#include <unistd.h>
#include <sys/stat.h>
#include <stdio.h>
#include <limits.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <inttypes.h>

#include <libdaemon/dlog.h>

#include "lock.h"
#include "util.h"
#include "main.h"

/* Where do lockfiles reside? */
#define LOCK_PATH "/var/lock"

static const char *lockfile(const char *dev) {
    static char lockfile[PATH_MAX];
    snprintf(lockfile, sizeof(lockfile), "%s/LCK..%s", LOCK_PATH, basename((char*) dev));
    return lockfile;
}

static const char *tempfile(const char *path) {
    static char t[PATH_MAX];
    snprintf(t, sizeof(t), "%s.tmp.%lu", path, (unsigned long) getpid());
    return t;
}

int device_lock(const char *dev) {
    struct stat st;
    int fd;
    const char *path, *temp;
    char buf[100];

    if (stat(LOCK_PATH, &st) != 0 || !S_ISDIR(st.st_mode)) {
        daemon_log(LOG_ERR, "Failed to lock device, directory "LOCK_PATH" not existent.");
        return -1;
    }

    path = lockfile(dev);
    temp = tempfile(path);

    for (;;) {
        
        if ((fd = open(path, O_RDONLY)) < 0) {
            if (errno != ENOENT) {
                daemon_log(LOG_ERR, "Failed to open lock file: %s", strerror(errno));
                return -1;
            }
        }
        
        if (fd >= 0) {
            ssize_t n;

            n = loop_read(fd, buf, sizeof(buf) - 1);
            close(fd);

            if (n < 0) {
                close(fd);
                daemon_log(LOG_ERR, "Failed to read from lock file: %s", strerror(errno));
                return -1;
            }
            
            if (n > 0) {
                pid_t pid;
                
                if (n == 4)
                    pid = (pid_t) *((uint32_t*) buf);
                else {
                    unsigned long v;
                    buf[n] = 0;
                    sscanf(buf, "%lu", &v);
                    pid = (pid_t) v;
                }
                
                if (pid > 0) {
                    if (kill(pid, 0) < 0 && errno == ESRCH) {
                        daemon_log(LOG_WARNING, "Lockfile is stale. Overriding it.");
                        /* Yes, here is a race condition */
                        unlink(path);
                    } else
                        return 1;
                }
            }
        }
        
        if ((fd = open(temp, O_WRONLY | O_CREAT | O_EXCL, 0666)) < 0) {
            daemon_log(LOG_ERR, "Failed to create temporary lock file: %s", strerror(errno));
            return -1;
        }

        snprintf(buf, sizeof(buf), "%10lu %s %.20s\n", (unsigned long) getpid(), appname, username);
        if (loop_write(fd, buf, strlen(buf)) < 0) {
            daemon_log(LOG_ERR, "Failed to write to temporary lock file: %s", strerror(errno));
            close(fd);
            return -1;
        }
    
        close(fd);

        if (link(temp, path) < 0) {
            if (errno == EEXIST)
                continue;

            daemon_log(LOG_ERR, "Failed to link temporary lock file: %s", strerror(errno));
        }

        unlink(temp);

        return 0;
    }
}

int device_unlock(const char *dev) {

    if (unlink(lockfile(dev)) < 0) {
        daemon_log(LOG_ERR, "Failed to remove lock file: %s", strerror(errno));
        return -1;
    }

    return 0;
}