#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>

#include <cairo/cairo.h>
#include <cairo/cairo-xcb.h>
#include <xcb/xcb.h>
#include <xcb/present.h>

/************************************************************************************************************/
/************************************************************************************************************/
/************************************************************************************************************/

#define WIN_W 600
#define WIN_H 400

#define RECT_W     100
#define RECT_SPEED 5  /* 300 px/s at 60 Hz */

/************************************************************************************************************/
/************************************************************************************************************/
/************************************************************************************************************/

static void _draw          (void);
static void _init_graphics (void);
static void _init_threads  (void);
static void _reset         (void);

static void * _thread_event  (void *p);
static void * _thread_render (void *p);

/************************************************************************************************************/
/************************************************************************************************************/
/************************************************************************************************************/

static xcb_connection_t    *_x_con = NULL;
static xcb_screen_t        *_x_scr = NULL;
static xcb_visualtype_t    *_x_vis = NULL;
static xcb_window_t         _x_win = 0;
static xcb_pixmap_t         _x_pix = 0;
static xcb_gcontext_t       _x_ctx = 0;

static uint8_t _x_opcode = 0;

static cairo_surface_t *_c_srf = NULL;
static cairo_t         *_c_ctx = NULL;

static pthread_t       _t_id_ev;
static pthread_t       _t_id_rd;
static pthread_cond_t  _t_cond_rd_1;
static pthread_cond_t  _t_cond_rd_2;
static pthread_mutex_t _t_mutex_rd_1;
static pthread_mutex_t _t_mutex_rd_2;

static int _rect_pos = WIN_W;
static int _update = 1;
static int _serial = 0;

/************************************************************************************************************/
/************************************************************************************************************/
/************************************************************************************************************/

int
main(int argc, char **argv)
{
	/* initialisation */

	_init_graphics();
	_init_threads();
	
	/* initial render for first expose event */

	_draw(); 

	/* start the threads                */
	/* the event thread leads the tempo */

	pthread_create(&_t_id_ev, NULL, _thread_event,  NULL);
	pthread_create(&_t_id_rd, NULL, _thread_render, NULL);

	pthread_join(_t_id_ev, NULL);

	pthread_cancel(_t_id_rd);
	pthread_join(_t_id_rd, NULL);

	/* end */

	_reset();
}

/************************************************************************************************************/
/************************************************************************************************************/
/************************************************************************************************************/

static void
_draw(void)
{
	/* update position */

	_rect_pos += RECT_SPEED;
	if (_rect_pos >= WIN_W) {
		_rect_pos = -RECT_W;
	}

	/* update pixmap */

	cairo_set_source_rgb(_c_ctx, 0.3, 0.3, 0.3);
	cairo_paint(_c_ctx);

	cairo_set_source_rgb(_c_ctx, 0.7, 0.7, 0.7);
	cairo_rectangle(_c_ctx, _rect_pos, 0, RECT_W, WIN_H);
	cairo_fill(_c_ctx);

	cairo_surface_flush(_c_srf);
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -*/

static void
_init_graphics(void)
{
	/* setup xcb */

	_x_con = xcb_connect(NULL, NULL);
	_x_scr = xcb_setup_roots_iterator(xcb_get_setup(_x_con)).data;

	xcb_visualtype_iterator_t x_vi;
	xcb_depth_iterator_t      x_di;

	x_di = xcb_screen_allowed_depths_iterator(_x_scr);
	for (; x_di.rem; xcb_depth_next(&x_di)) {
		x_vi = xcb_depth_visuals_iterator(x_di.data);
		for (; x_vi.rem; xcb_visualtype_next(&x_vi)) {
			if (_x_scr->root_visual == x_vi.data->visual_id) {
				_x_vis = x_vi.data;
				break;
			}
		}
	}

	/* setup generic xcb graphical context for copying the pixmap */

	_x_ctx = xcb_generate_id(_x_con);
	xcb_create_gc(
		_x_con,
		_x_ctx,
		_x_scr->root,
		XCB_GC_FOREGROUND | XCB_GC_GRAPHICS_EXPOSURES,
		&(uint32_t[2]){_x_scr->black_pixel, 0});

	/* setup xcb window */

	uint32_t mask_vals[2];
	mask_vals[0] = _x_scr->black_pixel;
	mask_vals[1] = XCB_EVENT_MASK_EXPOSURE |
	               XCB_EVENT_MASK_STRUCTURE_NOTIFY |
				   XCB_EVENT_MASK_KEY_PRESS |
				   XCB_EVENT_MASK_BUTTON_PRESS;

	_x_win = xcb_generate_id(_x_con);
	xcb_create_window(
		_x_con,
		XCB_COPY_FROM_PARENT,
		_x_win,
		_x_scr->root,
		0, 0,
		WIN_W, WIN_H,
		0,
		XCB_WINDOW_CLASS_INPUT_OUTPUT,
		_x_scr->root_visual,
		XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK,
		mask_vals);

	xcb_map_window(_x_con, _x_win);

