#include <cassert>
#include <cstdlib>
#include <cstring>
#include <string>
#include <fstream>
#include <iostream>

#include <SDL2/SDL.h>
#include <glm/geometric.hpp>
#include <glm/gtc/matrix_transform.hpp>

#include "shader_testing.h"

#include "dumpShader.inl"


SDL_Window *g_window = 0;
SDL_GLContext g_glContext;
SDL_DisplayMode g_display_mode;

transforms g_xforms;
mesh g_cube_mesh;
const u32 NUM_CUBES = 4;
gl_mesh g_gl_cubes[NUM_CUBES];
glm::vec3 g_cube_locs[NUM_CUBES] = {
	glm::vec3(-10,  10,  0),
	glm::vec3(-10, -10,  0),
	glm::vec3( 10,  10,  0),
	glm::vec3( 10, -10,  0),
};


void
openglDebugCallback(GLenum source,
	GLenum type,
	GLuint id,
	GLenum severity,
	GLsizei length,
	const GLchar* message,
	const void* userParam)
{
	std::cout << ((type == GL_DEBUG_TYPE_ERROR) ? "Error" : "Debug")
		<< (type == GL_DEBUG_TYPE_ERROR ? "** GL Error **" : "")
		<< ", type: " << type
		<< ", severity: " << severity
		<< ", message: " << message << "\n";
}

bool
init()
{
	g_window = SDL_CreateWindow(
		"shader_testing",
		SDL_WINDOWPOS_CENTERED_DISPLAY(0),
		SDL_WINDOWPOS_CENTERED_DISPLAY(0),
		1280,
		720,
		SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);

	if (SDL_Init(SDL_INIT_VIDEO) != 0) {
		std::cout << "error, sdl init: " << SDL_GetError() << "\n";
		return false;
	}

	SDL_GL_SetSwapInterval(1);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS,
		SDL_GL_CONTEXT_FORWARD_COMPATIBLE_FLAG);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK,
		SDL_GL_CONTEXT_PROFILE_CORE);
	SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
	SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
	SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
	SDL_GetCurrentDisplayMode(0, &g_display_mode);

	g_glContext = SDL_GL_CreateContext(g_window);

	if (!g_glContext) {
		std::cout << "error creating context\n";
		return false;
	}

	if (glewInit()) {
		std::cout << "error initializing opengl\n";
		return false;
	}

	std::cout << "opengl vendor: " << glGetString(GL_VENDOR) << "\n";
	std::cout << "opengl renderer: " << glGetString(GL_RENDERER) << "\n";
	std::cout << "opengl version: " << glGetString(GL_VERSION) << "\n";

	glEnable(GL_DEPTH_TEST);
	glEnable(GL_LINE_SMOOTH);
	glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

	glEnable (GL_DEBUG_OUTPUT);
	glDebugMessageCallback((GLDEBUGPROC) openglDebugCallback, 0);

	return g_window != nullptr;
}

const std::string
dumpTextFile(const char* filepath)
{
	std::ifstream fs { filepath };
	std::string s {
		std::istreambuf_iterator<char>(fs),
		std::istreambuf_iterator<char>()};

	if (!fs || !fs.good())
		std::cout << "error reading file, " << filepath << "\n";

	return s;
}

bool
loadShaderProgram(const char* vs, const char* fs, shader* s)
{
	std::string vert = dumpTextFile(vs);
	std::string frag = dumpTextFile(fs);

	if (vert.size() > 0 && frag.size() > 0) {
		const char* vert_c = vert.c_str();
		const char* frag_c = frag.c_str();

		GLuint vs_id = glCreateShader(GL_VERTEX_SHADER);
		GLuint fs_id = glCreateShader(GL_FRAGMENT_SHADER);
		glShaderSource(vs_id, 1, &vert_c, NULL);
		glShaderSource(fs_id, 1, &frag_c, NULL);
		glCompileShader(vs_id);
		glCompileShader(fs_id);
		s->prog_id = glCreateProgram();
		glAttachShader(s->prog_id, vs_id);
		glAttachShader(s->prog_id, fs_id);

		glLinkProgram(s->prog_id);

		glDetachShader(s->prog_id, vs_id);
		glDetachShader(s->prog_id, fs_id);
		glDeleteShader(vs_id);
		glDeleteShader(fs_id);

		GLint is_linked = 0;
		glGetProgramiv(s->prog_id, GL_LINK_STATUS, &is_linked);
		return (is_linked == GL_TRUE);
	}

	return false;
}

transforms
initXformUBO(shader* s,
	float fov,
	float near_clip_plane,
	float aspect_ratio,
	glm::vec3 cam_pos,
	glm::vec3 look_pos)
{
	transforms xforms;
	xforms.view_xform = glm::lookAt(cam_pos, look_pos, glm::vec3(0, 1, 0));
	xforms.proj_xform = glm::infinitePerspective(
		glm::radians(fov), aspect_ratio, near_clip_plane);
	xforms.normal_xform = glm::mat4(1);

	glGenBuffers(1, &s->xforms_ubo_id);
	glBindBufferBase(GL_UNIFORM_BUFFER, 0, s->xforms_ubo_id);
	glBindBuffer(GL_UNIFORM_BUFFER, s->xforms_ubo_id);
	glBufferData(GL_UNIFORM_BUFFER, sizeof(xforms), &xforms, GL_STATIC_DRAW);
	glBindBuffer(GL_UNIFORM_BUFFER, 0);

	return xforms;
};

