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

void add_entry_to_dir(struct ref_dir *dir, struct ref_entry *entry)
{
        ALLOC_GROW(dir->entries, dir->nr + 1, dir->alloc);
        dir->entries[dir->nr++] = entry;
        /* optimize for the case that entries are added in order */
        if (dir->nr == 1 ||
            (dir->nr == dir->sorted + 1 &&
             strcmp(dir->entries[dir->nr - 2]->name,
                    dir->entries[dir->nr - 1]->name) < 0))
                dir->sorted = dir->nr;
}

struct ref_dir *get_ref_dir(struct ref_entry *entry)
{
        struct ref_dir *dir;
        assert(entry->flag & REF_DIR);
        dir = &entry->u.subdir;
        if (entry->flag & REF_INCOMPLETE) {
                if (!dir->cache->fill_ref_dir)
                        die("BUG: incomplete ref_store without fill_ref_dir function");

                dir->cache->fill_ref_dir(dir->cache->ref_store, dir, entry->name);
                entry->flag &= ~REF_INCOMPLETE;
        }
        return dir;
}

struct ref_entry *create_ref_entry(const char *refname,
                                   const struct object_id *oid, int flag)
{
        struct ref_entry *ref;

        FLEX_ALLOC_STR(ref, name, refname);
        oidcpy(&ref->u.value.oid, oid);
        ref->flag = flag;
        return ref;
}

struct ref_cache *create_ref_cache(struct ref_store *refs,
                                   fill_ref_dir_fn *fill_ref_dir)
{
        struct ref_cache *ret = xcalloc(1, sizeof(*ret));

        ret->ref_store = refs;
        ret->fill_ref_dir = fill_ref_dir;
        ret->root = create_dir_entry(ret, "", 0, 1);
        return ret;
}

static void clear_ref_dir(struct ref_dir *dir);

static void free_ref_entry(struct ref_entry *entry)
{
        if (entry->flag & REF_DIR) {
                /*
                 * Do not use get_ref_dir() here, as that might
                 * trigger the reading of loose refs.
                 */
                clear_ref_dir(&entry->u.subdir);
        }
        free(entry);
}

void free_ref_cache(struct ref_cache *cache)
{
        free_ref_entry(cache->root);
        free(cache);
}

/*
 * Clear and free all entries in dir, recursively.
 */
static void clear_ref_dir(struct ref_dir *dir)
{
        int i;
        for (i = 0; i < dir->nr; i++)
                free_ref_entry(dir->entries[i]);
        FREE_AND_NULL(dir->entries);
        dir->sorted = dir->nr = dir->alloc = 0;
}

struct ref_entry *create_dir_entry(struct ref_cache *cache,
                                   const char *dirname, size_t len,
                                   int incomplete)
{
        struct ref_entry *direntry;

        FLEX_ALLOC_MEM(direntry, name, dirname, len);
        direntry->u.subdir.cache = cache;
        direntry->flag = REF_DIR | (incomplete ? REF_INCOMPLETE : 0);
        return direntry;
}

static int ref_entry_cmp(const void *a, const void *b)
{
        struct ref_entry *one = *(struct ref_entry **)a;
        struct ref_entry *two = *(struct ref_entry **)b;
        return strcmp(one->name, two->name);
}

static void sort_ref_dir(struct ref_dir *dir);

struct string_slice {
        size_t len;
        const char *str;
};

static int ref_entry_cmp_sslice(const void *key_, const void *ent_)
{
        const struct string_slice *key = key_;
        const struct ref_entry *ent = *(const struct ref_entry * const *)ent_;
        int cmp = strncmp(key->str, ent->name, key->len);
        if (cmp)
                return cmp;
        return '\0' - (unsigned char)ent->name[key->len];
}

int search_ref_dir(struct ref_dir *dir, const char *refname, size_t len)
{
        struct ref_entry **r;
        struct string_slice key;

        if (refname == NULL || !dir->nr)
                return -1;

        sort_ref_dir(dir);
        key.len = len;
        key.str = refname;
        r = bsearch(&key, dir->entries, dir->nr, sizeof(*dir->entries),
                    ref_entry_cmp_sslice);

        if (r == NULL)
                return -1;

