#include "refs.h"
#include "cache.h"
#include "object.h"
#include "tag.h"

#include <errno.h>

/* ISSYMREF=01 and ISPACKED=02 are public interfaces */
#define REF_KNOWS_PEELED 04

struct ref_list {
        struct ref_list *next;
        unsigned char flag; /* ISSYMREF? ISPACKED? */
        unsigned char sha1[20];
        unsigned char peeled[20];
        char name[FLEX_ARRAY];
};

static const char *parse_ref_line(char *line, unsigned char *sha1)
{
        /*
         * 42: the answer to everything.
         *
         * In this case, it happens to be the answer to
         *  40 (length of sha1 hex representation)
         *  +1 (space in between hex and name)
         *  +1 (newline at the end of the line)
         */
        int len = strlen(line) - 42;

        if (len <= 0)
                return NULL;
        if (get_sha1_hex(line, sha1) < 0)
                return NULL;
        if (!isspace(line[40]))
                return NULL;
        line += 41;
        if (isspace(*line))
                return NULL;
        if (line[len] != '\n')
                return NULL;
        line[len] = 0;

        return line;
}

static struct ref_list *add_ref(const char *name, const unsigned char *sha1,
                                int flag, struct ref_list *list,
                                struct ref_list **new_entry)
{
        int len;
        struct ref_list **p = &list, *entry;

        /* Find the place to insert the ref into.. */
        while ((entry = *p) != NULL) {
                int cmp = strcmp(entry->name, name);
                if (cmp > 0)
                        break;

                /* Same as existing entry? */
                if (!cmp) {
                        if (new_entry)
                                *new_entry = entry;
                        return list;
                }
                p = &entry->next;
        }

        /* Allocate it and add it in.. */
        len = strlen(name) + 1;
        entry = xmalloc(sizeof(struct ref_list) + len);
        hashcpy(entry->sha1, sha1);
        hashclr(entry->peeled);
        memcpy(entry->name, name, len);
        entry->flag = flag;
        entry->next = *p;
        *p = entry;
        if (new_entry)
                *new_entry = entry;
        return list;
}

/*
 * Future: need to be in "struct repository"
 * when doing a full libification.
 */
struct cached_refs {
        char did_loose;
        char did_packed;
        struct ref_list *loose;
        struct ref_list *packed;
} cached_refs;

static void free_ref_list(struct ref_list *list)
{
        struct ref_list *next;
        for ( ; list; list = next) {
                next = list->next;
                free(list);
        }
}

static void invalidate_cached_refs(void)
{
        struct cached_refs *ca = &cached_refs;

        if (ca->did_loose && ca->loose)
                free_ref_list(ca->loose);
        if (ca->did_packed && ca->packed)
                free_ref_list(ca->packed);
        ca->loose = ca->packed = NULL;
        ca->did_loose = ca->did_packed = 0;
}

static void read_packed_refs(FILE *f, struct cached_refs *cached_refs)
{
        struct ref_list *list = NULL;
        struct ref_list *last = NULL;
        char refline[PATH_MAX];
        int flag = REF_ISPACKED;

        while (fgets(refline, sizeof(refline), f)) {
                unsigned char sha1[20];
                const char *name;
                static const char header[] = "# pack-refs with:";

                if (!strncmp(refline, header, sizeof(header)-1)) {
                        const char *traits = refline + sizeof(header) - 1;
                        if (strstr(traits, " peeled "))
                                flag |= REF_KNOWS_PEELED;
                        /* perhaps other traits later as well */
                        continue;
                }

                name = parse_ref_line(refline, sha1);
                if (name) {
                        list = add_ref(name, sha1, flag, list, &last);
                        continue;
                }
                if (last &&
                    refline[0] == '^' &&
                    strlen(refline) == 42 &&
                    refline[41] == '\n' &&
                    !get_sha1_hex(refline + 1, sha1))
                        hashcpy(last->peeled, sha1);
        }
        cached_refs->packed = list;
}

