Middleware stack for Ava that adds the system command check for all commands

MiddlewareStack.java

package com.avairebot.middleware;

import com.avairebot.AvaIre;
import com.avairebot.commands.CommandContainer;
import com.avairebot.contracts.commands.Command;
import com.avairebot.contracts.middleware.Middleware;
import com.avairebot.handlers.DatabaseEventHolder;
import com.avairebot.middleware.global.IncrementMetricsForCommand;
import com.avairebot.middleware.global.IsCategoryEnabled;
import com.avairebot.middleware.global.ProcessCommand;
import net.dv8tion.jda.core.entities.Message;

import java.util.ArrayList;
import java.util.List;
import java.util.ListIterator;

public class MiddlewareStack {

    private static ProcessCommand PROCESS_COMMAND;
    private static IsCategoryEnabled IS_CATEGORY_ENABLED;
    private static IncrementMetricsForCommand INCREMENT_METRICS_FOR_COMMAND;
    private static IsBotAdminMiddleware IS_BOT_ADMIN_MIDDLEWARE;

    private final Message message;
    private final CommandContainer command;
    private final List<MiddlewareContainer> middlewares = new ArrayList<>();
    private final DatabaseEventHolder databaseEventHolder;
    private final boolean mentionableCommand;

    private int index = -1;

    public MiddlewareStack(Message message, CommandContainer command, DatabaseEventHolder databaseEventHolder, boolean mentionableCommand) {
        this.message = message;
        this.command = command;
        this.mentionableCommand = mentionableCommand;
        this.databaseEventHolder = databaseEventHolder;

        middlewares.add(new MiddlewareContainer(PROCESS_COMMAND));

        buildMiddlewareStack();

        middlewares.add(new MiddlewareContainer(IS_CATEGORY_ENABLED));
        middlewares.add(new MiddlewareContainer(INCREMENT_METRICS_FOR_COMMAND));
        middlewares.add(new MiddlewareContainer(IS_BOT_ADMIN_MIDDLEWARE));
    }

    public MiddlewareStack(Message message, CommandContainer command, DatabaseEventHolder databaseEventHolder) {
        this(message, command, databaseEventHolder, false);
    }

    /**
     * Builds the global messages so they can be used when building the middleware stack.
     *
     * @param avaire The AvaIre application instance.
     */
    static void buildGlobalMiddlewares(AvaIre avaire) {
        PROCESS_COMMAND = new ProcessCommand(avaire);
        IS_CATEGORY_ENABLED = new IsCategoryEnabled(avaire);
        INCREMENT_METRICS_FOR_COMMAND = new IncrementMetricsForCommand(avaire);
        IS_BOT_ADMIN_MIDDLEWARE = new IsBotAdminMiddleware(avaire);
    }

    /**
     * Builds the middleware stack from the commands {@link Command#getMiddleware() getMiddleware()} method.
     */
    private void buildMiddlewareStack() {
        List<String> middleware = command.getCommand().getMiddleware();
        if (middleware.isEmpty()) {
            return;
        }

        ListIterator middlewareIterator = middleware.listIterator(middleware.size());
        while (middlewareIterator.hasPrevious()) {
            String previous = (String) middlewareIterator.previous();
            String[] split = previous.split(":");

            Middleware middlewareReference = MiddlewareHandler.getMiddleware(split[0]);
            if (middlewareReference == null) {
                continue;
            }

            if (split.length == 1) {
                middlewares.add(new MiddlewareContainer(middlewareReference));
                continue;
            }
            middlewares.add(new MiddlewareContainer(middlewareReference, split[1].split(",")));
        }
    }

    /**
     * Jumps to the next middleware in the stack, the end of the stack should
     * always be the {@link ProcessCommand Process Command} middleware in
     * order for the command to be invoked.
     *
     * @return <code>True</code> if the next middleware in the stack executed successfully, <code>False</code> otherwise.
     */
    public boolean next() {
        if (index == -1) {
            index = middlewares.size();
        }

        MiddlewareContainer middlewareContainer = middlewares.get(--index);

        return middlewareContainer
            .getMiddleware()
            .handle(message, this, middlewareContainer.getArguments());
    }

    /**
     * Gets the {@link Command command} the middleware stack is running for.
     *
     * @return The {@link Command command} the middleware stack is running for.
     */
    public Command getCommand() {
        return command.getCommand();
    }

    /**
     * Gets the {@link CommandContainer command container} the middleware stack is running for.
     *
     * @return the {@link CommandContainer command container} the middleware stack is running for.
     */
    public CommandContainer getCommandContainer() {
        return command;
    }

    /**
     * Returns <code>True</code> if the command was invoked through mentioning the bot first.
     *
     * @return <code>True</code> if the command was invoked through mentioning the bot first.
     */
    public boolean isMentionableCommand() {
        return mentionableCommand;
    }

    /**
     * Returns the {@link DatabaseEventHolder database event holder} object for the given
     * message, the object can be used to get the database record for the guild or user.
     *
     * @return The {@link DatabaseEventHolder database event holder} object.
     */
    public DatabaseEventHolder getDatabaseEventHolder() {
        return databaseEventHolder;
    }
}