import {parseVars, requireAllCasesHandledFor} from "./lib";
import {Collection} from "discord.js";
import {Client, Message, TextChannel, DMChannel, NewsChannel, Guild, User, GuildMember, GuildChannel} from "discord.js";
import {getPrefix} from "../core/structures";
import {SingleMessageOptions} from "./libd";
import {hasPermission, getPermissionLevel, getPermissionName} from "./permissions";
import {client} from "../index";

export enum TYPES {
    SUBCOMMAND,
    USER,
    NUMBER,
    ANY,
    NONE
}

// RegEx patterns used for identifying/extracting each type from a string argument.
const patterns = {
    channel: /^<#(\d{17,19})>$/,
    role: /^<@&(\d{17,19})>$/,
    emote: /^<a?:.*?:(\d{17,19})>$/,
    message: /(?:\d{17,19}\/(\d{17,19})\/(\d{17,19})$)|(?:^(\d{17,19})-(\d{17,19})$)/,
    user: /^<@!?(\d{17,19})>$/,
    id: /^(\d{17,19})$/
};

// Callbacks don't work with discriminated unions:
// - https://github.com/microsoft/TypeScript/issues/41759
// - https://github.com/microsoft/TypeScript/issues/35769
// Therefore, there won't by any type narrowing on channel or guild of CommandMenu until this is fixed.
// Otherwise, you'd have to define channelType for every single subcommand, which would get very tedious.
// Just use type assertions when you specify a channel type.
export enum CHANNEL_TYPE {
    ANY,
    GUILD,
    DM
}

interface CommandMenu {
    readonly args: any[];
    readonly client: Client;
    readonly message: Message;
    readonly channel: TextChannel | DMChannel | NewsChannel;
    readonly guild: Guild | null;
    readonly author: User;
    // According to the documentation, a message can be part of a guild while also not having a
    // member object for the author. This will happen if the author of a message left the guild.
    readonly member: GuildMember | null;
}

interface CommandOptionsBase {
    readonly description?: string;
    readonly endpoint?: boolean;
    readonly usage?: string;
    readonly permission?: number;
    readonly nsfw?: boolean;
    readonly channelType?: CHANNEL_TYPE;
    readonly run?: (($: CommandMenu) => Promise<any>) | string;
}

interface CommandOptionsEndpoint {
    readonly endpoint: true;
}

// Prevents subcommands from being added by compile-time.
interface CommandOptionsNonEndpoint {
    readonly endpoint?: false;
    readonly subcommands?: {[key: string]: NamedCommand};
    readonly user?: Command;
    readonly number?: Command;
    readonly any?: Command;
}

type CommandOptions = CommandOptionsBase & (CommandOptionsEndpoint | CommandOptionsNonEndpoint);
type NamedCommandOptions = CommandOptions & {aliases?: string[]};

interface ExecuteCommandMetadata {
    readonly header: string;
    readonly args: string[];
    permission: number;
    nsfw: boolean;
    channelType: CHANNEL_TYPE;
}

export class Command {
    public readonly description: string;
    public readonly endpoint: boolean;
    public readonly usage: string;
    public readonly permission: number; // -1 (default) indicates to inherit, 0 is the lowest rank, 1 is second lowest rank, and so on.
    public readonly nsfw: boolean | null; // null (default) indicates to inherit
    public readonly channelType: CHANNEL_TYPE | null; // null (default) indicates to inherit
    protected run: (($: CommandMenu) => Promise<any>) | string;
    protected readonly subcommands: Collection<string, Command>; // This is the final data structure you'll actually use to work with the commands the aliases point to.
    protected user: Command | null;
    protected number: Command | null;
    protected any: Command | null;
    public static readonly CHANNEL_TYPE = CHANNEL_TYPE;

    constructor(options?: CommandOptions) {
        this.description = options?.description || "No description.";
        this.endpoint = !!options?.endpoint;
        this.usage = options?.usage ?? "";
        this.permission = options?.permission ?? -1;
        this.nsfw = options?.nsfw ?? null;
        this.channelType = options?.channelType ?? null;
        this.run = options?.run || "No action was set on this command!";
        this.subcommands = new Collection(); // Populate this collection after setting subcommands.
        this.user = null;
        this.number = null;
        this.any = null;

        if (options && !options.endpoint) {
            this.user = options?.user || null;
            this.number = options?.number || null;
            this.any = options?.any || null;

            if (options?.subcommands) {
                const baseSubcommands = Object.keys(options.subcommands);

