using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System.Linq;
using System;

public class Pathfinder 
{

    // used to store all unique states that agent has visited (holds agent and sample coords)
    public static HashSet<string> closed = new HashSet<string>();

    LogicGrid world;
    public Vector2Int agent;
    public HashSet<Vector2Int> obstacles;
    public HashSet<Vector2Int> samples;

    public int algorithm; // 0 = A* | 1 = dfs | 2 = bfs
    public int heuristic; // 0 = h0 | 1 = h1  | 2 = h2

    public static int height;
    public static int width;

    public Stack<Node> result;


    public Pathfinder(LogicGrid world, Vector2Int a, HashSet<Vector2Int> o, HashSet<Vector2Int> s, int algo, int heu)
    {
		closed = new HashSet<string>();

		this.world = world;
        height = world.GetHeight();
        width = world.GetWidth();

        agent = a;
        obstacles = o;
        samples = s;

        algorithm = algo;
        heuristic = heu;

        //printInfo();

        StartWork();

    }
/*   public void printInfo()
    {
        Debug.Log("Agent: " + agent[0] + "," + agent[1]);

        for (int i = 0; i < obstacles.Count; i++)
        {
            Debug.Log("Obstacle " + i + ": " + obstacles[i].x + ", " + obstacles[i].y);
        }

        for (int i = 0; i < samples.Count; i++)
        {
            Debug.Log("Sample " + i + ": " + samples[i].x + ", " + samples[i].y);
        }
    }*/

    public void StartWork()
    {
        Node initialState = new Node(null, agent, obstacles, samples, '0', 0, 0);
        result = new Stack<Node>();

        // Run AStar
        if (algorithm == 0)
        {
            result = StartAStar(initialState, heuristic);
        }
		// Run DFS
		if (algorithm == 1)
        {
			result = StartDFS(initialState, -1);
        }
		// Run IDS
		if (algorithm == 2)
		{
			result = StartIDS(initialState);
		}
	}

    public static Stack<Node> StartAStar(Node initialState, int heuristic)
    {
		Stack<Node> solution = new Stack<Node>();

        List<Node> open = new List<Node>();
		open.Add(initialState);

		Debug.Log("GO!");

        int cap = 200000;
        while (true && cap > 0)
        {
            if (!open.Any())
			{
				return solution;
			}

			//open = open.OrderBy(Node => Node.fn).ToList();

			Node currentNode = FindBestNode(open);
            open.Remove(currentNode);


            // check whether we are in goal state
            if (currentNode.samples.Count == 0)
            {
                Debug.Log("Gottem");
				
                while (currentNode.parent != null)
                {
                    solution.Push(currentNode);
                    currentNode = currentNode.parent;
                }

                return solution;
            }

            // if not, expand children and continue
            List<Node> children = currentNode.expand(-1);

            if (heuristic == 0)
                h0(children);
            else if (heuristic == 1)
                h1(children);
            else if (heuristic == 2)
                h2(children);

            foreach (Node child in children)
            {
                open.Add(child);
            }
            cap--;
        }
		Debug.Log("too much work :(");
        return solution;
    }

	public static Node FindBestNode(List<Node> open)
    {
		Node lowest = open[0];
		for(int i = 1; i < open.Count; i++)
        {
			if (open[i].fn < lowest.fn)
				lowest = open[i];
        }
		return lowest;
    }

    // HEURISTICS FOR ASTAR
    public static List<Node> h0(List<Node> children)
    {
        List<Node> sorted = new List<Node>();

        for (int i = 0; i < children.Count(); i++)
        {
            // estimated moves left: zero
            children[i].heuristic = 0;
            sorted.Add(children[i]);
        }

        //sorted = sorted.OrderBy(Node => Node.fn).ToList();

        return sorted;
    }

    public static List<Node> h1(List<Node> children)
    {
		List<Node> sorted = new List<Node>();

		for (int i = 0; i < children.Count; i++)
        {
            // estimated moves left: samples left
            children[i].heuristic = children[i].samples.Count;
            sorted.Add(children[i]);
        }
        return children;
    }

    public static List<Node> h2(List<Node> children)
    {
        if (children.Count() == 0)
            return children;

        Node child;

        for (int i = 0; i < children.Count(); i++)
        {
            // estimated moves left: 
            // distance to nearest sample + 1 (+1 to account for sample action)
            child = children[i];
			child.heuristic = Vector2.Distance(child.agent, child.nearestSample()) + 1;

