#include <stdio.h>
#include <unistd.h>

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

#include "glad.c"

#include "fswatcher/fswatcher.h"
#include "fswatcher/fswatcher.cpp"

#include "core.h"

#if defined(_WIN32)
#define BUILD_GAME() system("build_game.bat")
#else
#define BUILD_GAME() system("sh build_game.sh")
#endif

// GAME LIBRARY FUNCTIONS
typedef void (*GameHandleEvent)(GameState*, GameEventType);
typedef void (*GameSetup)(GameState*);
typedef void (*GameUpdateAndRender)(GameState*);

struct GameLayer {
    void *lib;
    GameHandleEvent handle_event;
    GameSetup setup;
    GameUpdateAndRender update_and_render;
};
internal GameLayer game_layer;

bool load_game_layer() 
{
    // @hack: recompile game here before load object call
    BUILD_GAME();

    SDL_UnloadObject(game_layer.lib);
    game_layer.lib = SDL_LoadObject("build/libgame.so");
    if (game_layer.lib == NULL) {
        return false;
    }
    game_layer.handle_event = 
        (GameHandleEvent)SDL_LoadFunction(game_layer.lib,
                                          "game_handle_event");
    game_layer.setup = 
        (GameSetup)SDL_LoadFunction(game_layer.lib,
                                    "game_setup");
    game_layer.update_and_render =
        (GameUpdateAndRender)SDL_LoadFunction(game_layer.lib,
                                              "game_update_and_render");

    return true;
}

bool game_file_update(fswatcher_event_handler *handler,
                      fswatcher_event_type evtype, 
                      const char *src,
                      const char *dst) {
    return load_game_layer();
}

//bool game_shader_update(fswatcher_event_handler *handler,
//                        fswatcher_event_type evtype,
//                        const char *src,
//                        const char *dst) {
//}

u32 gl_shader_program(char *vs, char *fs)
{
    //==============
    // Vertex Shader
    u32 handle_vs = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(handle_vs, 1, &vs, NULL); 
    glCompileShader(handle_vs);

    i32 vertex_compiled;
    glGetShaderiv(handle_vs,
                  GL_COMPILE_STATUS,
                  &vertex_compiled);

    if (vertex_compiled != GL_TRUE)
    {
        i32 log_length = 0;
        char message[1024];

        glGetShaderInfoLog(handle_vs, 1024, &log_length, message);

        fprintf(stderr, "===Error compiling vertex shader===\n");
        fprintf(stderr, "%s\n", message);
    }

    //================
    // Fragment Shader
    u32 handle_fs = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(handle_fs, 1, &fs, NULL);
    glCompileShader(handle_fs);

    i32 fragment_compiled;
    glGetShaderiv(handle_fs,
                  GL_COMPILE_STATUS,
                  &fragment_compiled);

    if (fragment_compiled != GL_TRUE)
    {
        i32 log_length = 0;
        char message[1024];

        glGetShaderInfoLog(handle_fs, 1024, &log_length, message);

        fprintf(stderr, "===Error compiling fragment shader===\n");
        fprintf(stderr, "%s\n", message);
    }

    //===============
    // Shader Program
    u32 shader_program = glCreateProgram();

    glAttachShader(shader_program, handle_vs);
    glAttachShader(shader_program, handle_fs);
    glLinkProgram(shader_program);

    GLint program_compiled;
    glGetProgramiv(shader_program, GL_LINK_STATUS, &program_compiled);

    if (program_compiled != GL_TRUE)
    {
        i32 log_length = 0;
        char message[1024];

        glGetShaderInfoLog(shader_program, 1024, &log_length, message);

        fprintf(stderr, "===Error linking shader program===\n");
        fprintf(stderr, "%s\n", message);
    }

    glDeleteShader(handle_vs);
    glDeleteShader(handle_fs);

    return shader_program;
}

u32 gl_shader_program_from_path(const char *vspath, const char *fspath) 
{
    size_t read_count;
    char *vs = (char *)SDL_LoadFile(vspath, &read_count);
    if (vs == NULL)
    {
        const char *error_msg = SDL_GetError();
        fprintf(stderr, "Error loading file %s: %s\n", vspath, error_msg);
    }

    read_count = 0;
    char *fs = (char *)SDL_LoadFile(fspath, &read_count);
    if (fs == NULL)
    {
        const char *error_msg = SDL_GetError();
        fprintf(stderr, "Error loading file %s: %s\n", fspath, error_msg);
    }

    u32 shader_program = gl_shader_program(vs, fs);

