Resolve (partially) the issue with mentions without server.

Mastodon (mainly from the API) usually include mentions without server,
which is just stupid. This patch tries to resolve these broken mentions in
process_tags() by looking for a user name starting with it in the already
pre-populated tag list. As of now, this only works if the message is an
inReplyTo and the broken mention is the one of the original
(attributedTo) poster.

activitypub.c

@@ -368,36 +368,69 @@ void process_tags(snac *snac, const char *content, xs_str **n_content, xs_list *
     xs_val *v;
     int n = 0;
 
-    split = xs_regex_split(content, "(@[A-Za-z0-9_]+@[A-Za-z0-9\\.-]+|&#[0-9]+;|#[^ ,\\.:;<]+)");
+    split = xs_regex_split(content, "(@[A-Za-z0-9_]+(@[A-Za-z0-9\\.-]+)?|&#[0-9]+;|#[^ ,\\.:;<]+)");
 
     p = split;
     while (xs_list_iter(&p, &v)) {
         if ((n & 0x1)) {
             if (*v == '@') {
-                /* query the webfinger about this fellow */
-                xs *v2    = xs_strip_chars_i(xs_dup(v), "@.");
-                xs *actor = NULL;
-                xs *uid   = NULL;
-                int status;
+                xs *link = NULL;
+
+                if (strchr(v + 1, '@') == NULL) {
+                    /* only one @? it's a dumb Mastodon-like mention
+                       without server; check if there is anybody
+                       whose name starts with this in the tag list */
+                    xs_list *p2 = tl;
+                    xs_dict *v2;
+                    xs *pname = xs_fmt("%s@", v);
+
+                    while (xs_list_iter(&p2, &v2)) {
+                        const char *type = xs_dict_get(v2, "type");
+
+                        if (type && strcmp(type, "Mention") == 0) {
+                            const char *name = xs_dict_get(v2, "name");
+                            const char *href = xs_dict_get(v2, "href");
+
+                            if (name && href && (xs_startswith(name, pname) ||
+                                                 xs_startswith(name, pname + 1))) {
+                                /* good enough :shrug2: */
+                                link = xs_fmt(
+                                    "<a href=\"%s\" class=\"u-url mention\">%s</a>", href, name);
+
+                                break;
+                            }
+                        }
+                    }
+
+                    snac_debug(snac, 2, xs_fmt(
+                        "mention without server '%s' (%s)", v, link ? link : "none"));
+                }
+                else {
+                    /* query the webfinger about this fellow */
+                    xs *v2    = xs_strip_chars_i(xs_dup(v), "@.");
+                    xs *actor = NULL;
+                    xs *uid   = NULL;
+                    int status;
 
-                status = webfinger_request(v2, &actor, &uid);
+                    status = webfinger_request(v2, &actor, &uid);
 
-                if (valid_status(status)) {
-                    xs *d = xs_dict_new();
-                    xs *n = xs_fmt("@%s", uid);
-                    xs *l = xs_fmt("<a href=\"%s\" class=\"u-url mention\">%s</a>", actor, n);
+                    if (valid_status(status)) {
+                        xs *d = xs_dict_new();
+                        xs *n = xs_fmt("@%s", uid);
 
-                    d = xs_dict_append(d, "type",   "Mention");
-                    d = xs_dict_append(d, "href",   actor);
-                    d = xs_dict_append(d, "name",   n);
+                        d = xs_dict_append(d, "type",   "Mention");
+                        d = xs_dict_append(d, "href",   actor);
+                        d = xs_dict_append(d, "name",   n);
 
-                    tl = xs_list_append(tl, d);
+                        tl = xs_list_append(tl, d);
 
-                    /* add the code */
-                    nc = xs_str_cat(nc, l);
+                        link = xs_fmt("<a href=\"%s\" class=\"u-url mention\">%s</a>", actor, n);
+                    }
                 }
+
+                if (!xs_is_null(link))
+                    nc = xs_str_cat(nc, link);
                 else
-                    /* store as is */
                     nc = xs_str_cat(nc, v);
             }
             else