/* -------------------------------------------------------------
 * framebuffer_demo_tcp.c
 *
 *  * 600×400 ARGB8888 framebuffer in RAM
 *  * SDL2 window that displays the framebuffer
 *  * Simple TCP server (single client) that streams raw pixel data
 *
 * Build (Linux/macOS):
 *   gcc -Wall -Wextra -pedantic -std=c11 framebuffer_demo_tcp.c \
 *       -lSDL2 -lpthread -o framebuffer_demo_tcp
 *
 * Run:
 *   ./framebuffer_demo_tcp          # opens a window and listens on 0.0.0.0:12345
 *
 * Test client (Unix‑like):
 *   # Send a static colour (red) for one frame
 *   dd if=/dev/zero bs=1 count=$((600*400*4)) | tr \\0 \\377 > red.bin
 *   cat red.bin | nc 127.0.0.1 12345
 *
 * ------------------------------------------------------------- */
#include <SDL2/SDL.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>               // memcpy, memset
#include <unistd.h>               // close, read, write
#include <fcntl.h>                // fcntl
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/select.h>           // select()
#include <errno.h>

/* -------------------------------------------------------------
 * Configuration
 * ------------------------------------------------------------- */
#define WIDTH          600
#define HEIGHT         400
#define LISTEN_PORT    12345          // change if you like
#define BACKLOG        1              // only one pending connection

/* -------------------------------------------------------------
 * Simple pixel format helpers
 * ------------------------------------------------------------- */
typedef Uint32 pixel_t;               // 0xAARRGGBB in memory (little‑endian)

static inline pixel_t make_pixel(Uint8 r, Uint8 g, Uint8 b, Uint8 a)
{
    return (pixel_t)((a << 24) | (r << 16) | (g << 8) | b);
}
#define MAKE_OPAQUE_PIXEL(r,g,b)  make_pixel((r),(g),(b),0xFF)

/* -------------------------------------------------------------
 * Global framebuffer (contiguous block)
 * ------------------------------------------------------------- */
static pixel_t framebuffer[HEIGHT][WIDTH];      // 600*400*4 = 960 000 bytes

/* -------------------------------------------------------------
 * Fill with a cute demo pattern (visible before any network data)
 * ------------------------------------------------------------- */
static void init_demo_pattern(void)
{
    for (int y = 0; y < HEIGHT; ++y) {
        for (int x = 0; x < WIDTH; ++x) {
            Uint8 r = (Uint8)((x * 255) / (WIDTH - 1));
            Uint8 g = (Uint8)((y * 255) / (HEIGHT - 1));
            Uint8 b = 0x80;
            framebuffer[y][x] = MAKE_OPAQUE_PIXEL(r, g, b);
        }
    }
}

/* -------------------------------------------------------------
 * ----------  TCP SERVER  ------------------------------------
 * ------------------------------------------------------------- */

/* Returns a non‑blocking listening socket, or -1 on error. */
static int create_listen_socket(void)
{
    int lst = socket(AF_INET, SOCK_STREAM, 0);
    if (lst < 0) {
        perror("socket");
        return -1;
    }

    /* Allow immediate reuse of the address (helps during rapid restarts). */
    int opt = 1;
    setsockopt(lst, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

    struct sockaddr_in addr = {
        .sin_family = AF_INET,
        .sin_port   = htons(LISTEN_PORT),
        .sin_addr   = { .s_addr = INADDR_ANY }
    };

    if (bind(lst, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
        perror("bind");
        close(lst);
        return -1;
    }

    if (listen(lst, BACKLOG) < 0) {
        perror("listen");
        close(lst);
        return -1;
    }

    /* Make the socket non‑blocking so that accept() never blocks. */
    int flags = fcntl(lst, F_GETFL, 0);
    fcntl(lst, F_SETFL, flags | O_NONBLOCK);

    printf("[net] Listening on 0.0.0.0:%d (single client allowed)\n", LISTEN_PORT);
    return lst;
}

/* -------------------------------------------------------------
 * Helper: set a socket to non‑blocking mode
 * ------------------------------------------------------------- */
static void set_nonblocking(int fd)
{
    int flags = fcntl(fd, F_GETFL, 0);
    if (flags != -1) fcntl(fd, F_SETFL, flags | O_NONBLOCK);
}

/* -------------------------------------------------------------
 * Main entry point
 * ------------------------------------------------------------- */
int main(void)
{
    /* ---------- SDL initialisation -------------------------------- */
    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        fprintf(stderr, "SDL_Init error: %s\n", SDL_GetError());
        return EXIT_FAILURE;
    }

    SDL_Window   *window   = SDL_CreateWindow("Framebuffer Demo – TCP Input",
                               SDL_WINDOWPOS_CENTERED,
                               SDL_WINDOWPOS_CENTERED,
                               WIDTH, HEIGHT,
                               SDL_WINDOW_SHOWN);
    if (!window) {
        fprintf(stderr, "SDL_CreateWindow error: %s\n", SDL_GetError());
        SDL_Quit();
        return EXIT_FAILURE;
    }

