#include <stdio.h>
#include <stdlib.h>
#include <math.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;
GLuint ibo;
GLuint projMatrLoc;

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 Triangles! Framelimit: %6.3f Hz", FPS);
    SDL_SetWindowTitle(window, title);
}

float toRad ( float deg )
{
    /* 180 deg = pi */
    /* "deg" deg = x */
    return deg * 3.141593f / 180.0f;
}

void resizeWindow ( int width, int height )
{
    float n = 1.0f; // near
    float f = 3.0f; // far
    float fov = toRad(90); // 90 or 65 for console
    float aspect = width / (float) height;
    float t = n * tanf (fov / 2.0f);
    float r = t * aspect;

    float projMatr[] = {
        n/r, 0,   0,              0,
        0,   n/t, 0,              0,
        0,   0,   (f+n)/(n-f),    -1,
        0,   0,   2.0f*n*f/(n-f), 0
    }; // it's not rows, it's columns, 'GL_FALSE'
    SDL_LogVerbose(SDL_LOG_CATEGORY_RENDER, "n=%.1f f=%.1f fov=%.2f aspect=%.2f t=%.2f r=%.2f\n", n, f, fov, aspect, t, r);
    glUseProgram(program);
    glUniformMatrix4fv(projMatrLoc, 1, GL_FALSE, projMatr);
    glUseProgram(0);
    glViewport(0, 0, (GLsizei)width, (GLsizei)height);
}

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 )
{
    GLushort indices[] = {
        0, 1, 2,
        0, 2, 3
    };
    float vertices[] = {
      -1.0f, -1.0f, -2.0f, 1.0f, // left-bottom
      -1.0f,  1.0f, -2.0f, 1.0f, // left-top
       1.0f,  1.0f, -2.0f, 1.0f, // right-top
       1.0f, -1.0f, -2.0f, 1.0f, // right-bottom

       // colours
       1.0f, 0.0f, 0.0f, 1.0f, // red
       0.0f, 1.0f, 0.0f, 1.0f, // green
       1.0f, 0.0f, 1.0f, 1.0f, // purple
       1.0f, 1.0f, 0.0f, 1.0f  // yellow
    };
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    glGenBuffers(1, &ibo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}

void setUniformLocation ( void )
{
    projMatrLoc = glGetUniformLocation(program, "projMatr");
}

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]);
    }

    setUniformLocation();
    glEnable(GL_DEPTH_TEST);
    glDepthMask(GL_TRUE);
    glDepthFunc(GL_LEQUAL);
    glDepthRange(0.0f, 1.0f);
}

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

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
    glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0);
    glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, (void *) (4*4*sizeof(float)));
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, 0);
    glDisableVertexAttribArray(0);
    glDisableVertexAttribArray(1);

    glUseProgram(0);
}

int main( int argc, char* argv[] )
{
    const int WIDTH = 640;
    const int HEIGHT = 480;
    int delayThreshold = 2;
    int r, g, b, alpha_s, depth_s, stencil_s, dbuffer, glVersionMa, glVersionMi, glAccel, glProfile = 0;
    double sleepTime = 0;
    double timeCounter = 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());
        panicError();
    }

    if (!SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE)) {
        SDL_LogCritical(SDL_LOG_CATEGORY_ASSERT, "Set atrribute SDL_GL_CONTEXT_PROFILE_MASK: %s", SDL_GetError());
        panicError();
    }

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);

    PerformancePeriod = 1.0 / SDL_GetPerformanceFrequency();
    timeCounter = 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));
    SDL_GL_GetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, &glProfile);
    SDL_GL_GetAttribute(SDL_GL_ACCELERATED_VISUAL, &glAccel);
    SDL_GL_GetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, &glVersionMa);
    SDL_GL_GetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, &glVersionMi);
    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_GL_GetAttribute(SDL_GL_ALPHA_SIZE, &alpha_s);
    SDL_GL_GetAttribute(SDL_GL_DEPTH_SIZE, &depth_s);
    SDL_GL_GetAttribute(SDL_GL_STENCIL_SIZE, &stencil_s);
    SDL_GL_GetAttribute(SDL_GL_DOUBLEBUFFER, &dbuffer);

    SDL_LogVerbose(SDL_LOG_CATEGORY_RENDER, "OpenGL Version: %d.%d, OpenGL Accelerated: %d, OpenGL Profile Mask: %d",
                   glVersionMa, glVersionMi, glAccel, glProfile);
    SDL_LogVerbose(SDL_LOG_CATEGORY_RENDER, "Red size: %d, Green size: %d, Blue size: %d, Alpha size: %d, Depth size: %d, Stencil size: %d, DoubleBuffer: %d",
                   r, g, b, alpha_s, depth_s, stencil_s, dbuffer);

    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_WINDOW_RESIZED) {
                resizeWindow(e.window.data1, e.window.data2);
            }
            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();
        }

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

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

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