//#define ASTAR_POOL_DEBUG //@SHOWINEDITOR Enables debugging of path pooling. Will log warnings and info messages about paths not beeing pooled correctly.

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using Unity.Mathematics;

namespace Pathfinding {
	/// <summary>Base class for all path types</summary>
	[Unity.Burst.BurstCompile]
	public abstract class Path : IPathInternals {
#if ASTAR_POOL_DEBUG
		private string pathTraceInfo = "";
		private List<string> claimInfo = new List<string>();
		~Path() {
			Debug.Log("Destroying " + GetType().Name + " instance");
			if (claimed.Count > 0) {
				Debug.LogWarning("Pool Is Leaking. See list of claims:\n" +
					"Each message below will list what objects are currently claiming the path." +
					" These objects have removed their reference to the path object but has not called .Release on it (which is bad).\n" + pathTraceInfo+"\n");
				for (int i = 0; i < claimed.Count; i++) {
					Debug.LogWarning("- Claim "+ (i+1) + " is by a " + claimed[i].GetType().Name + "\n"+claimInfo[i]);
				}
			} else {
				Debug.Log("Some scripts are not using pooling.\n" + pathTraceInfo + "\n");
			}
		}
#endif

		/// <summary>Data for the thread calculating this path</summary>
		protected PathHandler pathHandler;

		/// <summary>
		/// Callback to call when the path is complete.
		/// This is usually sent to the Seeker component which post processes the path and then calls a callback to the script which requested the path
		/// </summary>
		public OnPathDelegate callback;

		/// <summary>
		/// Immediate callback to call when the path is complete.
		/// Warning: This may be called from a separate thread. Usually you do not want to use this one.
		///
		/// See: callback
		/// </summary>
		public OnPathDelegate immediateCallback;

		/// <summary>Returns the state of the path in the pathfinding pipeline</summary>
		public PathState PipelineState { get; private set; }

		/// <summary>
		/// Provides additional traversal information to a path request.
		/// See: traversal_provider (view in online documentation for working links)
		/// </summary>
		public ITraversalProvider traversalProvider;


		/// <summary>Backing field for <see cref="CompleteState"/></summary>
		protected PathCompleteState completeState;

		/// <summary>
		/// Current state of the path.
		/// Bug: This may currently be set to Complete before the path has actually been fully calculated. In particular the vectorPath and path lists may not have been fully constructed.
		/// This can lead to race conditions when using multithreading. Try to avoid using this method to check for if the path is calculated right now, use <see cref="IsDone"/> instead.
		/// </summary>
		public PathCompleteState CompleteState {
			get { return completeState; }
			protected set {
				// Locking is used to avoid multithreading race conditions in which, for example,
				// the error state is set on the main thread to cancel the path,
				// and then a pathfinding thread marks the path as completed,
				// which would replace the error state (if a lock and check would not have been used).
				// We lock on the path object itself. Users should rarely have to use the path object
				// themselves for anything before the path is calculated, much less take a lock on it.
				lock (this) {
					// Once the path is put in the error state, it cannot be set to any other state
					if (completeState != PathCompleteState.Error) completeState = value;
				}
			}
		}

		/// <summary>
		/// If the path failed, this is true.
		/// See: <see cref="errorLog"/>
		/// See: This is equivalent to checking path.CompleteState == PathCompleteState.Error
		/// </summary>
		public bool error { get { return CompleteState == PathCompleteState.Error; } }

		/// <summary>
		/// Additional info on why a path failed.
		/// See: <see cref="AstarPath.logPathResults"/>
		/// </summary>
		public string errorLog { get; private set; }

		/// <summary>
		/// Holds the path as a <see cref="GraphNode"/> list.
		///
		/// These are all nodes that the path traversed, as calculated by the pathfinding algorithm.
		/// This may not be the same nodes as the post processed path traverses.
		///
		/// See: <see cref="vectorPath"/>
		/// </summary>
		public List<GraphNode> path;

		/// <summary>
		/// Holds the (possibly post-processed) path as a Vector3 list.
		///
		/// This list may be modified by path modifiers to be smoother or simpler compared to the raw path generated by the pathfinding algorithm.
		///
		/// See: modifiers (view in online documentation for working links)
		/// See: <see cref="path"/>
		/// </summary>
		public List<Vector3> vectorPath;

		/// <summary>How long it took to calculate this path in milliseconds</summary>
		public float duration;

		/// <summary>Number of nodes this path has searched</summary>
		public int searchedNodes { get; protected set; }

		/// <summary>
		/// True if the path is currently pooled.
		/// Do not set this value. Only read. It is used internally.
		///
		/// See: <see cref="PathPool"/>
		/// </summary>
		bool IPathInternals.Pooled { get; set; }

		/// <summary>
		/// True if the Reset function has been called.
		/// Used to alert users when they are doing something wrong.
		/// </summary>
		protected bool hasBeenReset;

		/// <summary>Constraint for how to search for nodes</summary>
		public NNConstraint nnConstraint = PathNNConstraint.Walkable;

		/// <summary>Determines which heuristic to use</summary>
		public Heuristic heuristic;

		/// <summary>
		/// Scale of the heuristic values.
		/// See: AstarPath.heuristicScale
		/// </summary>
		public float heuristicScale = 1F;

		/// <summary>ID of this path. Used to distinguish between different paths</summary>
		public ushort pathID { get; private set; }

		/// <summary>Target to use for H score calculation.</summary>
		protected GraphNode hTargetNode;

