#ifndef VLIBC_SYSLOG_H
#define VLIBC_SYSLOG_H

/*
 * vlibc — <syslog.h>.
 *
 * The syslog(3) logging interface, writing BSD-syslog datagrams to the
 * /dev/log socket (see src/misc/syslog.c for the wire details). syslog is
 * NOT POSIX.1-2008 base — it is XSI [CX] (and historical BSD), so this
 * ENTIRE header is gated at `VLIBC_LEVEL >= 2`: at level 1 (onlyposix) it is
 * empty, exactly like <strings.h>.
 *
 * The interface has three parts:
 *
 *   - facilities and severities, plus the option flags of openlog. The
 *     facility constants carry the classic BSD values, which are the Linux
 *     wire ABI for /dev/log: facility = code << 3, severity = 0..7, and the
 *     datagram's numeric priority is facility | severity. The facility code
 *     is passed on the wire, so these numbers must match what syslogd
 *     expects and are therefore kernel-ABI facts, not invented values;
 *
 *   - LOG_MASK / LOG_UPTO, the two macros that build the mask argument of
 *     setlogmask (LOG_MASK is POSIX; LOG_UPTO is the classic convenience
 *     form both musl and glibc provide);
 *
 *   - openlog / syslog / closelog / setlogmask and the vsyslog entry point
 *     the standard requires syslog to be implemented in terms of. None of
 *     them carries an intent attribute: every one reads and writes global
 *     logging state and performs I/O, so const/pure would be unsound.
 *
 * %m handling: inside the syslog format string, "%m" is replaced by the
 * strerror(errno) text (a syslog-specific feature, implemented in syslog.c —
 * NOT a printf conversion). All other conversions are the standard ones,
 * handled by the library's own vsnprintf.
 *
 * This header includes <vlibc/features.h> itself, so the gate below always
 * sees the configured VLIBC_LEVEL even when the caller included no vlibc
 * header first, and <stdarg.h> for va_list.
 */

#include <vlibc/features.h>

#if VLIBC_LEVEL_GE(2)

#include <stdarg.h>

#ifdef __cplusplus
extern "C" {
#endif

/* ---- openlog option flags (bit mask) ---- */

#define LOG_PID 0x01    /* include the calling process' PID in each message */
#define LOG_CONS 0x02   /* on send failure, write the message to the console */
#define LOG_ODELAY 0x04 /* delay opening the /dev/log socket until first use */
#define LOG_NDELAY 0x08 /* open the /dev/log socket immediately in openlog */
#define LOG_NOWAIT 0x10 /* do not wait for child processes (accepted, unused) */
#define LOG_PERROR 0x20 /* also write each message to standard error */

/* ---- facility codes (code << 3; the wire value of the datagram) ---- */

#define LOG_KERN 0           /* kernel messages */
#define LOG_USER (1 << 3)    /* random user-level messages */
#define LOG_MAIL (2 << 3)    /* mail system */
#define LOG_DAEMON (3 << 3)  /* system daemons */
#define LOG_AUTH (4 << 3)    /* security/authorization messages */
#define LOG_LPR (6 << 3)     /* line printer subsystem */
#define LOG_NEWS (7 << 3)    /* network news subsystem */
#define LOG_UUCP (8 << 3)    /* UUCP subsystem */
#define LOG_CRON (9 << 3)    /* clock daemon */
#define LOG_LOCAL0 (16 << 3) /* reserved for local use */
#define LOG_LOCAL1 (17 << 3) /* reserved for local use */
#define LOG_LOCAL2 (18 << 3) /* reserved for local use */
#define LOG_LOCAL3 (19 << 3) /* reserved for local use */
#define LOG_LOCAL4 (20 << 3) /* reserved for local use */
#define LOG_LOCAL5 (21 << 3) /* reserved for local use */
#define LOG_LOCAL6 (22 << 3) /* reserved for local use */
#define LOG_LOCAL7 (23 << 3) /* reserved for local use */

/* ---- severities (the low three bits of the priority value) ---- */

#define LOG_EMERG 0   /* system is unusable */
#define LOG_ALERT 1   /* action must be taken immediately */
#define LOG_CRIT 2    /* critical conditions */
#define LOG_ERR 3     /* error conditions */
#define LOG_WARNING 4 /* warning conditions */
#define LOG_NOTICE 5  /* normal but significant condition */
#define LOG_INFO 6    /* informational */
#define LOG_DEBUG 7   /* debug-level messages */

/* Bit field holding the facility part (bits 3..9) of a priority value. */
#define LOG_FACMASK 0x03f8

/* Bit field holding the severity part (bits 0..2) of a priority value. */
#define LOG_PRIMASK 0x07

/* A mask with exactly pri's bit set (pri is a LOG_* severity, 0..7). */
#define LOG_MASK(pri) (1 << (pri))

/* A mask with every severity from LOG_EMERG through pri included. */
#define LOG_UPTO(pri) ((1 << ((pri) + 1)) - 1)

/*
 * Open a connection to the system logger. ident, when non-NULL, is copied
 * (a caller-owned pointer is not retained) and prefixes every message; a
 * NULL ident logs messages with no tag. option ORs in the LOG_* option
 * flags; facility is one of the LOG_* facility constants and is used for
 * messages whose priority carries no facility of its own. With LOG_NDELAY
 * the /dev/log socket is opened here; otherwise (and by default) it is
 * opened lazily on the first syslog call, and a failure to open it is
 * silent. Prior state — the mask from setlogmask and the default facility
 * LOG_USER — persists.
 *
 * I/O and global state: no intent attribute.
 */
void
openlog(const char *ident, int option, int facility);

/*
 * Log a message: build "<facility|severity>ident[pid]: message" and send it
 * as one datagram to /dev/log, subject to the setlogmask mask. severity is
 * the low three bits of priority; a facility encoded in priority overrides
 * the openlog facility, and an out-of-range (high-bit) facility is ignored,
 * falling back to the openlog facility. The format string is the printf
 * family's, with "%m" additionally meaning the strerror(errno) text. When
 * LOG_PERROR was passed to openlog the composed line also goes to standard
 * error; when the send fails and LOG_CONS was passed, it goes to the console
 * instead. A failed open or send never terminates the process.
 *
 * I/O and global state: no intent attribute.
 */
void
syslog(int priority, const char *format, ...);

/*
 * Close the connection to the system logger: close the /dev/log socket if
 * one is open, and clear the ident and option state installed by openlog
 * (the facility and mask are retained). A later syslog reopens the socket
 * lazily.
 *
 * I/O and global state: no intent attribute.
 */
void
closelog(void);

/*
 * The engine behind syslog: identical semantics, taking a va_list instead
 * of the variadic tail. Each message is formatted exactly once (through
 * vsnprintf into an internal buffer) before any send, so LOG_PERROR and the
 * datagram always carry the same text.
 *
 * I/O and global state: no intent attribute.
 */
void
vsyslog(int priority, const char *format, va_list ap);

/*
 * Set the process' log priority mask to maskpri — a bit per severity where
 * bit LOG_MASK(severity) set means "log this severity" — and return the
 * previous mask. A mask of 0 suppresses every message. The mask applies to
 * the severity only: facility is never filtered.
 */
int
setlogmask(int maskpri);

#ifdef __cplusplus
}
#endif

#endif /* VLIBC_LEVEL_GE(2) */

#endif /* VLIBC_SYSLOG_H */