/*
 * Created by Brett Terpstra 6920201 on 17/10/22.
 * Copyright (c) 2022 Brett Terpstra. All Rights Reserved.
 */

#ifndef STEP_2_BVH_H
#define STEP_2_BVH_H

#include "engine/util/std.h"
#include "engine/types.h"
#include <config.h>

#ifdef COMPILE_GUI
    
    #include <graphics/gl/gl.h>
    #include <graphics/imgui/imgui.h>

#endif

#include <utility>

namespace Raytracing {
    
    #ifdef COMPILE_GUI
    extern std::shared_ptr<VAO> aabbVAO;
    extern int count;
    extern int selected;
    #endif
    
    struct BVHObject {
        Object* ptr = nullptr;
        AABB aabb;
    };
    
    struct BVHPartitionedSpace {
        std::vector<BVHObject> left;
        std::vector<BVHObject> right;
    };
    
    struct BVHNode {
        public:
            struct BVHHitData {
                BVHNode* ptr{};
                AABBHitData data{};
                bool hit = false;
            };
            std::vector<BVHObject> objs;
            AABB aabb;
            BVHNode* left;
            BVHNode* right;
            int index;
            int hit = 0;
            BVHNode(std::vector<BVHObject> objs, AABB aabb, BVHNode* left, BVHNode* right): objs(std::move(objs)), aabb(std::move(aabb)),
                                                                                            left(left), right(right) {
                index = count++;
            }
            BVHHitData firstHitRayIntersectTraversal(const Ray& r, PRECISION_TYPE min, PRECISION_TYPE max);
            ~BVHNode() {
                delete (left);
                delete (right);
            }
    };
    
    class BVHTree {
        private:
            BVHNode* root = nullptr;
            
            // splits the objs in the vector based on the provided AABBs
            static BVHPartitionedSpace partition(const std::pair<AABB, AABB>& aabbs, const std::vector<BVHObject>& objs);
            static bool vectorEquals(const BVHPartitionedSpace& oldSpace, const BVHPartitionedSpace& newSpace);
            BVHNode* addObjectsRecur(const std::vector<BVHObject>& objects, const BVHPartitionedSpace& prevSpace);
        public:
            std::vector<Object*> noAABBObjects;
            explicit BVHTree(const std::vector<Object*>& objectsInWorld) {
                addObjects(objectsInWorld);
                #ifdef COMPILE_GUI
                auto aabbVertexData = Shapes::cubeVertexBuilder{};
                if (aabbVAO == nullptr)
                    aabbVAO = std::make_shared<VAO>(aabbVertexData.cubeVerticesRaw, aabbVertexData.cubeUVs);
                #endif
            }
            
            void addObjects(const std::vector<Object*>& objects);
            
            std::vector<BVHObject> rayFirstHitIntersect(const Ray& ray, PRECISION_TYPE min, PRECISION_TYPE max);
            std::vector<BVHObject> rayAnyHitIntersect(const Ray& ray, PRECISION_TYPE min, PRECISION_TYPE max);
            ~BVHTree() {
                delete (root);
            }
    };
    
}

#endif //STEP_2_BVH_H