#include <stdio.h>
#include <stdlib.h>
#include <SDL2/SDL.h>
#include <glad/glad.h>
#include <vector>

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

#include <ft2build.h>
#include FT_FREETYPE_H

/* @lookup:
*  - understand kernals, how they work and how they affect post processing
*  - Check to see why it is necessary to do glBindTexture() 
*    - understand the difference between binding textures, and activating a texture unit
*  - I do not understand how floating point numbers work, so I should probably look into that.
*	 - The normal matrix calculation in the fragment shader for the object affected by light has been mainly copied.
*		 I have tried to understand the formula, and whilst it made some sense, it is not fully clear to me, and I cannot picture it yet.
*		 Revisit the derivation for the normal matrix some time in the future.
*  - Lookup the derivation of the formula for reflecting a vector about a normal. I am doing that for specular lighting, but the learnopengl tutorial
*		 just uses a glsl reflect formula, and at the time of writing it is also very late so I am not in the mood or position to look into it at present.
*  - One of the things I have observed with specular lights is that the circle/specular highlight follows the camera (me) when I move. I would like to figure
*		 out a way by which this does not happen and it remains fixed on the object, at the angle at which it hits. All of this will be made complicated by the fact
*		 that ofcourse everything is actually happening from the cameras' perspective. I would still love to figure this out.
*/

/*
 * @note:
 * Model loading is busted and is missing a lot of things, not that it matters for now, 
 * but it will be useful for the future
 */

typedef uint8_t   u8;
typedef uint16_t u16;
typedef uint32_t u32;
typedef uint64_t u64;

typedef int8_t    s8;
typedef int16_t  s16;
typedef int32_t  s32;
typedef int64_t  s64;

typedef float    r32;
typedef double   r64;

typedef u8        b8;

#include "math.h"

// =========== Shader Loading =============

enum Texture_Filtering { TF_NEAREST, TF_LINEAR };

struct GlTexturedQuad {
  u32 vao;
  u32 vbo;
  u32 texture_id;
};

struct GlShader {
  u32 id;
  s32 model_loc;
  s32 view_loc;
  s32 proj_loc;
};

void gl_shader_load_locations(GlShader *shader)
{
  glUseProgram(shader->id);
  shader->model_loc = glGetUniformLocation(shader->id, "Model");
  shader->view_loc = glGetUniformLocation(shader->id, "View");
  shader->proj_loc = glGetUniformLocation(shader->id, "Projection");

  return;
}

unsigned int gl_create_vertex_shader(char* vertex_shader_source)
{
	unsigned int vertex_shader = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vertex_shader, 1, &vertex_shader_source, NULL);
	glCompileShader(vertex_shader);
    
	int success;
	char info_log[512];
	glGetShaderiv(vertex_shader, GL_COMPILE_STATUS, &success);
	if (!success)
	{
		glGetShaderInfoLog(vertex_shader, 512, NULL, info_log);
		printf("================================\n");
		printf("vertex shader compilation failed:\n%s\n", info_log);
	}
    
	return vertex_shader;
}

unsigned int gl_create_fragment_shader(char* fragment_shader_source)
{
	unsigned int fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragment_shader, 1, &fragment_shader_source, NULL);
	glCompileShader(fragment_shader);
    
	int success;
	char info_log[512];
	glGetShaderiv(fragment_shader, GL_COMPILE_STATUS, &success);
	if (!success)
	{
		glGetShaderInfoLog(fragment_shader, 512, NULL, info_log);
		printf("================================\n");
		printf("fragment shader compilation failed:\n%s\n", info_log);
	}
    
	return fragment_shader;
}

unsigned int gl_create_shader_program(unsigned int vertex_shader, unsigned int fragment_shader)
{
	unsigned int shader_program = glCreateProgram();
    
	glAttachShader(shader_program, vertex_shader);
	glAttachShader(shader_program, fragment_shader);
	glLinkProgram(shader_program);
    