static struct ref_list *get_packed_refs(void)
{
        if (!cached_refs.did_packed) {
                FILE *f = fopen(git_path("packed-refs"), "r");
                cached_refs.packed = NULL;
                if (f) {
                        read_packed_refs(f, &cached_refs);
                        fclose(f);
                }
                cached_refs.did_packed = 1;
        }
        return cached_refs.packed;
}

static struct ref_list *get_ref_dir(const char *base, struct ref_list *list)
{
        DIR *dir = opendir(git_path("%s", base));

        if (dir) {
                struct dirent *de;
                int baselen = strlen(base);
                char *ref = xmalloc(baselen + 257);

                memcpy(ref, base, baselen);
                if (baselen && base[baselen-1] != '/')
                        ref[baselen++] = '/';

                while ((de = readdir(dir)) != NULL) {
                        unsigned char sha1[20];
                        struct stat st;
                        int flag;
                        int namelen;

                        if (de->d_name[0] == '.')
                                continue;
                        namelen = strlen(de->d_name);
                        if (namelen > 255)
                                continue;
                        if (has_extension(de->d_name, ".lock"))
                                continue;
                        memcpy(ref + baselen, de->d_name, namelen+1);
                        if (stat(git_path("%s", ref), &st) < 0)
                                continue;
                        if (S_ISDIR(st.st_mode)) {
                                list = get_ref_dir(ref, list);
                                continue;
                        }
                        if (!resolve_ref(ref, sha1, 1, &flag)) {
                                error("%s points nowhere!", ref);
                                continue;
                        }
                        list = add_ref(ref, sha1, flag, list, NULL);
                }
                free(ref);
                closedir(dir);
        }
        return list;
}

static struct ref_list *get_loose_refs(void)
{
        if (!cached_refs.did_loose) {
                cached_refs.loose = get_ref_dir("refs", NULL);
                cached_refs.did_loose = 1;
        }
        return cached_refs.loose;
}

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

const char *resolve_ref(const char *ref, unsigned char *sha1, int reading, int *flag)
{
        int depth = MAXDEPTH, len;
        char buffer[256];
        static char ref_buffer[256];

        if (flag)
                *flag = 0;

        for (;;) {
                const char *path = git_path("%s", ref);
                struct stat st;
                char *buf;
                int fd;

                if (--depth < 0)
                        return NULL;

                /* Special case: non-existing file.
                 * Not having the refs/heads/new-branch is OK
                 * if we are writing into it, so is .git/HEAD
                 * that points at refs/heads/master still to be
                 * born.  It is NOT OK if we are resolving for
                 * reading.
                 */
                if (lstat(path, &st) < 0) {
                        struct ref_list *list = get_packed_refs();
                        while (list) {
                                if (!strcmp(ref, list->name)) {
                                        hashcpy(sha1, list->sha1);
                                        if (flag)
                                                *flag |= REF_ISPACKED;
                                        return ref;
                                }
                                list = list->next;
                        }
                        if (reading || errno != ENOENT)
                                return NULL;
                        hashclr(sha1);
                        return ref;
                }

                /* Follow "normalized" - ie "refs/.." symlinks by hand */
                if (S_ISLNK(st.st_mode)) {
                        len = readlink(path, buffer, sizeof(buffer)-1);
                        if (len >= 5 && !memcmp("refs/", buffer, 5)) {
                                buffer[len] = 0;
                                strcpy(ref_buffer, buffer);
                                ref = ref_buffer;
                                if (flag)
                                        *flag |= REF_ISSYMREF;
                                continue;
                        }
                }

                /* Is it a directory? */
                if (S_ISDIR(st.st_mode)) {
                        errno = EISDIR;
                        return NULL;
                }

                /*
                 * Anything else, just open it and try to use it as
                 * a ref
                 */
                fd = open(path, O_RDONLY);
                if (fd < 0)
                        return NULL;
                len = read(fd, buffer, sizeof(buffer)-1);
                close(fd);