		/// <summary>
		/// Target to use for H score calculations.
		/// See: https://en.wikipedia.org/wiki/Admissible_heuristic
		/// </summary>
		protected HeuristicObjective heuristicObjective;

		internal ref HeuristicObjective heuristicObjectiveInternal => ref heuristicObjective;

		/// <summary>
		/// Which graph tags are traversable.
		/// This is a bitmask so -1 = all bits set = all tags traversable.
		/// For example, to set bit 5 to true, you would do
		/// <code> myPath.enabledTags |= 1 << 5; </code>
		/// To set it to false, you would do
		/// <code> myPath.enabledTags &= ~(1 << 5); </code>
		///
		/// The Seeker has a popup field where you can set which tags to use.
		/// Note: If you are using a Seeker. The Seeker will set this value to what is set in the inspector field on StartPath.
		/// So you need to change the Seeker value via script, not set this value if you want to change it via script.
		///
		/// See: <see cref="CanTraverse"/>
		/// See: bitmasks (view in online documentation for working links)
		/// </summary>
		public int enabledTags = -1;

		/// <summary>List of zeroes to use as default tag penalties</summary>
		internal static readonly int[] ZeroTagPenalties = new int[32];

		/// <summary>
		/// The tag penalties that are actually used.
		/// See: <see cref="tagPenalties"/>
		/// </summary>
		protected int[] internalTagPenalties;

		/// <summary>
		/// Penalties for each tag.
		/// Tag 0 which is the default tag, will get a penalty of tagPenalties[0].
		/// These should only be non-negative values since the A* algorithm cannot handle negative penalties.
		///
		/// When assigning an array to this property it must have a length of 32.
		///
		/// Note: Setting this to null will make all tag penalties be treated as if they are zero.
		///
		/// Note: If you are using a Seeker. The Seeker will set this value to what is set in the inspector field when you call seeker.StartPath.
		/// So you need to change the Seeker's value via script, not set this value.
		///
		/// See: <see cref="Seeker.tagPenalties"/>
		/// </summary>
		public int[] tagPenalties {
			get {
				return internalTagPenalties == ZeroTagPenalties ? null : internalTagPenalties;
			}
			set {
				if (value == null) {
					internalTagPenalties = ZeroTagPenalties;
				} else {
					if (value.Length != 32) throw new System.ArgumentException("tagPenalties must have a length of 32");

					internalTagPenalties = value;
				}
			}
		}

		/// <summary>Copies the given settings into this path</summary>
		public void UseSettings (PathRequestSettings settings) {
			nnConstraint.graphMask = settings.graphMask;
			traversalProvider = settings.traversalProvider;
			enabledTags = settings.traversableTags;
			tagPenalties = settings.tagPenalties;
		}

		/// <summary>
		/// Total Length of the path.
		/// Calculates the total length of the <see cref="vectorPath"/>.
		/// Cache this rather than call this function every time since it will calculate the length every time, not just return a cached value.
		/// Returns: Total length of <see cref="vectorPath"/>, if <see cref="vectorPath"/> is null positive infinity is returned.
		/// </summary>
		public float GetTotalLength () {
			if (vectorPath == null) return float.PositiveInfinity;
			float tot = 0;
			for (int i = 0; i < vectorPath.Count-1; i++) tot += Vector3.Distance(vectorPath[i], vectorPath[i+1]);
			return tot;
		}

		/// <summary>
		/// Waits until this path has been calculated and returned.
		/// Allows for very easy scripting.
		///
		/// <code>
		/// IEnumerator Start () {
		///     // Get the seeker component attached to this GameObject
		///     var seeker = GetComponent<Seeker>();
		///
		///     var path = seeker.StartPath(transform.position, transform.position + Vector3.forward * 10, null);
		///     // Wait... This may take a frame or two depending on how complex the path is
		///     // The rest of the game will continue to run while we wait
		///     yield return StartCoroutine(path.WaitForPath());
		///     // The path is calculated now
		///
		///     // Draw the path in the scene view for 10 seconds
		///     for (int i = 0; i < path.vectorPath.Count - 1; i++) {
		///         Debug.DrawLine(path.vectorPath[i], path.vectorPath[i+1], Color.red, 10);
		///     }
		/// }
		/// </code>
		///
		/// Note: Do not confuse this with AstarPath.BlockUntilCalculated. This one will wait using yield until it has been calculated
		/// while AstarPath.BlockUntilCalculated will halt all operations until the path has been calculated.
		///
		/// Throws: System.InvalidOperationException if the path is not started. Send the path to <see cref="Seeker.StartPath(Path)"/> or <see cref="AstarPath.StartPath"/> before calling this function.
		///
		/// See: <see cref="BlockUntilCalculated"/>
		/// See: https://docs.unity3d.com/Manual/Coroutines.html
		/// </summary>
		public IEnumerator WaitForPath () {
			if (PipelineState == PathState.Created) throw new System.InvalidOperationException("This path has not been started yet");

			while (PipelineState != PathState.Returned) yield return null;
		}

		/// <summary>
		/// Blocks until this path has been calculated and returned.
		/// Normally it takes a few frames for a path to be calculated and returned.
		/// This function will ensure that the path will be calculated when this function returns
		/// and that the callback for that path has been called.
		///
		/// Use this function only if you really need to.
		/// There is a point to spreading path calculations out over several frames.
		/// It smoothes out the framerate and makes sure requesting a large
		/// number of paths at the same time does not cause lag.
		///
		/// Note: Graph updates and other callbacks might get called during the execution of this function.
		///
		/// <code>
		/// var path = seeker.StartPath(transform.position, transform.position + Vector3.forward * 10, OnPathComplete);
		/// path.BlockUntilCalculated();
		///
		/// // The path is calculated now, and the OnPathComplete callback has been called
		/// </code>
		///
		/// See: This is equivalent to calling <see cref="AstarPath.BlockUntilCalculated(Path)"/>
		/// See: <see cref="WaitForPath"/>
		/// </summary>
		public void BlockUntilCalculated () {
			AstarPath.BlockUntilCalculated(this);
		}