        return r - dir->entries;
}

/*
 * Search for a directory entry directly within dir (without
 * recursing).  Sort dir if necessary.  subdirname must be a directory
 * name (i.e., end in '/').  If mkdir is set, then create the
 * directory if it is missing; otherwise, return NULL if the desired
 * directory cannot be found.  dir must already be complete.
 */
static struct ref_dir *search_for_subdir(struct ref_dir *dir,
                                         const char *subdirname, size_t len,
                                         int mkdir)
{
        int entry_index = search_ref_dir(dir, subdirname, len);
        struct ref_entry *entry;
        if (entry_index == -1) {
                if (!mkdir)
                        return NULL;
                /*
                 * Since dir is complete, the absence of a subdir
                 * means that the subdir really doesn't exist;
                 * therefore, create an empty record for it but mark
                 * the record complete.
                 */
                entry = create_dir_entry(dir->cache, subdirname, len, 0);
                add_entry_to_dir(dir, entry);
        } else {
                entry = dir->entries[entry_index];
        }
        return get_ref_dir(entry);
}

/*
 * If refname is a reference name, find the ref_dir within the dir
 * tree that should hold refname. If refname is a directory name
 * (i.e., it ends in '/'), then return that ref_dir itself. dir must
 * represent the top-level directory and must already be complete.
 * Sort ref_dirs and recurse into subdirectories as necessary. If
 * mkdir is set, then create any missing directories; otherwise,
 * return NULL if the desired directory cannot be found.
 */
static struct ref_dir *find_containing_dir(struct ref_dir *dir,
                                           const char *refname, int mkdir)
{
        const char *slash;
        for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
                size_t dirnamelen = slash - refname + 1;
                struct ref_dir *subdir;
                subdir = search_for_subdir(dir, refname, dirnamelen, mkdir);
                if (!subdir) {
                        dir = NULL;
                        break;
                }
                dir = subdir;
        }

        return dir;
}

struct ref_entry *find_ref_entry(struct ref_dir *dir, const char *refname)
{
        int entry_index;
        struct ref_entry *entry;
        dir = find_containing_dir(dir, refname, 0);
        if (!dir)
                return NULL;
        entry_index = search_ref_dir(dir, refname, strlen(refname));
        if (entry_index == -1)
                return NULL;
        entry = dir->entries[entry_index];
        return (entry->flag & REF_DIR) ? NULL : entry;
}

int remove_entry_from_dir(struct ref_dir *dir, const char *refname)
{
        int refname_len = strlen(refname);
        int entry_index;
        struct ref_entry *entry;
        int is_dir = refname[refname_len - 1] == '/';
        if (is_dir) {
                /*
                 * refname represents a reference directory.  Remove
                 * the trailing slash; otherwise we will get the
                 * directory *representing* refname rather than the
                 * one *containing* it.
                 */
                char *dirname = xmemdupz(refname, refname_len - 1);
                dir = find_containing_dir(dir, dirname, 0);
                free(dirname);
        } else {
                dir = find_containing_dir(dir, refname, 0);
        }
        if (!dir)
                return -1;
        entry_index = search_ref_dir(dir, refname, refname_len);
        if (entry_index == -1)
                return -1;
        entry = dir->entries[entry_index];

        memmove(&dir->entries[entry_index],
                &dir->entries[entry_index + 1],
                (dir->nr - entry_index - 1) * sizeof(*dir->entries)
                );
        dir->nr--;
        if (dir->sorted > entry_index)
                dir->sorted--;
        free_ref_entry(entry);
        return dir->nr;
}

int add_ref_entry(struct ref_dir *dir, struct ref_entry *ref)
{
        dir = find_containing_dir(dir, ref->name, 1);
        if (!dir)
                return -1;
        add_entry_to_dir(dir, ref);
        return 0;
}

/*
 * Emit a warning and return true iff ref1 and ref2 have the same name
 * and the same oid. Die if they have the same name but different
 * oids.
 */
static int is_dup_ref(const struct ref_entry *ref1, const struct ref_entry *ref2)
{
        if (strcmp(ref1->name, ref2->name))
                return 0;

