#include <stdio.h>
#include <stdlib.h>

#include <GL/glew.h>
#include <SDL3/SDL.h>
#include <SDL3/SDL_opengl.h>
#include <SDL3/SDL_main.h> // only include this one in the source file with main()!

#define INITIAL_FPS 60

SDL_Window* window = NULL;
SDL_GLContext glcontext = NULL;

GLuint program;
GLuint vbo;

static double FPS = INITIAL_FPS;
static double FrameTime = 1.0 / INITIAL_FPS;

static double PerformancePeriod;

static void panicError ( void ) __attribute__((noreturn));

static double GetTime( void )
{
    return PerformancePeriod * SDL_GetPerformanceCounter();
}

static void SetTitle ( SDL_Window *window )
{
    char title[48] = {0};
    SDL_snprintf(title, sizeof(title), "Hello Triangle! Framelimit: %6.3f Hz", FPS);
    SDL_SetWindowTitle(window, title);
}

void panicError ( void )
{
    SDL_GL_DestroyContext(glcontext);
    SDL_DestroyWindow(window);
    SDL_Quit();
    exit(EXIT_FAILURE);
}

char *readFile ( const char *fileName )
{
    SDL_IOStream *ioStream = SDL_IOFromFile(fileName, "rb");
    if (!ioStream) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "ioStream: %s.", SDL_GetError());
        panicError();
    }
    if (SDL_SeekIO(ioStream, 0, SDL_IO_SEEK_END) == -1) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_SeekIO_END: %s.", SDL_GetError());
        panicError();
    }
    long len = SDL_TellIO(ioStream);
    if (len == -1) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_TellIO: %s.", SDL_GetError());
        panicError();
    }
    if (SDL_SeekIO(ioStream, 0, SDL_IO_SEEK_SET) == -1) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_IO_SEEK_SET: %s.", SDL_GetError());
        panicError();
    }
    char *res = SDL_malloc(len + 1);
    if (!res) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_malloc: %s.", SDL_GetError());
        panicError();
    }
    if (SDL_ReadIO(ioStream, res, len) != (size_t)len) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_ReadIO: %s.", SDL_GetError());
        panicError();
    }
    if (!SDL_CloseIO(ioStream)) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_CloseIO: %s.", SDL_GetError());
        panicError();
    }
    res[len] = 0;
    return res;
}

GLuint createShader ( const char *shaderFile, GLenum shaderType )
{
    const char *strShaderType;
    if (shaderType == GL_VERTEX_SHADER) {
        strShaderType = "vertex";
    } else if (shaderType == GL_GEOMETRY_SHADER) {
        strShaderType = "geometry";
    } else if (shaderType == GL_FRAGMENT_SHADER) {
        strShaderType = "fragment";
    } else {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Unrecognized shader type.");
        panicError();
    }
    GLuint shader = glCreateShader(shaderType);
    if (!shader) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Error create shader type %s.", strShaderType);
        panicError();
    }
    GLchar *content = readFile(shaderFile);
    glShaderSource(shader, 1, (const GLchar **)&content, NULL);
    SDL_free(content);
    glCompileShader(shader);
    GLint status;
    glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
    if (status == GL_FALSE) {
        GLint infoLen;
        glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLen);
        GLchar *info = SDL_malloc(sizeof(GLchar) * (infoLen + 1));
        glGetShaderInfoLog(shader, infoLen, NULL, info);
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Filed to compile %s shader:\n%s.", strShaderType, info);
        panicError();
    }
    return shader;
}

void createProgram ( GLuint *shaders, int len )
{
    program = glCreateProgram();
    if (!program) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Can't to create shader program.");
        panicError();
    }
    for (int i = 0; i < len; i++) {
        glAttachShader(program, shaders[i]);
    }
    glLinkProgram(program);
    GLint status;
    glGetProgramiv(program, GL_LINK_STATUS, &status);
    if (status == GL_FALSE) {
        GLint infoLen;
        glGetProgramiv(program, GL_INFO_LOG_LENGTH, &infoLen);
        GLchar *info = SDL_malloc(sizeof(GLchar) * (infoLen + 1));
        glGetProgramInfoLog(program, infoLen, NULL, info);
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Link failed: %s.", info);
        panicError();
    }
}

void createBuffer ( void )
{
    float vertices[] = {
        -1.0f, -1.0f, 0.0f,
        1.0f, -1.0f, 0.0f,
        0.0f, 1.0f, 0.0f
    };
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
}

void startShaderProg ( void )
{
    createBuffer();

