#include "../cache.h"
#include "../refs.h"
#include "refs-internal.h"
#include "ref-cache.h"
#include "packed-backend.h"
#include "../iterator.h"
#include "../lockfile.h"

struct packed_ref_cache {
        struct ref_cache *cache;

        /*
         * Count of references to the data structure in this instance,
         * including the pointer from files_ref_store::packed if any.
         * The data will not be freed as long as the reference count
         * is nonzero.
         */
        unsigned int referrers;

        /* The metadata from when this packed-refs cache was read */
        struct stat_validity validity;
};

/*
 * Increment the reference count of *packed_refs.
 */
static void acquire_packed_ref_cache(struct packed_ref_cache *packed_refs)
{
        packed_refs->referrers++;
}

/*
 * Decrease the reference count of *packed_refs.  If it goes to zero,
 * free *packed_refs and return true; otherwise return false.
 */
static int release_packed_ref_cache(struct packed_ref_cache *packed_refs)
{
        if (!--packed_refs->referrers) {
                free_ref_cache(packed_refs->cache);
                stat_validity_clear(&packed_refs->validity);
                free(packed_refs);
                return 1;
        } else {
                return 0;
        }
}

/*
 * A container for `packed-refs`-related data. It is not (yet) a
 * `ref_store`.
 */
struct packed_ref_store {
        unsigned int store_flags;

        /* The path of the "packed-refs" file: */
        char *path;

        /*
         * A cache of the values read from the `packed-refs` file, if
         * it might still be current; otherwise, NULL.
         */
        struct packed_ref_cache *cache;

        /*
         * Lock used for the "packed-refs" file. Note that this (and
         * thus the enclosing `packed_ref_store`) must not be freed.
         */
        struct lock_file lock;
};

struct packed_ref_store *packed_ref_store_create(
                const char *path, unsigned int store_flags)
{
        struct packed_ref_store *refs = xcalloc(1, sizeof(*refs));

        refs->store_flags = store_flags;
        refs->path = xstrdup(path);
        return refs;
}

/*
 * Die if refs is not the main ref store. caller is used in any
 * necessary error messages.
 */
static void packed_assert_main_repository(struct packed_ref_store *refs,
                                          const char *caller)
{
        if (refs->store_flags & REF_STORE_MAIN)
                return;

        die("BUG: operation %s only allowed for main ref store", caller);
}

static void clear_packed_ref_cache(struct packed_ref_store *refs)
{
        if (refs->cache) {
                struct packed_ref_cache *cache = refs->cache;

                if (is_lock_file_locked(&refs->lock))
                        die("BUG: packed-ref cache cleared while locked");
                refs->cache = NULL;
                release_packed_ref_cache(cache);
        }
}

/* The length of a peeled reference line in packed-refs, including EOL: */
#define PEELED_LINE_LENGTH 42

/*
 * Parse one line from a packed-refs file.  Write the SHA1 to sha1.
 * Return a pointer to the refname within the line (null-terminated),
 * or NULL if there was a problem.
 */
static const char *parse_ref_line(struct strbuf *line, struct object_id *oid)
{
        const char *ref;

        if (parse_oid_hex(line->buf, oid, &ref) < 0)
                return NULL;
        if (!isspace(*ref++))
                return NULL;

        if (isspace(*ref))
                return NULL;

        if (line->buf[line->len - 1] != '\n')
                return NULL;
        line->buf[--line->len] = 0;

        return ref;
}

/*
 * Read from `packed_refs_file` into a newly-allocated
 * `packed_ref_cache` and return it. The return value will already
 * have its reference count incremented.
 *
 * A comment line of the form "# pack-refs with: " may contain zero or
 * more traits. We interpret the traits as follows:
 *
 *   No traits:
 *
 *      Probably no references are peeled. But if the file contains a
 *      peeled value for a reference, we will use it.
 *
 *   peeled:
 *
 *      References under "refs/tags/", if they *can* be peeled, *are*
 *      peeled in this file. References outside of "refs/tags/" are
 *      probably not peeled even if they could have been, but if we find
 *      a peeled value for such a reference we will use it.
 *
 *   fully-peeled:
 *
 *      All references in the file that can be peeled are peeled.
 *      Inversely (and this is more important), any references in the
 *      file for which no peeled value is recorded is not peelable. This
 *      trait should typically be written alongside "peeled" for
 *      compatibility with older clients, but we do not require it
 *      (i.e., "peeled" is a no-op if "fully-peeled" is set).
 */
static struct packed_ref_cache *read_packed_refs(const char *packed_refs_file)
{
        FILE *f;
        struct packed_ref_cache *packed_refs = xcalloc(1, sizeof(*packed_refs));
        struct ref_entry *last = NULL;
        struct strbuf line = STRBUF_INIT;
        enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE;
        struct ref_dir *dir;

