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

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

#pragma comment(lib, "SDL2.lib")
#pragma comment(lib, "SDL2main.lib")

/* @lookup:
*	 - 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 it. 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.
*/

/* @todo:
*/


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

unsigned int create_vertex_shader(const 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 create_fragment_shader(const 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 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;
}

// =========================================================== MATH ==================================================
#define PI 3.14159265358979323846264338327950288
#define Square(x) ((x)*(x))
#define To_Radian(x) ((x) * PI / 180.0f)
#define To_Degree(x) ((x) * 180.0f / PI)

float clampf(float x, float bottom, float top)
{
  if (x < bottom)
  {
    x = bottom;
  } 
  else if (x > top)
  {
    x = top;
  }

  return x;
}

// ==== Vector Math ====

union Vec3 {
	struct {
		float x;
		float y;
		float z;
	};
	float data[3];
};

union Vec4 {
	struct {
		float x;
		float y;
		float z;
		float w;
	};
	float data[4];
};

union Mat4 {
	Vec4 xyzw[4];
	float data[4][4];
	float buffer[16];
};

// ========================================================== Vec3 ==========================================================

Vec3 init3v(float x, float y, float z)
{
	Vec3 res;
	res.x = x;
	res.y = y;
	res.z = z;

	return res;
}

Vec3 scaler_add3v(Vec3 vec, float scaler)
{
	Vec3 res;
	res.x = vec.x + scaler;
	res.y = vec.y + scaler;
	res.z = vec.z + scaler;

	return res;
}

Vec3 scaler_multiply3v(Vec3 vec, float scaler)
{
	Vec3 res;
	res.x = vec.x * scaler;
	res.y = vec.y * scaler;
	res.z = vec.z * scaler;

	return res;
}

Vec3 scaler_divide3v(Vec3 vec, float scaler)
{
	Vec3 res;
	res.x = vec.x / scaler;
	res.y = vec.y / scaler;
	res.z = vec.z / scaler;

	return res;
}


Vec3 add3v(Vec3 a, Vec3 b)
{
	Vec3 res;
	res.x = a.x + b.x;
	res.y = a.y + b.y;
	res.z = a.z + b.z;

	return res;
}

Vec3 subtract3v(Vec3 a, Vec3 b)
{
	Vec3 res;
	res.x = a.x - b.x;
	res.y = a.y - b.y;
	res.z = a.z - b.z;

	return res;
}

float dot_multiply3v(Vec3 a, Vec3 b)
{
	float x = a.x * b.x;
	float y = a.y * b.y;
	float z = a.z * b.z;

	float res = x + y + z;

	return res;
}

float magnitude3v(Vec3 vec)
{
	float res = sqrtf(Square(vec.x) + Square(vec.y) + Square(vec.z));
	return res;
}

Vec3 normalize3v(Vec3 vec)
{
	float magnitude = magnitude3v(vec);
	Vec3 res = scaler_divide3v(vec, magnitude);
	return res;
}

#ifndef FUN_CALCS
float angle3v(Vec3 a, Vec3 b)
{
	Vec3 a_norm = normalize3v(a);
	Vec3 b_norm = normalize3v(b);

	float dot_product = dot_multiply3v(a_norm, b_norm);
	float res = acosf(dot_product);

	return res;
}
#endif

Vec3 cross_multiply3v(Vec3 a, Vec3 b)
{
	Vec3 res;
	res.x = (a.y * b.z) - (a.z * b.y);
	res.y = (a.z * b.x) - (a.x * b.z);
	res.z = (a.x * b.y) - (a.y * b.x);

	return res;
}

// ============================================== Vec4, Mat4 ==============================================

Vec4 init4v(float x, float y, float z, float w)
{
	Vec4 res;
	res.x = x;
	res.y = y;
	res.z = z;
	res.w = w;

	return res;
}

Mat4 init_value4m(float value)
{
	Mat4 res = {0};
	res.data[0][0] = value;
	res.data[1][1] = value;
	res.data[2][2] = value;
	res.data[3][3] = value;

	return res;
}

// @note: These operations are just defined and not expressed. They are kept here for completeness sake BUT
// since I have not had to do anything related to these, I have not created them.
Vec4 scaler_add4v(Vec4 vec, float scaler);
Vec4 scaler_subtract4v(Vec4 vec, float scaler);
Vec4 scaler_multiply4v(Vec4 vec, float scaler);
Vec4 scaler_divide4v(Vec4 vec, float scaler);
Vec4 add4v(Vec4 a, Vec4 b);
Vec4 subtract4v(Vec4 a, Vec4 b);
Vec4 dot_multiply4v(Vec4 a, Vec4 b);