    SDL_free(vs);
    SDL_free(fs);

    return shader_program;
}

int main(int argc, char *argv[])
{
    i32 raw_width = 1920;
    i32 raw_height = 1080;
    i32 dpi_width;
    i32 dpi_height;
    r32 scale_width;
    r32 scale_height;
    i32 width;
    i32 height;

    GameState state = {};

    if (SDL_Init(SDL_INIT_VIDEO) != 0)
    {
        printf("Error initialising SDL2: %s\n", SDL_GetError());
        return 0;
    };

    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", 
                                          SDL_WINDOWPOS_UNDEFINED, 
                                          SDL_WINDOWPOS_UNDEFINED, 
                                          raw_width, 
                                          raw_height, 
                                          SDL_WINDOW_OPENGL |
                                          SDL_WINDOW_RESIZABLE|SDL_WINDOW_ALLOW_HIGHDPI);

    // create an opengl context
    SDL_GLContext context = SDL_GL_CreateContext(window);
    if (!context)
    {
        printf("OpenGL context creation failed: %s\n", SDL_GetError());
        return -1;
    }

    // calculate correct window size due to scaling
    SDL_GL_GetDrawableSize(window, &dpi_width, &dpi_height);

    scale_width = (r32)raw_width/(r32)dpi_width;
    scale_height = (r32)raw_height/(r32)dpi_height;

    state.width = raw_width * scale_width;
    state.height = raw_height * scale_height;

    SDL_SetWindowSize(window, state.width, state.height);

    // load glad
    if (!gladLoadGLLoader((GLADloadproc)SDL_GL_GetProcAddress)) {
        printf("Failed to initialize Glad\n");
        return 1;
    }

    SDL_GL_SetSwapInterval(1);

    u32 shader_program = gl_shader_program_from_path("./shaders/quad.vs.glsl", 
                                                     "./shaders/quad.fs.glsl");

    state.triangle_sp = shader_program;
    glUseProgram(state.triangle_sp);

    // @func: gl_setup_triangle
    {
        GLfloat vertices[9] = {
            -0.5f, -0.5f, 0.0f,
             0.5f, -0.5f, 0.0f,
             0.0f,  0.5f, 0.0f
        };

        GLuint VBO, VAO;
        glGenVertexArrays(1, &VAO);
        glGenBuffers(1, &VBO);

        glBindVertexArray(VAO);

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

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

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

        state.triangle_vao = VAO;
        state.triangle_vbo = VBO;
    }
    glUseProgram(0);

    // add file watcher
    fswatcher_t game_watcher = fswatcher_create(FSWATCHER_CREATE_DEFAULT,
                                                FSWATCHER_EVENT_MODIFY, 
                                                "source/game", NULL);
    fswatcher_event_handler game_file_update_handler;
    game_file_update_handler.callback = game_file_update;
    // load game layer
    if (!load_game_layer()) {
        return -1;
    }

    game_layer.setup(&state);

    for(;;)
    {
        SDL_Event ev;
        while(SDL_PollEvent(&ev))
        {
            if (ev.type == SDL_QUIT)
            {
                return 0;
            }
            if (ev.type == SDL_WINDOWEVENT)
            {
                if (ev.window.event == SDL_WINDOWEVENT_RESIZED) 
                {
                    state.width = ev.window.data1;
                    state.height = ev.window.data2;
                    game_layer.handle_event(&state, GAME_EVENT_RESIZE);
                }
            }
            if (ev.type == SDL_KEYDOWN) {
                if (ev.key.keysym.sym == SDLK_SPACE) {
                }
            }
        }
        fswatcher_poll(game_watcher, &game_file_update_handler, NULL);

        // opengl rendering code here
        game_layer.update_and_render(&state);
        SDL_GL_SwapWindow(window);
    }

    // filewatcher
    fswatcher_destroy(game_watcher);

    // opengl free calls
    glDeleteVertexArrays(1, &state.triangle_vao);
    glDeleteBuffers(1, &state.triangle_vbo);
    glDeleteProgram(state.triangle_sp);

    // sdl free calls
    SDL_GL_DeleteContext(context);
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}