        acquire_packed_ref_cache(packed_refs);
        packed_refs->cache = create_ref_cache(NULL, NULL);
        packed_refs->cache->root->flag &= ~REF_INCOMPLETE;

        f = fopen(packed_refs_file, "r");
        if (!f) {
                if (errno == ENOENT) {
                        /*
                         * This is OK; it just means that no
                         * "packed-refs" file has been written yet,
                         * which is equivalent to it being empty.
                         */
                        return packed_refs;
                } else {
                        die_errno("couldn't read %s", packed_refs_file);
                }
        }

        stat_validity_update(&packed_refs->validity, fileno(f));

        dir = get_ref_dir(packed_refs->cache->root);
        while (strbuf_getwholeline(&line, f, '\n') != EOF) {
                struct object_id oid;
                const char *refname;
                const char *traits;

                if (skip_prefix(line.buf, "# pack-refs with:", &traits)) {
                        if (strstr(traits, " fully-peeled "))
                                peeled = PEELED_FULLY;
                        else if (strstr(traits, " peeled "))
                                peeled = PEELED_TAGS;
                        /* perhaps other traits later as well */
                        continue;
                }

                refname = parse_ref_line(&line, &oid);
                if (refname) {
                        int flag = REF_ISPACKED;

                        if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
                                if (!refname_is_safe(refname))
                                        die("packed refname is dangerous: %s", refname);
                                oidclr(&oid);
                                flag |= REF_BAD_NAME | REF_ISBROKEN;
                        }
                        last = create_ref_entry(refname, &oid, flag);
                        if (peeled == PEELED_FULLY ||
                            (peeled == PEELED_TAGS && starts_with(refname, "refs/tags/")))
                                last->flag |= REF_KNOWS_PEELED;
                        add_ref_entry(dir, last);
                        continue;
                }
                if (last &&
                    line.buf[0] == '^' &&
                    line.len == PEELED_LINE_LENGTH &&
                    line.buf[PEELED_LINE_LENGTH - 1] == '\n' &&
                    !get_oid_hex(line.buf + 1, &oid)) {
                        oidcpy(&last->u.value.peeled, &oid);
                        /*
                         * Regardless of what the file header said,
                         * we definitely know the value of *this*
                         * reference:
                         */
                        last->flag |= REF_KNOWS_PEELED;
                }
        }

        fclose(f);
        strbuf_release(&line);

        return packed_refs;
}

/*
 * Check that the packed refs cache (if any) still reflects the
 * contents of the file. If not, clear the cache.
 */
static void validate_packed_ref_cache(struct packed_ref_store *refs)
{
        if (refs->cache &&
            !stat_validity_check(&refs->cache->validity, refs->path))
                clear_packed_ref_cache(refs);
}

/*
 * Get the packed_ref_cache for the specified packed_ref_store,
 * creating and populating it if it hasn't been read before or if the
 * file has been changed (according to its `validity` field) since it
 * was last read. On the other hand, if we hold the lock, then assume
 * that the file hasn't been changed out from under us, so skip the
 * extra `stat()` call in `stat_validity_check()`.
 */
static struct packed_ref_cache *get_packed_ref_cache(struct packed_ref_store *refs)
{
        if (!is_lock_file_locked(&refs->lock))
                validate_packed_ref_cache(refs);

        if (!refs->cache)
                refs->cache = read_packed_refs(refs->path);

        return refs->cache;
}

static struct ref_dir *get_packed_ref_dir(struct packed_ref_cache *packed_ref_cache)
{
        return get_ref_dir(packed_ref_cache->cache->root);
}

static struct ref_dir *get_packed_refs(struct packed_ref_store *refs)
{
        return get_packed_ref_dir(get_packed_ref_cache(refs));
}

/*
 * Add or overwrite a reference in the in-memory packed reference
 * cache. This may only be called while the packed-refs file is locked
 * (see lock_packed_refs()). To actually write the packed-refs file,
 * call commit_packed_refs().
 */
void add_packed_ref(struct packed_ref_store *refs,
                    const char *refname, const struct object_id *oid)
{
        struct ref_dir *packed_refs;
        struct ref_entry *packed_entry;

        if (!is_lock_file_locked(&refs->lock))
                die("BUG: packed refs not locked");

        if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
                die("Reference has invalid format: '%s'", refname);

        packed_refs = get_packed_refs(refs);
        packed_entry = find_ref_entry(packed_refs, refname);
        if (packed_entry) {
                /* Overwrite the existing entry: */
                oidcpy(&packed_entry->u.value.oid, oid);
                packed_entry->flag = REF_ISPACKED;
                oidclr(&packed_entry->u.value.peeled);
        } else {
                packed_entry = create_ref_entry(refname, oid, REF_ISPACKED);
                add_ref_entry(packed_refs, packed_entry);
        }
}

