package io.papermc.paper.command.subcommands;

import com.destroystokyo.paper.util.SneakyThrow;
import io.papermc.paper.command.PaperSubcommand;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.reflect.Field;
import java.util.Collections;
import java.util.List;
import java.util.Locale;
import java.util.Set;
import java.util.stream.Stream;
import net.minecraft.server.MinecraftServer;
import org.bukkit.Bukkit;
import org.bukkit.command.CommandSender;
import org.bukkit.event.HandlerList;
import org.bukkit.plugin.Plugin;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.framework.qual.DefaultQualifier;

import static net.kyori.adventure.text.Component.space;
import static net.kyori.adventure.text.Component.text;
import static net.kyori.adventure.text.format.NamedTextColor.GRAY;
import static net.kyori.adventure.text.format.NamedTextColor.GREEN;
import static net.kyori.adventure.text.format.NamedTextColor.RED;

@DefaultQualifier(NonNull.class)
public final class DumpListenersCommand implements PaperSubcommand {
    private static final MethodHandle EVENT_TYPES_HANDLE;

    static {
        try {
            final Field eventTypesField = HandlerList.class.getDeclaredField("EVENT_TYPES");
            eventTypesField.setAccessible(true);
            EVENT_TYPES_HANDLE = MethodHandles.lookup().unreflectGetter(eventTypesField);
        } catch (final ReflectiveOperationException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public boolean execute(final CommandSender sender, final String subCommand, final String[] args) {
        this.doDumpListeners(sender, args);
        return true;
    }

    private void doDumpListeners(final CommandSender sender, final String[] args) {
        if (args.length == 0) {
            sender.sendMessage(text("Usage: /paper dumplisteners [className]", RED));
            return;
        }

        try {
            final HandlerList handlers = (HandlerList) findClass(args[0]).getMethod("getHandlerList").invoke(null);

            if (handlers.getRegisteredListeners().length == 0) {
                sender.sendMessage(text(args[0] + " does not have any registered listeners."));
                return;
            }

            sender.sendMessage(text("Listeners for " + args[0] + ":"));

            Stream.of(handlers.getRegisteredListeners())
                .map(listener -> text(listener.getPlugin().getName(), GREEN)
                    .append(space())
                    .append(text("(" + listener.getListener().getClass().getName() + ")", GRAY)
                        .hoverEvent(text("Priority: " + listener.getPriority().name() + " (" + listener.getPriority().getSlot() + ")", GRAY))))
                .forEach(sender::sendMessage);

            sender.sendMessage(text("Total listeners: " + handlers.getRegisteredListeners().length));

        } catch (final ClassNotFoundException e) {
            sender.sendMessage(text("Unable to find a class named '" + args[0] + "'. Make sure to use the fully qualified name.", RED));
        } catch (final NoSuchMethodException e) {
            sender.sendMessage(text("Class '" + args[0] + "' does not have a valid getHandlerList method.", RED));
        } catch (final ReflectiveOperationException e) {
            sender.sendMessage(text("Something went wrong, see the console for more details.", RED));
            MinecraftServer.LOGGER.warn("Error occurred while dumping listeners for class " + args[0], e);
        }
    }

    @Override
    public List<String> tabComplete(final CommandSender sender, final String subCommand, final String[] args) {
        return switch (args.length) {
            case 0 -> List.copyOf(getEventClasses());
            case 1 -> getEventClasses().stream()
                .filter(clazz -> clazz.toLowerCase(Locale.ROOT).contains(args[0].toLowerCase(Locale.ROOT)))
                .toList();
            default -> Collections.emptyList();
        };
    }

    @SuppressWarnings("unchecked")
    private static Set<String> getEventClasses() {
        try {
            return (Set<String>) EVENT_TYPES_HANDLE.invokeExact();
        } catch (final Throwable e) {
            SneakyThrow.sneaky(e);
            return Collections.emptySet(); // Unreachable
        }
    }

    private static Class<?> findClass(final String className) throws ClassNotFoundException {
        try {
            return Class.forName(className);
        } catch (final ClassNotFoundException ignore) {
            for (final Plugin plugin : Bukkit.getServer().getPluginManager().getPlugins()) {
                if (!plugin.isEnabled()) {
                    continue;
                }

                try {
                    return Class.forName(className, false, plugin.getClass().getClassLoader());
                } catch (final ClassNotFoundException ignore0) {
                }
            }
        }
        throw new ClassNotFoundException(className);
    }
}