        /* Duplicate name; make sure that they don't conflict: */

        if ((ref1->flag & REF_DIR) || (ref2->flag & REF_DIR))
                /* This is impossible by construction */
                die("Reference directory conflict: %s", ref1->name);

        if (oidcmp(&ref1->u.value.oid, &ref2->u.value.oid))
                die("Duplicated ref, and SHA1s don't match: %s", ref1->name);

        warning("Duplicated ref: %s", ref1->name);
        return 1;
}

/*
 * Sort the entries in dir non-recursively (if they are not already
 * sorted) and remove any duplicate entries.
 */
static void sort_ref_dir(struct ref_dir *dir)
{
        int i, j;
        struct ref_entry *last = NULL;

        /*
         * This check also prevents passing a zero-length array to qsort(),
         * which is a problem on some platforms.
         */
        if (dir->sorted == dir->nr)
                return;

        QSORT(dir->entries, dir->nr, ref_entry_cmp);

        /* Remove any duplicates: */
        for (i = 0, j = 0; j < dir->nr; j++) {
                struct ref_entry *entry = dir->entries[j];
                if (last && is_dup_ref(last, entry))
                        free_ref_entry(entry);
                else
                        last = dir->entries[i++] = entry;
        }
        dir->sorted = dir->nr = i;
}

enum prefix_state {
        /* All refs within the directory would match prefix: */
        PREFIX_CONTAINS_DIR,

        /* Some, but not all, refs within the directory might match prefix: */
        PREFIX_WITHIN_DIR,

        /* No refs within the directory could possibly match prefix: */
        PREFIX_EXCLUDES_DIR
};

/*
 * Return a `prefix_state` constant describing the relationship
 * between the directory with the specified `dirname` and `prefix`.
 */
static enum prefix_state overlaps_prefix(const char *dirname,
                                         const char *prefix)
{
        while (*prefix && *dirname == *prefix) {
                dirname++;
                prefix++;
        }
        if (!*prefix)
                return PREFIX_CONTAINS_DIR;
        else if (!*dirname)
                return PREFIX_WITHIN_DIR;
        else
                return PREFIX_EXCLUDES_DIR;
}

/*
 * Load all of the refs from `dir` (recursively) that could possibly
 * contain references matching `prefix` into our in-memory cache. If
 * `prefix` is NULL, prime unconditionally.
 */
static void prime_ref_dir(struct ref_dir *dir, const char *prefix)
{
        /*
         * The hard work of loading loose refs is done by get_ref_dir(), so we
         * just need to recurse through all of the sub-directories. We do not
         * even need to care about sorting, as traversal order does not matter
         * to us.
         */
        int i;
        for (i = 0; i < dir->nr; i++) {
                struct ref_entry *entry = dir->entries[i];
                if (!(entry->flag & REF_DIR)) {
                        /* Not a directory; no need to recurse. */
                } else if (!prefix) {
                        /* Recurse in any case: */
                        prime_ref_dir(get_ref_dir(entry), NULL);
                } else {
                        switch (overlaps_prefix(entry->name, prefix)) {
                        case PREFIX_CONTAINS_DIR:
                                /*
                                 * Recurse, and from here down we
                                 * don't have to check the prefix
                                 * anymore:
                                 */
                                prime_ref_dir(get_ref_dir(entry), NULL);
                                break;
                        case PREFIX_WITHIN_DIR:
                                prime_ref_dir(get_ref_dir(entry), prefix);
                                break;
                        case PREFIX_EXCLUDES_DIR:
                                /* No need to prime this directory. */
                                break;
                        }
                }
        }
}

/*
 * A level in the reference hierarchy that is currently being iterated
 * through.
 */
struct cache_ref_iterator_level {
        /*
         * The ref_dir being iterated over at this level. The ref_dir
         * is sorted before being stored here.
         */
        struct ref_dir *dir;

        enum prefix_state prefix_state;

        /*
         * The index of the current entry within dir (which might
         * itself be a directory). If index == -1, then the iteration
         * hasn't yet begun. If index == dir->nr, then the iteration
         * through this level is over.
         */
        int index;
};

/*
 * Represent an iteration through a ref_dir in the memory cache. The
 * iteration recurses through subdirectories.
 */
struct cache_ref_iterator {
        struct ref_iterator base;

        /*
         * The number of levels currently on the stack. This is always
         * at least 1, because when it becomes zero the iteration is
         * ended and this struct is freed.
         */
        size_t levels_nr;

