Command API: Custom parameter types

Uppercore by itself can parse the main parameter types such as Java primitives and some Bukkit utility. If you want Uppercore's command-api to be able to parse a custom class you need to register your own ParameterHandler.

A ParameterHandler is composed of a Parser and a Prompter. The parser is the function in charge of translating the stringy arguments into your Object instance. The prompter suggests and tab-complete the parameter while the player is entering it.

Registering a new type is simple:

ParameterHandler.register(
        // The classes to use this ParameterHandler for.
        Collections.singletonList(QuakeArena.class),
        // Parser
        args -> {
            String arg = args.take();
            QuakeArena arena = (QuakeArena) Quake.get().getArenaManager().get(arg);
            if (arena == null) {
                throw args.areWrong(); // The inserted arg doesn't correspond to any arena.
            }
            return arena;
        },
        // Prompter
        args -> {
            if (args.remaining() > 1) // This parameter has already been skipped, what do we suggest?
                return Collections.emptyList();
            String arg = args.take();
            // Suggests all the arenas whose name starts with arg.
            return Quake.get().getArenaManager().getArenas()
                    .stream()
                    .map(Arena::getName)
                    .filter(name -> StringUtil.startsWithIgnoreCase(name, arg))
                    .collect(Collectors.toList());
        });

Done! ParameterHandler#register should be called when the plugin starts up, soon after Uppercore#hook.