                /*
                 * Is it a symbolic ref?
                 */
                if (len < 4 || memcmp("ref:", buffer, 4))
                        break;
                buf = buffer + 4;
                len -= 4;
                while (len && isspace(*buf))
                        buf++, len--;
                while (len && isspace(buf[len-1]))
                        len--;
                buf[len] = 0;
                memcpy(ref_buffer, buf, len + 1);
                ref = ref_buffer;
                if (flag)
                        *flag |= REF_ISSYMREF;
        }
        if (len < 40 || get_sha1_hex(buffer, sha1))
                return NULL;
        return ref;
}

int create_symref(const char *ref_target, const char *refs_heads_master)
{
        const char *lockpath;
        char ref[1000];
        int fd, len, written;
        const char *git_HEAD = git_path("%s", ref_target);

#ifndef NO_SYMLINK_HEAD
        if (prefer_symlink_refs) {
                unlink(git_HEAD);
                if (!symlink(refs_heads_master, git_HEAD))
                        return 0;
                fprintf(stderr, "no symlink - falling back to symbolic ref\n");
        }
#endif

        len = snprintf(ref, sizeof(ref), "ref: %s\n", refs_heads_master);
        if (sizeof(ref) <= len) {
                error("refname too long: %s", refs_heads_master);
                return -1;
        }
        lockpath = mkpath("%s.lock", git_HEAD);
        fd = open(lockpath, O_CREAT | O_EXCL | O_WRONLY, 0666); 
        written = write(fd, ref, len);
        close(fd);
        if (written != len) {
                unlink(lockpath);
                error("Unable to write to %s", lockpath);
                return -2;
        }
        if (rename(lockpath, git_HEAD) < 0) {
                unlink(lockpath);
                error("Unable to create %s", git_HEAD);
                return -3;
        }
        if (adjust_shared_perm(git_HEAD)) {
                unlink(lockpath);
                error("Unable to fix permissions on %s", lockpath);
                return -4;
        }
        return 0;
}

int read_ref(const char *ref, unsigned char *sha1)
{
        if (resolve_ref(ref, sha1, 1, NULL))
                return 0;
        return -1;
}

static int do_one_ref(const char *base, each_ref_fn fn, int trim,
                      void *cb_data, struct ref_list *entry)
{
        if (strncmp(base, entry->name, trim))
                return 0;
        if (is_null_sha1(entry->sha1))
                return 0;
        if (!has_sha1_file(entry->sha1)) {
                error("%s does not point to a valid object!", entry->name);
                return 0;
        }
        return fn(entry->name + trim, entry->sha1, entry->flag, cb_data);
}

int peel_ref(const char *ref, unsigned char *sha1)
{
        int flag;
        unsigned char base[20];
        struct object *o;

        if (!resolve_ref(ref, base, 1, &flag))
                return -1;

        if ((flag & REF_ISPACKED)) {
                struct ref_list *list = get_packed_refs();

                while (list) {
                        if (!strcmp(list->name, ref)) {
                                if (list->flag & REF_KNOWS_PEELED) {
                                        hashcpy(sha1, list->peeled);
                                        return 0;
                                }
                                /* older pack-refs did not leave peeled ones */
                                break;
                        }
                        list = list->next;
                }
        }

        /* fallback - callers should not call this for unpacked refs */
        o = parse_object(base);
        if (o->type == OBJ_TAG) {
                o = deref_tag(o, ref, 0);
                if (o) {
                        hashcpy(sha1, o->sha1);
                        return 0;
                }
        }
        return -1;
}

static int do_for_each_ref(const char *base, each_ref_fn fn, int trim,
                           void *cb_data)
{
        int retval;
        struct ref_list *packed = get_packed_refs();
        struct ref_list *loose = get_loose_refs();

        while (packed && loose) {
                struct ref_list *entry;
                int cmp = strcmp(packed->name, loose->name);
                if (!cmp) {
                        packed = packed->next;
                        continue;
                }
                if (cmp > 0) {
                        entry = loose;
                        loose = loose->next;
                } else {
                        entry = packed;
                        packed = packed->next;
                }
                retval = do_one_ref(base, fn, trim, cb_data, entry);
                if (retval)
                        return retval;
        }

        for (packed = packed ? packed : loose; packed; packed = packed->next) {
                retval = do_one_ref(base, fn, trim, cb_data, packed);
                if (retval)
                        return retval;
        }
        return 0;
}

