notmuch: Make the command of "notmuch" walk the user through the next step.

If this is run first, it will run "notmuch setup" directly. After that
is successful, it will look for a databae and tell the user to run
"notmuch new" if the database doesn't exist yet. Finally, if the
database is present, it will provide some example "notmuch search"
commands for the user to try.

notmuch.c

@@ -212,7 +212,60 @@ notmuch_help_command (unused (void *ctx), int argc, char *argv[])
 static int
 notmuch (void *ctx)
 {
-    return notmuch_setup_command (ctx, 0, NULL);
+    notmuch_config_t *config;
+    notmuch_bool_t is_new;
+    char *db_path;
+    struct stat st;
+
+    config = notmuch_config_open (ctx, NULL, &is_new);
+
+    /* If the user has never configured notmuch, then run
+     * notmuch_setup_command which will give a nice welcome message,
+     * and interactively guide the user through the configuration. */
+    if (is_new) {
+	notmuch_config_close (config);
+	return notmuch_setup_command (ctx, 0, NULL);
+    }
+
+    /* Notmuch is already configured, but is there a database? */
+    db_path = talloc_asprintf (ctx, "%s/%s",
+			       notmuch_config_get_database_path (config),
+			       ".notmuch");
+    if (stat (db_path, &st)) {
+	notmuch_config_close (config);
+	if (errno != ENOENT) {
+	    fprintf (stderr, "Error looking for notmuch database at %s: %s\n",
+		     db_path, strerror (errno));
+	    return 1;
+	}
+	printf ("Notmuch is configured, but there's not yet a database at\n\n\t%s\n\n",
+		db_path);
+	printf ("You probably want to run \"notmuch new\" now to create that database.\n\n"
+		"Note that the first run of \"notmuch new\" can take a very long time\n"
+		"and that the resulting database will use roughly the same amount of\n"
+		"storage space as the email being indexed.\n\n");
+	return 0;
+    }
+
+    printf ("Notmuch is configured and appears to have a database. Excellent!\n\n"
+	    "At this point you can start exploring the functionality of notmuch by\n"
+	    "using commands such as:\n\n"
+	    "\tnotmuch search tag:inbox\n\n"
+	    "\tnotmuch search to:\"%s\"\n\n"
+	    "\tnotmuch search from:\"%s\"\n\n"
+	    "\tnotmuch search subject:\"my favorite things\"\n\n"
+	    "See \"notmuch help search\" for more details.\n\n"
+	    "You can also use \"notmuch show\" with any of the thread IDs resulting\n"
+	    "from a search. Finally, you may want to explore using a more sophisticated\n"
+	    "interface to notmuch such as the emacs interface implemented in notmuch.el\n"
+	    "or any other interface described at http://notmuchmail.org\n\n"
+	    "Have fun, and may your inbox never have much mail.\n\n",
+	    notmuch_config_get_user_name (config),
+	    notmuch_config_get_user_primary_email (config));
+
+    notmuch_config_close (config);
+
+    return 0;
 }
 
 int