Mat4 add4m(Mat4 a, Mat4 b)
{
	Mat4 res;
	// row 0
	res.data[0][0] = a.data[0][0] + b.data[0][0];
	res.data[0][1] = a.data[0][1] + b.data[0][1];
	res.data[0][2] = a.data[0][2] + b.data[0][2];
	res.data[0][3] = a.data[0][3] + b.data[0][3];
	// row 1
	res.data[1][0] = a.data[1][0] + b.data[1][0];
	res.data[1][1] = a.data[1][1] + b.data[1][1];
	res.data[1][2] = a.data[1][2] + b.data[1][2];
	res.data[1][3] = a.data[1][3] + b.data[1][3];
	// row 2
	res.data[2][0] = a.data[2][0] + b.data[2][0];
	res.data[2][1] = a.data[2][1] + b.data[2][1];
	res.data[2][2] = a.data[2][2] + b.data[2][2];
	res.data[2][3] = a.data[2][3] + b.data[2][3];
	// row 3
	res.data[3][0] = a.data[3][0] + b.data[3][0];
	res.data[3][1] = a.data[3][1] + b.data[3][1];
	res.data[3][2] = a.data[3][2] + b.data[3][2];
	res.data[3][3] = a.data[3][3] + b.data[3][3];
	
	return res;
}

Mat4 subtract4m(Mat4 a, Mat4 b)
{
	Mat4 res;
	// row 0
	res.data[0][0] = a.data[0][0] - b.data[0][0];
	res.data[0][1] = a.data[0][1] - b.data[0][1];
	res.data[0][2] = a.data[0][2] - b.data[0][2];
	res.data[0][3] = a.data[0][3] - b.data[0][3];
	// row 1
	res.data[1][0] = a.data[1][0] - b.data[1][0];
	res.data[1][1] = a.data[1][1] - b.data[1][1];
	res.data[1][2] = a.data[1][2] - b.data[1][2];
	res.data[1][3] = a.data[1][3] - b.data[1][3];
	// row 2
	res.data[2][0] = a.data[2][0] - b.data[2][0];
	res.data[2][1] = a.data[2][1] - b.data[2][1];
	res.data[2][2] = a.data[2][2] - b.data[2][2];
	res.data[2][3] = a.data[2][3] - b.data[2][3];
	// row 3
	res.data[3][0] = a.data[3][0] - b.data[3][0];
	res.data[3][1] = a.data[3][1] - b.data[3][1];
	res.data[3][2] = a.data[3][2] - b.data[3][2];
	res.data[3][3] = a.data[3][3] - b.data[3][3];

	return res;
}

Vec4 multiply4vm(Vec4 vec, Mat4 mat)
{
  /*
   * @note: Incase I get confused about this in the future.
   *
   * Everything is row-order, which means that things in memory are laid out row first. So with a sample matrix
   * we have this order in memory: r1c1 r1c2 r1c3 r1c4 r2c1 ... (r = row, c = column). The same holds true for 
   * vectors. (maybe move this explanation to the top)
   *
   * Now, multiply4vm will multiply a vector with a matrix. Conventionally that does not make any sense as
   * a vector is usually 4x1 and a matrix ix 4x4.
   * What this function considers a vector, while it is a vector, it is infact a row from a matrix, which
   * means that the vector is 1x4 and the matrix is 4x4.
   * 
   * The function is meant to supplement the matrix multiplication process to alleviate the multiple lines of code
   * we have to write when multiplying the row of a left matrix to each column of the right matrix
   */
	Vec4 res = { 0 };
	res.x = (mat.data[0][0] * vec.x) + (mat.data[0][1] * vec.y) + (mat.data[0][2] * vec.z) + (mat.data[0][3] * vec.w);
	res.y = (mat.data[1][0] * vec.x) + (mat.data[1][1] * vec.y) + (mat.data[1][2] * vec.z) + (mat.data[1][3] * vec.w);
	res.z = (mat.data[2][0] * vec.x) + (mat.data[2][1] * vec.y) + (mat.data[2][2] * vec.z) + (mat.data[2][3] * vec.w);
	res.w = (mat.data[3][0] * vec.x) + (mat.data[3][1] * vec.y) + (mat.data[3][2] * vec.z) + (mat.data[3][3] * vec.w);
	
