using System.Collections.Generic;
using UnityEngine;

// A Dynamic, Loose Octree for storing any objects that can be described with AABB bounds
// See also: PointOctree, where objects are stored as single points and some code can be simplified
// Octree:  An octree is a tree data structure which divides 3D space into smaller partitions (nodes)
//          and places objects into the appropriate nodes. This allows fast access to objects
//          in an area of interest without having to check every object.
// Dynamic: The octree grows or shrinks as required when objects as added or removed
//          It also splits and merges nodes as appropriate. There is no maximum depth.
//          Nodes have a constant - numObjectsAllowed - which sets the amount of items allowed in a node before it splits.
// Loose:   The octree's nodes can be larger than 1/2 their parent's length and width, so they overlap to some extent.
//          This can alleviate the problem of even tiny objects ending up in large nodes if they're near boundaries.
//          A looseness value of 1.0 will make it a "normal" octree.
// T:       The content of the octree can be anything, since the bounds data is supplied separately.

// Originally written for my game Scraps (http://www.scrapsgame.com) but intended to be general-purpose.
// Copyright 2014 Nition, BSD licence (see LICENCE file). http://nition.co
// Unity-based, but could be adapted to work in pure C#

// Note: For loops are often used here since in some cases (e.g. the IsColliding method)
// they actually give much better performance than using Foreach, even in the compiled build.
// Using a LINQ expression is worse again than Foreach.
public class BoundsOctree<T> {
    // The total amount of objects currently in the tree
    public int Count { get; private set; }

    // Root node of the octree
    BoundsOctreeNode<T> rootNode;
    // Should be a value between 1 and 2. A multiplier for the base size of a node.
    // 1.0 is a "normal" octree, while values > 1 have overlap
    readonly float looseness;
    // Size that the octree was on creation
    readonly float initialSize;
    // Minimum side length that a node can be - essentially an alternative to having a max depth
    readonly float minSize;
    // For collision visualisation. Automatically removed in builds.
    #if UNITY_EDITOR
    const int numCollisionsToSave = 4;
    readonly Queue<Bounds> lastBoundsCollisionChecks = new Queue<Bounds>();
    readonly Queue<Ray> lastRayCollisionChecks = new Queue<Ray>();
    #endif

    /// <summary>
    /// Constructor for the bounds octree.
    /// </summary>
    /// <param name="initialWorldSize">Size of the sides of the initial node, in metres. The octree will never shrink smaller than this.</param>
    /// <param name="initialWorldPos">Position of the centre of the initial node.</param>
    /// <param name="minNodeSize">Nodes will stop splitting if the new nodes would be smaller than this (metres).</param>
    /// <param name="loosenessVal">Clamped between 1 and 2. Values > 1 let nodes overlap.</param>
    public BoundsOctree(float initialWorldSize, Vector3 initialWorldPos, float minNodeSize, float loosenessVal) {
        if (minNodeSize > initialWorldSize) {
            Debug.LogWarning("Minimum node size must be at least as big as the initial world size. Was: " + minNodeSize + " Adjusted to: " + initialWorldSize);
            minNodeSize = initialWorldSize;
        }
        Count = 0;
        initialSize = initialWorldSize;
        minSize = minNodeSize;
        looseness = Mathf.Clamp(loosenessVal, 1.0f, 2.0f);
        rootNode = new BoundsOctreeNode<T>(initialSize, minSize, loosenessVal, initialWorldPos);
    }

    // #### PUBLIC METHODS ####

    /// <summary>
    /// Add an object.
    /// </summary>
    /// <param name="obj">Object to add.</param>
    /// <param name="objBounds">3D bounding box around the object.</param>
    public void Add(T obj, Bounds objBounds) {
        // Add object or expand the octree until it can be added
        int count = 0; // Safety check against infinite/excessive growth
        while (!rootNode.Add(obj, objBounds)) {
            Grow(objBounds.center - rootNode.Center);
            if (++count > 20) {
                Debug.LogError("Aborted Add operation as it seemed to be going on forever (" + (count - 1) + ") attempts at growing the octree.");
                return;
            }
        }
        Count++;
    }