        }

        return children;
    }

	// ALTERNATE SEARCH ALGORITHMS
	public static Stack<Node> StartDFS(Node initialState, int depth)
	{
        Debug.Log("DOING DFS");
        Stack<Node> solution = new Stack<Node>();
        Stack<Node> dfsStack = new Stack<Node>();  // Stack for DFS
        HashSet<string> visited = new HashSet<string>();  // For avoiding revisiting states

        dfsStack.Push(initialState);

        int cap = 2000000;
        while (dfsStack.Count > 0 && cap > 0)
        {
            Node currentNode = dfsStack.Pop();

            // If we have already visited this state, skip processing
            if (visited.Contains(currentNode.getStateString())) continue;
            visited.Add(currentNode.getStateString());

            // check if agent is in goal state
            if (currentNode.samples.Count == 0)
            {
                while (currentNode.parent != null)
                {
                    solution.Push(currentNode);
                    currentNode = currentNode.parent;
                }
                return solution;
            }

            List<Node> children = currentNode.expand(-1);
            foreach (Node child in children)
            {
                dfsStack.Push(child);
            }
            cap--;
        }

        Debug.Log("Too much work :(");
        return solution;
    }
	public static Stack<Node> StartIDS(Node initialState)
	{
		Debug.Log("RUNNING IDS");
		Stack<Node> result = new Stack<Node>();
		int depth = 1;

		while (true)
		{
			result = StartDFS(initialState, depth);
			if (result.Count != 0)
				return result;
			depth++;
			closed.Clear();
		}
	}
}

public class Node
	{
		// helper variables just to make indexing arrays easier to read
		public static int row = 0;
		public static int col = 1;

		public Node parent;

		public Vector2Int agent;
		public HashSet<Vector2Int> obstacles;
		public HashSet<Vector2Int> samples;

		public char lastMove; // for output/animation
		public int distanceTraveled; // for calculating f(n) value
		public double heuristic;
		public double fn; // distance traveled + heuristic value
		//bool canSample; // for expansion 

		// construct node :)
		public Node(Node parent, Vector2Int agent, HashSet<Vector2Int> obstacles, HashSet<Vector2Int> samples, char lastMove, int distanceTraveled, double heuristic)
		{
			this.parent = parent;
			this.agent = agent;
			this.obstacles = new HashSet<Vector2Int>(obstacles);
			this.samples = new HashSet<Vector2Int>(samples);
			this.lastMove = lastMove;
			this.distanceTraveled = distanceTraveled;
			this.heuristic = heuristic;
			fn = distanceTraveled + heuristic;
		}

		// determine valid moves and collect children to be sent back to search
		public List<Node> expand(int depth)
		{
			List<Node> children = new List<Node>();
			if (this.distanceTraveled >= depth && depth != -1)
				return children;

			// document expansion of node and get ready to collect this node's children
			// SampleWorld.expansions++;
			Vector2Int onSample = new Vector2Int();

			// since this state is being currently visited (expanded), put in closed list
			Pathfinder.closed.Add(this.getStateString());

			////////////////////////////////////
			// BEGIN CHECKING FOR VALID MOVES //
			////////////////////////////////////

			// store coordinates for all potential moves to be checked
			Vector2Int up    = new Vector2Int( this.agent.x, this.agent.y + 1 );
			Vector2Int down  = new Vector2Int( this.agent.x, this.agent.y - 1 );
			Vector2Int left  = new Vector2Int( this.agent.x - 1,  this.agent.y );
			Vector2Int right = new Vector2Int( this.agent.x + 1,  this.agent.y);

			// make sure going up doesn't go outside world-bounds or into obstacle
			if (isOpen(up))
			{
				// if move is valid, create that new node/state and document
				Node child = new Node(this, up, this.obstacles, this.samples, 'U', this.distanceTraveled + 1, this.heuristic);
				//SampleWorld.nodesGenerated++;

				// make sure that we have not already made that move
				if (!Pathfinder.closed.Contains(child.getStateString()))
					children.Add(child);
			}

			// same idea but for the different potential moves
			if (isOpen(down))
			{
				Node child = new Node(this, down, this.obstacles, this.samples, 'D', this.distanceTraveled + 1, this.heuristic);
				//SampleWorld.nodesGenerated++;

				if (!Pathfinder.closed.Contains(child.getStateString()))
					children.Add(child);
			}

			if (isOpen(left))
			{
				Node child = new Node(this, left, this.obstacles, this.samples, 'L', this.distanceTraveled + 1, this.heuristic);
				//SampleWorld.nodesGenerated++;

				if (!Pathfinder.closed.Contains(child.getStateString()))
					children.Add(child);
		}

			if (isOpen(right))
			{
				Node child = new Node(this, right, this.obstacles, this.samples, 'R', this.distanceTraveled + 1, this.heuristic);
				//SampleWorld.nodesGenerated++;

				if (!Pathfinder.closed.Contains(child.getStateString()))
					children.Add(child);
		}

