// Copyright (c) 2014-2015 Robert Rouhani <robert.rouhani@gmail.com> and other contributors (see CONTRIBUTORS file).
// Licensed under the MIT License - https://raw.github.com/Robmaister/SharpNav/master/LICENSE

using System;
using SharpNav.Geometry;
using SharpNav.Pathfinding;

#if MONOGAME
using Vector3 = Microsoft.Xna.Framework.Vector3;
#elif OPENTK
using Vector3 = OpenTK.Vector3;
#elif SHARPDX
using Vector3 = SharpDX.Vector3;
#endif

namespace SharpNav.Crowds
{
	public class PathQueue
	{
		#region Fields

		public const byte Invalid = 0;
		private const int MaxQueue = 8;

		private PathQuery[] queue; //size = MAX_QUEUE
		private int nextHandle = 1;
		private int maxPathSize;
		private int queueHead;
		private NavMeshQuery navquery;

		#endregion

		#region Constructors

		public PathQueue(int maxPathSize, int maxSearchNodeCount, ref TiledNavMesh nav)
		{
			this.navquery = new NavMeshQuery(nav, maxSearchNodeCount);

			this.maxPathSize = maxPathSize;
			this.queue = new PathQuery[MaxQueue];
			for (int i = 0; i < MaxQueue; i++)
			{
				queue[i].Reference = Invalid;
				queue[i].Path = new int[maxPathSize];
			}

			this.queueHead = 0;
		}

		#endregion

		#region Methods

		public void Update(int maxIters)
		{
			const int MAX_KEEP_ALIVE = 2; //in update ticks

			//update path request until there is nothing left to update
			//or up to maxIters pathfinder iterations have been consumed
			int iterCount = maxIters;

			for (int i = 0; i < MaxQueue; i++)
			{
				PathQuery q = queue[queueHead % MaxQueue];

				//skip inactive requests
				if (q.Reference == Invalid)
				{
					queueHead++;
					continue;
				}

				//handle completed request
				if (q.status == Status.Success || q.status == Status.Failure)
				{
					q.KeepAlive++;
					if (q.KeepAlive > MAX_KEEP_ALIVE)
					{
						q.Reference = Invalid;
						q.status = 0;
					}

					queueHead++;
					continue;
				}

				//handle query start
				if (q.status == 0)
				{
					q.status = navquery.InitSlicedFindPath(new NavPoint(q.StartRef, q.StartPos), new NavPoint(q.EndRef, q.EndPos)).ToStatus();
				}

				//handle query in progress
				if (q.status == Status.InProgress)
				{
					int iters = 0;
					q.status = navquery.UpdateSlicedFindPath(iterCount, ref iters).ToStatus();

					iterCount -= iters;
				}

				if (q.status == Status.Success)
				{
					q.status = navquery.FinalizeSlicedFindPath(q.Path, ref q.PathCount, maxPathSize).ToStatus();
				}

				if (iterCount <= 0)
					break;

				queueHead++;
			}
		}

		/// <summary>
		/// Request an empty slot in the path queue
		/// </summary>
		/// <param name="startRef">Start polygon reference</param>
		/// <param name="endRef">End polygon reference</param>
		/// <param name="startPos">Start position</param>
		/// <param name="endPos">End position</param>
		/// <returns>Index of empty slot</returns>
		public int Request(int startRef, int endRef, Vector3 startPos, Vector3 endPos)
		{
			//find empty slot
			int slot = -1;
			for (int i = 0; i < MaxQueue; i++)
			{
				if (queue[i].Reference == Invalid)
				{
					slot = i;
					break;
				}
			}

			//could not find slot
			if (slot == -1)
				return Invalid;

			int reference = nextHandle++;
			if (nextHandle == Invalid) nextHandle++;

			PathQuery q = queue[slot];
			q.Reference = reference;
			q.StartPos = startPos;
			q.StartRef = startRef;
			q.EndPos = endPos;
			q.EndRef = endRef;

			q.status = 0;
			q.PathCount = 0;
			q.KeepAlive = 0;

			queue[slot] = q;

			return reference;
		}

		/// <summary>
		/// Get the status of the polygon in the path queue
		/// </summary>
		/// <param name="reference">The polygon reference</param>
		/// <returns>The status in the queue</returns>
		public Status GetRequestStatus(int reference)
		{
			for (int i = 0; i < MaxQueue; i++)
			{
				if (queue[i].Reference == reference)
					return queue[i].status;
			}

			return Status.Failure;
		}

		public bool GetPathResult(int reference, int[] path, ref int pathSize, int maxPath)
		{
			for (int i = 0; i < MaxQueue; i++)
			{
				if (queue[i].Reference == reference)
				{
					PathQuery q = queue[i];
					
					//free request for reuse
					q.Reference = Invalid;
					q.status = 0;
					
					//copy path
					int n = Math.Min(q.PathCount, maxPath);
					q.Path.CopyTo(path, 0);
					pathSize = n;

					queue[i] = q;

					return true;
				}
			}

			return false;
		}

		#endregion

		private struct PathQuery
		{
			public int Reference;
			
			//path find start and end location
			public Vector3 StartPos, EndPos;
			public int StartRef, EndRef;

			//result
			public int[] Path;
			public int PathCount;

			//state
			public Status status;
			public int KeepAlive;
		}
	}
}