use x11::xlib::{XGrabPointer, XCreateFontCursor, XOpenDisplay, Display, XDefaultRootWindow, XAllPlanes, ZPixmap, XGetImage, ButtonMotionMask, ButtonPressMask, ButtonReleaseMask, CurrentTime, GrabModeAsync, GrabSuccess, XNextEvent, XEvent, XPending, ButtonPress, ButtonRelease, XButtonEvent, XGrabKeyboard, KeyPress, XKeyEvent};
use std::mem::MaybeUninit;
use image::RgbaImage;
use std::convert::TryInto;

#[derive(Debug)]
struct Position {
  origin_x: u32,
  origin_y: u32,
  height: u32,
  width: u32,
}

fn screenshot(pos: &Position) {
    unsafe {
      let display: *mut Display = XOpenDisplay(std::ptr::null());
      let root_window = XDefaultRootWindow(display);

      let ximg = XGetImage(display, root_window, pos.origin_x.try_into().unwrap(), pos.origin_y.try_into().unwrap(), pos.width.try_into().unwrap(), pos.height.try_into().unwrap(), XAllPlanes(), ZPixmap);
      let len = pos.height*pos.width*4;
      let v = Vec::<u8>::from_raw_parts((*ximg).data as *mut _, len.try_into().unwrap(), len.try_into().unwrap());
      //println!("{:?}", v);
      let img = RgbaImage::from_raw(pos.width, pos.height, v).unwrap();

      img.save("empty.jpg").unwrap();
    }

}

// https://bbs.archlinux.org/viewtopic.php?id=85378
fn trigger_selection() -> Option<Position> {

    unsafe {
      let display: *mut Display = XOpenDisplay(std::ptr::null());
      let root_window = XDefaultRootWindow(display);
      
      let c = XCreateFontCursor(display, 130); // XC_tcross = 130
      let button_mask = ButtonMotionMask as u32 | ButtonPressMask as u32 | ButtonReleaseMask as u32;
 
      if XGrabPointer(display, root_window, 0, button_mask, GrabModeAsync, GrabModeAsync, root_window, c, CurrentTime) != GrabSuccess {
        panic!("could not grab");
      }

      if XGrabKeyboard(display, root_window, 0, GrabModeAsync, GrabModeAsync, CurrentTime) != GrabSuccess {
        panic!("could not grab");
      }

      let mut pos = Position { origin_x: 0, origin_y: 0, width: 0, height: 0};

      'main: loop {
        while XPending(display) > 0 {
          let mut e: MaybeUninit<XEvent> = MaybeUninit::uninit();
          XNextEvent(display, e.as_mut_ptr());

          let event = unsafe { e.assume_init() };
          match event.type_ {
            KeyPress => {
               let event = XKeyEvent::from(event);
               if event.keycode == 9 { // escape keycode (xev)
                  return None;
               }
            },
            ButtonPress => {
               let event = XButtonEvent::from(event);
               println!("origin = ({},{})", event.x, event.y);
               pos.origin_x = event.x_root.try_into().unwrap();
               pos.origin_y = event.y_root.try_into().unwrap();
            },
            ButtonRelease => {
                // assuming that the upper left corner is the origin
                let event = XButtonEvent::from(event);
                let x: u32 = event.x_root.try_into().unwrap();
                let y: u32 = event.y_root.try_into().unwrap();

                pos.width = x - pos.origin_x;
                pos.height = y - pos.origin_y;
                
                if pos.height == 0 || pos.width == 0 {
                  return None
                }

                return Some(pos);
            }
            _ => { println!("type unknown: {}", event.type_); }
          }
        }
      }

    }


}

fn main() {
  let s = trigger_selection();
  println!("{:?}", s);
  if let Some(select) = s {
    screenshot(&select);
  }
}