/*
 * Copyright (c) 2005, Junio C Hamano
 */
#include "cache.h"

static struct lock_file *lock_file_list;
static const char *alternate_index_output;

static void remove_lock_file(void)
{
        pid_t me = getpid();

        while (lock_file_list) {
                if (lock_file_list->owner == me &&
                    lock_file_list->filename[0])
                        unlink(lock_file_list->filename);
                lock_file_list = lock_file_list->next;
        }
}

static void remove_lock_file_on_signal(int signo)
{
        remove_lock_file();
        signal(SIGINT, SIG_DFL);
        raise(signo);
}

/*
 * p = absolute or relative path name
 *
 * Return a pointer into p showing the beginning of the last path name
 * element.  If p is empty or the root directory ("/"), just return p.
 */
static char *last_path_elm(char *p)
{
        /* r starts pointing to null at the end of the string */
        char *r = strchr(p, '\0');

        if (r == p)
                return p; /* just return empty string */

        r--; /* back up to last non-null character */

        /* back up past trailing slashes, if any */
        while (r > p && *r == '/')
                r--;

        /*
         * then go backwards until I hit a slash, or the beginning of
         * the string
         */
        while (r > p && *(r-1) != '/')
                r--;
        return r;
}


/* We allow "recursive" symbolic links. Only within reason, though */
#define MAXDEPTH 5

/*
 * p = path that may be a symlink
 * s = full size of p
 *
 * If p is a symlink, attempt to overwrite p with a path to the real
 * file or directory (which may or may not exist), following a chain of
 * symlinks if necessary.  Otherwise, leave p unmodified.
 *
 * This is a best-effort routine.  If an error occurs, p will either be
 * left unmodified or will name a different symlink in a symlink chain
 * that started with p's initial contents.
 *
 * Always returns p.
 */

static char *resolve_symlink(char *p, size_t s)
{
        int depth = MAXDEPTH;

        while (depth--) {
                char link[PATH_MAX];
                int link_len = readlink(p, link, sizeof(link));
                if (link_len < 0) {
                        /* not a symlink anymore */
                        return p;
                }
                else if (link_len < sizeof(link))
                        /* readlink() never null-terminates */
                        link[link_len] = '\0';
                else {
                        warning("%s: symlink too long", p);
                        return p;
                }

                if (link[0] == '/') {
                        /* absolute path simply replaces p */
                        if (link_len < s)
                                strcpy(p, link);
                        else {
                                warning("%s: symlink too long", p);
                                return p;
                        }
                } else {
                        /*
                         * link is a relative path, so I must replace the
                         * last element of p with it.
                         */
                        char *r = (char*)last_path_elm(p);
                        if (r - p + link_len < s)
                                strcpy(r, link);
                        else {
                                warning("%s: symlink too long", p);
                                return p;
                        }
                }
        }
        return p;
}


static int lock_file(struct lock_file *lk, const char *path)
{
        int fd;

        if (strlen(path) >= sizeof(lk->filename)) return -1;
        strcpy(lk->filename, path);
        /*
         * subtract 5 from size to make sure there's room for adding
         * ".lock" for the lock file name
         */
        resolve_symlink(lk->filename, sizeof(lk->filename)-5);
        strcat(lk->filename, ".lock");
        fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
        if (0 <= fd) {
                if (!lock_file_list) {
                        signal(SIGINT, remove_lock_file_on_signal);
                        atexit(remove_lock_file);
                }
                lk->owner = getpid();
                if (!lk->on_list) {
                        lk->next = lock_file_list;
                        lock_file_list = lk;
                        lk->on_list = 1;
                }
                if (adjust_shared_perm(lk->filename))
                        return error("cannot fix permission bits on %s",
                                     lk->filename);
        }
        else
                lk->filename[0] = 0;
        return fd;
}

int hold_lock_file_for_update(struct lock_file *lk, const char *path, int die_on_error)
{
        int fd = lock_file(lk, path);
        if (fd < 0 && die_on_error)
                die("unable to create '%s.lock': %s", path, strerror(errno));
        return fd;
}

int commit_lock_file(struct lock_file *lk)
{
        char result_file[PATH_MAX];
        int i;
        strcpy(result_file, lk->filename);
        i = strlen(result_file) - 5; /* .lock */
        result_file[i] = 0;
        i = rename(lk->filename, result_file);
        lk->filename[0] = 0;
        return i;
}

int hold_locked_index(struct lock_file *lk, int die_on_error)
{
        return hold_lock_file_for_update(lk, get_index_file(), die_on_error);
}

void set_alternate_index_output(const char *name)
{
        alternate_index_output = name;
}

int commit_locked_index(struct lock_file *lk)
{
        if (alternate_index_output) {
                int result = rename(lk->filename, alternate_index_output);
                lk->filename[0] = 0;
                return result;
        }
        else
                return commit_lock_file(lk);
}

void rollback_lock_file(struct lock_file *lk)
{
        if (lk->filename[0])
                unlink(lk->filename);
        lk->filename[0] = 0;
}