package rsx;

/**
 * Builds the echo packet.
 *
 * The nonce travels in the packet's channel name, so no payload buffer has to
 * be built or parsed: a server that supports the mod echoes the channel back
 * and the client recognises its own echo by the name.
 *
 * The packet class is vendor code with no stable name, so the profile has to
 * carry it. When it does not, the echo is simply unavailable and the modloader
 * falls back to the keep-alive estimate - which is why nothing here fails loudly
 * on a build it does not recognise.
 */
public final class EchoPacket {

    public static final String CHANNEL = "rsx_echo";

    private EchoPacket() {
    }

    /**
     * @return a packet carrying the nonce, or null when this build has no echo
     */
    public static Object create(Object netHandlerPlayClient, int nonce) {
        Profile p = Resolver.profile();
        if (p == null) {
            return null;
        }
        String[] ctor = p.member("rsx.net.echoPacket", "ctor");
        if (ctor == null) {
            return null;
        }
        try {
            Class<?> cls = Resolver.findLoaded(p.obf("rsx.net.echoPacket"));
            if (cls == null) {
                return null;
            }
            Class<?> buffer = Resolver.findLoaded(
                    p.obf("rsx.net.echoBuffer"));
            java.lang.reflect.Constructor<?> c = cls.getDeclaredConstructor(
                    String.class, buffer);
            c.setAccessible(true);
            return c.newInstance(CHANNEL + ":" + nonce, null);
        } catch (Throwable t) {
            return null;
        }
    }

    /** The nonce from a channel name, or -1 when it is not ours. */
    public static int nonceOf(String channel) {
        if (channel == null || !channel.startsWith(CHANNEL + ":")) {
            return -1;
        }
        try {
            return Integer.parseInt(channel.substring(CHANNEL.length() + 1));
        } catch (Throwable t) {
            return -1;
        }
    }

    /** True when this build can send an echo at all. */
    public static boolean available() {
        Profile p = Resolver.profile();
        return p != null && p.member("rsx.net.echoPacket", "ctor") != null;
    }
}