int head_ref(each_ref_fn fn, void *cb_data)
{
        unsigned char sha1[20];
        int flag;

        if (resolve_ref("HEAD", sha1, 1, &flag))
                return fn("HEAD", sha1, flag, cb_data);
        return 0;
}

int for_each_ref(each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref("refs/", fn, 0, cb_data);
}

int for_each_tag_ref(each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref("refs/tags/", fn, 10, cb_data);
}

int for_each_branch_ref(each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref("refs/heads/", fn, 11, cb_data);
}

int for_each_remote_ref(each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref("refs/remotes/", fn, 13, cb_data);
}

/* NEEDSWORK: This is only used by ssh-upload and it should go; the
 * caller should do resolve_ref or read_ref like everybody else.  Or
 * maybe everybody else should use get_ref_sha1() instead of doing
 * read_ref().
 */
int get_ref_sha1(const char *ref, unsigned char *sha1)
{
        if (check_ref_format(ref))
                return -1;
        return read_ref(mkpath("refs/%s", ref), sha1);
}

/*
 * Make sure "ref" is something reasonable to have under ".git/refs/";
 * We do not like it if:
 *
 * - any path component of it begins with ".", or
 * - it has double dots "..", or
 * - it has ASCII control character, "~", "^", ":" or SP, anywhere, or
 * - it ends with a "/".
 */

static inline int bad_ref_char(int ch)
{
        return (((unsigned) ch) <= ' ' ||
                ch == '~' || ch == '^' || ch == ':' ||
                /* 2.13 Pattern Matching Notation */
                ch == '?' || ch == '*' || ch == '[');
}

int check_ref_format(const char *ref)
{
        int ch, level;
        const char *cp = ref;

        level = 0;
        while (1) {
                while ((ch = *cp++) == '/')
                        ; /* tolerate duplicated slashes */
                if (!ch)
                        return -1; /* should not end with slashes */

                /* we are at the beginning of the path component */
                if (ch == '.' || bad_ref_char(ch))
                        return -1;

                /* scan the rest of the path component */
                while ((ch = *cp++) != 0) {
                        if (bad_ref_char(ch))
                                return -1;
                        if (ch == '/')
                                break;
                        if (ch == '.' && *cp == '.')
                                return -1;
                }
                level++;
                if (!ch) {
                        if (level < 2)
                                return -2; /* at least of form "heads/blah" */
                        return 0;
                }
        }
}

static struct ref_lock *verify_lock(struct ref_lock *lock,
        const unsigned char *old_sha1, int mustexist)
{
        if (!resolve_ref(lock->ref_name, lock->old_sha1, mustexist, NULL)) {
                error("Can't verify ref %s", lock->ref_name);
                unlock_ref(lock);
                return NULL;
        }
        if (hashcmp(lock->old_sha1, old_sha1)) {
                error("Ref %s is at %s but expected %s", lock->ref_name,
                        sha1_to_hex(lock->old_sha1), sha1_to_hex(old_sha1));
                unlock_ref(lock);
                return NULL;
        }
        return lock;
}

static int remove_empty_dir_recursive(char *path, int len)
{
        DIR *dir = opendir(path);
        struct dirent *e;
        int ret = 0;

        if (!dir)
                return -1;
        if (path[len-1] != '/')
                path[len++] = '/';
        while ((e = readdir(dir)) != NULL) {
                struct stat st;
                int namlen;
                if ((e->d_name[0] == '.') &&
                    ((e->d_name[1] == 0) ||
                     ((e->d_name[1] == '.') && e->d_name[2] == 0)))
                        continue; /* "." and ".." */

                namlen = strlen(e->d_name);
                if ((len + namlen < PATH_MAX) &&
                    strcpy(path + len, e->d_name) &&
                    !lstat(path, &st) &&
                    S_ISDIR(st.st_mode) &&
                    !remove_empty_dir_recursive(path, len + namlen))
                        continue; /* happy */

