#include "cache.h"

static struct cache_def {
        char path[PATH_MAX];
        int len;
        int flags;
        int track_flags;
} cache;

/*
 * Returns the length (on a path component basis) of the longest
 * common prefix match of 'name' and the cached path string.
 */
static inline int longest_match_lstat_cache(int len, const char *name)
{
        int max_len, match_len = 0, i = 0;

        max_len = len < cache.len ? len : cache.len;
        while (i < max_len && name[i] == cache.path[i]) {
                if (name[i] == '/')
                        match_len = i;
                i++;
        }
        /* Is the cached path string a substring of 'name'? */
        if (i == cache.len && cache.len < len && name[cache.len] == '/')
                match_len = cache.len;
        /* Is 'name' a substring of the cached path string? */
        else if ((i == len && len < cache.len && cache.path[len] == '/') ||
                 (i == len && len == cache.len))
                match_len = len;
        return match_len;
}

static inline void reset_lstat_cache(int track_flags)
{
        cache.path[0] = '\0';
        cache.len = 0;
        cache.flags = 0;
        cache.track_flags = track_flags;
}

#define FL_DIR      (1 << 0)
#define FL_NOENT    (1 << 1)
#define FL_SYMLINK  (1 << 2)
#define FL_LSTATERR (1 << 3)
#define FL_ERR      (1 << 4)

/*
 * Check if name 'name' of length 'len' has a symlink leading
 * component, or if the directory exists and is real, or not.
 *
 * To speed up the check, some information is allowed to be cached.
 * This can be indicated by the 'track_flags' argument.
 */
static int lstat_cache(int len, const char *name,
                       int track_flags)
{
        int match_len, last_slash, last_slash_dir;
        int match_flags, ret_flags, save_flags, max_len;
        struct stat st;

        if (cache.track_flags != track_flags) {
                /*
                 * As a safeguard we clear the cache if the value of
                 * track_flags does not match with the last supplied
                 * value.
                 */
                reset_lstat_cache(track_flags);
                match_len = last_slash = 0;
        } else {
                /*
                 * Check to see if we have a match from the cache for
                 * the 2 "excluding" path types.
                 */
                match_len = last_slash = longest_match_lstat_cache(len, name);
                match_flags = cache.flags & track_flags & (FL_NOENT|FL_SYMLINK);
                if (match_flags && match_len == cache.len)
                        return match_flags;
                /*
                 * If we now have match_len > 0, we would know that
                 * the matched part will always be a directory.
                 *
                 * Also, if we are tracking directories and 'name' is
                 * a substring of the cache on a path component basis,
                 * we can return immediately.
                 */
                match_flags = track_flags & FL_DIR;
                if (match_flags && len == match_len)
                        return match_flags;
        }

        /*
         * Okay, no match from the cache so far, so now we have to
         * check the rest of the path components.
         */
        ret_flags = FL_DIR;
        last_slash_dir = last_slash;
        max_len = len < PATH_MAX ? len : PATH_MAX;
        while (match_len < max_len) {
                do {
                        cache.path[match_len] = name[match_len];
                        match_len++;
                } while (match_len < max_len && name[match_len] != '/');
                if (match_len >= max_len)
                        break;
                last_slash = match_len;
                cache.path[last_slash] = '\0';

                if (lstat(cache.path, &st)) {
                        ret_flags = FL_LSTATERR;
                        if (errno == ENOENT)
                                ret_flags |= FL_NOENT;
                } else if (S_ISDIR(st.st_mode)) {
                        last_slash_dir = last_slash;
                        continue;
                } else if (S_ISLNK(st.st_mode)) {
                        ret_flags = FL_SYMLINK;
                } else {
                        ret_flags = FL_ERR;
                }
                break;
        }

        /*
         * At the end update the cache.  Note that max 3 different
         * path types, FL_NOENT, FL_SYMLINK and FL_DIR, can be cached
         * for the moment!
         */
        save_flags = ret_flags & track_flags & (FL_NOENT|FL_SYMLINK);
        if (save_flags && last_slash > 0 && last_slash < PATH_MAX) {
                cache.path[last_slash] = '\0';
                cache.len = last_slash;
                cache.flags = save_flags;
        } else if (track_flags & FL_DIR &&
                   last_slash_dir > 0 && last_slash_dir < PATH_MAX) {
                /*
                 * We have a separate test for the directory case,
                 * since it could be that we have found a symlink or a
                 * non-existing directory and the track_flags says
                 * that we cannot cache this fact, so the cache would
                 * then have been left empty in this case.
                 *
                 * But if we are allowed to track real directories, we
                 * can still cache the path components before the last
                 * one (the found symlink or non-existing component).
                 */
                cache.path[last_slash_dir] = '\0';
                cache.len = last_slash_dir;
                cache.flags = FL_DIR;
        } else {
                reset_lstat_cache(track_flags);
        }
        return ret_flags;
}

/*
 * Return non-zero if path 'name' has a leading symlink component
 */
int has_symlink_leading_path(int len, const char *name)
{
        return lstat_cache(len, name,
                           FL_SYMLINK|FL_DIR) &
                FL_SYMLINK;
}

/*
 * Return non-zero if path 'name' has a leading symlink component or
 * if some leading path component does not exists.
 */
int has_symlink_or_noent_leading_path(int len, const char *name)
{
        return lstat_cache(len, name,
                           FL_SYMLINK|FL_NOENT|FL_DIR) &
                (FL_SYMLINK|FL_NOENT);
}