	return res;
}

Mat4 multiply4m(Mat4 a, Mat4 b)
{
	Mat4 res = { 0 };
	
	res.xyzw[0] = multiply4vm(a.xyzw[0], b);
	res.xyzw[1] = multiply4vm(a.xyzw[1], b);
	res.xyzw[2] = multiply4vm(a.xyzw[2], b);
	res.xyzw[3] = multiply4vm(a.xyzw[3], b);

	return res;
}

// ==== Matrix Transformation ====

Mat4 scaling_matrix4m(float x, float y, float z)	// generates a 4x4 scaling matrix for scaling each of the x,y,z axis
{
	Mat4 res = init_value4m(1.0f);
	res.data[0][0] = x;
	res.data[1][1] = y;
	res.data[2][2] = z;

	return res;
}

Mat4 translation_matrix4m(float x, float y, float z)	// generates a 4x4 translation matrix for translation along each of the x,y,z axis
{
	Mat4 res = init_value4m(1.0f);
	res.data[0][3] = x;
	res.data[1][3] = y;
	res.data[2][3] = z;

	return res;
}

Mat4 rotation_matrix4m(float angle_radians, Vec3 axis)	// generates a 4x4 rotation matrix for rotation along each of the x,y,z axis
{
	Mat4 res = init_value4m(1.0f);
	axis = normalize3v(axis);
	
	float cos_theta = cosf(angle_radians);
	float sin_theta = sinf(angle_radians);
	float cos_value = 1.0f - cos_theta;

	res.data[0][0] = (axis.x * axis.x * cos_value) + cos_theta;
	res.data[0][1] = (axis.x * axis.y * cos_value) + (axis.z * sin_theta);
	res.data[0][2] = (axis.x * axis.z * cos_value) - (axis.y * sin_theta);
	
	res.data[1][0] = (axis.x * axis.y * cos_value) - (axis.z * sin_theta);
	res.data[1][1] = (axis.y * axis.y * cos_value) + cos_theta;
	res.data[1][2] = (axis.y * axis.z * cos_value) + (axis.x * sin_theta);

	res.data[2][0] = (axis.x * axis.z * cos_value) + (axis.y * sin_theta);
	res.data[2][1] = (axis.z * axis.y * cos_value) - (axis.x * sin_theta);
	res.data[2][2] = (axis.z * axis.z * cos_value) + cos_theta;

	return res;
}

Mat4 perspective_projection_matrix4m(float left, float right, float bottom, float top, float near, float far)
{
	Mat4 res = { 0 };
	
	res.data[0][0] = (2.0 * near)/(right - left);
	res.data[0][2] = (right + left)/(right - left);

	res.data[1][1] = (2.0 * near)/(top - bottom);
	res.data[1][2] = (top + bottom)/(top - bottom);

	res.data[2][2] = -(far + near)/(far - near);
	res.data[2][3] = -2.0*far*near/(far - near);

	res.data[3][2] = -1.0;

	return res;
}

Mat4 perspective4m(float fov, float aspect_ratio, float near, float far)
{
	float cotangent = 1.0f / tanf(fov / 2.0f);
	
	Mat4 res = { 0 };

	res.data[0][0] = cotangent / aspect_ratio;
	
	res.data[1][1] = cotangent;

	res.data[2][2] = -(far + near) / (far - near);
	res.data[2][3] = -2.0 * far * near / (far - near);

	res.data[3][2] = -1.0;

