using System;
using System.IO;

namespace BizHawk.Client.Common
{
	/// <summary>
	/// Represents a savestate in the <seealso cref="TasStateManager"/>
	/// </summary>
	internal class StateManagerState : IDisposable
	{
		private static long _stateId;
		private readonly TasStateManager _manager;
		private readonly long _id;

		private byte[] _state;

		public int Frame { get; }

		public static StateManagerState Read(BinaryReader r, TasStateManager m)
		{
			int frame = r.ReadInt32();
			byte[] data = r.ReadBytes(r.ReadInt32());
			return new StateManagerState(m, data, frame);
		}

		public void Write(BinaryWriter w)
		{
			w.Write(Frame);
			w.Write(_state.Length);
			w.Write(_state);
		}

		public byte[] State
		{
			get
			{
				if (_state != null)
				{
					return _state;
				}

				return _manager.NdbDatabase.FetchAll(_id.ToString());
			}

			set
			{
				if (_state != null)
				{
					_state = value;
				}
				else
				{
					throw new Exception("Attempted to set a state to null.");
				}
			}
		}

		public int Length => State.Length;

	    public bool IsOnDisk => _state == null;

	    public StateManagerState(TasStateManager manager, byte[] state, int frame)
		{
			_manager = manager;
			_state = state;
			Frame = frame;

			if (_stateId > long.MaxValue - 100)
			{
				throw new InvalidOperationException();
			}

			_id = System.Threading.Interlocked.Increment(ref _stateId);
		}

		public void MoveToDisk()
		{
			if (IsOnDisk)
			{
				return;
			}

			_manager.NdbDatabase.Store(_id.ToString(), _state, 0, _state.Length);
			_state = null;
		}

		public void MoveToRAM()
		{
			if (!IsOnDisk)
			{
				return;
			}

			string key = _id.ToString();
			_state = _manager.NdbDatabase.FetchAll(key);
			_manager.NdbDatabase.Release(key);
		}

		public void Dispose()
		{
			if (!IsOnDisk)
			{
				return;
			}

			_manager.NdbDatabase.Release(_id.ToString());
		}
	}
}