	int success;
	char info_log[512];
	glGetProgramiv(shader_program, GL_LINK_STATUS, &success);
	if (!success)
	{
		glGetProgramInfoLog(shader_program, 512, NULL, info_log);
		printf("================================\n");
		printf("shader program linking failed:\n%s\n", info_log);
	}
    
	glDeleteShader(vertex_shader);
	glDeleteShader(fragment_shader);
    
	return shader_program;
}

unsigned int gl_shader_program(char* vertex_shader_source, char* fragment_shader_source)
{
  unsigned int vertex_shader = gl_create_vertex_shader(vertex_shader_source);
  unsigned int fragment_shader = gl_create_fragment_shader(fragment_shader_source);
  unsigned int shader_program = gl_create_shader_program(vertex_shader, fragment_shader);

  return shader_program;
}

u32 gl_shader_program_from_path(char* vs_path, char* fs_path)
{
  // @todo: add failure handling here
  // what to do if we fail to read the shaders
  size_t read_count;
  char* vs = (char*)SDL_LoadFile(vs_path, &read_count);
  char* fs = (char*)SDL_LoadFile(fs_path, &read_count);

  u32 shader_program = gl_shader_program(vs, fs);

  return shader_program;
}

s32 gl_load_texture(u32 texture_id, char *path, enum Texture_Filtering filter)
{
  s32 width, height, nrChannels;
  stbi_set_flip_vertically_on_load(1);
  unsigned char *data = stbi_load(path, &width, &height, &nrChannels, 0);
  stbi_set_flip_vertically_on_load(0);
  if (data)
  {
    GLenum format;
    if (nrChannels == 1)
      format = GL_RED;
    else if (nrChannels == 3)
      format = GL_RGB;
    else if (nrChannels == 4)
      format = GL_RGBA;

    glBindTexture(GL_TEXTURE_2D, texture_id);
    glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
    glGenerateMipmap(GL_TEXTURE_2D);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    u32 min_filter;
    u32 max_filter;

    if (filter == TF_LINEAR)
    {
      min_filter = GL_LINEAR_MIPMAP_LINEAR;
      max_filter = GL_LINEAR;
    }
    else if (filter == TF_NEAREST)
    {
      min_filter = GL_NEAREST_MIPMAP_LINEAR;
      max_filter = GL_NEAREST;
    }

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, min_filter);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, max_filter);
    stbi_image_free(data);
  }
  else
  {
    // @todo: logging
    printf("failed to load image texture at path: %s", path);
    stbi_image_free(data);
    return -1; 
  }

  return 0;
}

GlTexturedQuad gl_setup_textured_quad(char* texture_path, enum Texture_Filtering filter)
{
  // rendering is clock-wise
  r32 quad_vertices[] = {
    -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, // bottom-left
     1.0f, -1.0f,  0.0f,  1.0f, 0.0f, // bottom-right
     1.0f,  1.0f,  0.0f,  1.0f, 1.0f, // top-right
     1.0f,  1.0f,  0.0f,  1.0f, 1.0f, // top-right
    -1.0f,  1.0f,  0.0f,  0.0f, 1.0f, // top-left
    -1.0f, -1.0f,  0.0f,  0.0f, 0.0f, // bottom-left
  };
  u32 vao, vbo, tex_id;
	glGenVertexArrays(1, &vao);
	glGenBuffers(1, &vbo);

	glBindVertexArray(vao);
  glBindBuffer(GL_ARRAY_BUFFER, vbo);
  glBufferData(GL_ARRAY_BUFFER, sizeof(quad_vertices), &quad_vertices, GL_STATIC_DRAW);
  glEnableVertexAttribArray(0);
  glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(r32), (void*)0);
  glEnableVertexAttribArray(1);
  glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(r32), (void*)(3*sizeof(r32)));
  glBindVertexArray(0);

  glGenTextures(1, &tex_id);
  glActiveTexture(GL_TEXTURE0);
  gl_load_texture(tex_id, texture_path, filter);