		/// <summary>
		/// True if this path node might be worth exploring.
		///
		/// This is used during a search to filter out nodes which have already been fully searched.
		/// </summary>
		public bool ShouldConsiderPathNode (uint pathNodeIndex) {
			var node = pathHandler.pathNodes[pathNodeIndex];
			return node.pathID != pathID || node.heapIndex != BinaryHeap.NotInHeap;
		}

		public static readonly Unity.Profiling.ProfilerMarker MarkerOpenCandidateConnectionsToEnd = new Unity.Profiling.ProfilerMarker("OpenCandidateConnectionsToEnd");
		public static readonly Unity.Profiling.ProfilerMarker MarkerTrace = new Unity.Profiling.ProfilerMarker("Trace");

		/// <summary>
		/// Open a connection to the temporary end node if necessary.
		///
		/// The start and end nodes are temporary nodes and are not included in the graph itself.
		/// This means that we need to handle connections to and from those nodes as a special case.
		/// This function will open a connection from the given node to the end node, if such a connection exists.
		///
		/// It is called from the <see cref="GraphNode.Open"/> function.
		/// </summary>
		/// <param name="position">Position of the path node that is being opened. This may be different from the node's position if \reflink{PathNode.fractionAlongEdge} is being used.</param>
		/// <param name="parentPathNode">Index of the path node that is being opened. This is often the same as parentNodeIndex, but may be different if the node has multiple path node variants.</param>
		/// <param name="parentNodeIndex">Index of the node that is being opened.</param>
		/// <param name="parentG">G score of the parent node. The cost to reach the parent node from the start of the path.</param>
		public void OpenCandidateConnectionsToEndNode (Int3 position, uint parentPathNode, uint parentNodeIndex, uint parentG) {
			// True iff this node has a connection to one or more temporary nodes
			if (pathHandler.pathNodes[parentNodeIndex].flag1) {
				MarkerOpenCandidateConnectionsToEnd.Begin();
				for (uint i = 0; i < pathHandler.numTemporaryNodes; i++) {
					var nodeIndex = pathHandler.temporaryNodeStartIndex + i;
					ref var node = ref pathHandler.GetTemporaryNode(nodeIndex);
					if (node.type == TemporaryNodeType.End && node.associatedNode == parentNodeIndex) {
						var cost = (uint)(position - node.position).costMagnitude;
						OpenCandidateConnection(parentPathNode, nodeIndex, parentG, cost, 0, node.position);
					}
				}
				MarkerOpenCandidateConnectionsToEnd.End();
			}
		}

		/// <summary>
		/// Opens a connection between two nodes during the A* search.
		///
		/// When a node is "opened" (i.e. searched by the A* algorithm), it will open connections to all its neighbours.
		/// This function checks those connections to see if passing through the node to its neighbour is the best way to reach the neighbour that we have seen so far,
		/// and if so, it will push the neighbour onto the search heap.
		/// </summary>
		/// <param name="parentPathNode">The node that is being opened.</param>
		/// <param name="targetPathNode">A neighbour of the parent that is being considered.</param>
		/// <param name="parentG">The G value of the parent node. This is the cost to reach the parent node from the start of the path.</param>
		/// <param name="connectionCost">The cost of moving from the parent node to the target node.</param>
		/// <param name="fractionAlongEdge">Internal value used by the TriangleMeshNode to store where on the shared edge between the nodes we say we cross over.</param>
		/// <param name="targetNodePosition">The position of the target node. This is used by the heuristic to estimate the cost to reach the end node.</param>
		public void OpenCandidateConnection (uint parentPathNode, uint targetPathNode, uint parentG, uint connectionCost, uint fractionAlongEdge, Int3 targetNodePosition) {
			if (!ShouldConsiderPathNode(targetPathNode)) {
				// We have seen this node before, but it is not in the heap.
				// This means we have already processed it and it must have had a better F score than this node (or the heuristic was not admissable).
				// We can safely discard this connection.
				return;
			}

			uint candidateEnteringCost;
			uint targetNodeIndex;
			if (pathHandler.IsTemporaryNode(targetPathNode)) {
				candidateEnteringCost = 0;
				targetNodeIndex = 0;
			} else {
				var targetNode = pathHandler.GetNode(targetPathNode);
				candidateEnteringCost = GetTraversalCost(targetNode);
				targetNodeIndex = targetNode.NodeIndex;
			}
			var candidateG = parentG + connectionCost + candidateEnteringCost;
			var pars = new OpenCandidateParams {
				pathID = pathID,
				parentPathNode = parentPathNode,
				targetPathNode = targetPathNode,
				targetNodeIndex = targetNodeIndex,
				candidateG = candidateG,
				fractionAlongEdge = fractionAlongEdge,
				targetNodePosition = (int3)targetNodePosition,
				pathNodes = pathHandler.pathNodes,
			};
			OpenCandidateConnectionBurst(ref pars,
				ref pathHandler.heap, ref heuristicObjective
				);
		}