                // Loop once to set the base subcommands.
                for (const name in options.subcommands) this.subcommands.set(name, options.subcommands[name]);

                // Then loop again to make aliases point to the base subcommands and warn if something's not right.
                // This shouldn't be a problem because I'm hoping that JS stores these as references that point to the same object.
                for (const name in options.subcommands) {
                    const subcmd = options.subcommands[name];
                    subcmd.originalCommandName = name;
                    const aliases = subcmd.aliases;

                    for (const alias of aliases) {
                        if (baseSubcommands.includes(alias))
                            console.warn(
                                `"${alias}" in subcommand "${name}" was attempted to be declared as an alias but it already exists in the base commands! (Look at the next "Loading Command" line to see which command is affected.)`
                            );
                        else if (this.subcommands.has(alias))
                            console.warn(
                                `Duplicate alias "${alias}" at subcommand "${name}"! (Look at the next "Loading Command" line to see which command is affected.)`
                            );
                        else this.subcommands.set(alias, subcmd);
                    }
                }
            }
        }
    }

    // Go through the arguments provided and find the right subcommand, then execute with the given arguments.
    // Will return null if it successfully executes, SingleMessageOptions if there's an error (to let the user know what it is).
    public async execute(
        args: string[],
        menu: CommandMenu,
        metadata: ExecuteCommandMetadata
    ): Promise<SingleMessageOptions | null> {
        const param = args.shift();

        // If there are no arguments left, execute the current command. Otherwise, continue on.
        if (!param) {
            // See if there is anything that'll prevent the user from executing the command.

            // 1. Does this command specify a required channel type? If so, does the channel type match?
            if (
                metadata.channelType === CHANNEL_TYPE.GUILD &&
                (!(menu.channel instanceof GuildChannel) || menu.guild === null)
            ) {
                return {content: "This command must be executed in a server."};
            } else if (
                metadata.channelType === CHANNEL_TYPE.DM &&
                (menu.channel.type !== "dm" || menu.guild !== null)
            ) {
                return {content: "This command must be executed as a direct message."};
            }

            // 2. Is this an NSFW command where the channel prevents such use? (DM channels bypass this requirement.)
            if (metadata.nsfw && menu.channel.type !== "dm" && !menu.channel.nsfw) {
                return {content: "This command must be executed in either an NSFW channel or as a direct message."};
            }

            // 3. Does the user have permission to execute the command?
            if (!hasPermission(menu.author, menu.member, metadata.permission)) {
                const userPermLevel = getPermissionLevel(menu.author, menu.member);

                return {
                    content: `You don't have access to this command! Your permission level is \`${getPermissionName(
                        userPermLevel
                    )}\` (${userPermLevel}), but this command requires a permission level of \`${getPermissionName(
                        metadata.permission
                    )}\` (${metadata.permission}).`
                };
            }

            // Then capture any potential errors.
            try {
                if (typeof this.run === "string") {
                    await menu.channel.send(
                        parseVars(
                            this.run,
                            {
                                author: menu.author.toString(),
                                prefix: getPrefix(menu.guild)
                            },
                            "???"
                        )
                    );
                } else {
                    await this.run(menu);
                }

                return null;
            } catch (error) {
                const errorMessage = error.stack ?? error;
                console.error(`Command Error: ${metadata.header} (${metadata.args})\n${errorMessage}`);

                return {
                    content: `There was an error while trying to execute that command!\`\`\`${errorMessage}\`\`\``
                };
            }
        }