  GlTexturedQuad tex_quad;
  tex_quad.vao = vao;
  tex_quad.vbo = vbo;
  tex_quad.texture_id = tex_id;

  return tex_quad;
}

void gl_draw_tex_quad(u32 shader_program, GlTexturedQuad tex_quad)
{
  glUseProgram(shader_program);
  s32 tex_id_loc = glGetUniformLocation(shader_program, "Texture");
  glUniform1i(tex_id_loc, 0);
  glBindVertexArray(tex_quad.vao);
  glBindTexture(GL_TEXTURE_2D, tex_quad.texture_id);
  glDrawArrays(GL_TRIANGLES, 0, 6);
}

// =============== CAMERA STUFF =================
// @note: Be sure to update and refactor the camera
Mat4 camera_create4m(Vec3 camera_pos, Vec3 camera_look, Vec3 camera_up)
{
	// @note: We do this because this allows the camera to have the axis it looks at
	// inwards be the +z axis.
	// If we did not do this, then the inward axis the camera looks at would be negative. 
	// I am still learning from learnopengl.com but I imagine that this was done for conveniences' sake.
	Vec3 camera_forward_dir = normalize3v(subtract3v(camera_pos, camera_look));
	Vec3 camera_right_dir   = normalize3v(cross_multiply3v(camera_up, camera_forward_dir));
	Vec3 camera_up_dir      = normalize3v(cross_multiply3v(camera_forward_dir, camera_right_dir));
    
	Mat4 res = lookat4m(camera_up_dir, camera_forward_dir, camera_right_dir, camera_pos);
    
	return res;
}

Vec3 camera_look_around(r32 angle_pitch, r32 angle_yaw)
{
    Vec3 camera_look = {0.0};
    camera_look.x = cosf(angle_yaw) * cosf(angle_pitch);
    camera_look.y = sinf(angle_pitch);
    camera_look.z = sinf(angle_yaw) * cosf(angle_pitch);
    camera_look = normalize3v(camera_look);
    
    return camera_look;
}

int main(int argc, char* argv[])
{

  // Load freetype
  FT_Library library;
  FT_Face face;

  if (FT_Init_FreeType(&library))
  {
    printf("Error: Could not init freetype library\n");
    return -1;
  }

  FT_Error error = FT_New_Face(library, "assets/fonts/Arial.ttf", 0, &face);
  if (error == FT_Err_Unknown_File_Format) 
  {
    printf("Error: Font Loading Failed. The font format is unsupported.\n");
    return -1;
  }
  else if (error)
  {
    printf("Error: Font Loading Failed. Unknown error code: %d\n", error);
    return -1;
  }

  FT_Set_Pixel_Sizes(face, 0, 48);

	int width = 1024;
	int height = 768;
    
	if (SDL_Init(SDL_INIT_VIDEO) != 0)
	{
		printf("Error initialising SDL2: %s\n", SDL_GetError());
		return 0;
	};
    
	// set opengl version and profile
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
  SDL_GL_SetAttribute( SDL_GL_STENCIL_SIZE, 8 );
    
	// initialise window with opengl flag
	SDL_Window* window = SDL_CreateWindow("SDL Test",
                                          50,
                                          50,
                                          width,
                                          height,
                                          SDL_WINDOW_OPENGL);
    
  SDL_SetRelativeMouseMode(SDL_TRUE);
   
	// create an opengl context
	SDL_GLContext context = SDL_GL_CreateContext(window);
	if (!context)
	{
		printf("OpenGL context creation failed: %s\n", SDL_GetError());
		return -1;
	}
    
    
	// load glad
	if (!gladLoadGLLoader((GLADloadproc)SDL_GL_GetProcAddress)) {
		printf("Failed to initialize Glad\n");
		return 1;
	}

