firstboot: add similar input suggestion

This uses the same logic as similar verb suggestion for command line
utilities. Try to be helpful when the user entered something invalid
instead of just showing the prompt again.

src/basic/strv.c

@@ -66,6 +66,33 @@ char* strv_find_startswith(char * const *l, const char *name) {
         return NULL;
 }
 
+char* strv_find_closest_by_levenshtein(char * const *l, const char *name) {
+        ssize_t best_distance = SSIZE_MAX;
+        char *best = NULL;
+
+        assert(name);
+
+        STRV_FOREACH(i, l) {
+                ssize_t distance;
+
+                distance = strlevenshtein(*i, name);
+                if (distance < 0) {
+                        log_debug_errno(distance, "Failed to determine Levenshtein distance between %s and %s: %m", *i, name);
+                        return NULL;
+                }
+
+                if (distance > 5) /* If the distance is just too far off, don't make a bad suggestion */
+                        continue;
+
+                if (distance < best_distance) {
+                        best_distance = distance;
+                        best = *i;
+                }
+        }
+
+        return best;
+}
+
 char* strv_find_first_field(char * const *needles, char * const *haystack) {
         STRV_FOREACH(k, needles) {
                 char *value = strv_env_pairs_get((char **)haystack, *k);

src/basic/strv.h

@@ -17,6 +17,7 @@ char* strv_find(char * const *l, const char *name) _pure_;
 char* strv_find_case(char * const *l, const char *name) _pure_;
 char* strv_find_prefix(char * const *l, const char *name) _pure_;
 char* strv_find_startswith(char * const *l, const char *name) _pure_;
+char* strv_find_closest_by_levenshtein(char * const *l, const char *name) _pure_;
 /* Given two vectors, the first a list of keys and the second a list of key-value pairs, returns the value
  * of the first key from the first vector that is found in the second vector. */
 char* strv_find_first_field(char * const *needles, char * const *haystack) _pure_;