			// CHECK IF CAN SAMPLE
			onSample = CanSample();
			if (onSample.x != -1)
			{
				Node child = new Node(this, this.agent, this.obstacles, this.samples, 'S', this.distanceTraveled + 1, this.heuristic);
			
				child.samples.Remove(onSample);

				//SampleWorld.nodesGenerated++;
				children.Add(child);
			}

			return children;
		}

		// helper for expand, verifies whether potential move is legal
		public bool isOpen(Vector2Int position)
		{
			// check that agent is not trying to move into an obstacle
			if (obstacles.Contains(position))
				return false;

			if ((position.y < 0) || (position.y > Pathfinder.height - 1) || (position.x < 0) || (position.x > Pathfinder.width - 1))
				return false;

			// check that agent is not stepping out of the world
			// if (!((position.y >= 0) && (position.y <= Pathfinder.height - 1) && (position.x >= 0) && (position.x <= Pathfinder.width - 1)))
			//	return false;

			return true;
		}

		// returns the coordinates of the sample closest to the agent's current location
		public Vector2Int nearestSample()
		{
			Vector2Int s = new Vector2Int(-1, -1);
			if (samples.Count == 0)
				return agent;

			double lowest = 9999999;
			double dist = 0;

			foreach (Vector2Int sample in samples)
			{
				dist = Vector2Int.Distance(agent, sample);
				if(dist < lowest)
				{
					lowest = dist;
					s = sample;
				}				
			}
			return s;
/*
			Vector2Int s = samples[0];
			double lowest = Vector2.Distance(agent, samples[0]);
			double dist;

			for (int i = 1; i < samples.Count; i++)
			{
				dist = Vector2.Distance(agent, samples[i]);
				if (dist < lowest)
				{
					lowest = dist;
					s = samples[i];
				}
			}
			return s;*/
		}
		// helper function for nearestSample()
/*		public static double distance(Vector2Int a, Vector2Int b)
		{   //								 _________________________
			// distance between 2D points = √(y2 - y1)^2 + (x2 - x1)^2
			double total = (((b.y - a.y) * (b.y - a.y)) + ((b.x - a.x) * (b.x - a.x)));
			total = Math.Sqrt(total);

			return total;
		}*/

		// helper function for h2
		/////////////////////////////
		// returns two pieces of information if true: 
		// [0] is 1 to indicate agent can sample
		// [1] is the index of the valid sample in the list
		public Vector2Int CanSample()
		{
			// default to false
			Vector2Int result = new Vector2Int();
			result.x = -1;
			result.y = -1;

			if(samples.Contains(agent))
				result = agent;
		
			return result;
			
			/*
			for (int i = 0; i < this.samples.Count; i++)
			{
				if ((this.agent.y == samples[i].y) && (this.agent.x == samples[i].x))
				{
					result[0] = 1;
					result[1] = i;
					return result;
				}
			}
			return result;*/
		}

		// returns only the dynamic information directly related to the Node's state.
		// we need a way to extract just this information for the sake of our closed list
		public State getState()
		{
			return new State(this.agent, this.samples);
		}

        public string getStateString()
        {
            string stateStr = agent.ToString();
            foreach (var obstacle in obstacles)
                stateStr += obstacle.ToString();
            foreach (var sample in samples)
                stateStr += sample.ToString();
            return stateStr;
        }

    // we use to override comparisons for priorityQueues so that our heuristic calculations are actually used
    /*		public int CompareTo(Node other)
            {
                if (this.fn > other.fn)
                    return 1;
                else
                    return -1;
            }*/

}

	// helper class for Node
/*	class NodeComparator : Comparer<Node>
	{
		// used to sort nodes based on sum of distance traveled + heuristic estimation of work left
		public override int Compare(Node a, Node b)
		{
			if (a.fn > b.fn)
			return 1;
			else
			return -1;
		}
	}*/
	// helper class for Node
	public class State
	{
		Vector2Int agent;
		HashSet<Vector2Int> samples;

		public State(Vector2Int agent, HashSet<Vector2Int> samples)
		{
			this.agent = agent;
			this.samples = samples;

			// convert List<int[]> into 2D array of ints [][]
			/*for (int i = 0; i < samples.Count; i++)
			{
				this.samples[i] = samples[i];
			}*/
		}

		public bool equals(State other)
		{
			if (this.samples.Count != other.samples.Count)
				return false;

			if (!(this.agent.x.Equals(other.agent.x) && this.agent.y.Equals(other.agent.y)))
				return false;

			for (int i = 0; i < this.samples.Count; i++)
			{
				//if (Arrays.compare(this.samples[i], other.samples[i]) != 0)
				
				if (this.samples.SequenceEqual(other.samples))
					return false;
			}

			return true;
		}
	}