#ifndef VLIBC_SYS_SELECT_H
#define VLIBC_SYS_SELECT_H

/*
 * vlibc — <sys/select.h>.
 *
 * Synchronous I/O multiplexing: wait for readiness on file-descriptor sets
 * with select() or pselect(). Both are thin wrappers over the SYS_pselect6
 * kernel ABI, (nfds, readfds, writefds, exceptfds, struct timespec *,
 * { sigset_t *, size_t } *): pselect passes its timespec and optional signal
 * mask straight through, select converts its struct timeval timeout to a
 * timespec and passes a NULL sigset pair.
 *
 *   Level 1 (onlyposix): select, pselect, FD_* macros, fd_set, struct
 *                        timeval.
 *
 * fd_set is the kernel's bitmap layout on x86_64: an array of unsigned long
 * words, with descriptor d held in bit d % 64 of word d / 64. FD_SETSIZE
 * caps the tracked descriptors at 1024 (16 words), so select()/pselect()
 * must be called with nfds <= FD_SETSIZE and FD_SET() only ever receives
 * descriptors below FD_SETSIZE. select() and pselect() report the number of
 * ready descriptors, 0 on timeout, or -1 with errno set on error.
 *
 * The signal mask type is declared here under the shared guard; <signal.h>
 * is its canonical POSIX home and will own the full sig* API.
 */

#include <vlibc/features.h>

#include <sys/types.h>

#include <time.h>

#ifdef __cplusplus
extern "C" {
#endif

/* Maximum descriptors select()/pselect() track (fd_set's bit capacity). */
#define FD_SETSIZE 1024

/*
 * A set of file descriptors, one bit per descriptor, stored in the kernel
 * bitmap layout: an array of unsigned long words, bit d in word
 * d / (8 * sizeof(unsigned long)). Descriptors 0..FD_SETSIZE-1 fit; no
 * operation may touch a descriptor at or above FD_SETSIZE.
 */
typedef struct
{
    unsigned long fds_bits[FD_SETSIZE / (8 * sizeof(unsigned long))];
} fd_set;

/* The word holding bit d of an fd_set, and that bit's mask within the word. */
#define VLIBC_FDS_WORD(d) ((d) / (8 * sizeof(unsigned long)))
#define VLIBC_FDS_MASK(d) (1UL << ((d) % (8 * sizeof(unsigned long))))

/* Clear every descriptor bit of set. */
#define FD_ZERO(set)                                                                               \
    do                                                                                             \
    {                                                                                              \
        size_t fd_zero_i;                                                                          \
        for (fd_zero_i = 0; fd_zero_i < sizeof(fd_set) / sizeof(unsigned long); fd_zero_i++)       \
        {                                                                                          \
            (set)->fds_bits[fd_zero_i] = 0UL;                                                      \
        }                                                                                          \
    } while (0)

/* Add descriptor d to set. */
#define FD_SET(d, set) ((set)->fds_bits[VLIBC_FDS_WORD(d)] |= VLIBC_FDS_MASK(d))

/* Remove descriptor d from set. */
#define FD_CLR(d, set) ((set)->fds_bits[VLIBC_FDS_WORD(d)] &= ~VLIBC_FDS_MASK(d))

/* Nonzero when descriptor d is a member of set. */
#define FD_ISSET(d, set) ((set)->fds_bits[VLIBC_FDS_WORD(d)] & VLIBC_FDS_MASK(d))

#ifndef VLIBC_SIGSET_T_DEFINED
#define VLIBC_SIGSET_T_DEFINED
/*
 * Signal mask type: a single 64-bit word — the x86_64 Linux sigset_t (see
 * setjmp.h). pselect() and ppoll() only ever forward a pointer to the
 * kernel, which reads the word directly. <signal.h> is the canonical POSIX
 * home for sigset_t and builds the sig* API on this same layout; the
 * typedef is repeated in <poll.h> under this guard so the two headers stay
 * consistent.
 */
typedef unsigned long sigset_t;
#endif

/* Elapsed time in seconds and microseconds (see select()'s timeout). */
struct timeval
{
    time_t tv_sec;
    suseconds_t tv_usec;
};

/*
 * Wait for readiness on the descriptors marked in readfds, writefds and
 * exceptfds (each may be NULL), up to nfds descriptors (the highest
 * descriptor in any set plus one). timeout is an upper bound on the wait; a
 * NULL timeout blocks indefinitely, { 0, 0 } never blocks. On return each
 * non-NULL set holds only its ready descriptors. Return the number of ready
 * descriptors across the sets, 0 on timeout, or -1 with errno set.
 */
int
select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

/*
 * Like select(), but the timeout is a struct timespec and, when sigmask is
 * not NULL, the given signal mask is atomically installed for the duration
 * of the wait (the previous mask is restored before returning).
 */
int
pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
        const struct timespec *timeout, const sigset_t *sigmask);

#ifdef __cplusplus
}
#endif

#endif /* VLIBC_SYS_SELECT_H */