	return res;
}

Mat4 lookat4m(Vec3 up, Vec3 forward, Vec3 right, Vec3 position)
{
	/*
	* @note: The construction of the lookat matrix is not obvious. For that reason here is the supplemental matrial I have used to understand
	* things while I maintain my elementary understanding of linear algebra.
	* 1. This youtube video (https://www.youtube.com/watch?v=3ZmqJb7J5wE) helped me understand why we invert matrices. 
	*		 It is because, we are moving from the position matrix which is a global to the view matrix which
	*		 is a local. It won't be very clear from this illustration alone, so you would be best served watching the video and recollecting and understanding from there.
	* 2. This article (https://twodee.org/blog/17560) derives (or rather shows), in a very shallow way how we get to the look at matrix.
	*/
	Mat4 res = init_value4m(1.0);
	res.xyzw[0] = Vec4{ right.x,		right.y,	 right.z,		-dot_multiply3v(right, position) };
	res.xyzw[1] = Vec4{ up.x,				up.y,			 up.z,			-dot_multiply3v(up, position) };
	res.xyzw[2] = Vec4{ forward.x,  forward.y, forward.z, -dot_multiply3v(forward, position) };
	res.xyzw[3] = Vec4{ 0.0f,				0.0f,			 0.0f,			 1.0f };

	return res;
}

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(float angle_pitch, float 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[])
{
	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);

	// 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;
	}

	const char* vertex_source =
		"#version 330 core\n"
		"layout(location = 0) in vec3 position;\n"
		"layout(location = 1) in vec3 normal;\n"
		"uniform mat4 Model;\n"
		"uniform mat4 View;\n"
		"uniform mat4 Projection;\n"
    "out vec3 fragNormal;\n"
    "out vec3 worldPosition;\n"
		"void main() {\n"
		"    gl_Position = Projection * View * Model * vec4(position, 1.0);\n"
    "    worldPosition = vec3(Model * vec4(position, 1.0));\n"
    "    fragNormal = mat3(transpose(inverse(Model))) * normal;\n"
		"		 fragNormal = normalize(normal);\n"
		"}";

	const char* fragment_source =
		"#version 330 core\n"
		"in vec3 fragNormal;\n"
		"in vec3 worldPosition;\n"
		"out vec4 FragColor;\n"
		"uniform sampler2D smilingTexture;\n"
		"uniform sampler2D containerTexture;\n"
    "uniform vec3	     lightPosition;\n"
		"uniform vec3			 cameraPosition;\n"
    "uniform vec4      lightColor;\n"
		"uniform vec4      objectColor;\n"
		"void main() {\n"
    "		 float ambientLightStrength = 0.1;\n"
		"		 vec4 ambientLight = ambientLightStrength * lightColor;\n"
		"\n"
		"//	 @note: Diffuse calculations\n"
    "    vec3 lightDir = normalize(lightPosition - worldPosition);\n"
    "    float diffuseStrength = max(dot(lightDir, fragNormal), 0.0);\n"
		"    vec4 diffuseLight = diffuseStrength * lightColor;\n"
		"\n"
		"//	 @note: Specular calculations\n"
		"		 float specularStrength = 0.5;\n"
		"		 vec3  viewDir		      = normalize(cameraPosition - worldPosition);\n"
		"		 vec3  reflectDir				= reflect(-lightDir, fragNormal);\n"
		"		 float specularity			= max(dot(viewDir, reflectDir), 0.0);\n"
		"		 float shininess				= pow(specularity, 128.0);\n"
		"		 vec4  specularLight		= specularStrength * shininess * lightColor;\n"
		" "
		"\n"
		"    vec4 color = (ambientLight + diffuseLight + specularLight) * objectColor;\n"
		"    FragColor = color;\n"

		"}\n";

  const char* light_vertex_source = 
		"#version 330 core\n"
		"layout(location = 0) in vec3 position;\n"
		"uniform mat4 Model;\n"
		"uniform mat4 View;\n"
		"uniform mat4 Projection;\n"
		"void main() {\n"
		"    gl_Position = Projection * View * Model * vec4(position.x, position.y, position.z, 1.0);\n"
		"}\n";

  const char* light_fragment_source =
		"#version 330 core\n"
		"out vec4 FragColor;\n"
		"void main() {\n"
		"    FragColor = vec4(1.0);\n"
		"}\n";


	GLuint vertex_shader = create_vertex_shader(vertex_source);
	GLuint fragment_shader = create_fragment_shader(fragment_source);
	GLuint shader_program = create_shader_program(vertex_shader, fragment_shader);
	printf("Successfully compiled normal shaders.\n");
	GLuint light_vs = create_vertex_shader(light_vertex_source);
	GLuint light_fs = create_fragment_shader(light_fragment_source);
	GLuint light_sp = create_shader_program(light_vs, light_fs);