        /* The number of levels that have been allocated on the stack */
        size_t levels_alloc;

        /*
         * Only include references with this prefix in the iteration.
         * The prefix is matched textually, without regard for path
         * component boundaries.
         */
        const char *prefix;

        /*
         * A stack of levels. levels[0] is the uppermost level that is
         * being iterated over in this iteration. (This is not
         * necessary the top level in the references hierarchy. If we
         * are iterating through a subtree, then levels[0] will hold
         * the ref_dir for that subtree, and subsequent levels will go
         * on from there.)
         */
        struct cache_ref_iterator_level *levels;
};

static int cache_ref_iterator_advance(struct ref_iterator *ref_iterator)
{
        struct cache_ref_iterator *iter =
                (struct cache_ref_iterator *)ref_iterator;

        while (1) {
                struct cache_ref_iterator_level *level =
                        &iter->levels[iter->levels_nr - 1];
                struct ref_dir *dir = level->dir;
                struct ref_entry *entry;
                enum prefix_state entry_prefix_state;

                if (level->index == -1)
                        sort_ref_dir(dir);

                if (++level->index == level->dir->nr) {
                        /* This level is exhausted; pop up a level */
                        if (--iter->levels_nr == 0)
                                return ref_iterator_abort(ref_iterator);

                        continue;
                }

                entry = dir->entries[level->index];

                if (level->prefix_state == PREFIX_WITHIN_DIR) {
                        entry_prefix_state = overlaps_prefix(entry->name, iter->prefix);
                        if (entry_prefix_state == PREFIX_EXCLUDES_DIR)
                                continue;
                } else {
                        entry_prefix_state = level->prefix_state;
                }

                if (entry->flag & REF_DIR) {
                        /* push down a level */
                        ALLOC_GROW(iter->levels, iter->levels_nr + 1,
                                   iter->levels_alloc);

                        level = &iter->levels[iter->levels_nr++];
                        level->dir = get_ref_dir(entry);
                        level->prefix_state = entry_prefix_state;
                        level->index = -1;
                } else {
                        iter->base.refname = entry->name;
                        iter->base.oid = &entry->u.value.oid;
                        iter->base.flags = entry->flag;
                        return ITER_OK;
                }
        }
}

static int cache_ref_iterator_peel(struct ref_iterator *ref_iterator,
                                   struct object_id *peeled)
{
        return peel_object(ref_iterator->oid, peeled);
}

static int cache_ref_iterator_abort(struct ref_iterator *ref_iterator)
{
        struct cache_ref_iterator *iter =
                (struct cache_ref_iterator *)ref_iterator;

        free((char *)iter->prefix);
        free(iter->levels);
        base_ref_iterator_free(ref_iterator);
        return ITER_DONE;
}

static struct ref_iterator_vtable cache_ref_iterator_vtable = {
        cache_ref_iterator_advance,
        cache_ref_iterator_peel,
        cache_ref_iterator_abort
};

struct ref_iterator *cache_ref_iterator_begin(struct ref_cache *cache,
                                              const char *prefix,
                                              int prime_dir)
{
        struct ref_dir *dir;
        struct cache_ref_iterator *iter;
        struct ref_iterator *ref_iterator;
        struct cache_ref_iterator_level *level;

        dir = get_ref_dir(cache->root);
        if (prefix && *prefix)
                dir = find_containing_dir(dir, prefix, 0);
        if (!dir)
                /* There's nothing to iterate over. */
                return empty_ref_iterator_begin();

        if (prime_dir)
                prime_ref_dir(dir, prefix);

        iter = xcalloc(1, sizeof(*iter));
        ref_iterator = &iter->base;
        base_ref_iterator_init(ref_iterator, &cache_ref_iterator_vtable, 1);
        ALLOC_GROW(iter->levels, 10, iter->levels_alloc);

        iter->levels_nr = 1;
        level = &iter->levels[0];
        level->index = -1;
        level->dir = dir;

        if (prefix && *prefix) {
                iter->prefix = xstrdup(prefix);
                level->prefix_state = PREFIX_WITHIN_DIR;
        } else {
                level->prefix_state = PREFIX_CONTAINS_DIR;
        }

        return ref_iterator;
}