using System.Collections.Generic;
using Microsoft.Xna.Framework.Graphics;

namespace Foo
{
    public static class StateStack
    {
        static readonly Pool<ManagedRenderState> Pool = new Pool<ManagedRenderState>();
        static readonly Stack<ManagedRenderState> Stack = new Stack<ManagedRenderState>();

        public static ManagedRenderState PushState(this GraphicsDevice device)
        {
            var rs = Pool.Take();
            if (Stack.Count == 0) rs.Reset(device);
            else rs.Reset(Stack.Peek());
            Stack.Push(rs);
            return rs;
        }

        public static void PopState(this GraphicsDevice device)
        {
            var poppedRs = Stack.Pop();
            poppedRs.Refresh(Stack.Peek());
            poppedRs.Commit(device);
            Pool.Return(poppedRs);
        }

        public static ManagedRenderState PeekState(this GraphicsDevice device)
        {
            return Stack.Peek();
        }

        public static void ResetState(this GraphicsDevice device)
        {
            Stack.Peek().Reset(device);
        }

        public static void CommitState(this GraphicsDevice device)
        {
            Stack.Peek().Commit(device);
        }
    }

    public class Pool<T> where T : class, new()
    {
        readonly Stack<T> stack;

        public Pool() : this(0) { }
        public Pool(int size)
        {
            stack = new Stack<T>(size);

            for (int i = 0; i < size; i++)
                stack.Push(new T());
        }

        public T Take()
        {
            return stack.Count > 0 ? stack.Pop() : new T();
        }

        public void Return(T item)
        {
            stack.Push(item);
        }
    }
}