/// <summary>
	/// Lightweight Stack Pool.
	/// Handy class for pooling stacks of type T.
	///
	/// Usage:
	/// - Claim a new stack using <code> Stack<SomeClass> foo = StackPool<SomeClass>.Claim (); </code>
	/// - Use it and do stuff with it
	/// - Release it with <code> StackPool<SomeClass>.Release (foo); </code>
	///
	/// You do not need to clear the stack before releasing it.
	/// After you have released a stack, you should never use it again.
	///
	/// Warning: This class is not thread safe
	///
	/// \since Version 3.2
	/// See: Pathfinding.Util.ListPool
	/// </summary>
	public static class StackPool<T> {
		/// <summary>Internal pool</summary>
		static readonly List<Stack<T> > pool;

		/// <summary>Static constructor</summary>
		static StackPool () {
			pool = new List<Stack<T> >();
		}

		/// <summary>
		/// Claim a stack.
		/// Returns a pooled stack if any are in the pool.
		/// Otherwise it creates a new one.
		/// After usage, this stack should be released using the Release function (though not strictly necessary).
		/// </summary>
		public static Stack<T> Claim () {
#if ASTAR_NO_POOLING
			return new Stack<T>();
#else
			lock (pool) {
				if (pool.Count > 0) {
					Stack<T> ls = pool[pool.Count-1];
					pool.RemoveAt(pool.Count-1);
					return ls;
				}
			}

			return new Stack<T>();
#endif
		}

		/// <summary>
		/// Makes sure the pool contains at least count pooled items.
		/// This is good if you want to do all allocations at start.
		/// </summary>
		public static void Warmup (int count) {
			var tmp = new Stack<T>[count];

			for (int i = 0; i < count; i++) tmp[i] = Claim();
			for (int i = 0; i < count; i++) Release(tmp[i]);
		}

		/// <summary>
		/// Releases a stack.
		/// After the stack has been released it should not be used anymore.
		/// Releasing a stack twice will cause an error.
		/// </summary>
		public static void Release (Stack<T> stack) {
#if !ASTAR_NO_POOLING
			stack.Clear();

			lock (pool) {
				for (int i = 0; i < pool.Count; i++)
					if (pool[i] == stack) UnityEngine.Debug.LogError("The Stack is released even though it is inside the pool");

				pool.Add(stack);
			}
#endif
		}

		/// <summary>
		/// Clears all pooled stacks of this type.
		/// This is an O(n) operation, where n is the number of pooled stacks
		/// </summary>
		public static void Clear () {
			lock (pool) {
				pool.Clear();
			}
		}

		/// <summary>Number of stacks of this type in the pool</summary>
		public static int GetSize () {
			return pool.Count;
		}
	}
}