		/// <summary>
		/// Parameters to OpenCandidateConnectionBurst.
		/// Using a struct instead of passing the parameters as separate arguments is significantly faster.
		/// </summary>
		public struct OpenCandidateParams {
			public Util.UnsafeSpan<PathNode> pathNodes;
			public uint parentPathNode;
			public uint targetPathNode;
			public uint targetNodeIndex;
			public uint candidateG;
			public uint fractionAlongEdge;
			public int3 targetNodePosition;
			public ushort pathID;
		}

		/// <summary>
		/// Burst-compiled internal implementation of OpenCandidateConnection.
		/// Compiling it using burst provides a decent 25% speedup.
		/// The function itself is much faster, but the overhead of calling it from C# is quite significant.
		/// </summary>
		[Unity.Burst.BurstCompile]
		public static void OpenCandidateConnectionBurst (ref OpenCandidateParams pars, ref BinaryHeap heap, ref HeuristicObjective heuristicObjective) {
			var pathID = pars.pathID;
			var parentPathNode = pars.parentPathNode;
			var targetPathNode = pars.targetPathNode;
			var candidateG = pars.candidateG;
			var fractionAlongEdge = pars.fractionAlongEdge;
			var targetNodePosition = pars.targetNodePosition;
			var pathNodes = pars.pathNodes;
			ref var target = ref pathNodes[targetPathNode];
			if (target.pathID != pathID) {
				// This is the first time we have seen this node. This connection must be optimal.
				target.fractionAlongEdge = fractionAlongEdge;
				target.pathID = pathID;
				target.parentIndex = parentPathNode;
				var candidateH = (uint)heuristicObjective.Calculate(targetNodePosition, pars.targetNodeIndex);
				var candidateF = candidateG + candidateH;
				heap.Add(pathNodes, targetPathNode, candidateG, candidateF);
			} else {
				// Note: Before this method is called, a check is done for the case target.pathID==pathID && heapIndex == NotInHeap,
				// so we know target.heapIndex != NotInHeap here.

				// We have seen this node before and it is in the heap.
				// Now we check if this path to the target node is better than the previous one.

				var targetG = heap.GetG(target.heapIndex);
				// The previous F score of the node
				var targetF = heap.GetF(target.heapIndex);
				var targetH = targetF - targetG;
				uint candidateH;

				if (target.fractionAlongEdge != fractionAlongEdge) {
					// Different fractionAlongEdge, this means that targetNodePosition may have changed
					// and therefore the heuristic may also have changed.
					candidateH = (uint)heuristicObjective.Calculate(targetNodePosition, pars.targetNodeIndex);
				} else {
					// If fractionAlongEdge has not changed, then we assume the heuristic is also the same.
					// This saves us from having to calculate it again.
					candidateH = targetH;
				}

				var candidateF = candidateG + candidateH;
				if (candidateF < targetF) {
					// This connection is better than the previous one.
					target.fractionAlongEdge = fractionAlongEdge;
					target.parentIndex = parentPathNode;
					heap.Add(pathNodes, targetPathNode, candidateG, candidateF);
				} else {
					// This connection is not better than the previous one.
					// We can safely discard this connection.
				}
			}
		}

		/// <summary>Returns penalty for the given tag.</summary>
		/// <param name="tag">A value between 0 (inclusive) and 32 (exclusive).</param>
		public uint GetTagPenalty (int tag) {
			return (uint)internalTagPenalties[tag];
		}

		/// <summary>
		/// Returns if the node can be traversed.
		/// This by default equals to if the node is walkable and if the node's tag is included in <see cref="enabledTags"/>.
		///
		/// See: <see cref="traversalProvider"/>
		/// </summary>
		public bool CanTraverse (GraphNode node) {
			// Use traversal provider if set, otherwise fall back on default behaviour
			// This method is hot, but this branch is extremely well predicted so it
			// doesn't affect performance much (profiling indicates it is just above
			// the noise level, somewhere around 0%-0.3%)
			if (traversalProvider != null)
				return traversalProvider.CanTraverse(this, node);

			// Manually inlined code from DefaultITraversalProvider
			unchecked { return node.Walkable && (enabledTags >> (int)node.Tag & 0x1) != 0; }
		}


		/// <summary>
		/// Returns if the path can traverse a link between from and to and if to can be traversed itself.
		/// This by default equals to if the to is walkable and if the to's tag is included in <see cref="enabledTags"/>.
		///
		/// See: <see cref="traversalProvider"/>
		/// </summary>
		public bool CanTraverse (GraphNode from, GraphNode to) {
			// Use traversal provider if set, otherwise fall back on default behaviour
			// This method is hot, but this branch is extremely well predicted so it
			// doesn't affect performance much (profiling indicates it is just above
			// the noise level, somewhere around 0%-0.3%)
			if (traversalProvider != null)
				return traversalProvider.CanTraverse(this, from, to);

			// Manually inlined code from DefaultITraversalProvider
			unchecked { return to.Walkable && (enabledTags >> (int)to.Tag & 0x1) != 0; }
		}

		/// <summary>Returns the cost of traversing the given node</summary>
		public uint GetTraversalCost (GraphNode node) {
#if ASTAR_NO_TRAVERSAL_COST
			return 0;
#else
			// Use traversal provider if set, otherwise fall back on default behaviour
			if (traversalProvider != null)
				return traversalProvider.GetTraversalCost(this, node);

			unchecked { return GetTagPenalty((int)node.Tag) + node.Penalty; }
#endif
		}

		/// <summary>
		/// True if this path is done calculating.
		///
		/// Note: The callback for the path might not have been called yet.
		///
		/// See: <see cref="Seeker.IsDone"/> which also takes into account if the path callback has been called and had modifiers applied.
		/// </summary>
		public bool IsDone () {
			return PipelineState > PathState.Processing;
		}