/*
 * Return the ref_entry for the given refname from the packed
 * references.  If it does not exist, return NULL.
 */
static struct ref_entry *get_packed_ref(struct packed_ref_store *refs,
                                        const char *refname)
{
        return find_ref_entry(get_packed_refs(refs), refname);
}

int packed_read_raw_ref(struct packed_ref_store *refs,
                        const char *refname, unsigned char *sha1,
                        struct strbuf *referent, unsigned int *type)
{
        struct ref_entry *entry;

        *type = 0;

        entry = get_packed_ref(refs, refname);
        if (!entry) {
                errno = ENOENT;
                return -1;
        }

        hashcpy(sha1, entry->u.value.oid.hash);
        *type = REF_ISPACKED;
        return 0;
}

int packed_peel_ref(struct packed_ref_store *refs,
                    const char *refname, unsigned char *sha1)
{
        struct ref_entry *r = get_packed_ref(refs, refname);

        if (!r || peel_entry(r, 0))
                return -1;

        hashcpy(sha1, r->u.value.peeled.hash);
        return 0;
}

struct packed_ref_iterator {
        struct ref_iterator base;

        struct packed_ref_cache *cache;
        struct ref_iterator *iter0;
        unsigned int flags;
};

static int packed_ref_iterator_advance(struct ref_iterator *ref_iterator)
{
        struct packed_ref_iterator *iter =
                (struct packed_ref_iterator *)ref_iterator;
        int ok;

        while ((ok = ref_iterator_advance(iter->iter0)) == ITER_OK) {
                if (iter->flags & DO_FOR_EACH_PER_WORKTREE_ONLY &&
                    ref_type(iter->iter0->refname) != REF_TYPE_PER_WORKTREE)
                        continue;

                if (!(iter->flags & DO_FOR_EACH_INCLUDE_BROKEN) &&
                    !ref_resolves_to_object(iter->iter0->refname,
                                            iter->iter0->oid,
                                            iter->iter0->flags))
                        continue;

                iter->base.refname = iter->iter0->refname;
                iter->base.oid = iter->iter0->oid;
                iter->base.flags = iter->iter0->flags;
                return ITER_OK;
        }

        iter->iter0 = NULL;
        if (ref_iterator_abort(ref_iterator) != ITER_DONE)
                ok = ITER_ERROR;

        return ok;
}

static int packed_ref_iterator_peel(struct ref_iterator *ref_iterator,
                                   struct object_id *peeled)
{
        struct packed_ref_iterator *iter =
                (struct packed_ref_iterator *)ref_iterator;

        return ref_iterator_peel(iter->iter0, peeled);
}

static int packed_ref_iterator_abort(struct ref_iterator *ref_iterator)
{
        struct packed_ref_iterator *iter =
                (struct packed_ref_iterator *)ref_iterator;
        int ok = ITER_DONE;

        if (iter->iter0)
                ok = ref_iterator_abort(iter->iter0);

        release_packed_ref_cache(iter->cache);
        base_ref_iterator_free(ref_iterator);
        return ok;
}

static struct ref_iterator_vtable packed_ref_iterator_vtable = {
        packed_ref_iterator_advance,
        packed_ref_iterator_peel,
        packed_ref_iterator_abort
};

struct ref_iterator *packed_ref_iterator_begin(
                struct packed_ref_store *refs,
                const char *prefix, unsigned int flags)
{
        struct packed_ref_iterator *iter;
        struct ref_iterator *ref_iterator;

        iter = xcalloc(1, sizeof(*iter));
        ref_iterator = &iter->base;
        base_ref_iterator_init(ref_iterator, &packed_ref_iterator_vtable);

        /*
         * Note that get_packed_ref_cache() internally checks whether
         * the packed-ref cache is up to date with what is on disk,
         * and re-reads it if not.
         */

        iter->cache = get_packed_ref_cache(refs);
        acquire_packed_ref_cache(iter->cache);
        iter->iter0 = cache_ref_iterator_begin(iter->cache->cache, prefix, 0);

        iter->flags = flags;

        return ref_iterator;
}

/*
 * Write an entry to the packed-refs file for the specified refname.
 * If peeled is non-NULL, write it as the entry's peeled value.
 */
static void write_packed_entry(FILE *fh, const char *refname,
                               const unsigned char *sha1,
                               const unsigned char *peeled)
{
        fprintf_or_die(fh, "%s %s\n", sha1_to_hex(sha1), refname);
        if (peeled)
                fprintf_or_die(fh, "^%s\n", sha1_to_hex(peeled));
}

int lock_packed_refs(struct packed_ref_store *refs, int flags)
{
        static int timeout_configured = 0;
        static int timeout_value = 1000;
        struct packed_ref_cache *packed_ref_cache;

        packed_assert_main_repository(refs, "lock_packed_refs");

        if (!timeout_configured) {
                git_config_get_int("core.packedrefstimeout", &timeout_value);
                timeout_configured = 1;
        }

        if (hold_lock_file_for_update_timeout(
                            &refs->lock,
                            refs->path,
                            flags, timeout_value) < 0)
                return -1;

