/*
 *  <Short Description>
 *  Copyright (C) 2023  Brett Terpstra
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#ifndef BLT_WITH_GRAPHICS_MODEL_H
#define BLT_WITH_GRAPHICS_MODEL_H

#include <blt/math/vectors.h>
#include <vector>
#include <blt/gfx/gl_includes.h>
#include <variant>
#include <array>
#include <blt/std/hashmap.h>

namespace blt::gfx
{
    class model_data
    {
        public:
        private:
            std::vector<blt::vec3f> vertices;
            std::vector<blt::vec2f> uvs;
            std::vector<blt::vec3f> normals;
    };
    
    struct vbo_t
    {
        GLuint bufferID_ = 0;
        GLsizeiptr size_ = 0;
        GLint buffer_type;
        GLint memory_type;
        
        void create(GLint type);
        
        void bind() const;
        
        void allocate(GLsizeiptr size, GLint memory_type = GL_STATIC_DRAW, void* data = nullptr);
        
        void sub_update(GLsizeiptr offset, GLsizeiptr size, void* data);
        
        void update(GLsizeiptr size, void* data);
        
        void destroy();
    };
    
    /**
     * Since most VAOs will not use more than 8 VBOs it makes no sense to heap allocate memory to store them
     * This class is used to make that easier to handle
     */
    class static_dynamic_array
    {
        private:
            static constexpr size_t DATA_SIZE = 8;
            typedef std::array<vbo_t, DATA_SIZE> array_t;
            std::variant<array_t, vbo_t*> data_;
            size_t size_ = DATA_SIZE;
            size_t max = 0;
            
            void swap();
        
        public:
            static_dynamic_array();
            
            static_dynamic_array(const static_dynamic_array& copy) = delete;
            
            static_dynamic_array(static_dynamic_array&& move) noexcept = default;
            
            static_dynamic_array& operator=(const static_dynamic_array& copy) = delete;
            
            static_dynamic_array& operator=(static_dynamic_array&& move) noexcept = default;
            
            vbo_t& operator[](size_t index);
            
            [[nodiscard]] inline size_t used() const noexcept
            {
                return max;
            }
            
            ~static_dynamic_array()
            {
                if (std::holds_alternative<vbo_t*>(data_))
                    delete[] std::get<vbo_t*>(data_);
            }
    };
    
    /**
     * basic VAO class.
     */
    class basic_vertex_array
    {
        private:
            GLuint vaoID;
            static_dynamic_array VBOs;
            HASHSET<GLuint> used_attributes;
            vbo_t element;
        public:
            basic_vertex_array();
            
            basic_vertex_array(const basic_vertex_array&) = delete;
            
            basic_vertex_array(basic_vertex_array&&) = delete;
            
            basic_vertex_array& operator=(const basic_vertex_array&) = delete;
            
            basic_vertex_array& operator=(basic_vertex_array&&) = delete;
            
            /**
             * This function takes ownership of the underlying VBO (GPU side). It will be freed when the basic vertex array is deleted
             * @param vbo vbo to bind to this attribute
             * @param attribute_number attribute number to bind to
             * @param coordinate_size size of the data (number of
             * @param type type of data
             * @param stride how many bytes this data takes (for the entire per-vertex data structure) 0 will assume packed data
             * @param offset offset into the data structure to where the data is stored
             */
            void bindVBO(const vbo_t& vbo, int attribute_number, int coordinate_size, GLenum type, int stride, long offset);
            
            /**
             * Returns a non-owning reference to a vbo allowing for updating the VBO
             * The VBO is considered invalid if its ID is 0
             */
            inline vbo_t& operator[](size_t index)
            {
                return VBOs[index];
            }
            
            inline void bind()
            {
                glBindVertexArray(vaoID);
            }
            
            ~basic_vertex_array();
    };
    
}

#endif //BLT_WITH_GRAPHICS_MODEL_H