		/// <summary>Threadsafe increment of the state</summary>
		void IPathInternals.AdvanceState (PathState s) {
			lock (this) {
				PipelineState = (PathState)System.Math.Max((int)PipelineState, (int)s);
			}
		}

		/// <summary>Causes the path to fail and sets <see cref="errorLog"/> to msg</summary>
		public void FailWithError (string msg) {
			Error();
			if (errorLog != "") errorLog += "\n" + msg;
			else errorLog = msg;
		}

		/// <summary>
		/// Aborts the path because of an error.
		/// Sets <see cref="error"/> to true.
		/// This function is called when an error has occurred (e.g a valid path could not be found).
		/// See: <see cref="FailWithError"/>
		/// </summary>
		public void Error () {
			CompleteState = PathCompleteState.Error;
		}

		/// <summary>
		/// Performs some error checking.
		/// Makes sure the user isn't using old code paths and that no major errors have been made.
		///
		/// Causes the path to fail if any errors are found.
		/// </summary>
		private void ErrorCheck () {
			if (!hasBeenReset) FailWithError("Please use the static Construct function for creating paths, do not use the normal constructors.");
			if (((IPathInternals)this).Pooled) FailWithError("The path is currently in a path pool. Are you sending the path for calculation twice?");
			if (pathHandler == null) FailWithError("Field pathHandler is not set. Please report this bug.");
			if (PipelineState > PathState.Processing) FailWithError("This path has already been processed. Do not request a path with the same path object twice.");
		}

		/// <summary>
		/// Called when the path enters the pool.
		/// This method should release e.g pooled lists and other pooled resources
		/// The base version of this method releases vectorPath and path lists.
		/// Reset() will be called after this function, not before.
		/// Warning: Do not call this function manually.
		/// </summary>
		protected virtual void OnEnterPool () {
			if (vectorPath != null) Pathfinding.Util.ListPool<Vector3>.Release(ref vectorPath);
			if (path != null) Pathfinding.Util.ListPool<GraphNode>.Release(ref path);
			// Clear the callback to remove a potential memory leak
			// while the path is in the pool (which it could be for a long time).
			callback = null;
			immediateCallback = null;
			traversalProvider = null;
			pathHandler = null;
		}

		/// <summary>
		/// Reset all values to their default values.
		///
		/// Note: All inheriting path types (e.g ConstantPath, RandomPath, etc.) which declare their own variables need to
		/// override this function, resetting ALL their variables to enable pooling of paths.
		/// If this is not done, trying to use that path type for pooling could result in weird behaviour.
		/// The best way is to reset to default values the variables declared in the extended path type and then
		/// call the base function in inheriting types with base.Reset().
		/// </summary>
		protected virtual void Reset () {
#if ASTAR_POOL_DEBUG
			pathTraceInfo = "This path was got from the pool or created from here (stacktrace):\n";
			pathTraceInfo += System.Environment.StackTrace;
#endif

			if (System.Object.ReferenceEquals(AstarPath.active, null))
				throw new System.NullReferenceException("No AstarPath object found in the scene. " +
					"Make sure there is one or do not create paths in Awake");

			hasBeenReset = true;
			PipelineState = (int)PathState.Created;
			releasedNotSilent = false;

			pathHandler = null;
			callback = null;
			immediateCallback = null;
			errorLog = "";
			completeState = PathCompleteState.NotCalculated;

			path = Pathfinding.Util.ListPool<GraphNode>.Claim();
			vectorPath = Pathfinding.Util.ListPool<Vector3>.Claim();

			duration = 0;
			searchedNodes = 0;

			nnConstraint = PathNNConstraint.Walkable;

			heuristic = AstarPath.active.heuristic;
			heuristicScale = AstarPath.active.heuristicScale;

			enabledTags = -1;
			tagPenalties = null;

			pathID = AstarPath.active.GetNextPathID();

			hTargetNode = null;

			traversalProvider = null;
		}

		/// <summary>List of claims on this path with reference objects</summary>
		private List<System.Object> claimed = new List<System.Object>();

		/// <summary>
		/// True if the path has been released with a non-silent call yet.
		///
		/// See: Release
		/// See: Claim
		/// </summary>
		private bool releasedNotSilent;

		/// <summary>
		/// Increase the reference count on this path by 1 (for pooling).
		/// A claim on a path will ensure that it is not pooled.
		/// If you are using a path, you will want to claim it when you first get it and then release it when you will not
		/// use it anymore. When there are no claims on the path, it will be reset and put in a pool.
		///
		/// This is essentially just reference counting.
		///
		/// The object passed to this method is merely used as a way to more easily detect when pooling is not done correctly.
		/// It can be any object, when used from a movement script you can just pass "this". This class will throw an exception
		/// if you try to call Claim on the same path twice with the same object (which is usually not what you want) or
		/// if you try to call Release with an object that has not been used in a Claim call for that path.
		/// The object passed to the Claim method needs to be the same as the one you pass to this method.
		///
		/// See: Release
		/// See: Pool
		/// See: pooling (view in online documentation for working links)
		/// See: https://en.wikipedia.org/wiki/Reference_counting
		/// </summary>
		public void Claim (System.Object o) {
			if (System.Object.ReferenceEquals(o, null)) throw new System.ArgumentNullException("o");

			for (int i = 0; i < claimed.Count; i++) {
				// Need to use ReferenceEquals because it might be called from another thread
				if (System.Object.ReferenceEquals(claimed[i], o))
					throw new System.ArgumentException("You have already claimed the path with that object ("+o+"). Are you claiming the path with the same object twice?");
			}

			claimed.Add(o);
#if ASTAR_POOL_DEBUG
			claimInfo.Add(o.ToString() + "\n\nClaimed from:\n" + System.Environment.StackTrace);
#endif
		}

