using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Unity.Mathematics;
using Unity.Collections;
using Unity.Jobs;
using Unity.Burst;
using KairoEngine.Core;

public class GridPathfinding : MonoBehaviour {

    private const int MOVE_STRAIGHT_COST = 10;
    private const int MOVE_DIAGONAL_COST = 14;

    private int2 gridSize;
    private NativeArray<int> mapArray;

    private void Start() {
        gridSize = new int2(32, 32);
        mapArray = new NativeArray<int>(gridSize.x * gridSize.y, Allocator.Persistent);
        for (int x = 0; x < gridSize.x; x++) {
            for (int y = 0; y < gridSize.y; y++) {
                mapArray[x + y * gridSize.x] = 1;
            }
        }
        Timer.ExecuteRealTime(3000, () => {Loop(); });
    }

    private void OnDestroy()
    {
        mapArray.Dispose();
    }

    private void Loop()
    {
        Timer.ExecuteRealTime(2000, () => {
            float startTime = Time.realtimeSinceStartup;
            int findPathJobCount = 200;
            NativeArray<JobHandle> jobHandleArray = new NativeArray<JobHandle>(findPathJobCount, Allocator.TempJob);
            List<FindPathJob> jobsArray = new List<FindPathJob>();
            int2 startPosition = new int2(0, 0);
            int2 endPosition = new int2(31, 31);
            for (int i = 0; i < findPathJobCount; i++) {
                FindPathJob findPathJob = new FindPathJob { 
                    startPosition = startPosition, 
                    endPosition = endPosition,
                    gridSize = gridSize,
                    pathFound = new NativeArray<int>(2, Allocator.TempJob),
                    mapArray = mapArray
                };
                jobHandleArray[i] = findPathJob.Schedule();
                jobsArray.Add(findPathJob);
            }
            JobHandle.CompleteAll(jobHandleArray);
            for (int i = 0; i < jobsArray.Count; i++)
            {
                bool pathFound = jobsArray[i].pathFound[0] == 1 ? true : false;
                Debug.Log($"Path found: {pathFound} - {jobsArray[i].pathFound[1]} points");
                jobsArray[i].pathFound.Dispose();
            }
            jobHandleArray.Dispose();
            jobsArray.Clear();
            Debug.Log("Time: " + ((Time.realtimeSinceStartup - startTime) * 1000f));
            Loop();
        });
    }

    [BurstCompile]
    public struct FindPathJob : IJob {

        public int2 startPosition;
        public int2 endPosition;
        public int2 gridSize;
        public NativeArray<int> pathFound;
        [ReadOnly] public NativeArray<int> mapArray;


        public void Execute() {
            NativeArray<PathNode> pathNodeArray = new NativeArray<PathNode>(gridSize.x * gridSize.y, Allocator.Temp);
            for (int x = 0; x < gridSize.x; x++) {
                for (int y = 0; y < gridSize.y; y++) {
                    int index = CalculateIndex(x, y, gridSize.x);
                    PathNode pathNode = new PathNode();
                    pathNode.x = x;
                    pathNode.y = y;
                    pathNode.index = index;
                    pathNode.gCost = int.MaxValue;
                    pathNode.hCost = CalculateDistanceCost(new int2(x, y), endPosition);
                    pathNode.CalculateFCost();
                    pathNode.isWalkable = mapArray[index] == 1 ? true : false;
                    pathNode.cameFromNodeIndex = -1;
                    pathNodeArray[pathNode.index] = pathNode;
                }
            }
            NativeArray<int2> neighbourOffsetArray = new NativeArray<int2>(8, Allocator.Temp);
            neighbourOffsetArray[0] = new int2(-1, 0); // Left
            neighbourOffsetArray[1] = new int2(+1, 0); // Right
            neighbourOffsetArray[2] = new int2(0, +1); // Up
            neighbourOffsetArray[3] = new int2(0, -1); // Down
            neighbourOffsetArray[4] = new int2(-1, -1); // Left Down
            neighbourOffsetArray[5] = new int2(-1, +1); // Left Up
            neighbourOffsetArray[6] = new int2(+1, -1); // Right Down
            neighbourOffsetArray[7] = new int2(+1, +1); // Right Up

            int endNodeIndex = CalculateIndex(endPosition.x, endPosition.y, gridSize.x);

            PathNode startNode = pathNodeArray[CalculateIndex(startPosition.x, startPosition.y, gridSize.x)];
            startNode.gCost = 0;
            startNode.CalculateFCost();
            pathNodeArray[startNode.index] = startNode;

            NativeList<int> openList = new NativeList<int>(Allocator.Temp);
            NativeList<int> closedList = new NativeList<int>(Allocator.Temp);

            openList.Add(startNode.index);

            while (openList.Length > 0) {
                int currentNodeIndex = GetLowestCostFNodeIndex(openList, pathNodeArray);
                PathNode currentNode = pathNodeArray[currentNodeIndex];

                if (currentNodeIndex == endNodeIndex) {
                    // Reached our destination!
                    break;
                }

