#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <errno.h>

/*
 * vlibc — strerror / strerror_r (todo 2).
 *
 * strerror maps an errno value to an informative, descriptive message. The
 * messages are this libc's own standard English texts (they need not match
 * glibc verbatim). Known values resolve to immutable static string constants;
 * unknown values resolve to "Unknown error <N>" with <N> formatted in place.
 *
 * Thread-safety of the unknown-value path: the formatted string lives in a
 * single static buffer, so two threads formatting *unknown* errno values
 * concurrently can observe each other's text. This tradeoff is deliberate at
 * this stage: unknown errno values are a rare diagnostic path, the library
 * has no per-thread storage beyond the errno TCB slot yet, and strerror must
 * not depend on malloc (or any other subsystem). The pointer returned for
 * known values is unaffected. Once the real TCB layout lands (startup todo),
 * this can migrate to a per-thread buffer without changing the interface.
 *
 * The unknown-value formatter is hand-rolled: strerror is libc base and must
 * not pull in stdio/string before those exist.
 */

/*
 * Message table: one entry per defined E* value, indexed directly by the
 * errno number. Designated initializers keep name/value pairs provably in
 * sync with <errno.h>; entries for the ABI gaps (41, 58 — values the kernel
 * never produces) stay NULL and are treated as unknown. EWOULDBLOCK and
 * EDEADLOCK are aliases of EAGAIN and EDEADLK, so they share those entries.
 * The array auto-sizes to EHWPOISON + 1 (134) entries.
 */
static const char *const errmsg[] = {
    [0] = "Success",
    [EPERM] = "Operation not permitted",
    [ENOENT] = "No such file or directory",
    [ESRCH] = "No such process",
    [EINTR] = "Interrupted system call",
    [EIO] = "Input/output error",
    [ENXIO] = "No such device or address",
    [E2BIG] = "Argument list too long",
    [ENOEXEC] = "Exec format error",
    [EBADF] = "Bad file descriptor",
    [ECHILD] = "No child processes",
    [EAGAIN] = "Resource temporarily unavailable",
    [ENOMEM] = "Cannot allocate memory",
    [EACCES] = "Permission denied",
    [EFAULT] = "Bad address",
    [ENOTBLK] = "Block device required",
    [EBUSY] = "Device or resource busy",
    [EEXIST] = "File exists",
    [EXDEV] = "Invalid cross-device link",
    [ENODEV] = "No such device",
    [ENOTDIR] = "Not a directory",
    [EISDIR] = "Is a directory",
    [EINVAL] = "Invalid argument",
    [ENFILE] = "Too many open files in system",
    [EMFILE] = "Too many open files",
    [ENOTTY] = "Inappropriate ioctl for device",
    [ETXTBSY] = "Text file busy",
    [EFBIG] = "File too large",
    [ENOSPC] = "No space left on device",
    [ESPIPE] = "Illegal seek",
    [EROFS] = "Read-only file system",
    [EMLINK] = "Too many links",
    [EPIPE] = "Broken pipe",
    [EDOM] = "Numerical argument out of domain",
    [ERANGE] = "Numerical result out of range",
    [EDEADLK] = "Resource deadlock would occur",
    [ENAMETOOLONG] = "File name too long",
    [ENOLCK] = "No locks available",
    [ENOSYS] = "Function not implemented",
    [ENOTEMPTY] = "Directory not empty",
    [ELOOP] = "Too many levels of symbolic links",
    [ENOMSG] = "No message of desired type",
    [EIDRM] = "Identifier removed",
    [ECHRNG] = "Channel number out of range",
    [EL2NSYNC] = "Level 2 not synchronized",
    [EL3HLT] = "Level 3 halted",
    [EL3RST] = "Level 3 reset",
    [ELNRNG] = "Link number out of range",
    [EUNATCH] = "Protocol driver not attached",
    [ENOCSI] = "No CSI structure available",
    [EL2HLT] = "Level 2 halted",
    [EBADE] = "Invalid exchange",
