#define GL_GLEXT_PROTOTYPES

#include <stdio.h>
#include <time.h> 
#include <stdlib.h>
#include <GL/gl.h>
#include <SDL3/SDL.h>

void checkGlError() {
    const char *err = SDL_GetError();
    if (*err != 0) {
        printf("OpenGL error: %s", err);
    }
}

/// returns 0 if failed.
GLuint compile_shader(GLuint type, const char *src) {
    GLuint id = glCreateShader(type);
    glShaderSource(id, 1, &src, 0);
    glCompileShader(id);

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE) {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &result);
        char *message = alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        printf("failed to compile %s shader\n", type == GL_VERTEX_SHADER ? "vertex" : "fragment");
        printf("%s\n", message);
        glDeleteShader(id);
        return 0;
    }

    return id;
}

/// returns 0 if failed.
GLuint create_shader(const char *fragment_src) {
    GLuint program = glCreateProgram();
    GLuint fragment_shader = compile_shader(GL_FRAGMENT_SHADER, fragment_src);
    if (!(fragment_shader == 0)) {
        glAttachShader(program, fragment_shader);
        glLinkProgram(program);
        glValidateProgram(program);
        glDeleteShader(fragment_shader);
        return program;
    } else {
        return 0;
    }
}

GLuint load_shader(const char *path) {
    FILE *handle = fopen(path, "r");
    fseek(handle, 0L, SEEK_END);
    long length = ftell(handle);
    fseek(handle, 0L, SEEK_SET);
    char *string = malloc(length * sizeof(char));
    if (!fread(string, sizeof(char), length, handle)) {
        printf("failed to read shader file");
        exit(1);
    }
    fclose(handle);

    GLuint shader = create_shader(string);

    if (shader == 0) {
        // print file
        int line_count = 1;
        printf("%i\t", line_count);
        line_count++;
        for (int i = 0; i < length; i++) {
            printf("%c", string[i]);
            if (string[i] == '\n') {
                printf("%i\t", line_count);
                line_count++;
            }
        }
        printf("\n");
    }

    free(string);
    return shader;
}

struct timespec program_start;

void init_timer() {
    clock_gettime(CLOCK_MONOTONIC, &program_start);
}

double time_since_start() {
    struct timespec now;
    clock_gettime(CLOCK_MONOTONIC, &now);

    return (now.tv_sec - program_start.tv_sec) +
           (now.tv_nsec - program_start.tv_nsec) / 1e9;
}

int main() {
    init_timer();

    printf("Good Morning 🍵\n");
    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window* window = SDL_CreateWindow("SDL3 OpenGL Cube",
    800, 600, SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
    if (!window) {
        printf("CreateWindow Error: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }
    
    SDL_GLContext glContext = SDL_GL_CreateContext(window);
    if (!glContext) {
        printf("GL Context Error: %s\n", SDL_GetError());
        SDL_DestroyWindow(window);
        SDL_Quit();
        return 1;
    }
    glEnable(GL_DEPTH_TEST);

    SDL_Event e;
    int running = 1;

    GLuint shader = load_shader("fragment.glsl"); //create_shader(fragment_shader_source);

    int w, h;
    double time;
    while (running) {
        while (SDL_PollEvent(&e)) {
            if (e.type == SDL_EVENT_QUIT) running = false;
            if (e.type == SDL_EVENT_WINDOW_RESIZED) {
                SDL_GetWindowSize(window, &w, &h);
            }
        }
        checkGlError();

        // Rendorrrr
        glViewport(0, 0, w, h);

        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);  // Dark gray background
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // Shader parameters.
        glUseProgram(shader);
        
        int uniform_WindowSize = glGetUniformLocation(shader, "WindowSize");
        glUniform2f(uniform_WindowSize, w, h);

        time = time_since_start();
        int uniform_time = glGetUniformLocation(shader, "time");
        glUniform1f(uniform_time, (float)time);

        // Draw quad.
        glBegin(GL_QUADS);
        glVertex2f(-1, 1);
        glVertex2f(-1,-1);
        glVertex2f( 1,-1);
        glVertex2f( 1, 1);

        glEnd();

        SDL_GL_SwapWindow(window);
    }

    checkGlError();
}