/*
 * name-hash.c
 *
 * Hashing names in the index state
 *
 * Copyright (C) 2008 Linus Torvalds
 */
#define NO_THE_INDEX_COMPATIBILITY_MACROS
#include "cache.h"

/*
 * This removes bit 5 if bit 6 is set.
 *
 * That will make US-ASCII characters hash to their upper-case
 * equivalent. We could easily do this one whole word at a time,
 * but that's for future worries.
 */
static inline unsigned char icase_hash(unsigned char c)
{
        return c & ~((c & 0x40) >> 1);
}

static unsigned int hash_name(const char *name, int namelen)
{
        unsigned int hash = 0x123;

        while (namelen--) {
                unsigned char c = *name++;
                c = icase_hash(c);
                hash = hash*101 + c;
        }
        return hash;
}

struct dir_entry {
        struct dir_entry *next;
        struct dir_entry *parent;
        struct cache_entry *ce;
        int nr;
        unsigned int namelen;
};

static struct dir_entry *find_dir_entry(struct index_state *istate,
                const char *name, unsigned int namelen)
{
        unsigned int hash = hash_name(name, namelen);
        struct dir_entry *dir;

        for (dir = lookup_hash(hash, &istate->dir_hash); dir; dir = dir->next)
                if (dir->namelen == namelen &&
                    !strncasecmp(dir->ce->name, name, namelen))
                        return dir;
        return NULL;
}

static struct dir_entry *hash_dir_entry(struct index_state *istate,
                struct cache_entry *ce, int namelen)
{
        /*
         * Throw each directory component in the hash for quick lookup
         * during a git status. Directory components are stored with their
         * closing slash.  Despite submodules being a directory, they never
         * reach this point, because they are stored without a closing slash
         * in index_state.name_hash (as ordinary cache_entries).
         *
         * Note that the cache_entry stored with the dir_entry merely
         * supplies the name of the directory (up to dir_entry.namelen). We
         * track the number of 'active' files in a directory in dir_entry.nr,
         * so we can tell if the directory is still relevant, e.g. for git
         * status. However, if cache_entries are removed, we cannot pinpoint
         * an exact cache_entry that's still active. It is very possible that
         * multiple dir_entries point to the same cache_entry.
         */
        struct dir_entry *dir;

        /* get length of parent directory */
        while (namelen > 0 && !is_dir_sep(ce->name[namelen - 1]))
                namelen--;
        if (namelen <= 0)
                return NULL;

        /* lookup existing entry for that directory */
        dir = find_dir_entry(istate, ce->name, namelen);
        if (!dir) {
                /* not found, create it and add to hash table */
                void **pdir;
                unsigned int hash = hash_name(ce->name, namelen);

                dir = xcalloc(1, sizeof(struct dir_entry));
                dir->namelen = namelen;
                dir->ce = ce;

                pdir = insert_hash(hash, dir, &istate->dir_hash);
                if (pdir) {
                        dir->next = *pdir;
                        *pdir = dir;
                }

                /* recursively add missing parent directories */
                dir->parent = hash_dir_entry(istate, ce, namelen - 1);
        }
        return dir;
}

static void add_dir_entry(struct index_state *istate, struct cache_entry *ce)
{
        /* Add reference to the directory entry (and parents if 0). */
        struct dir_entry *dir = hash_dir_entry(istate, ce, ce_namelen(ce));
        while (dir && !(dir->nr++))
                dir = dir->parent;
}

static void remove_dir_entry(struct index_state *istate, struct cache_entry *ce)
{
        /*
         * Release reference to the directory entry (and parents if 0).
         *
         * Note: we do not remove / free the entry because there's no
         * hash.[ch]::remove_hash and dir->next may point to other entries
         * that are still valid, so we must not free the memory.
         */
        struct dir_entry *dir = hash_dir_entry(istate, ce, ce_namelen(ce));
        while (dir && dir->nr && !(--dir->nr))
                dir = dir->parent;
}

static void hash_index_entry(struct index_state *istate, struct cache_entry *ce)
{
        void **pos;
        unsigned int hash;

        if (ce->ce_flags & CE_HASHED)
                return;
        ce->ce_flags |= CE_HASHED;
        ce->next = NULL;
        hash = hash_name(ce->name, ce_namelen(ce));
        pos = insert_hash(hash, ce, &istate->name_hash);
        if (pos) {
                ce->next = *pos;
                *pos = ce;
        }