    GLuint shaders[] = {
        createShader("vertex.glsl", GL_VERTEX_SHADER),
        createShader("fragment.glsl", GL_FRAGMENT_SHADER)
    };
    int len = sizeof(shaders) / sizeof(shaders[0]);
    createProgram(shaders, len);
    for (int i = 0; i < len; i++) {
        glDeleteShader(shaders[i]);
    }
}

void _GLBuffer( void )
{
    glClearColor(0.0f, 0.0f, 1.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glUseProgram(program);

    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    glDisableVertexAttribArray(0);

    glUseProgram(0);
}

int main( int argc, char* argv[] )
{
    const int WIDTH = 640;
    const int HEIGHT = 480;
    int delay_threshold = 2;
    int r, g, b, GLJ, GLN = 0;
    double sleep_time = 0;
    double time_counter = 0;
    bool loopShouldStop = false;

    SDL_SetHint(SDL_HINT_RENDER_VSYNC, 0);
    if (!SDL_Init(SDL_INIT_VIDEO)) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_Init failed: %s.", SDL_GetError());
    }

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);

    PerformancePeriod = 1.0 / SDL_GetPerformanceFrequency();
    time_counter = GetTime();

    window = SDL_CreateWindow("Hello SDL", WIDTH, HEIGHT, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
    if (!window) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_CreateWindow: %s.", SDL_GetError());
        panicError();
    }

    glcontext = SDL_GL_CreateContext(window);
    if (!glcontext) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_GL_CreateContext: %s.", SDL_GetError());
        panicError();
    }

    SetTitle(window);

    SDL_HideCursor();

    glewExperimental = GL_TRUE;
    GLenum err = glewInit();
    if (err != GLEW_OK) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "glewInit: %s.", glewGetErrorString(err));
        panicError();
    }

    SDL_LogVerbose(SDL_LOG_CATEGORY_RENDER, "Status: Using GLEW %s\n", glewGetString(GLEW_VERSION));
    err = SDL_GL_GetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, &GLJ);
    SDL_GL_GetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, &GLN);
    SDL_GL_GetAttribute(SDL_GL_RED_SIZE, &r);
    SDL_GL_GetAttribute(SDL_GL_GREEN_SIZE, &g);
    SDL_GL_GetAttribute(SDL_GL_BLUE_SIZE, &b);

    SDL_Log("%s", SDL_GetError());

    SDL_LogVerbose(SDL_LOG_CATEGORY_RENDER, "Red size: %d, Green size: %d, Blue size: %d, OpenGL: %d.%d.", r, g, b, GLJ, GLN);

    SDL_GL_SetSwapInterval(0);
    startShaderProg();

    while (!loopShouldStop) {
        SDL_Event e;
        SDL_zero(e);
        while (SDL_PollEvent(&e)) {
            if (e.type == SDL_EVENT_QUIT)
                loopShouldStop = true;
            else if (e.type == SDL_EVENT_KEY_DOWN) {
                if (e.key.key == SDLK_X) {
                    FPS -= 0.1;
                    if (FPS < 1) {
                        FPS = 1;
                    }
                    FrameTime = 1.0 / FPS;
                    SetTitle(window);
                }
                else if (e.key.key == SDLK_C) {
                    FPS += 0.1;
                    FrameTime = 1.0 / FPS;
                    SetTitle(window);
                }
                if (e.key.key == SDLK_ESCAPE)
                    loopShouldStop = true;
            }
        }

        _GLBuffer();
        if (!SDL_GL_SwapWindow(window)) {
            SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "SDL_GL_SwapWwindow: %s.", SDL_GetError());
            panicError();
        }

        sleep_time = time_counter - GetTime();
        if (sleep_time * 1000 > delay_threshold) {
            Uint32 ms = (Uint32)(sleep_time * 1000) - delay_threshold;
            SDL_Delay(ms);
            if (time_counter < GetTime()) {
                delay_threshold++;
                SDL_Log("Slept too long. Increased threshold to %u ms.", delay_threshold);
            }
        }

        while (time_counter > GetTime()) {
        /* Waiting for the right moment. */
        }
        time_counter += FrameTime;
    }

    SDL_DestroyWindow(window);
    SDL_GL_DestroyContext(glcontext);
    SDL_Quit();
    exit(EXIT_SUCCESS);
}