	GLfloat rect_vertices[] = {
		// Position						// Color						// Texture
		-0.5f, -0.5f, 0.0f,		0.6f, 0.3f, 0.3f,		0.0f, 0.0f,		// bottom left
		 0.5f, -0.5f, 0.0f,		0.6f, 0.5f, 0.5f,		1.0f, 0.0f,		// bottom right
		-0.5f,  0.5f, 0.0f,   0.4f, 0.3f, 0.2f,		0.0f, 1.0f,		// top left
		 0.5f,  0.5f, 0.0f,		0.4f, 0.5f, 0.6f,		1.0f, 1.0f		// top right
	};

	unsigned int rect_indices[] = {
		0, 1, 2,
		2, 1, 3
	};

	float cube_normal_vertices[] = {
		-0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
		 0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
		 0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
		 0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
		-0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,
		-0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,

		-0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,           // this is the front side as seen from the camera starting at > 0.0f
		 0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,
		 0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,
		 0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,
		-0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,
		-0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,

		-0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,
		-0.5f,  0.5f, -0.5f, -1.0f,  0.0f,  0.0f,
		-0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,
		-0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,
		-0.5f, -0.5f,  0.5f, -1.0f,  0.0f,  0.0f,
		-0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,

		 0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,
		 0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,
		 0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,
		 0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,
		 0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,
		 0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,

		-0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,
		 0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,
		 0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,
		 0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,
		-0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,
		-0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,

		-0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,
		 0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,
		 0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
		 0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
		-0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,
		-0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f
	};

	float cube_vertices[] = {
		-0.5f, -0.5f, -0.5f,  0.0f, 0.0f,
		 0.5f, -0.5f, -0.5f,  1.0f, 0.0f,
		 0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
		 0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
		-0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
		-0.5f, -0.5f, -0.5f,  0.0f, 0.0f,

		-0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
		 0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
		 0.5f,  0.5f,  0.5f,  1.0f, 1.0f,
		 0.5f,  0.5f,  0.5f,  1.0f, 1.0f,
		-0.5f,  0.5f,  0.5f,  0.0f, 1.0f,
		-0.5f, -0.5f,  0.5f,  0.0f, 0.0f,

		-0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
		-0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
		-0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
		-0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
		-0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
		-0.5f,  0.5f,  0.5f,  1.0f, 0.0f,

		 0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
		 0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
		 0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
		 0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
		 0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
		 0.5f,  0.5f,  0.5f,  1.0f, 0.0f,

		-0.5f, -0.5f, -0.5f,  0.0f, 1.0f,
		 0.5f, -0.5f, -0.5f,  1.0f, 1.0f,
		 0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
		 0.5f, -0.5f,  0.5f,  1.0f, 0.0f,
		-0.5f, -0.5f,  0.5f,  0.0f, 0.0f,
		-0.5f, -0.5f, -0.5f,  0.0f, 1.0f,

		-0.5f,  0.5f, -0.5f,  0.0f, 1.0f,
		 0.5f,  0.5f, -0.5f,  1.0f, 1.0f,
		 0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
		 0.5f,  0.5f,  0.5f,  1.0f, 0.0f,
		-0.5f,  0.5f,  0.5f,  0.0f, 0.0f,
		-0.5f,  0.5f, -0.5f,  0.0f, 1.0f
	};
	
	GLuint light_VBO, light_VAO;
	{
		glGenVertexArrays(1, &light_VAO);
		glGenBuffers(1, &light_VBO);

		glBindVertexArray(light_VAO);

		glBindBuffer(GL_ARRAY_BUFFER, light_VBO);
		glBufferData(GL_ARRAY_BUFFER, sizeof(cube_vertices), cube_vertices, GL_STATIC_DRAW);

		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)0);
		glEnableVertexAttribArray(0);

		glBindVertexArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, 0);
	}

	GLuint VBO, VAO, EBO, container_texture, smiling_texture;
	{
		glGenVertexArrays(1, &VAO);
		glGenBuffers(1, &VBO);
		//glGenBuffers(1, &EBO);

		glBindVertexArray(VAO);


		glBindBuffer(GL_ARRAY_BUFFER, VBO);
		glBufferData(GL_ARRAY_BUFFER, sizeof(cube_normal_vertices), cube_normal_vertices, GL_STATIC_DRAW);