		/// <summary>
		/// Reduces the reference count on the path by 1 (pooling).
		/// Removes the claim on the path by the specified object.
		/// When the reference count reaches zero, the path will be pooled, all variables will be cleared and the path will be put in a pool to be used again.
		/// This is great for performance since fewer allocations are made.
		///
		/// If the silent parameter is true, this method will remove the claim by the specified object
		/// but the path will not be pooled if the claim count reches zero unless a non-silent Release call has been made earlier.
		/// This is used by the internal pathfinding components such as Seeker and AstarPath so that they will not cause paths to be pooled.
		/// This enables users to skip the claim/release calls if they want without the path being pooled by the Seeker or AstarPath and
		/// thus causing strange bugs.
		///
		/// See: Claim
		/// See: PathPool
		/// </summary>
		public void Release (System.Object o, bool silent = false) {
			if (o == null) throw new System.ArgumentNullException("o");

			for (int i = 0; i < claimed.Count; i++) {
				// Need to use ReferenceEquals because it might be called from another thread
				if (System.Object.ReferenceEquals(claimed[i], o)) {
					claimed.RemoveAt(i);
#if ASTAR_POOL_DEBUG
					claimInfo.RemoveAt(i);
#endif
					if (!silent) {
						releasedNotSilent = true;
					}

					if (claimed.Count == 0 && releasedNotSilent) {
						PathPool.Pool(this);
					}
					return;
				}
			}
			if (claimed.Count == 0) {
				throw new System.ArgumentException("You are releasing a path which is not claimed at all (most likely it has been pooled already). " +
					"Are you releasing the path with the same object ("+o+") twice?" +
					"\nCheck out the documentation on path pooling for help.");
			}
			throw new System.ArgumentException("You are releasing a path which has not been claimed with this object ("+o+"). " +
				"Are you releasing the path with the same object twice?\n" +
				"Check out the documentation on path pooling for help.");
		}

		/// <summary>
		/// Traces the calculated path from the end node to the start.
		/// This will build an array (<see cref="path)"/> of the nodes this path will pass through and also set the <see cref="vectorPath"/> array to the <see cref="path"/> arrays positions.
		/// Assumes the <see cref="vectorPath"/> and <see cref="path"/> are empty and not null (which will be the case for a correctly initialized path).
		/// </summary>
		protected virtual void Trace (uint fromPathNodeIndex) {
			MarkerTrace.Begin();
			// Current node we are processing
			var c = fromPathNodeIndex;
			int count = 0;
			var pathNodes = pathHandler.pathNodes;

			while (c != 0) {
				c = pathNodes[c].parentIndex;
				count++;
				if (count > 16384) {
					Debug.LogWarning("Infinite loop? >16384 node path. Remove this message if you really have that long paths (Path.cs, Trace method)");
					break;
				}
			}

			// Ensure the lists have enough capacity
			if (path.Capacity < count) path.Capacity = count;
			UnityEngine.Assertions.Assert.AreEqual(0, path.Count);

			c = fromPathNodeIndex;

			GraphNode lastNode = null;
			for (int i = 0; i < count; i++) {
				GraphNode node;
				if (pathHandler.IsTemporaryNode(c)) {
					node = pathHandler.GetNode(pathHandler.GetTemporaryNode(c).associatedNode);
				} else {
					node = pathHandler.GetNode(c);
				}
				// If a node has multiple variants (like the triangle mesh node), then we may visit
				// the same node multiple times in a sequence (but different variants of it).
				// In the final path we don't want the duplicates.
				if (node != lastNode) {
					path.Add(node);
					lastNode = node;
				}
				c = pathNodes[c].parentIndex;
			}

			// Reverse
			count = path.Count;
			int half = count/2;
			for (int i = 0; i < half; i++) {
				var tmp = path[i];
				path[i] = path[count-i-1];
				path[count - i - 1] = tmp;
			}

			if (vectorPath.Capacity < count) vectorPath.Capacity = count;
			for (int i = 0; i < count; i++) {
				vectorPath.Add((Vector3)path[i].position);
			}
			MarkerTrace.End();
		}

		/// <summary>
		/// Writes text shared for all overrides of DebugString to the string builder.
		/// See: DebugString
		/// </summary>
		protected void DebugStringPrefix (PathLog logMode, System.Text.StringBuilder text) {
			text.Append(error ? "Path Failed : " : "Path Completed : ");
			text.Append("Computation Time ");
			text.Append(duration.ToString(logMode == PathLog.Heavy ? "0.000 ms " : "0.00 ms "));

			text.Append("Searched Nodes ").Append(searchedNodes);

			if (!error) {
				text.Append(" Path Length ");
				text.Append(path == null ? "Null" : path.Count.ToString());
			}
		}

		/// <summary>
		/// Writes text shared for all overrides of DebugString to the string builder.
		/// See: DebugString
		/// </summary>
		protected void DebugStringSuffix (PathLog logMode, System.Text.StringBuilder text) {
			if (error) {
				text.Append("\nError: ").Append(errorLog);
			}

