/*
 * Minimal <sys/select.h> for the MontaukOS NetSurf port.
 *
 * MontaukOS has no select(). Readiness on a socket is expressed through the
 * kernel's waitset (SYS_WAITSET_*), which is a different shape entirely, and
 * stdio descriptors are not waitable objects at all.
 *
 * NetSurf's core uses select() in exactly one place -- content/fetch.c's
 * fetch_fdset() collects descriptors from the registered fetchers, and the
 * frontend's main loop selects over them plus its own input. With
 * NETSURF_USE_CURL=NO no fetcher registers a descriptor, so the only fd that
 * ever appears is the monkey frontend's stdin (fd 0).
 *
 * That makes a useful shim possible: fd 0 is answered from the libc's
 * montauk_stdin_ready(), which reports whether a COMPLETE line is buffered.
 * That is the readiness question monkey is really asking -- it goes on to call
 * fgets(), so reporting "readable" on a half-typed line would park the whole
 * browser inside stdio until Enter. With no line pending we sleep out the
 * caller's timeout and return 0, which lets the core's scheduled callbacks run
 * to completion: a fetch takes many main-loop iterations, and under the old
 * always-ready shim it got exactly one per line typed.
 *
 * LIMITATION: only fd 0 has a readiness source. Any other read descriptor is
 * still reported ready unconditionally, and write/except sets are always
 * empty. With NETSURF_USE_CURL=NO no fetcher registers a descriptor, so fd 0
 * is the only one that ever appears. When fetch_montauk lands it will register
 * descriptors here and this needs a genuine waitset-backed implementation.
 */
#ifndef _MONTAUK_COMPAT_SYS_SELECT_H_
#define _MONTAUK_COMPAT_SYS_SELECT_H_

#include <sys/time.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>

#define FD_SETSIZE 64

typedef struct {
	unsigned long fds_bits[(FD_SETSIZE + (8 * sizeof(unsigned long)) - 1) /
			       (8 * sizeof(unsigned long))];
} fd_set;

#define __NFDBITS (8 * (int) sizeof(unsigned long))

#define FD_ZERO(s)  memset((s), 0, sizeof(fd_set))
#define FD_SET(fd, s) \
	((void) ((s)->fds_bits[(fd) / __NFDBITS] |= \
		 (1UL << ((fd) % __NFDBITS))))
#define FD_CLR(fd, s) \
	((void) ((s)->fds_bits[(fd) / __NFDBITS] &= \
		 ~(1UL << ((fd) % __NFDBITS))))
#define FD_ISSET(fd, s) \
	(((s)->fds_bits[(fd) / __NFDBITS] & (1UL << ((fd) % __NFDBITS))) != 0)

static inline int montauk_fdset_empty(const fd_set *s)
{
	unsigned i;

	if (s == NULL)
		return 1;
	for (i = 0; i < sizeof(s->fds_bits) / sizeof(s->fds_bits[0]); i++) {
		if (s->fds_bits[i] != 0)
			return 0;
	}
	return 1;
}

static inline int montauk_fdset_count(const fd_set *s, int nfds)
{
	int fd, n = 0;

	if (s == NULL)
		return 0;
	for (fd = 0; fd < nfds && fd < FD_SETSIZE; fd++) {
		if (FD_ISSET(fd, s))
			n++;
	}
	return n;
}

static inline int select(int nfds, fd_set *readfds, fd_set *writefds,
			 fd_set *exceptfds, struct timeval *timeout)
{
	int stdin_wanted;
	int ready;

	if (writefds != NULL)
		FD_ZERO(writefds);
	if (exceptfds != NULL)
		FD_ZERO(exceptfds);

	stdin_wanted = (readfds != NULL) && (nfds > 0) && FD_ISSET(0, readfds);
	if (stdin_wanted) {
		FD_CLR(0, readfds);
		if (montauk_stdin_ready()) {
			FD_SET(0, readfds);
		}
	}

	/*
	 * Descriptors other than stdin have no readiness source here, so they
	 * keep the old unconditional-ready answer.
	 */
	ready = montauk_fdset_count(readfds, nfds);
	if (ready > 0)
		return ready;

	if (timeout == NULL) {
		/*
		 * The core has nothing scheduled ("POLL BLOCKING"), so blocking
		 * for a command is right -- and returning 0 here instead would
		 * spin the CPU at 100%.
		 */
		if (stdin_wanted && montauk_stdin_wait()) {
			FD_SET(0, readfds);
			return 1;
		}
		return 0;
	}

	{
		unsigned long usec = (unsigned long) timeout->tv_sec * 1000000UL +
				     (unsigned long) timeout->tv_usec;

		/*
		 * Sleep in slices rather than one long usleep: a scheduled
		 * timeout can be seconds long, and typing must not wait it out.
		 */
		while (usec > 0) {
			unsigned long slice = (usec > 5000UL) ? 5000UL : usec;

			usleep(slice);
			usec -= slice;

			if (stdin_wanted && montauk_stdin_ready()) {
				FD_SET(0, readfds);
				return 1;
			}
		}
	}

	return 0;
}

#endif