CommandImageFromChannel.java

package com.karelmikie3.wendybot.command;

import com.karelmikie3.wendybot.command.api.ICommand;
import com.karelmikie3.wendybot.command.api.IGeneralCommand;
import net.dv8tion.jda.core.EmbedBuilder;
import net.dv8tion.jda.core.JDA;
import net.dv8tion.jda.core.entities.Message;
import net.dv8tion.jda.core.entities.TextChannel;
import net.dv8tion.jda.core.entities.User;
import net.dv8tion.jda.core.requests.restaction.MessageAction;

import java.awt.*;
import java.util.*;
import java.util.List;
import java.util.stream.Collectors;

import static net.dv8tion.jda.core.Permission.ADMINISTRATOR;

public class CommandImageFromChannel implements IGeneralCommand {
    private final List<String> imageLinks = new ArrayList<>();
    private final Random random = new Random();
    private final long id;

    public CommandImageFromChannel(long id) {
        this.id = id;
    }

    @Override
    public MessageAction execute(TextChannel textChannel, User user, Message message) {
        TextChannel channel = textChannel.getJDA().getTextChannelById(id);

        if (message.getContentDisplay().contains("reload") &&
                channel.getGuild().getMember(user).hasPermission(ADMINISTRATOR)) {

            getAllImages(channel);

            return textChannel.sendMessage("Reloaded all images");
        } else {
            EmbedBuilder builder = new EmbedBuilder();
            builder.setColor(new Color(54, 57, 63));
            builder.setImage(imageLinks.get(random.nextInt(imageLinks.size())));
            return textChannel.sendMessage(builder.build());
        }
    }

    private void getAllImages(TextChannel channel) {
        imageLinks.addAll(channel.getIterableHistory().parallelStream()
                .map(Message::getAttachments)
                .flatMap(Collection::parallelStream)
                .filter(Message.Attachment::isImage)
                .map(Message.Attachment::getProxyUrl)
                .collect(Collectors.toList()));
    }

    @Override
    public void postInit(Map<String, ICommand> commands, JDA jda) {
        getAllImages(jda.getTextChannelById(id));
    }
}