			// Can only print this from the Unity thread
			// since otherwise an exception might be thrown
			if (logMode == PathLog.Heavy && !AstarPath.active.IsUsingMultithreading) {
				text.Append("\nCallback references ");
				if (callback != null) text.Append(callback.Target.GetType().FullName).AppendLine();
				else text.AppendLine("NULL");
			}

			text.Append("\nPath Number ").Append(pathID).Append(" (unique id)");
		}

		/// <summary>
		/// Returns a string with information about it.
		/// More information is emitted when logMode == Heavy.
		/// An empty string is returned if logMode == None
		/// or logMode == OnlyErrors and this path did not fail.
		/// </summary>
		protected virtual string DebugString (PathLog logMode) {
			if (logMode == PathLog.None || (!error && logMode == PathLog.OnlyErrors)) {
				return "";
			}

			// Get a cached string builder for this thread
			System.Text.StringBuilder text = pathHandler.DebugStringBuilder;
			text.Length = 0;

			DebugStringPrefix(logMode, text);
			DebugStringSuffix(logMode, text);

			return text.ToString();
		}

		/// <summary>Calls callback to return the calculated path. See: <see cref="callback"/></summary>
		protected virtual void ReturnPath () {
			if (callback != null) {
				callback(this);
			}
		}

		/// <summary>
		/// Prepares low level path variables for calculation.
		/// Called before a path search will take place.
		/// Always called before the Prepare, Initialize and CalculateStep functions
		/// </summary>
		protected void PrepareBase (PathHandler pathHandler) {
			//Make sure the path has a reference to the pathHandler
			this.pathHandler = pathHandler;
			//Assign relevant path data to the pathHandler
			pathHandler.InitializeForPath(this);

			// Make sure that internalTagPenalties is an array which has the length 32
			if (internalTagPenalties == null || internalTagPenalties.Length != 32)
				internalTagPenalties = ZeroTagPenalties;

			try {
				ErrorCheck();
			} catch (System.Exception e) {
				FailWithError(e.Message);
			}
		}

		/// <summary>
		/// Called before the path is started.
		/// Called right before Initialize
		/// </summary>
		protected abstract void Prepare();

		/// <summary>
		/// Always called after the path has been calculated.
		/// Guaranteed to be called before other paths have been calculated on
		/// the same thread.
		/// Use for cleaning up things like node tagging and similar.
		/// </summary>
		protected virtual void Cleanup () {
			// Cleanup any flags set by temporary nodes
			var pathNodes = pathHandler.pathNodes;
			for (uint i = 0; i < pathHandler.numTemporaryNodes; i++) {
				var nodeIndex = pathHandler.temporaryNodeStartIndex + i;
				ref var node = ref pathHandler.GetTemporaryNode(nodeIndex);

				var associatedNode = pathHandler.GetNode(node.associatedNode);
				for (uint v = 0; v < associatedNode.PathNodeVariants; v++) {
					pathNodes[node.associatedNode + v].flag1 = false;
					pathNodes[node.associatedNode + v].flag2 = false;
				}
			}
		}

		protected int3 FirstTemporaryEndNode () {
			for (uint i = 0; i < pathHandler.numTemporaryNodes; i++) {
				var nodeIndex = pathHandler.temporaryNodeStartIndex + i;
				ref var node = ref pathHandler.GetTemporaryNode(nodeIndex);
				if (node.type == TemporaryNodeType.End) {
					return (int3)node.position;
				}
			}
			throw new System.InvalidOperationException("There are no end nodes in the path");
		}


		protected void TemporaryEndNodesBoundingBox (out int3 mn, out int3 mx) {
			// These represent a bounding box containing all valid end points.
			// Typically there's only one end point, but in some cases there can be more.
			mn = (int3)int.MaxValue;
			mx = (int3)int.MinValue;

			for (uint i = 0; i < pathHandler.numTemporaryNodes; i++) {
				var nodeIndex = pathHandler.temporaryNodeStartIndex + i;
				ref var node = ref pathHandler.GetTemporaryNode(nodeIndex);
				if (node.type == TemporaryNodeType.End) {
					mn = math.min(mn, (int3)node.position);
					mx = math.max(mx, (int3)node.position);
				}
			}
		}

		protected void MarkNodesAdjacentToTemporaryEndNodes () {
			var pathNodes = pathHandler.pathNodes;

			for (uint i = 0; i < pathHandler.numTemporaryNodes; i++) {
				var nodeIndex = pathHandler.temporaryNodeStartIndex + i;
				ref var node = ref pathHandler.GetTemporaryNode(nodeIndex);
				if (node.type == TemporaryNodeType.End) {
					// Mark node with flag1 to mark it as a node connected to an end node
					var associatedNode = pathHandler.GetNode(node.associatedNode);
					for (uint v = 0; v < associatedNode.PathNodeVariants; v++) {
						pathNodes[node.associatedNode + v].flag1 = true;
					}
				}
			}
		}

		protected void AddStartNodesToHeap () {
			var pathNodes = pathHandler.pathNodes;
			for (uint i = 0; i < pathHandler.numTemporaryNodes; i++) {
				var nodeIndex = pathHandler.temporaryNodeStartIndex + i;
				ref var node = ref pathHandler.GetTemporaryNode(nodeIndex);
				if (node.type == TemporaryNodeType.Start) {
					// Note: Setting F score to 0 is technically incorrect, but it doesn't
					// matter since we will open the start nodes first anyway.
					pathHandler.heap.Add(pathNodes, nodeIndex, 0, 0);
				}
			}
		}

		/// <summary>
		/// Called when there are no more nodes to search.
		///
		/// This may be used to calculate a partial path as a fallback.
		/// </summary>
		protected abstract void OnHeapExhausted();