        /*
         * Now that we hold the `packed-refs` lock, make sure that our
         * cache matches the current version of the file. Normally
         * `get_packed_ref_cache()` does that for us, but that
         * function assumes that when the file is locked, any existing
         * cache is still valid. We've just locked the file, but it
         * might have changed the moment *before* we locked it.
         */
        validate_packed_ref_cache(refs);

        packed_ref_cache = get_packed_ref_cache(refs);
        /* Increment the reference count to prevent it from being freed: */
        acquire_packed_ref_cache(packed_ref_cache);
        return 0;
}

/*
 * The packed-refs header line that we write out.  Perhaps other
 * traits will be added later.  The trailing space is required.
 */
static const char PACKED_REFS_HEADER[] =
        "# pack-refs with: peeled fully-peeled \n";

/*
 * Write the current version of the packed refs cache from memory to
 * disk. The packed-refs file must already be locked for writing (see
 * lock_packed_refs()). Return zero on success. On errors, set errno
 * and return a nonzero value.
 */
int commit_packed_refs(struct packed_ref_store *refs)
{
        struct packed_ref_cache *packed_ref_cache =
                get_packed_ref_cache(refs);
        int ok, error = 0;
        int save_errno = 0;
        FILE *out;
        struct ref_iterator *iter;

        packed_assert_main_repository(refs, "commit_packed_refs");

        if (!is_lock_file_locked(&refs->lock))
                die("BUG: packed-refs not locked");

        out = fdopen_lock_file(&refs->lock, "w");
        if (!out)
                die_errno("unable to fdopen packed-refs descriptor");

        fprintf_or_die(out, "%s", PACKED_REFS_HEADER);

        iter = cache_ref_iterator_begin(packed_ref_cache->cache, NULL, 0);
        while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
                struct object_id peeled;
                int peel_error = ref_iterator_peel(iter, &peeled);

                write_packed_entry(out, iter->refname, iter->oid->hash,
                                   peel_error ? NULL : peeled.hash);
        }

        if (ok != ITER_DONE)
                die("error while iterating over references");

        if (commit_lock_file(&refs->lock)) {
                save_errno = errno;
                error = -1;
        }
        release_packed_ref_cache(packed_ref_cache);
        errno = save_errno;
        return error;
}

/*
 * Rollback the lockfile for the packed-refs file, and discard the
 * in-memory packed reference cache.  (The packed-refs file will be
 * read anew if it is needed again after this function is called.)
 */
static void rollback_packed_refs(struct packed_ref_store *refs)
{
        struct packed_ref_cache *packed_ref_cache = get_packed_ref_cache(refs);

        packed_assert_main_repository(refs, "rollback_packed_refs");

        if (!is_lock_file_locked(&refs->lock))
                die("BUG: packed-refs not locked");
        rollback_lock_file(&refs->lock);
        release_packed_ref_cache(packed_ref_cache);
        clear_packed_ref_cache(refs);
}

/*
 * Rewrite the packed-refs file, omitting any refs listed in
 * 'refnames'. On error, leave packed-refs unchanged, write an error
 * message to 'err', and return a nonzero value.
 *
 * The refs in 'refnames' needn't be sorted. `err` must not be NULL.
 */
int repack_without_refs(struct packed_ref_store *refs,
                        struct string_list *refnames, struct strbuf *err)
{
        struct ref_dir *packed;
        struct string_list_item *refname;
        int ret, needs_repacking = 0, removed = 0;

        packed_assert_main_repository(refs, "repack_without_refs");
        assert(err);

        /* Look for a packed ref */
        for_each_string_list_item(refname, refnames) {
                if (get_packed_ref(refs, refname->string)) {
                        needs_repacking = 1;
                        break;
                }
        }

        /* Avoid locking if we have nothing to do */
        if (!needs_repacking)
                return 0; /* no refname exists in packed refs */

        if (lock_packed_refs(refs, 0)) {
                unable_to_lock_message(refs->path, errno, err);
                return -1;
        }
        packed = get_packed_refs(refs);

        /* Remove refnames from the cache */
        for_each_string_list_item(refname, refnames)
                if (remove_entry_from_dir(packed, refname->string) != -1)
                        removed = 1;
        if (!removed) {
                /*
                 * All packed entries disappeared while we were
                 * acquiring the lock.
                 */
                rollback_packed_refs(refs);
                return 0;
        }

        /* Write what remains */
        ret = commit_packed_refs(refs);
        if (ret)
                strbuf_addf(err, "unable to overwrite old ref-pack file: %s",
                            strerror(errno));
        return ret;
}