    [EBADR] = "Invalid request descriptor",
    [EXFULL] = "Exchange full",
    [ENOANO] = "No anode",
    [EBADRQC] = "Invalid request code",
    [EBADSLT] = "Invalid slot",
    [EBFONT] = "Bad font file format",
    [ENOSTR] = "Device not a stream",
    [ENODATA] = "No data available",
    [ETIME] = "Timer expired",
    [ENOSR] = "Out of streams resources",
    [ENONET] = "Machine is not on the network",
    [ENOPKG] = "Package not installed",
    [EREMOTE] = "Object is remote",
    [ENOLINK] = "Link has been severed",
    [EADV] = "Advertise error",
    [ESRMNT] = "Srmount error",
    [ECOMM] = "Communication error on send",
    [EPROTO] = "Protocol error",
    [EMULTIHOP] = "Multihop attempted",
    [EDOTDOT] = "RFS specific error",
    [EBADMSG] = "Bad message",
    [EOVERFLOW] = "Value too large for defined data type",
    [ENOTUNIQ] = "Name not unique on network",
    [EBADFD] = "File descriptor in bad state",
    [EREMCHG] = "Remote address changed",
    [ELIBACC] = "Can not access a needed shared library",
    [ELIBBAD] = "Accessing a corrupted shared library",
    [ELIBSCN] = ".lib section in a.out corrupted",
    [ELIBMAX] = "Attempting to link in too many shared libraries",
    [ELIBEXEC] = "Cannot exec a shared library directly",
    [EILSEQ] = "Invalid or incomplete multibyte or wide character",
    [ERESTART] = "Interrupted system call should be restarted",
    [ESTRPIPE] = "Streams pipe error",
    [EUSERS] = "Too many users",
    [ENOTSOCK] = "Socket operation on non-socket",
    [EDESTADDRREQ] = "Destination address required",
    [EMSGSIZE] = "Message too long",
    [EPROTOTYPE] = "Protocol wrong type for socket",
    [ENOPROTOOPT] = "Protocol not available",
    [EPROTONOSUPPORT] = "Protocol not supported",
    [ESOCKTNOSUPPORT] = "Socket type not supported",
    [EOPNOTSUPP] = "Operation not supported",
    [EPFNOSUPPORT] = "Protocol family not supported",
    [EAFNOSUPPORT] = "Address family not supported by protocol",
    [EADDRINUSE] = "Address already in use",
    [EADDRNOTAVAIL] = "Cannot assign requested address",
    [ENETDOWN] = "Network is down",
    [ENETUNREACH] = "Network is unreachable",
    [ENETRESET] = "Network dropped connection on reset",
    [ECONNABORTED] = "Software caused connection abort",
    [ECONNRESET] = "Connection reset by peer",
    [ENOBUFS] = "No buffer space available",
    [EISCONN] = "Transport endpoint is already connected",
    [ENOTCONN] = "Transport endpoint is not connected",
    [ESHUTDOWN] = "Cannot send after transport endpoint shutdown",
    [ETOOMANYREFS] = "Too many references: cannot splice",
    [ETIMEDOUT] = "Connection timed out",
    [ECONNREFUSED] = "Connection refused",
    [EHOSTDOWN] = "Host is down",
    [EHOSTUNREACH] = "No route to host",
    [EALREADY] = "Operation already in progress",
    [EINPROGRESS] = "Operation now in progress",
    [ESTALE] = "Stale file handle",
    [EUCLEAN] = "Structure needs cleaning",
    [ENOTNAM] = "Not a XENIX named type file",
    [ENAVAIL] = "No XENIX semaphores available",
    [EISNAM] = "Is a named type file",
    [EREMOTEIO] = "Remote I/O error",
    [EDQUOT] = "Disk quota exceeded",
    [ENOMEDIUM] = "No medium found",
    [EMEDIUMTYPE] = "Wrong medium type",
    [ECANCELED] = "Operation canceled",
    [ENOKEY] = "Required key not available",
    [EKEYEXPIRED] = "Key has expired",
    [EKEYREVOKED] = "Key has been revoked",
    [EKEYREJECTED] = "Key was rejected by service",
    [EOWNERDEAD] = "Owner died",
    [ENOTRECOVERABLE] = "State not recoverable",
    [ERFKILL] = "Operation not possible due to RF-kill",
    [EHWPOISON] = "Memory page has hardware error",
};