        // If the current command is an endpoint but there are still some arguments left, don't continue.
        if (this.endpoint) return {content: "Too many arguments!"};

        // If the current command's permission level isn't -1 (inherit), then set the permission metadata equal to that.
        if (this.permission !== -1) metadata.permission = this.permission;

        // If the current command has an NSFW setting specified, set it.
        if (this.nsfw !== null) metadata.nsfw = this.nsfw;

        // If the current command doesn't inherit its channel type, set it.
        if (this.channelType !== null) metadata.channelType = this.channelType;

        // Resolve the value of the current command's argument (adding it to the resolved args),
        // then pass the thread of execution to whichever subcommand is valid (if any).
        if (this.subcommands.has(param)) {
            return this.subcommands.get(param)!.execute(args, menu, metadata);
        } else if (this.user && patterns.user.test(param)) {
            const id = patterns.user.exec(param)![1];

            try {
                menu.args.push(await client.users.fetch(id));
                return this.user.execute(args, menu, metadata);
            } catch {
                return {
                    content: `No user found by the ID \`${id}\`!`
                };
            }
        } else if (this.number && !Number.isNaN(Number(param)) && param !== "Infinity" && param !== "-Infinity") {
            menu.args.push(Number(param));
            return this.number.execute(args, menu, metadata);
        } else if (this.any) {
            menu.args.push(param);
            return this.any.execute(args, menu, metadata);
        } else {
            // Continue adding on the rest of the arguments if there's no valid subcommand.
            menu.args.push(param);
            return this.execute(args, menu, metadata);
        }

        // Note: Do NOT add a return statement here. In case one of the other sections is missing
        // a return statement, there'll be a compile error to catch that.
    }
}

export class NamedCommand extends Command {
    public readonly aliases: string[]; // This is to keep the array intact for parent Command instances to use. It'll also be used when loading top-level aliases.
    public originalCommandName: string | null; // If the command is an alias, what's the original name?

    constructor(options?: NamedCommandOptions) {
        super(options);
        this.aliases = options?.aliases || [];
        this.originalCommandName = null;
    }

    // Returns: [category, command name, command, available subcommands: [type, subcommand]]
    public async resolveInfo(args: string[]): [string, string, Command, Collection<string, Command>] | null {
        // For debug info, use this.originalCommandName? (if it exists?)
        const commands = await loadableCommands;
        let header = args.shift();
        let command = commands.get(header);

        if (!command || header === "test") {
            $.channel.send(`No command found by the name \`${header}\`!`);
            return;
        }

        if (command.originalCommandName) header = command.originalCommandName;
        else console.warn(`originalCommandName isn't defined for ${header}?!`);

        let permLevel = command.permission ?? 0;
        let usage = command.usage;
        let invalid = false;

        let selectedCategory = "Unknown";

        for (const [category, headers] of categories) {
            if (headers.includes(header)) {
                if (selectedCategory !== "Unknown")
                    console.warn(
                        `Command "${header}" is somehow in multiple categories. This means that the command loading stage probably failed in properly adding categories.`
                    );
                else selectedCategory = toTitleCase(category);
            }
        }

        for (const param of args) {
            const type = command.resolve(param);
            command = command.get(param);
            permLevel = command.permission ?? permLevel;

            if (permLevel === -1) permLevel = command.permission;

            // Switch over to doing `$help info <user>`
            switch (type) {
                case TYPES.SUBCOMMAND:
                    header += ` ${command.originalCommandName}`;
                    break;
                case TYPES.USER:
                    header += " <user>";
                    break;
                case TYPES.NUMBER:
                    header += " <number>";
                    break;
                case TYPES.ANY:
                    header += " <any>";
                    break;
                case TYPES.NONE:
                    header += ` ${param}`;
                    break;
                default:
                    requireAllCasesHandledFor(type);
            }

            if (type === TYPES.NONE) {
                invalid = true;
                break;
            }
        }

        if (invalid) {
            $.channel.send(`No command found by the name \`${header}\`!`);
            return;
        }
    }
}