check for last owner on user kick from group

public/language/en_GB/error.json

@@ -125,5 +125,6 @@
 
 	"no-session-found": "No login session found!",
 	"not-in-room": "User not in room",
-	"no-users-in-room": "No users in this room"
+	"no-users-in-room": "No users in this room",
+	"cant-kick-self": "You can't kick yourself from the group"
 }

src/groups/membership.js

@@ -413,4 +413,24 @@ module.exports = function(Groups) {
 		}
 		db.getSetMembers('group:' + groupName + ':pending', callback);
 	};
+	
+	Groups.kick = function(uid, groupName, isOwner, callback) {
+		if (isOwner) {
+			// If the owners set only contains one member, error out!
+			async.waterfall([
+				function (next) {
+					db.setCount('group:' + groupName + ':owners', next);
+				},
+				function (numOwners, next) {
+					if (numOwners <= 1) {
+						return next(new Error('[[error:group-needs-owner]]'));
+					}
+					Groups.leave(groupName, uid, callback);
+					next();
+				}
+			], callback);
+		} else {
+			Groups.leave(groupName, uid, callback);
+		}
+	};
 };

src/socket.io/groups.js

@@ -155,9 +155,15 @@ SocketGroups.kick = isOwner(function(socket, data, callback) {
 	if (socket.uid === parseInt(data.uid, 10)) {
 		return callback(new Error('[[error:cant-kick-self]]'));
 	}
-	groups.leave(data.groupName, data.uid, callback);
-});
 	
+	groups.ownership.isOwner(data.uid, data.groupName, function(err, isOwner) {
+		if (err) {
+			callback(err);
+		}
+		groups.kick(data.uid, data.groupName, isOwner, callback);
+	});
+
+});
 
 SocketGroups.create = function(socket, data, callback) {
 	if (!socket.uid) {