    SDL_Renderer *renderer = SDL_CreateRenderer(window, -1,
                               SDL_RENDERER_ACCELERATED |
                               SDL_RENDERER_PRESENTVSYNC);
    if (!renderer) {
        fprintf(stderr, "SDL_CreateRenderer error: %s\n", SDL_GetError());
        SDL_DestroyWindow(window);
        SDL_Quit();
        return EXIT_FAILURE;
    }

    SDL_Texture *texture = SDL_CreateTexture(renderer,
                               SDL_PIXELFORMAT_ARGB8888,
                               SDL_TEXTUREACCESS_STREAMING,
                               WIDTH, HEIGHT);
    if (!texture) {
        fprintf(stderr, "SDL_CreateTexture error: %s\n", SDL_GetError());
        SDL_DestroyRenderer(renderer);
        SDL_DestroyWindow(window);
        SDL_Quit();
        return EXIT_FAILURE;
    }

    /* ---------- Initialise demo framebuffer ----------------------- */
    init_demo_pattern();

    /* ---------- Initialise networking ----------------------------- */
    int listen_sock = create_listen_socket();
    if (listen_sock < 0) {
        /* Continue without network – the window will just show the demo. */
        fprintf(stderr, "[net] Continuing without network input.\n");
    }

    int client_sock = -1;                // -1 means “no client connected”
    size_t bytes_needed = WIDTH * HEIGHT * sizeof(pixel_t);
    size_t recv_offset  = 0;             // how many bytes of the current frame we already have

    bool quit = false;
    SDL_Event ev;

    /* ---------- Main loop ---------------------------------------- */
    while (!quit) {
        /* ---- 1) Process SDL events (non‑blocking) ------------- */
        while (SDL_PollEvent(&ev)) {
            if (ev.type == SDL_QUIT) quit = true;
            else if (ev.type == SDL_KEYDOWN && ev.key.keysym.sym == SDLK_ESCAPE)
                quit = true;
        }

        /* ---- 2) Accept a client if we have none yet ------------- */
        if (listen_sock >= 0 && client_sock < 0) {
            struct sockaddr_in remote;
            socklen_t remote_len = sizeof(remote);
            int tmp = accept(listen_sock,
                             (struct sockaddr *)&remote,
                             &remote_len);
            if (tmp >= 0) {
                client_sock = tmp;
                set_nonblocking(client_sock);
                recv_offset = 0;          // start a fresh frame
                char ip[INET_ADDRSTRLEN];
                inet_ntop(AF_INET, &remote.sin_addr, ip, sizeof(ip));
                printf("[net] Client connected from %s:%d\n", ip, ntohs(remote.sin_port));
            } else if (errno != EAGAIN && errno != EWOULDBLOCK) {
                perror("[net] accept");
            }
        }

        /* ---- 3) Read raw pixel data from the client ------------- */
        if (client_sock >= 0) {
            /* Try to read the remainder of the current frame. */
            size_t still_needed = bytes_needed - recv_offset;
            ssize_t n = recv(client_sock,
                             ((Uint8 *)framebuffer) + recv_offset,
                             still_needed,
                             0);
            if (n > 0) {
                recv_offset += (size_t)n;
                if (recv_offset == bytes_needed) {
                    /* Full frame received – it will be displayed on the next render pass. */
                    recv_offset = 0;          // start collecting the next frame
                }
            } else if (n == 0) {
                /* Client performed an orderly shutdown. */
                printf("[net] Client disconnected.\n");
                close(client_sock);
                client_sock = -1;
            } else if (n < 0) {
                if (errno != EAGAIN && errno != EWOULDBLOCK) {
                    perror("[net] recv");
                    close(client_sock);
                    client_sock = -1;
                }
                /* If EAGAIN/EWOULDBLOCK we simply have no more data right now. */
            }
        }

        /* ---- 4) Copy framebuffer into texture ------------------- */
        void *tex_pixels;
        int   tex_pitch;
        if (SDL_LockTexture(texture, NULL, &tex_pixels, &tex_pitch) != 0) {
            fprintf(stderr, "SDL_LockTexture error: %s\n", SDL_GetError());
            break;
        }

        /* The texture pitch may be larger than WIDTH*4, so copy line‑by‑line. */
        for (int y = 0; y < HEIGHT; ++y) {
            memcpy((Uint8 *)tex_pixels + y * tex_pitch,
                   framebuffer[y],
                   WIDTH * sizeof(pixel_t));
        }
        SDL_UnlockTexture(texture);

        /* ---- 5) Render ------------------------------------------ */
        SDL_RenderClear(renderer);
        SDL_RenderCopy(renderer, texture, NULL, NULL);
        SDL_RenderPresent(renderer);
        /* VSYNC in the renderer caps the loop to the monitor refresh rate. */
    }

    /* -------------------------------------------------------------
     * Cleanup
     * ------------------------------------------------------------- */
    if (client_sock >= 0) close(client_sock);
    if (listen_sock >= 0) close(listen_sock);

    SDL_DestroyTexture(texture);
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();

    return EXIT_SUCCESS;
}