  // vsync controls: 0 = OFF | 1 = ON (Default)
  // SDL_GL_SetSwapInterval(0);
    
  // filesystem playground stuff
  size_t read_count;
  GlShader tex_quad_shader;
  tex_quad_shader.id = gl_shader_program_from_path("./source/shaders/textured_quad.vs.glsl", "./source/shaders/textured_quad.fs.glsl");
  gl_shader_load_locations(&tex_quad_shader);

  GlTexturedQuad tex_quad1 = gl_setup_textured_quad("./assets/smiling.png", TF_LINEAR);
  GlTexturedQuad tex_quad2 = gl_setup_textured_quad("./assets/container.jpg", TF_LINEAR);
  
	// objects
	Vec3 model_translations[] = {
		Vec3{  0.5, 0.0,  0.0}, // 0: origin square
		Vec3{ -1.0, 0.0, -1.0}, // 1: plane
		Vec3{ -1.0, 0.0, -0.5}, // 2: window between squares
		Vec3{  0.0, 0.0,  3.0}, // 3: window infront of origin square
		Vec3{ -2.5, 0.0, -0.5}, // 4: square to the left
		Vec3{ -1.0, 0.0, -1.5}, // 5: random square behind window between squares
    Vec3{ -1.0, 0.0, -8.0}, // 6: reflective plane
    Vec3{ -1.0, 2.0, -8.0}, // 6: refractive "window"
	};

	r32 FOV = 90.0;
	r32 time_curr;
	r32 time_prev = SDL_GetTicks64() / 100.0;
	// camera stuff
	Vec3 camera_pos  = Vec3{ 0.0, 0.0, 10.0f};
	Vec3 preset_up_dir = Vec3{ 0.0, 1.0, 0.0 };
    
  r32 angle_yaw, angle_pitch, angle_roll;
  angle_pitch = (r32)To_Radian(0.0f);
  angle_yaw = (r32)-To_Radian(90.0f);
  
  Vec3 camera_look = camera_look_around(angle_pitch, angle_yaw);
  
  // @todo: remove this, I dont like this and think that this is unnecessary
  Vec3 camera_look_increment;
	r32 camera_speed = 2.5f;
    
	Mat4 view = camera_create4m(camera_pos, camera_look, preset_up_dir);
	
	Mat4 proj = perspective4m((r32)To_Radian(90.0), (r32)width / (r32)height, 0.1f, 1000.0f);

  s32 proj_loc;
  glUniformMatrix4fv(tex_quad_shader.proj_loc, 1, GL_TRUE, proj.buffer);

	glEnable(GL_DEPTH_TEST);
  glEnable(GL_CULL_FACE);
  glCullFace(GL_BACK);

	u8 game_running = true;
    
  u8 hold_lshift = false;
	u8 move_w = false;
	u8 move_a = false;
	u8 move_s = false;
	u8 move_d = false;
    
	while(game_running)
	{
		
		// frame delta
		time_curr = SDL_GetTicks64() / 100.0;
		r32 time_delta = time_curr - time_prev;
		
		r32 camera_speed_adjusted = time_delta * camera_speed;
		camera_look_increment = scaler_multiply3v(camera_look, camera_speed_adjusted);
        