mesh
initCubeMesh()
{
	mesh m = {0};
	m.num_vertices = 8;
	m.vertices = (glm::vec3*) std::calloc(m.num_vertices, sizeof(glm::vec3));
	m.vertices[0] = { -1,  1, -1 };
	m.vertices[1] = { -1, -1, -1 };
	m.vertices[2] = {  1, -1, -1 };
	m.vertices[3] = {  1,  1, -1 };
	m.vertices[4] = { -1,  1,  1 };
	m.vertices[5] = { -1, -1,  1 };
	m.vertices[6] = {  1, -1,  1 };
	m.vertices[7] = {  1,  1,  1 };

	m.num_indices = 36; // 6 sides, 2 tris per side, 3 verts per tri
	m.indices = (u32*) std::calloc(m.num_indices, sizeof(u32));
	u32 indices[36] = {
		0, 1, 2, 0, 2, 3,
		3, 2, 6, 3, 6, 7,
		7, 6, 5, 7, 5, 4,
		4, 5, 0, 4, 1, 0,
		0, 3, 4, 0, 3, 7,
		1, 2, 5, 2, 6, 5
	};
	std::memcpy(m.indices, indices, m.num_indices * sizeof(u32));

	return m;
}

gl_mesh
loadGLMesh(shader* s, const mesh& m, GLenum draw_mode, const glm::vec3& pos)
{
	gl_mesh gm = {0};
	gm.num_indices = m.num_indices;
	gm.draw_mode = draw_mode;

	glUseProgram(s->prog_id);
	glGenVertexArrays(1, &gm.vao_id);
	glBindVertexArray(gm.vao_id);

	gm.model_xform = (glm::mat4*) std::calloc(1, sizeof(glm::mat4));
	*gm.model_xform = glm::translate(glm::mat4(1), pos);

	gm.model_xform_id = glGetUniformLocation(s->prog_id, "model_xform");
	glUniformMatrix4fv(
		gm.model_xform_id, 1, GL_FALSE, (float*) gm.model_xform);

	glGenBuffers(1, &gm.vert_buf_id);
	glBindBuffer(GL_ARRAY_BUFFER, gm.vert_buf_id);
	glBufferData(GL_ARRAY_BUFFER,
		m.num_vertices * 3 * sizeof(GLfloat),
		m.vertices,
		GL_STATIC_DRAW);
	glVertexAttribPointer(POSITION, 3, GL_FLOAT, GL_FALSE, 0, 0);
	glEnableVertexAttribArray(POSITION);

	glGenBuffers(1, &gm.idx_buf_id);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, gm.idx_buf_id);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER,
		m.num_indices * sizeof(GLuint),
		m.indices,
		GL_STATIC_DRAW);

	glBindVertexArray(0);
	glUseProgram(0);

	return gm;
}

void
loop(shader* s, gl_mesh* mesh_arr, u32 num_meshes)
{
	u32 delay = 60;
	u32 frame_start, frame_time;
	bool running = true;
	SDL_Event e;

	while (running) {
		frame_start = SDL_GetTicks();

		while (SDL_PollEvent(&e)) {
			if (e.type == SDL_QUIT ||
				(e.type == SDL_KEYDOWN && e.key.keysym.sym == SDLK_ESCAPE))
			{
				running = false;
				break;
			}
		}

		glClearColor(0.2, 0.2, 0.2, 1);
		glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
		glUseProgram(s->prog_id);
		glBindBuffer(GL_UNIFORM_BUFFER, s->xforms_ubo_id);

		for (u32 i = 0; i < num_meshes; i++) {
			const gl_mesh& m = mesh_arr[i];
			*m.model_xform = glm::rotate(
				*m.model_xform, (float) M_PI / 60, glm::vec3(0, 1, 0));
			glBindVertexArray(m.vao_id);
			glUniformMatrix4fv(
				m.model_xform_id, 1, GL_FALSE, (float*) m.model_xform);
			glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m.idx_buf_id);
			glDrawElements(m.draw_mode, m.num_indices, GL_UNSIGNED_INT, 0);
			glBindVertexArray(0);
		}

		SDL_GL_SwapWindow(g_window);
		glUseProgram(0);
		frame_time = SDL_GetTicks() - frame_start;

		if (delay > frame_time)
			SDL_Delay(delay - frame_time);
	}
}

void
quit(shader* s)
{
	glDeleteProgram(s->prog_id);
	SDL_GL_DeleteContext(g_glContext);
	SDL_DestroyWindow(g_window);
	SDL_Quit();

	for (u32 i = 0; i < NUM_CUBES; i++) {
		gl_mesh& c = g_gl_cubes[i];

		if (c.model_xform != nullptr)
			free(c.model_xform);
	}

	mesh& cm = g_cube_mesh;

	if (cm.vertices != nullptr)
		free(cm.vertices);
	if (cm.normals != nullptr)
		free(cm.normals);
	if (cm.uvs != nullptr)
		free(cm.uvs);
	if (cm.colors != nullptr)
		free(cm.colors);
	if (cm.indices != nullptr)
		free(cm.indices);
}

int
main()
{
	if (!init())
		return 1;

	shader s = {0};

	if (loadShaderProgram("data/shader.vert", "data/shader.frag", &s)) {
		dumpShader(s.prog_id);
		g_xforms = initXformUBO(&s);
		g_cube_mesh = initCubeMesh();

		for (u32 i = 0; i < NUM_CUBES; i++) {
			g_gl_cubes[i] =
				loadGLMesh(&s, g_cube_mesh, GL_TRIANGLES, g_cube_locs[i]);
			assert(g_gl_cubes[i].vao_id != 0);
		}

		loop(&s, g_gl_cubes, NUM_CUBES);
		quit(&s);
		return 0;
	}

	std::cout << "error loading shader program\n";
	quit(&s);
	return 1;
}