        if (ignore_case && !(ce->ce_flags & CE_UNHASHED))
                add_dir_entry(istate, ce);
}

static void lazy_init_name_hash(struct index_state *istate)
{
        int nr;

        if (istate->name_hash_initialized)
                return;
        if (istate->cache_nr)
                preallocate_hash(&istate->name_hash, istate->cache_nr);
        for (nr = 0; nr < istate->cache_nr; nr++)
                hash_index_entry(istate, istate->cache[nr]);
        istate->name_hash_initialized = 1;
}

void add_name_hash(struct index_state *istate, struct cache_entry *ce)
{
        /* if already hashed, add reference to directory entries */
        if (ignore_case && (ce->ce_flags & CE_STATE_MASK) == CE_STATE_MASK)
                add_dir_entry(istate, ce);

        ce->ce_flags &= ~CE_UNHASHED;
        if (istate->name_hash_initialized)
                hash_index_entry(istate, ce);
}

/*
 * We don't actually *remove* it, we can just mark it invalid so that
 * we won't find it in lookups.
 *
 * Not only would we have to search the lists (simple enough), but
 * we'd also have to rehash other hash buckets in case this makes the
 * hash bucket empty (common). So it's much better to just mark
 * it.
 */
void remove_name_hash(struct index_state *istate, struct cache_entry *ce)
{
        /* if already hashed, release reference to directory entries */
        if (ignore_case && (ce->ce_flags & CE_STATE_MASK) == CE_HASHED)
                remove_dir_entry(istate, ce);

        ce->ce_flags |= CE_UNHASHED;
}

static int slow_same_name(const char *name1, int len1, const char *name2, int len2)
{
        if (len1 != len2)
                return 0;

        while (len1) {
                unsigned char c1 = *name1++;
                unsigned char c2 = *name2++;
                len1--;
                if (c1 != c2) {
                        c1 = toupper(c1);
                        c2 = toupper(c2);
                        if (c1 != c2)
                                return 0;
                }
        }
        return 1;
}

static int same_name(const struct cache_entry *ce, const char *name, int namelen, int icase)
{
        int len = ce_namelen(ce);

        /*
         * Always do exact compare, even if we want a case-ignoring comparison;
         * we do the quick exact one first, because it will be the common case.
         */
        if (len == namelen && !cache_name_compare(name, namelen, ce->name, len))
                return 1;

        if (!icase)
                return 0;

        return slow_same_name(name, namelen, ce->name, len);
}

struct cache_entry *index_name_exists(struct index_state *istate, const char *name, int namelen, int icase)
{
        unsigned int hash = hash_name(name, namelen);
        struct cache_entry *ce;

        lazy_init_name_hash(istate);
        ce = lookup_hash(hash, &istate->name_hash);

        while (ce) {
                if (!(ce->ce_flags & CE_UNHASHED)) {
                        if (same_name(ce, name, namelen, icase))
                                return ce;
                }
                ce = ce->next;
        }

        /*
         * When looking for a directory (trailing '/'), it might be a
         * submodule or a directory. Despite submodules being directories,
         * they are stored in the name hash without a closing slash.
         * When ignore_case is 1, directories are stored in a separate hash
         * table *with* their closing slash.
         *
         * The side effect of this storage technique is we have need to
         * lookup the directory in a separate hash table, and if not found
         * remove the slash from name and perform the lookup again without
         * the slash.  If a match is made, S_ISGITLINK(ce->mode) will be
         * true.
         */
        if (icase && name[namelen - 1] == '/') {
                struct dir_entry *dir = find_dir_entry(istate, name, namelen);
                if (dir && dir->nr)
                        return dir->ce;

                ce = index_name_exists(istate, name, namelen - 1, icase);
                if (ce && S_ISGITLINK(ce->ce_mode))
                        return ce;
        }
        return NULL;
}

static int free_dir_entry(void *entry, void *unused)
{
        struct dir_entry *dir = entry;
        while (dir) {
                struct dir_entry *next = dir->next;
                free(dir);
                dir = next;
        }
        return 0;
}

void free_name_hash(struct index_state *istate)
{
        if (!istate->name_hash_initialized)
                return;
        istate->name_hash_initialized = 0;
        if (ignore_case)
                /* free directory entries */
                for_each_hash(&istate->dir_hash, free_dir_entry, NULL);

        free_hash(&istate->name_hash);
        free_hash(&istate->dir_hash);
}