TravBot-v3/src/core/handler.ts

import {client} from "../index";
import Command, {loadableCommands} from "./command";
import {hasPermission, getPermissionLevel, getPermissionName} from "./permissions";
import {Permissions, Message} from "discord.js";
import {getPrefix} from "./structures";
import {Config} from "./structures";

///////////
// Steps //
///////////
// 1. Someone sends a message in chat.
// 2. Check if bot, then load commands.
// 3. Check if "<prefix>...". If not, check if "@<bot>...". Resolve prefix and cropped message (if possible).
// 4. Test if bot has permission to send messages.
// 5. Once confirmed as a command, resolve the subcommand.
// 6. Check permission level and whether or not it's an endpoint.
// 7. Execute command if all successful.

// For custom message events that want to cancel this one on certain conditions.
const interceptRules: ((message: Message) => boolean)[] = [(message) => message.author.bot];

export function addInterceptRule(handler: (message: Message) => boolean) {
    interceptRules.push(handler);
}

client.on("message", async (message) => {
    for (const shouldIntercept of interceptRules) {
        if (shouldIntercept(message)) {
            return;
        }
    }

    const commands = await loadableCommands;

    let prefix = getPrefix(message.guild);
    const originalPrefix = prefix;
    let exitEarly = !message.content.startsWith(prefix);
    const clientUser = message.client.user;
    let usesBotSpecificPrefix = false;

    // If the client user exists, check if it starts with the bot-specific prefix.
    if (clientUser) {
        // If the prefix starts with the bot-specific prefix, go off that instead (these two options must mutually exclude each other).
        // The pattern here has an optional space at the end to capture that and make it not mess with the header and args.
        const matches = message.content.match(new RegExp(`^<@!?${clientUser.id}> ?`));

        if (matches) {
            prefix = matches[0];
            exitEarly = false;
            usesBotSpecificPrefix = true;
        }
    }

    // If it doesn't start with the current normal prefix or the bot-specific unique prefix, exit the thread of execution early.
    // Inline replies should still be captured here because if it doesn't exit early, two characters for a two-length prefix would still trigger commands.
    if (exitEarly) return;

    const [header, ...args] = message.content.substring(prefix.length).split(/ +/);

    // If the message is just the prefix itself, move onto this block.
    if (header === "" && args.length === 0) {
        // I moved the bot-specific prefix to a separate conditional block to separate the logic.
        // And because it listens for the mention as a prefix instead of a free-form mention, inline replies (probably) shouldn't ever trigger this unintentionally.
        if (usesBotSpecificPrefix) {
            message.channel.send(`${message.author.toString()}, my prefix on this guild is \`${originalPrefix}\`.`);
            return;
        }
    }

    if (!commands.has(header)) return;

    if (
        message.channel.type === "text" &&
        !message.channel.permissionsFor(message.client.user || "")?.has(Permissions.FLAGS.SEND_MESSAGES)
    ) {
        let status;

        if (message.member?.hasPermission(Permissions.FLAGS.ADMINISTRATOR))
            status =
                "Because you're a server admin, you have the ability to change that channel's permissions to match if that's what you intended.";
        else
            status =
                "Try using a different channel or contacting a server admin to change permissions of that channel if you think something's wrong.";

        return message.author.send(
            `I don't have permission to send messages in ${message.channel.toString()}. ${status}`
        );
    }

    console.log(
        `${message.author.username}#${message.author.discriminator} executed the command "${header}" with arguments "${args}".`
    );

    // Subcommand Recursion //
    let command = commands.get(header)!;
    //resolveSubcommand()

    if (!message.member)
        return console.warn("This command was likely called from a DM channel meaning the member object is null.");

    if (!hasPermission(message.member, permLevel)) {
        const userPermLevel = getPermissionLevel(message.member);
        return message.channel.send(
            `You don't have access to this command! Your permission level is \`${getPermissionName(
                userPermLevel
            )}\` (${userPermLevel}), but this command requires a permission level of \`${getPermissionName(
                permLevel
            )}\` (${permLevel}).`
        );
    }

    if (isEndpoint) return message.channel.send("Too many arguments!");

    // Execute with dynamic library attached. //
    // The purpose of using $.bind($) is to clone the function so as to not modify the original $.
    // The cloned function doesn't copy the properties, so Object.assign() is used.
    // Object.assign() modifies the first element and returns that, the second element applies its properties and the third element applies its own overriding the second one.
    command.execute({
        args: params,
        author: message.author,
        channel: message.channel,
        client: message.client,
        guild: message.guild,
        member: message.member,
        message: message
    });
});

// Takes a base command and a list of string parameters and returns:
// - The resolved subcommand
// - The resolved parameters
// - Whether or not an endpoint has been broken
// - The permission level required
async function resolveSubcommand(command: Command, args: string[]): [Command, any[], boolean, number] {
    const params: any[] = [];
    let isEndpoint = false;
    let permLevel = command.permission ?? 0;

    for (const param of args) {
        if (command.endpoint) {
            if (command.subcommands.size > 0 || command.user || command.number || command.any)
                console.warn("An endpoint cannot have subcommands!");
            isEndpoint = true;
            break;
        }

        const type = command.resolve(param);
        command = command.get(param);
        permLevel = command.permission ?? permLevel;

        if (type === Command.TYPES.USER) {
            const id = param.match(/\d+/g)![0];
            try {
                params.push(await message.client.users.fetch(id));
            } catch (error) {
                return message.channel.send(`No user found by the ID \`${id}\`!`);
            }
        } else if (type === Command.TYPES.NUMBER) params.push(Number(param));
        else if (type !== Command.TYPES.SUBCOMMAND) params.push(param);
    }
}

client.once("ready", () => {
    if (client.user) {
        console.ready(`Logged in as ${client.user.username}#${client.user.discriminator}.`);
        client.user.setActivity({
            type: "LISTENING",
            name: `${Config.prefix}help`
        });
    }
});