		/// <summary>
		/// Called when a valid node has been found for the end of the path.
		///
		/// This function should trace the path back to the start node, and set CompleteState to Complete.
		/// If CompleteState is unchanged, the search will continue.
		/// </summary>
		protected abstract void OnFoundEndNode(uint pathNode, uint hScore, uint gScore);

		/// <summary>
		/// Called for every node that the path visits.
		///
		/// This is used by path types to check if the target node has been reached, to log debug data, etc.
		/// </summary>
		public virtual void OnVisitNode (uint pathNode, uint hScore, uint gScore) {}

		/// <summary>
		/// Calculates the path until completed or until the time has passed targetTick.
		/// Usually a check is only done every 500 nodes if the time has passed targetTick.
		/// Time/Ticks are got from System.DateTime.UtcNow.Ticks.
		///
		/// Basic outline of what the function does for the standard path (Pathfinding.ABPath).
		/// <code>
		/// while the end has not been found and no error has occurred
		/// pop the next node of the heap and set it as current
		/// check if we have reached the end
		/// if so, exit and return the path
		///
		/// open the current node, i.e loop through its neighbours, mark them as visited and put them on a heap
		///
		/// check if there are still nodes left to process (or have we searched the whole graph)
		/// if there are none, flag error and exit
		///
		/// check if the function has exceeded the time limit
		/// if so, return and wait for the function to get called again
		/// </code>
		/// </summary>
		protected virtual void CalculateStep (long targetTick) {
			int counter = 0;
			var pathNodes = pathHandler.pathNodes;
			var temporaryNodeStartIndex = pathHandler.temporaryNodeStartIndex;

			// Continue to search as long as we haven't encountered an error and we haven't found the target
			while (CompleteState == PathCompleteState.NotCalculated) {
				searchedNodes++;

				// Any nodes left to search?
				if (pathHandler.heap.isEmpty) {
					OnHeapExhausted();
					return;
				}

				// Select the node with the lowest F score and remove it from the open list
				var currentPathNodeIndex = pathHandler.heap.Remove(pathNodes, out uint currentNodeG, out uint currentNodeF);
				var currentNodeH = currentNodeF - currentNodeG;

				if (currentPathNodeIndex >= temporaryNodeStartIndex) {
					// This is a special node
					var node = pathHandler.GetTemporaryNode(currentPathNodeIndex);
					if (node.type == TemporaryNodeType.Start) {
						// A start node. We should open the associated node at this point
						pathHandler.GetNode(node.associatedNode).OpenAtPoint(this, currentPathNodeIndex, node.position, currentNodeG);
					} else if (node.type == TemporaryNodeType.End) {
						// An end node. Yay! We found the path we wanted.
						// Now we can just trace the path back to the start and return that.
						// However, some path types may choose to continue the search to find more end points (e.g. the multi target path).
						{
							// Make sure we visit the node associated with the end node.
							// This is usually redundant, but it can matter in some cases.
							// In particular, triangle mesh nodes can be opened in such a way that the temporary end node
							// gets a lower F score than the individual sides of the triangle. This means that the temporary end
							// node will be searched before the triangle sides are searched and that might complete the path.
							// This would lead to us never actually calling LogVisitedNode for the triangle node, if we didn't have this code.
							pathHandler.LogVisitedNode(node.associatedNode, currentNodeH, currentNodeG);
						}
						OnFoundEndNode(currentPathNodeIndex, currentNodeH, currentNodeG);
						if (CompleteState == PathCompleteState.Complete) {
							return;
						}
					}
				} else {
					pathHandler.LogVisitedNode(currentPathNodeIndex, currentNodeH, currentNodeG);

					OnVisitNode(currentPathNodeIndex, currentNodeH, currentNodeG);

					// Loop through all walkable neighbours of the node and add them to the open list.
					var node = pathHandler.GetNode(currentPathNodeIndex);
					node.Open(this, currentPathNodeIndex, currentNodeG);
				}

				// Check for time every 500 nodes, roughly every 0.5 ms usually
				if (counter > 500) {
					// Have we exceded the maxFrameTime, if so we should wait one frame before continuing the search since we don't want the game to lag
					if (System.DateTime.UtcNow.Ticks >= targetTick) {
						return;
					}
					counter = 0;

					// Mostly for development
					if (searchedNodes > 1000000) {
						throw new System.Exception("Probable infinite loop. Over 1,000,000 nodes searched");
					}
				}

				counter++;
			}
		}

		PathHandler IPathInternals.PathHandler { get { return pathHandler; } }
		void IPathInternals.OnEnterPool () { OnEnterPool(); }
		void IPathInternals.Reset () { Reset(); }
		void IPathInternals.ReturnPath () { ReturnPath(); }
		void IPathInternals.PrepareBase (PathHandler handler) { PrepareBase(handler); }
		void IPathInternals.Prepare () { Prepare(); }
		void IPathInternals.Cleanup () { Cleanup(); }
		void IPathInternals.CalculateStep (long targetTick) { CalculateStep(targetTick); }
		string IPathInternals.DebugString (PathLog logMode) { return DebugString(logMode); }
	}

	/// <summary>Used for hiding internal methods of the Path class</summary>
	internal interface IPathInternals {
		PathHandler PathHandler { get; }
		bool Pooled { get; set; }
		void AdvanceState(PathState s);
		void OnEnterPool();
		void Reset();
		void ReturnPath();
		void PrepareBase(PathHandler handler);
		void Prepare();
		void Cleanup();
		void CalculateStep(long targetTick);
		string DebugString(PathLog logMode);
	}
}