/* The table spans 0..EHWPOISON exactly: the ABI gaps stay NULL entries. */
_Static_assert(sizeof errmsg / sizeof errmsg[0] == EHWPOISON + 1,
               "strerror table must cover every E* value 0..EHWPOISON");

/* Shared storage for the unknown-value path (see the file-top comment). */
static char errbuf[32];

/*
 * Write "Unknown error <errnum>" into dst, truncating to cap bytes and always
 * NUL-terminating when cap > 0. Hand-rolled so this file needs no stdio.
 */
static void
format_unknown(int errnum, char *dst, size_t cap)
{
    static const char prefix[] = "Unknown error ";
    char digits[12]; /* enough for "-2147483648" */
    size_t ndigits;
    size_t i;
    unsigned long mag;

    if (cap == 0)
    {
        return;
    }

    /* Absolute value as unsigned long; INT_MIN negates safely in long. */
    mag = (unsigned long)(errnum < 0 ? -(long)errnum : errnum);

    /* Digits, least significant first. */
    ndigits = 0;
    do
    {
        digits[ndigits] = (char)('0' + (int)(mag % 10));
        ndigits++;
        mag /= 10;
    } while (mag != 0);

    i = 0;
    while (i + 1 < cap && prefix[i] != '\0')
    {
        dst[i] = prefix[i];
        i++;
    }
    if (i + 1 < cap && errnum < 0)
    {
        dst[i] = '-';
        i++;
    }
    while (i + 1 < cap && ndigits > 0)
    {
        ndigits--;
        dst[i] = digits[ndigits];
        i++;
    }
    dst[i] = '\0';
}

/*
 * Return the message for errnum, or NULL when it is unknown (out of table
 * range or an ABI gap).
 */
static const char *
lookup(int errnum)
{
    if (errnum >= 0 && errnum < (int)(sizeof errmsg / sizeof errmsg[0]))
    {
        return errmsg[errnum];
    }
    return NULL;
}

char *
strerror(int errnum)
{
    const char *msg;

    msg = lookup(errnum);
    if (msg == NULL)
    {
        format_unknown(errnum, errbuf, sizeof errbuf);
        msg = errbuf;
    }
    return (char *)msg;
}

#if VLIBC_LEVEL_GE(2)
/*
 * XSI strerror_r: copy the message for errnum into buf (truncated to buflen,
 * always NUL-terminated when buflen > 0) and return 0. Unknown errnum values
 * produce "Unknown error <errnum>" with the same success return; buf == NULL
 * with buflen > 0 yields EINVAL; buflen == 0 writes nothing and returns 0.
 * The GNU char*-returning semantics are deliberately not implemented.
 */
int
strerror_r(int errnum, char *buf, size_t buflen)
{
    const char *msg;
    char unknown[32];
    size_t i;

    if (buflen == 0)
    {
        return 0;
    }
    if (buf == NULL)
    {
        return EINVAL;
    }

    msg = lookup(errnum);
    if (msg == NULL)
    {
        format_unknown(errnum, unknown, sizeof unknown);
        msg = unknown;
    }

    i = 0;
    while (i + 1 < buflen && msg[i] != '\0')
    {
        buf[i] = msg[i];
        i++;
    }
    buf[i] = '\0';
    return 0;
}
#endif /* VLIBC_LEVEL_GE(2) */