#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#include <xf86drm.h>
#include <xf86drmMode.h>

#define DRM_MODULE_NAME "starfive"
#define DRM_BUSID NULL

struct buffer_object {
    uint32_t width;
    uint32_t height;
    uint32_t pitch;
    uint32_t handle;
    uint32_t size;
    uint32_t *vaddr;
    uint32_t fb_id;
};

struct buffer_object buf[2];

static int modeset_create_fb(int fd, struct buffer_object *bo, uint32_t color)
{
    struct drm_mode_create_dumb create = {};
    struct drm_mode_map_dumb map = {};
    uint32_t i;

    create.width = bo->width;
    create.height = bo->height;
    create.bpp = 32;
    drmIoctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create);

    bo->pitch = create.pitch;
    bo->size = create.size;
    bo->handle = create.handle;
    // {24, 32}
    drmModeAddFB(fd, bo->width, bo->height, 32, 32, bo->pitch,
               bo->handle, &bo->fb_id);

    map.handle = create.handle;
    drmIoctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &map);

    bo->vaddr = mmap(0, create.size, PROT_READ | PROT_WRITE,
            MAP_SHARED, fd, map.offset);

    for (i = 0; i < (bo->size / 4); i++)
        bo->vaddr[i] = color;

    return 0;
}

static void modeset_destroy_fb(int fd, struct buffer_object *bo)
{
    struct drm_mode_destroy_dumb destroy = {};

    drmModeRmFB(fd, bo->fb_id);

    munmap(bo->vaddr, bo->size);

    destroy.handle = bo->handle;
    drmIoctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroy);
}

int main(int argc, char **argv)
{
    int fd;
    drmModeConnector *conn;
    drmModeRes *res;
    uint32_t conn_id;
    uint32_t crtc_id;
    int ret = -1;

    fd = drmOpen(DRM_MODULE_NAME, DRM_BUSID);

    res = drmModeGetResources(fd);
    crtc_id = res->crtcs[0];
    conn_id = res->connectors[0];

    conn = drmModeGetConnector(fd, conn_id);
    buf[0].width = conn->modes[0].hdisplay;
    buf[0].height = conn->modes[0].vdisplay;
    buf[1].width = conn->modes[0].hdisplay;
    buf[1].height = conn->modes[0].vdisplay;

    modeset_create_fb(fd, &buf[0], 0xFF0000);
    modeset_create_fb(fd, &buf[1], 0x0000FF);

    ret = drmModeSetCrtc(fd, crtc_id, buf[0].fb_id,
            0, 0, &conn_id, 1, &conn->modes[0]);
    if (ret) {
        fprintf(stderr, "1. cannot set CRTC for connector %u (%d): %m\n",
                crtc_id, errno);
    }

    getchar();
    int cnt = 10;
    while (cnt--) {
        ret = drmModeSetCrtc(fd, crtc_id, buf[cnt%2].fb_id,
            0, 0, &conn_id, 1, &conn->modes[0]);
        if (ret) {
            fprintf(stderr, "2. cannot set CRTC for connector %u (%d): %m\n",
                    crtc_id, errno);
        }
        usleep(500 * 1000);
    }

    getchar();
    modeset_destroy_fb(fd, &buf[1]);
    modeset_destroy_fb(fd, &buf[0]);

    drmModeFreeConnector(conn);
    drmModeFreeResources(res);

    close(fd);

    return 0;
}