	/* setup xcb pixmap */

	_x_pix = xcb_generate_id(_x_con);
	xcb_create_pixmap(_x_con, _x_scr->root_depth, _x_pix, _x_win, WIN_W, WIN_H);

	/* setup xcb present extension */

	xcb_present_select_input(
		_x_con,
		xcb_generate_id(_x_con),
		_x_win,
		XCB_PRESENT_EVENT_MASK_COMPLETE_NOTIFY);

	/* dynamicaly get the present extention opcode for event identification */

	xcb_query_extension_reply_t *r =
		xcb_query_extension_reply(_x_con, xcb_query_extension(_x_con, 7, "Present"), NULL);

	_x_opcode = r->major_opcode;
	free(r);

	/* setup cairo drawable */

	_c_srf = cairo_xcb_surface_create(_x_con, _x_pix, _x_vis, WIN_W, WIN_H);
	_c_ctx = cairo_create(_c_srf);

	/* end */

	cairo_surface_flush(_c_srf);
	xcb_flush(_x_con);
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -*/

static void
_init_threads(void)
{
	pthread_mutex_init(&_t_mutex_rd_1, NULL);
	pthread_mutex_init(&_t_mutex_rd_2, NULL);

	pthread_cond_init(&_t_cond_rd_1, NULL);
	pthread_cond_init(&_t_cond_rd_2, NULL);
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -*/

void
_reset(void)
{
	pthread_mutex_destroy(&_t_mutex_rd_1);
	pthread_mutex_destroy(&_t_mutex_rd_2);

	pthread_cond_destroy(&_t_cond_rd_1);
	pthread_cond_destroy(&_t_cond_rd_2);

	cairo_destroy(_c_ctx);
	cairo_surface_destroy(_c_srf);

	xcb_free_gc(_x_con, _x_ctx);
	xcb_free_pixmap(_x_con, _x_pix);
	xcb_destroy_window(_x_con, _x_win);
	xcb_disconnect(_x_con);
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -*/

static void *
_thread_event(void *p)
{
	int run = 1;
	int x_pev_serial;

	xcb_generic_event_t                 *x_ev;
	xcb_ge_generic_event_t              *x_gev;
	xcb_present_complete_notify_event_t *x_pev;

	while (run && (x_ev = xcb_wait_for_event(_x_con))) {
		switch (x_ev->response_type & ~0x80) {
			
			case XCB_EXPOSE:
				/* immediate update without syncing to the refresh rate          */
				/* without it there are visual glitches when resizing the window */
				xcb_copy_area(_x_con, _x_pix, _x_win, _x_ctx, 0, 0, 0, 0, WIN_W, WIN_H);
				break;

			case XCB_BUTTON_PRESS:
				pthread_mutex_lock(&_t_mutex_rd_2);
				_update = !_update;
				pthread_mutex_unlock(&_t_mutex_rd_2);
				pthread_cond_signal(&_t_cond_rd_2);
				break;

			case XCB_KEY_PRESS:
				run = 0;
				break;

			case XCB_GE_GENERIC:
				/* most of this is just checking that we got the right event */
				/* unecessary in simple cases                                */
				x_gev = (xcb_ge_generic_event_t*)x_ev;
				if (x_gev->extension == _x_opcode && x_gev->event_type == XCB_PRESENT_EVENT_COMPLETE_NOTIFY) {
					x_pev = (xcb_present_complete_notify_event_t*)x_ev;	
					pthread_mutex_lock(&_t_mutex_rd_2);
					x_pev_serial = _serial;
					pthread_mutex_unlock(&_t_mutex_rd_2);
					if (x_pev->kind == XCB_PRESENT_COMPLETE_KIND_PIXMAP && x_pev->serial == x_pev_serial) {
						pthread_cond_signal(&_t_cond_rd_1);
					}
				}
				break;
		}
		xcb_flush(_x_con);
		free(x_ev);
	}

	pthread_exit(NULL);
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -*/

static void *
_thread_render(void *p)
{
	pthread_mutex_lock(&_t_mutex_rd_1);

	while (1) {

		/* check if an update is needed, if not, wait */

		pthread_mutex_lock(&_t_mutex_rd_2);
		if (!_update) {
			pthread_cond_wait(&_t_cond_rd_2, &_t_mutex_rd_2);
		}
		pthread_mutex_unlock(&_t_mutex_rd_2);

		/* update pixmap */

		_draw();

		/* update window with pixmap */

		_serial++;

		xcb_present_pixmap(
			_x_con,
			_x_win,
			_x_pix,
			_serial,
			XCB_XFIXES_REGION_NONE,
			XCB_XFIXES_REGION_NONE,
			0, 0,
			0,
			0,
			0,
			XCB_PRESENT_OPTION_NONE,
			0, 0, 0,
			0,
			NULL);
		
		/* important af, don't forget it */

		xcb_flush(_x_con); 

		/* wait for present event notification in the event thread */

		pthread_cond_wait(&_t_cond_rd_1, &_t_mutex_rd_1);
	}

	pthread_mutex_unlock(&_t_mutex_rd_1);
	pthread_exit(NULL);
}