#ifndef ATMB_BOOT_LINK_H
#define ATMB_BOOT_LINK_H

/* Linux-only boot-project pathname workaround. Include in CmpFrame.c only,
 * with _GNU_SOURCE defined before all system headers.
 * No PLC memory, communication state, worker thread or cyclic work is involved.
 */
#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <syslog.h>
#include <unistd.h>
#include <stdint.h>

static void atmb_ensure_boot_link(void)
{
    /* ComponentEntry is called at module initialization, not on each scan.
     * Guard against repeated entry; failure is deliberately not retried.
     */
    static int attempted;
    const char *name = "libCmpAtomModbus.so";
    const char *problem = NULL;
    Dl_info info;
    struct stat source, existing;
    char *module_path = NULL;
    int directory = -1;
    int error = 0;
    int saved_errno = errno;

    if (attempted)
        return;
    attempted = 1;

    /* The component function address identifies this loaded ELF object. Using
     * code rather than a local data symbol also works with runtimes that do not
     * expose local data addresses through dladdr().
     */
    if (!dladdr((void *)(uintptr_t)&atmb_ensure_boot_link, &info) || !info.dli_fname) {
        problem = "cannot locate loaded module";
        goto finish;
    }
    module_path = realpath(info.dli_fname, NULL);
    if (!module_path) {
        error = errno;
        problem = "cannot resolve loaded module pathname";
        goto finish;
    }
    if (stat(module_path, &source) != 0) {
        error = errno;
        problem = "cannot inspect loaded module file";
        goto finish;
    }
    if (!S_ISREG(source.st_mode)) {
        problem = "loaded module pathname is not a regular file";
        goto finish;
    }

    /* Boot creation was observed looking up the bare filename relative to
     * runtime cwd. Anchor this directory with an FD; never change cwd.
     */
    directory = open(".", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
    if (directory < 0) {
        error = errno;
        problem = "cannot open runtime working directory";
        goto finish;
    }
    if (fstatat(directory, name, &existing, AT_SYMLINK_NOFOLLOW) == 0) {
        struct stat resolved;
        if (fstatat(directory, name, &resolved, 0) == 0 &&
            resolved.st_dev == source.st_dev &&
            resolved.st_ino == source.st_ino)
            goto finish; /* Correct link, hard link, or the source itself. */
        problem = "existing file or link left untouched; check boot-project path";
        goto finish;
    }
    if (errno != ENOENT) {
        error = errno;
        problem = "cannot inspect boot-project pathname";
        goto finish;
    }

    /* symlinkat fails on EEXIST: even a concurrent creator cannot be replaced.
     * Keep this link on shutdown; boot-project creation may still need it.
     */
    if (symlinkat(module_path, directory, name) != 0) {
        error = errno;
        problem = "cannot create boot-project link";
        goto finish;
    }
    syslog(LOG_INFO, "CmpAtomModbus: created boot link %s -> %s in runtime cwd",
           name, module_path);

finish:
    if (problem) {
        if (error)
            syslog(LOG_WARNING, "CmpAtomModbus: %s: %s (errno=%d); Modbus startup continues",
                   problem, strerror(error), error);
        else
            syslog(LOG_WARNING, "CmpAtomModbus: %s; Modbus startup continues", problem);
    }
    if (directory >= 0)
        close(directory);
    free(module_path);
    errno = saved_errno;
}
#endif