                /* path too long, stat fails, or non-directory still exists */
                ret = -1;
                break;
        }
        closedir(dir);
        if (!ret) {
                path[len] = 0;
                ret = rmdir(path);
        }
        return ret;
}

static int remove_empty_directories(char *file)
{
        /* we want to create a file but there is a directory there;
         * if that is an empty directory (or a directory that contains
         * only empty directories), remove them.
         */
        char path[PATH_MAX];
        int len = strlen(file);

        if (len >= PATH_MAX) /* path too long ;-) */
                return -1;
        strcpy(path, file);
        return remove_empty_dir_recursive(path, len);
}

static struct ref_lock *lock_ref_sha1_basic(const char *ref, const unsigned char *old_sha1, int *flag)
{
        char *ref_file;
        const char *orig_ref = ref;
        struct ref_lock *lock;
        struct stat st;
        int last_errno = 0;
        int mustexist = (old_sha1 && !is_null_sha1(old_sha1));

        lock = xcalloc(1, sizeof(struct ref_lock));
        lock->lock_fd = -1;

        ref = resolve_ref(ref, lock->old_sha1, mustexist, flag);
        if (!ref && errno == EISDIR) {
                /* we are trying to lock foo but we used to
                 * have foo/bar which now does not exist;
                 * it is normal for the empty directory 'foo'
                 * to remain.
                 */
                ref_file = git_path("%s", orig_ref);
                if (remove_empty_directories(ref_file)) {
                        last_errno = errno;
                        error("there are still refs under '%s'", orig_ref);
                        goto error_return;
                }
                ref = resolve_ref(orig_ref, lock->old_sha1, mustexist, flag);
        }
        if (!ref) {
                last_errno = errno;
                error("unable to resolve reference %s: %s",
                        orig_ref, strerror(errno));
                goto error_return;
        }
        if (is_null_sha1(lock->old_sha1)) {
                /* The ref did not exist and we are creating it.
                 * Make sure there is no existing ref that is packed
                 * whose name begins with our refname, nor a ref whose
                 * name is a proper prefix of our refname.
                 */
                int namlen = strlen(ref); /* e.g. 'foo/bar' */
                struct ref_list *list = get_packed_refs();
                while (list) {
                        /* list->name could be 'foo' or 'foo/bar/baz' */
                        int len = strlen(list->name);
                        int cmplen = (namlen < len) ? namlen : len;
                        const char *lead = (namlen < len) ? list->name : ref;

                        if (!strncmp(ref, list->name, cmplen) &&
                            lead[cmplen] == '/') {
                                error("'%s' exists; cannot create '%s'",
                                      list->name, ref);
                                goto error_return;
                        }
                        list = list->next;
                }
        }

        lock->lk = xcalloc(1, sizeof(struct lock_file));

        lock->ref_name = xstrdup(ref);
        lock->log_file = xstrdup(git_path("logs/%s", ref));
        ref_file = git_path("%s", ref);
        lock->force_write = lstat(ref_file, &st) && errno == ENOENT;

        if (safe_create_leading_directories(ref_file)) {
                last_errno = errno;
                error("unable to create directory for %s", ref_file);
                goto error_return;
        }
        lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, 1);

        return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;

 error_return:
        unlock_ref(lock);
        errno = last_errno;
        return NULL;
}

struct ref_lock *lock_ref_sha1(const char *ref, const unsigned char *old_sha1)
{
        char refpath[PATH_MAX];
        if (check_ref_format(ref))
                return NULL;
        strcpy(refpath, mkpath("refs/%s", ref));
        return lock_ref_sha1_basic(refpath, old_sha1, NULL);
}

struct ref_lock *lock_any_ref_for_update(const char *ref, const unsigned char *old_sha1)
{
        return lock_ref_sha1_basic(ref, old_sha1, NULL);
}

static struct lock_file packlock;

static int repack_without_ref(const char *refname)
{
        struct ref_list *list, *packed_ref_list;
        int fd;
        int found = 0;

        packed_ref_list = get_packed_refs();
        for (list = packed_ref_list; list; list = list->next) {
                if (!strcmp(refname, list->name)) {
                        found = 1;
                        break;
                }
        }
        if (!found)
                return 0;
        memset(&packlock, 0, sizeof(packlock));
        fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
        if (fd < 0)
                return error("cannot delete '%s' from packed refs", refname);