		//glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
		//glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(rect_indices), rect_indices, GL_STATIC_DRAW);

		// Position Attribute
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)0);
		glEnableVertexAttribArray(0);

		// Color Attribute
		//glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
		//glEnableVertexAttribArray(1);

		// Texture Attributes
		//glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
		//glEnableVertexAttribArray(1);

		// normal attribute
		glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
		glEnableVertexAttribArray(1);

		int img_width, img_height, img_nrChannels;

		// ==== Texture 1 ====
		glGenTextures(1, &smiling_texture);
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, smiling_texture);

		const char* smiling_path = "assets/smiling.png";
		stbi_set_flip_vertically_on_load(1);
		unsigned char* smiling_data = stbi_load(smiling_path, &img_width, &img_height, &img_nrChannels, 0);

		// Texture Properties
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);

		// Texture Data
		if (smiling_data)
		{
			glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, img_width, img_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, smiling_data);
			glGenerateMipmap(GL_TEXTURE_2D);
		}
		else
		{
			printf("Error! Failed to load image from `%s`\n", smiling_path);
		}
		stbi_image_free(smiling_data);

		// ==== Texture 2 ====
		glGenTextures(1, &container_texture);
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, container_texture);
		const char* container_path = "assets/container.jpg";
		unsigned char* container_data = stbi_load(container_path, &img_width, &img_height, &img_nrChannels, 0);

		// Texture Properties
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);

		// Texture Data
		if (container_data)
		{
			glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, img_width, img_height, 0, GL_RGB, GL_UNSIGNED_BYTE, container_data);
			glGenerateMipmap(GL_TEXTURE_2D);
		}
		else
		{
			printf("Error! Failed to load image from `%s`\n", container_path);
		}
		stbi_image_free(container_data);

		glBindVertexArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, 0);
		//glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
		glBindTexture(GL_TEXTURE_2D, 0);
	}

	Vec3 light_location = Vec3{ 0.0, 0.0, 3.0 };
	glUseProgram(shader_program);

	// texture uniforms
	int smiling_loc = glGetUniformLocation(shader_program, "smilingTexture");
	glUniform1i(smiling_loc, 0);

	int container_loc = glGetUniformLocation(shader_program, "containerTexture");
	glUniform1i(container_loc, 1);

  Vec4 light_color = Vec4{1.0, 1.0, 1.0, 1.0};
  int light_uniform_loc = glGetUniformLocation(shader_program, "lightColor");
  glUniform4fv(light_uniform_loc, 1, light_color.data);
	
	Vec4 object_color = Vec4{ 1.0, 1.0, 0.0, 1.0 };
	int object_uniform_loc = glGetUniformLocation(shader_program, "objectColor");
	glUniform4fv(object_uniform_loc, 1, object_color.data);
	
	int light_pos_loc = glGetUniformLocation(shader_program, "lightPosition");
	glUniform3fv(light_pos_loc, 1, light_location.data);

	int camera_pos_loc = glGetUniformLocation(shader_program, "cameraPosition");

	// objects
	Vec3 model_translations[] = {
		Vec3{  0.0, 0.0,  0.0},
		Vec3{ -5.0, -1.0, -4.0},
		Vec3{  5.0,  2.0, -4.0},
		Vec3{ -3.0,  5.0, -6.0},
		Vec3{  3.0, -7.0, -6.0},
	};

	float FOV = 90.0;
	float time_curr;
	float time_prev = SDL_GetTicks64() / 100.0;
	uint32_t model_loc = glGetUniformLocation(shader_program, "Model");

	// camera stuff
	Vec3 camera_pos  = Vec3{ 0.0, 5.0, 10.0f};
	Vec3 preset_up_dir = Vec3{ 0.0, 1.0, 0.0 };

  float angle_yaw, angle_pitch, angle_roll;
  angle_pitch = To_Radian(0.0);
  angle_yaw = -To_Radian(90.0);

  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;
	float camera_speed = 1.0f;

	Mat4 view = camera_create4m(camera_pos, camera_look, preset_up_dir);
	
	uint32_t view_loc = glGetUniformLocation(shader_program, "View");
	glUniformMatrix4fv(view_loc, 1, GL_TRUE, view.buffer);