    /// <summary>
    /// Remove an object. Makes the assumption that the object only exists once in the tree.
    /// </summary>
    /// <param name="obj">Object to remove.</param>
    /// <returns>True if the object was removed successfully.</returns>
    public bool Remove(T obj) {
        bool removed = rootNode.Remove(obj);

        // See if we can shrink the octree down now that we've removed the item
        if (removed) {
            Count--;
            Shrink();
        }

        return removed;
    }

    /// <summary>
    /// Check if the specified bounds intersect with anything in the tree. See also: GetColliding.
    /// </summary>
    /// <param name="checkBounds">bounds to check.</param>
    /// <returns>True if there was a collision.</returns>
    public bool IsColliding(Bounds checkBounds) {
        //#if UNITY_EDITOR
        // For debugging
        //AddCollisionCheck(checkBounds);
        //#endif
        return rootNode.IsColliding(ref checkBounds);
    }

    /// <summary>
    /// Check if the specified ray intersects with anything in the tree. See also: GetColliding.
    /// </summary>
    /// <param name="checkRay">ray to check.</param>
    /// <param name="maxDistance">distance to check.</param>
    /// <returns>True if there was a collision.</returns>
    public bool IsColliding(Ray checkRay, float maxDistance) {
        //#if UNITY_EDITOR
        // For debugging
        //AddCollisionCheck(checkRay);
        //#endif
        return rootNode.IsColliding(ref checkRay, maxDistance);
    }

    /// <summary>
    /// Returns an array of objects that intersect with the specified bounds, if any. Otherwise returns an empty array. See also: IsColliding.
    /// </summary>
    /// <param name="collidingWith">list to store intersections.</param>
    /// <param name="checkBounds">bounds to check.</param>
    /// <returns>Objects that intersect with the specified bounds.</returns>
    public void GetColliding(List<T> collidingWith, Bounds checkBounds) {
        //#if UNITY_EDITOR
        // For debugging
        //AddCollisionCheck(checkBounds);
        //#endif
        rootNode.GetColliding(ref checkBounds, collidingWith);
    }

    /// <summary>
    /// Returns an array of objects that intersect with the specified ray, if any. Otherwise returns an empty array. See also: IsColliding.
    /// </summary>
    /// <param name="collidingWith">list to store intersections.</param>
    /// <param name="checkRay">ray to check.</param>
    /// <param name="maxDistance">distance to check.</param>
    /// <returns>Objects that intersect with the specified ray.</returns>
    public void GetColliding(List<T> collidingWith, Ray checkRay, float maxDistance = float.PositiveInfinity) {
        //#if UNITY_EDITOR
        // For debugging
        //AddCollisionCheck(checkRay);
        //#endif
        rootNode.GetColliding(ref checkRay, collidingWith, maxDistance);
    }

    public Bounds GetMaxBounds()
    {
        return rootNode.GetBounds();
    }

    /// <summary>
    /// Draws node boundaries visually for debugging.
    /// Must be called from OnDrawGizmos externally. See also: DrawAllObjects.
    /// </summary>
    public void DrawAllBounds() {
        rootNode.DrawAllBounds();
    }

    /// <summary>
    /// Draws the bounds of all objects in the tree visually for debugging.
    /// Must be called from OnDrawGizmos externally. See also: DrawAllBounds.
    /// </summary>
    public void DrawAllObjects() {
        rootNode.DrawAllObjects();
    }

    // Intended for debugging. Must be called from OnDrawGizmos externally
    // See also DrawAllBounds and DrawAllObjects
    /// <summary>
    /// Visualises collision checks from IsColliding and GetColliding.
    /// Collision visualisation code is automatically removed from builds so that collision checks aren't slowed down.
    /// </summary>
    #if UNITY_EDITOR
    public void DrawCollisionChecks() {
        int count = 0;
        foreach (Bounds collisionCheck in lastBoundsCollisionChecks) {
            Gizmos.color = new Color(1.0f, 1.0f - ((float)count / numCollisionsToSave), 1.0f);
            Gizmos.DrawCube(collisionCheck.center, collisionCheck.size);
            count++;
        }

        foreach (Ray collisionCheck in lastRayCollisionChecks) {
            Gizmos.color = new Color(1.0f, 1.0f - ((float)count / numCollisionsToSave), 1.0f);
            Gizmos.DrawRay(collisionCheck.origin, collisionCheck.direction);
            count++;
        }
        Gizmos.color = Color.white;
    }
    #endif