        for (list = packed_ref_list; list; list = list->next) {
                char line[PATH_MAX + 100];
                int len;

                if (!strcmp(refname, list->name))
                        continue;
                len = snprintf(line, sizeof(line), "%s %s\n",
                               sha1_to_hex(list->sha1), list->name);
                /* this should not happen but just being defensive */
                if (len > sizeof(line))
                        die("too long a refname '%s'", list->name);
                write_or_die(fd, line, len);
        }
        return commit_lock_file(&packlock);
}

int delete_ref(const char *refname, unsigned char *sha1)
{
        struct ref_lock *lock;
        int err, i, ret = 0, flag = 0;

        lock = lock_ref_sha1_basic(refname, sha1, &flag);
        if (!lock)
                return 1;
        if (!(flag & REF_ISPACKED)) {
                /* loose */
                i = strlen(lock->lk->filename) - 5; /* .lock */
                lock->lk->filename[i] = 0;
                err = unlink(lock->lk->filename);
                if (err) {
                        ret = 1;
                        error("unlink(%s) failed: %s",
                              lock->lk->filename, strerror(errno));
                }
                lock->lk->filename[i] = '.';
        }
        /* removing the loose one could have resurrected an earlier
         * packed one.  Also, if it was not loose we need to repack
         * without it.
         */
        ret |= repack_without_ref(refname);

        err = unlink(lock->log_file);
        if (err && errno != ENOENT)
                fprintf(stderr, "warning: unlink(%s) failed: %s",
                        lock->log_file, strerror(errno));
        invalidate_cached_refs();
        unlock_ref(lock);
        return ret;
}

void unlock_ref(struct ref_lock *lock)
{
        if (lock->lock_fd >= 0) {
                close(lock->lock_fd);
                /* Do not free lock->lk -- atexit() still looks at them */
                if (lock->lk)
                        rollback_lock_file(lock->lk);
        }
        free(lock->ref_name);
        free(lock->log_file);
        free(lock);
}

static int log_ref_write(struct ref_lock *lock,
        const unsigned char *sha1, const char *msg)
{
        int logfd, written, oflags = O_APPEND | O_WRONLY;
        unsigned maxlen, len;
        char *logrec;
        const char *committer;

        if (log_all_ref_updates &&
            !strncmp(lock->ref_name, "refs/heads/", 11)) {
                if (safe_create_leading_directories(lock->log_file) < 0)
                        return error("unable to create directory for %s",
                                lock->log_file);
                oflags |= O_CREAT;
        }

        logfd = open(lock->log_file, oflags, 0666);
        if (logfd < 0) {
                if (!(oflags & O_CREAT) && errno == ENOENT)
                        return 0;

                if ((oflags & O_CREAT) && errno == EISDIR) {
                        if (remove_empty_directories(lock->log_file)) {
                                return error("There are still logs under '%s'",
                                             lock->log_file);
                        }
                        logfd = open(lock->log_file, oflags, 0666);
                }

                if (logfd < 0)
                        return error("Unable to append to %s: %s",
                                     lock->log_file, strerror(errno));
        }

        committer = git_committer_info(1);
        if (msg) {
                maxlen = strlen(committer) + strlen(msg) + 2*40 + 5;
                logrec = xmalloc(maxlen);
                len = snprintf(logrec, maxlen, "%s %s %s\t%s\n",
                        sha1_to_hex(lock->old_sha1),
                        sha1_to_hex(sha1),
                        committer,
                        msg);
        }
        else {
                maxlen = strlen(committer) + 2*40 + 4;
                logrec = xmalloc(maxlen);
                len = snprintf(logrec, maxlen, "%s %s %s\n",
                        sha1_to_hex(lock->old_sha1),
                        sha1_to_hex(sha1),
                        committer);
        }
        written = len <= maxlen ? write(logfd, logrec, len) : -1;
        free(logrec);
        close(logfd);
        if (written != len)
                return error("Unable to append to %s", lock->log_file);
        return 0;
}