		SDL_Event ev;
		while(SDL_PollEvent(&ev))
		{
            
			// INPUT
			switch (ev.type)
			{
				case (SDL_QUIT):
				{
					game_running = false;
				} break;
				case (SDL_KEYDOWN):
				{
          if (ev.key.keysym.sym == SDLK_LSHIFT)
          {
              hold_lshift = true;
          }
					if (ev.key.keysym.sym == SDLK_w)
					{
						move_w = true;
					}
					if (ev.key.keysym.sym == SDLK_s)
					{
						move_s = true;
					}
					if (ev.key.keysym.sym == SDLK_a)
					{
						move_a = true;
					}
					if (ev.key.keysym.sym == SDLK_d)
					{
						move_d = true;
					}
				} break;
				case (SDL_KEYUP):
				{
          if (ev.key.keysym.sym == SDLK_LSHIFT)
          {
              hold_lshift = false;
          }
					if (ev.key.keysym.sym == SDLK_w)
					{
						move_w = false;
					}
					if (ev.key.keysym.sym == SDLK_s)
					{
						move_s = false;
					}
					if (ev.key.keysym.sym == SDLK_a)
					{
						move_a = false;
					}
					if (ev.key.keysym.sym == SDLK_d)
					{
						move_d = false;
					}
				} break;
        case (SDL_MOUSEMOTION):
        {
          SDL_MouseMotionEvent mouse_event = ev.motion;
          r32 x_motion = (r32)mouse_event.xrel;
          r32 y_motion = (r32)mouse_event.yrel;
					if (x_motion != 0.0 || y_motion != 0.0)
					{
						angle_yaw = angle_yaw + To_Radian(x_motion * 0.1f);
						angle_pitch = clampf(angle_pitch + To_Radian(-y_motion * 0.1f), To_Radian(-89.0f), To_Radian(89.0f));
						
						camera_look = camera_look_around(angle_pitch, angle_yaw);
					}
        } break;
				default:
				{
					break;
				}
			}
		}
        
		// PROCESS
		if (move_w)
		{
			camera_pos = add3v(camera_pos, camera_look_increment);
		}
		if (move_s)
		{
			camera_pos = subtract3v(camera_pos, camera_look_increment);
		}
		if (move_a)
		{
			Vec3 camera_right = normalize3v(cross_multiply3v(preset_up_dir, camera_look));
			Vec3 camera_right_scaled = scaler_multiply3v(camera_right, camera_speed_adjusted);
			camera_pos = add3v(camera_pos, camera_right_scaled);
		}
		if (move_d)
		{
			Vec3 camera_right = normalize3v(cross_multiply3v(preset_up_dir, camera_look));
			Vec3 camera_right_scaled = scaler_multiply3v(camera_right, camera_speed_adjusted);
			camera_pos = subtract3v(camera_pos, camera_right_scaled);
		}
    view = camera_create4m(camera_pos, add3v(camera_pos, camera_look), preset_up_dir);
        
		// object shader program stuff
		time_prev = time_curr;
    glUniformMatrix4fv(tex_quad_shader.view_loc, 1, GL_TRUE, view.buffer);
		
		// OUTPUT
		glClearColor(1.0f, 0.6f, .6f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    {
      glUseProgram(tex_quad_shader.id);
      Vec3 pos = model_translations[0];
      Mat4 translation = translation_matrix4m(pos.x, pos.y, pos.z);
      glUniformMatrix4fv(tex_quad_shader.model_loc, 1, GL_TRUE, translation.buffer);
      gl_draw_tex_quad(tex_quad_shader.id, tex_quad1);
    }

    {
      glUseProgram(tex_quad_shader.id);
      Vec3 pos = model_translations[1];
      Mat4 translation = translation_matrix4m(pos.x, pos.y, pos.z);
      glUniformMatrix4fv(tex_quad_shader.model_loc, 1, GL_TRUE, translation.buffer);
      gl_draw_tex_quad(tex_quad_shader.id, tex_quad2);
    }

		SDL_GL_SwapWindow(window);
	}
	
	// opengl free calls
  // it is up to the renderer to free everything here
  // of course I have not bothered to set that up so it does not matter
	glDeleteVertexArrays(1, &tex_quad1.vao);
	glDeleteVertexArrays(1, &tex_quad2.vao);
	glDeleteBuffers(1, &tex_quad1.vao);
	glDeleteBuffers(1, &tex_quad2.vao);
	
	// sdl free calls
	SDL_GL_DeleteContext(context);
	SDL_DestroyWindow(window);
	SDL_Quit();
	return 0;
}