	Mat4 proj = perspective4m(To_Radian(90.0), (float)width / (float)height, 0.1, 100.0);
	uint32_t proj_loc = glGetUniformLocation(shader_program, "Projection");
	glUniformMatrix4fv(proj_loc, 1, GL_TRUE, proj.buffer);
	
	glUseProgram(light_sp);
	Mat4 light_model = translation_matrix4m(light_location.x, light_location.y, light_location.z);
	//Mat4 light_model = init_value4m(1.0);
	//light_model = multiply4m(light_translation, light_model);
	uint32_t light_model_loc = glGetUniformLocation(light_sp, "Model");
	glUniformMatrix4fv(light_model_loc, 1, GL_TRUE, light_model.buffer);

	uint32_t light_view_loc = glGetUniformLocation(light_sp,  "View");
	glUniformMatrix4fv(light_view_loc, 1, GL_TRUE, view.buffer);

	uint32_t light_proj_loc = glGetUniformLocation(light_sp,  "Projection");
	glUniformMatrix4fv(light_proj_loc, 1, GL_TRUE, proj.buffer);

	glEnable(GL_DEPTH_TEST);

	bool game_running = true;
	bool move_w = false;
	bool move_a = false;
	bool move_s = false;
	bool move_d = false;
	while(game_running)
	{
		
		// frame delta
		time_curr = SDL_GetTicks64() / 100.0;
		float time_delta = time_curr - time_prev;
		
		float 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_SPACE)
					{}
					if (ev.key.keysym.sym == SDLK_UP)
					{
#if TESTING_FOV
						FOV += 5.0;
						Mat4 proj = perspective4m(To_Radian(FOV), (float)width / (float)height, 0.1, 100.0);
#endif
					}
					if (ev.key.keysym.sym == SDLK_DOWN)
					{
#if TESTING_FOV
						FOV -= 5.0;
						Mat4 proj = perspective4m(To_Radian(FOV), (float)width / (float)height, 0.1, 100.0);
#endif
					}
					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_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;
          float x_motion = mouse_event.xrel;
          float y_motion = 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);
		}
		// light_location.z = 10.00 * sinf(time_curr/10.0);
 		view = camera_create4m(camera_pos, add3v(camera_pos, camera_look), preset_up_dir);
		// object shader program stuff
		glUseProgram(shader_program);
		glUniformMatrix4fv(view_loc, 1, GL_TRUE, view.buffer);
		glUniform3fv(light_pos_loc, 1, light_location.data);
		glUniform3fv(camera_pos_loc, 1, camera_pos.data);
		
		// light/lamp shader program stuff
		glUseProgram(light_sp);
		light_model = translation_matrix4m(light_location.x, light_location.y, light_location.z);
		glUniformMatrix4fv(light_model_loc, 1, GL_TRUE, light_model.buffer);
		glUniformMatrix4fv(light_view_loc, 1, GL_TRUE, view.buffer);
		
		time_prev = time_curr;
		

		// OUTPUT
		glClearColor(1.0f, 0.6f, .6f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, smiling_texture);

		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, container_texture);
		
		glUseProgram(light_sp);
		glBindVertexArray(light_VAO);
		glDrawArrays(GL_TRIANGLES, 0, 36);
		glBindVertexArray(0);
		glUseProgram(0);

		glUseProgram(shader_program);
		glBindVertexArray(VAO);
		
		for (int i = 0; i < 5; i++)
		{
			Vec3 translation_iter = model_translations[i];
			Mat4 model = init_value4m(1.0);
			Mat4 model_translation = translation_matrix4m(translation_iter.x, translation_iter.y, translation_iter.z);
			model = multiply4m(model_translation, model);
			glUniformMatrix4fv(model_loc, 1, GL_TRUE, model.buffer);
			glDrawArrays(GL_TRIANGLES, 0, 36);
		}

		glBindVertexArray(0);

		
		SDL_GL_SwapWindow(window);
	}
	
	// opengl free calls
	glDeleteVertexArrays(1, &VAO);
	glDeleteBuffers(1, &VBO);
	glDeleteProgram(shader_program);
	
	// sdl free calls
	SDL_GL_DeleteContext(context);
	SDL_DestroyWindow(window);
	SDL_Quit();
	return 0;
}