    // #### PRIVATE METHODS ####

    /// <summary>
    /// Used for visualising collision checks with DrawCollisionChecks.
    /// Automatically removed from builds so that collision checks aren't slowed down.
    /// </summary>
    /// <param name="checkBounds">bounds that were passed in to check for collisions.</param>
    #if UNITY_EDITOR
    void AddCollisionCheck(Bounds checkBounds) {
        lastBoundsCollisionChecks.Enqueue(checkBounds);
        if (lastBoundsCollisionChecks.Count > numCollisionsToSave) {
            lastBoundsCollisionChecks.Dequeue();
        }
    }
    #endif

    /// <summary>
    /// Used for visualising collision checks with DrawCollisionChecks.
    /// Automatically removed from builds so that collision checks aren't slowed down.
    /// </summary>
    /// <param name="checkRay">ray that was passed in to check for collisions.</param>
    #if UNITY_EDITOR
    void AddCollisionCheck(Ray checkRay) {
        lastRayCollisionChecks.Enqueue(checkRay);
        if (lastRayCollisionChecks.Count > numCollisionsToSave) {
            lastRayCollisionChecks.Dequeue();
        }
    }
    #endif

    /// <summary>
    /// Grow the octree to fit in all objects.
    /// </summary>
    /// <param name="direction">Direction to grow.</param>
    void Grow(Vector3 direction) {
        int xDirection = direction.x >= 0 ? 1 : -1;
        int yDirection = direction.y >= 0 ? 1 : -1;
        int zDirection = direction.z >= 0 ? 1 : -1;
        BoundsOctreeNode<T> oldRoot = rootNode;
        float half = rootNode.BaseLength / 2;
        float newLength = rootNode.BaseLength * 2;
        Vector3 newCenter = rootNode.Center + new Vector3(xDirection * half, yDirection * half, zDirection * half);

        // Create a new, bigger octree root node
        rootNode = new BoundsOctreeNode<T>(newLength, minSize, looseness, newCenter);

        if (oldRoot.HasAnyObjects())
        {
            // Create 7 new octree children to go with the old root as children of the new root
            int rootPos = GetRootPosIndex(xDirection, yDirection, zDirection);
            BoundsOctreeNode<T>[] children = new BoundsOctreeNode<T>[8];
            for (int i = 0; i < 8; i++)
            {
                if (i == rootPos)
                {
                    children[i] = oldRoot;
                }
                else
                {
                    xDirection = i % 2 == 0 ? -1 : 1;
                    yDirection = i > 3 ? -1 : 1;
                    zDirection = (i < 2 || (i > 3 && i < 6)) ? -1 : 1;
                    children[i] = new BoundsOctreeNode<T>(rootNode.BaseLength, minSize, looseness, newCenter + new Vector3(xDirection * half, yDirection * half, zDirection * half));
                }
            }

            // Attach the new children to the new root node
            rootNode.SetChildren(children);
        }
    }

    /// <summary>
    /// Shrink the octree if possible, else leave it the same.
    /// </summary>
    void Shrink() {
        rootNode = rootNode.ShrinkIfPossible(initialSize);
    }

    /// <summary>
    /// Used when growing the octree. Works out where the old root node would fit inside a new, larger root node.
    /// </summary>
    /// <param name="xDir">X direction of growth. 1 or -1.</param>
    /// <param name="yDir">Y direction of growth. 1 or -1.</param>
    /// <param name="zDir">Z direction of growth. 1 or -1.</param>
    /// <returns>Octant where the root node should be.</returns>
    static int GetRootPosIndex(int xDir, int yDir, int zDir) {
        int result = xDir > 0 ? 1 : 0;
        if (yDir < 0) result += 4;
        if (zDir > 0) result += 2;
        return result;
    }
}