                // Remove current node from Open List
                for (int i = 0; i < openList.Length; i++) {
                    if (openList[i] == currentNodeIndex) {
                        openList.RemoveAtSwapBack(i);
                        break;
                    }
                }

                closedList.Add(currentNodeIndex);

                for (int i = 0; i < neighbourOffsetArray.Length; i++) {
                    int2 neighbourOffset = neighbourOffsetArray[i];
                    int2 neighbourPosition = new int2(currentNode.x + neighbourOffset.x, currentNode.y + neighbourOffset.y);

                    if (!IsPositionInsideGrid(neighbourPosition, gridSize)) {
                        // Neighbour not valid position
                        continue;
                    }

                    int neighbourNodeIndex = CalculateIndex(neighbourPosition.x, neighbourPosition.y, gridSize.x);

                    if (closedList.Contains(neighbourNodeIndex)) {
                        // Already searched this node
                        continue;
                    }

                    PathNode neighbourNode = pathNodeArray[neighbourNodeIndex];
                    if (!neighbourNode.isWalkable) {
                        // Not walkable
                        continue;
                    }

                    int2 currentNodePosition = new int2(currentNode.x, currentNode.y);

	                int tentativeGCost = currentNode.gCost + CalculateDistanceCost(currentNodePosition, neighbourPosition);
	                if (tentativeGCost < neighbourNode.gCost) {
		                neighbourNode.cameFromNodeIndex = currentNodeIndex;
		                neighbourNode.gCost = tentativeGCost;
		                neighbourNode.CalculateFCost();
		                pathNodeArray[neighbourNodeIndex] = neighbourNode;

		                if (!openList.Contains(neighbourNode.index)) {
			                openList.Add(neighbourNode.index);
		                }
	                }

                }
            }

            PathNode endNode = pathNodeArray[endNodeIndex];
            if (endNode.cameFromNodeIndex == -1) {
                // Didn't find a path!
                //Debug.Log("Didn't find a path!");
                pathFound[0] = 0;
                pathFound[1] = 0;
            } else {
                // Found a path
                pathFound[0] = 1;
                NativeList<int2> path = CalculatePath(pathNodeArray, endNode);
                pathFound[1] = path.Length;
                /*
                foreach (int2 pathPosition in path) {
                    Debug.Log(pathPosition);
                }
                */
                path.Dispose();
            }

            //pathNodeArray.Dispose();
            neighbourOffsetArray.Dispose();
            openList.Dispose();
            closedList.Dispose();
        }
        
        public NativeList<int2> CalculatePath(NativeArray<PathNode> pathNodeArray, PathNode endNode) {
            if (endNode.cameFromNodeIndex == -1) {
                // Couldn't find a path!
                return new NativeList<int2>(Allocator.Temp);
            } else {
                // Found a path
                NativeList<int2> path = new NativeList<int2>(Allocator.Temp);
                path.Add(new int2(endNode.x, endNode.y));

                PathNode currentNode = endNode;
                while (currentNode.cameFromNodeIndex != -1) {
                    PathNode cameFromNode = pathNodeArray[currentNode.cameFromNodeIndex];
                    path.Add(new int2(cameFromNode.x, cameFromNode.y));
                    currentNode = cameFromNode;
                }

                return path;
            }
        }

        public bool IsPositionInsideGrid(int2 gridPosition, int2 gridSize) {
            return
                gridPosition.x >= 0 && 
                gridPosition.y >= 0 &&
                gridPosition.x < gridSize.x &&
                gridPosition.y < gridSize.y;
        }

        public int CalculateIndex(int x, int y, int gridWidth) {
            return x + y * gridWidth;
        }

        public int CalculateDistanceCost(int2 aPosition, int2 bPosition) {
            int xDistance = math.abs(aPosition.x - bPosition.x);
            int yDistance = math.abs(aPosition.y - bPosition.y);
            int remaining = math.abs(xDistance - yDistance);
            return MOVE_DIAGONAL_COST * math.min(xDistance, yDistance) + MOVE_STRAIGHT_COST * remaining;
        }

    
        public int GetLowestCostFNodeIndex(NativeList<int> openList, NativeArray<PathNode> pathNodeArray) {
            PathNode lowestCostPathNode = pathNodeArray[openList[0]];
            for (int i = 1; i < openList.Length; i++) {
                PathNode testPathNode = pathNodeArray[openList[i]];
                if (testPathNode.fCost < lowestCostPathNode.fCost) {
                    lowestCostPathNode = testPathNode;
                }
            }
            return lowestCostPathNode.index;
        }
    }

    public struct PathNode {
            public int x;
            public int y;

            public int index;

            public int gCost;
            public int hCost;
            public int fCost;

            public bool isWalkable;

            public int cameFromNodeIndex;

            public void CalculateFCost() {
                fCost = gCost + hCost;
            }

            public void SetIsWalkable(bool isWalkable) {
                this.isWalkable = isWalkable;
            }
        }

}