int write_ref_sha1(struct ref_lock *lock,
        const unsigned char *sha1, const char *logmsg)
{
        static char term = '\n';

        if (!lock)
                return -1;
        if (!lock->force_write && !hashcmp(lock->old_sha1, sha1)) {
                unlock_ref(lock);
                return 0;
        }
        if (write(lock->lock_fd, sha1_to_hex(sha1), 40) != 40 ||
            write(lock->lock_fd, &term, 1) != 1
                || close(lock->lock_fd) < 0) {
                error("Couldn't write %s", lock->lk->filename);
                unlock_ref(lock);
                return -1;
        }
        invalidate_cached_refs();
        if (log_ref_write(lock, sha1, logmsg) < 0) {
                unlock_ref(lock);
                return -1;
        }
        if (commit_lock_file(lock->lk)) {
                error("Couldn't set %s", lock->ref_name);
                unlock_ref(lock);
                return -1;
        }
        lock->lock_fd = -1;
        unlock_ref(lock);
        return 0;
}

int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *sha1)
{
        const char *logfile, *logdata, *logend, *rec, *lastgt, *lastrec;
        char *tz_c;
        int logfd, tz;
        struct stat st;
        unsigned long date;
        unsigned char logged_sha1[20];

        logfile = git_path("logs/%s", ref);
        logfd = open(logfile, O_RDONLY, 0);
        if (logfd < 0)
                die("Unable to read log %s: %s", logfile, strerror(errno));
        fstat(logfd, &st);
        if (!st.st_size)
                die("Log %s is empty.", logfile);
        logdata = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, logfd, 0);
        close(logfd);

        lastrec = NULL;
        rec = logend = logdata + st.st_size;
        while (logdata < rec) {
                if (logdata < rec && *(rec-1) == '\n')
                        rec--;
                lastgt = NULL;
                while (logdata < rec && *(rec-1) != '\n') {
                        rec--;
                        if (*rec == '>')
                                lastgt = rec;
                }
                if (!lastgt)
                        die("Log %s is corrupt.", logfile);
                date = strtoul(lastgt + 1, &tz_c, 10);
                if (date <= at_time || cnt == 0) {
                        if (lastrec) {
                                if (get_sha1_hex(lastrec, logged_sha1))
                                        die("Log %s is corrupt.", logfile);
                                if (get_sha1_hex(rec + 41, sha1))
                                        die("Log %s is corrupt.", logfile);
                                if (hashcmp(logged_sha1, sha1)) {
                                        tz = strtoul(tz_c, NULL, 10);
                                        fprintf(stderr,
                                                "warning: Log %s has gap after %s.\n",
                                                logfile, show_rfc2822_date(date, tz));
                                }
                        }
                        else if (date == at_time) {
                                if (get_sha1_hex(rec + 41, sha1))
                                        die("Log %s is corrupt.", logfile);
                        }
                        else {
                                if (get_sha1_hex(rec + 41, logged_sha1))
                                        die("Log %s is corrupt.", logfile);
                                if (hashcmp(logged_sha1, sha1)) {
                                        tz = strtoul(tz_c, NULL, 10);
                                        fprintf(stderr,
                                                "warning: Log %s unexpectedly ended on %s.\n",
                                                logfile, show_rfc2822_date(date, tz));
                                }
                        }
                        munmap((void*)logdata, st.st_size);
                        return 0;
                }
                lastrec = rec;
                if (cnt > 0)
                        cnt--;
        }

        rec = logdata;
        while (rec < logend && *rec != '>' && *rec != '\n')
                rec++;
        if (rec == logend || *rec == '\n')
                die("Log %s is corrupt.", logfile);
        date = strtoul(rec + 1, &tz_c, 10);
        tz = strtoul(tz_c, NULL, 10);
        if (get_sha1_hex(logdata, sha1))
                die("Log %s is corrupt.", logfile);
        munmap((void*)logdata, st.st_size);
        fprintf(stderr, "warning: Log %s only goes back to %s.\n",
                logfile, show_rfc2822_date(date, tz));
        return 0;
}