import crypto from 'crypto';
import * as textToImage from 'text-to-image';

const GEN_POOL = 'aceoxyABCEHKMOPTX3';
const RUS_POOL = 'асеохуАВСЕНКМОРТХЗ';
const ALL_RUS_POOL = 'абвгдежзийклмнопрстуфхцчшщьыэюяАБВГДЕЖЗИЙКЛМНОПРСТУФХЦЧШЩЫЬЭЮЯ';
const FONTS = ['calico_cyrillic.ttf', 'sawesome.ttf']

type Captcha = {
    key: string;
    value: string;
    img: string;
    instructionImg: string;
    createdAt: number;
}

const captchasPool = new Set<Captcha>();

const chooseLetter = (rusPool: boolean = false) => {
    const pool = rusPool ? RUS_POOL : ALL_RUS_POOL;
    return pool[Math.floor(Math.random() * pool.length)];
};

const chooseFont = () => FONTS[Math.floor(Math.random() * FONTS.length)];

const encodeLetter = (letter: string) => {
    const idx = RUS_POOL.indexOf(letter);
    if (idx < 0) return letter;
    return GEN_POOL[idx];
}

const encodeString = (string: string) => Array.from(string).map(encodeLetter).join('');

const generate = async () => {
    const captcha: Captcha = {
        createdAt: Date.now(),
        key: crypto.randomUUID(),
        value: '',
        img: '',
        instructionImg: '',
    }

    for (let i = 0; i < 6; i++) {
        captcha.value += chooseLetter();
    }

    captcha.img = await textToImage.generate(captcha.value, {
        fontSize: 32,
        bgColor: '#222',
        textColor: '#fff',
        fontPath: chooseFont(),
        margin: 0,
        maxWidth: 155,
    });

    const hasAddon = Math.random() < 0.5;
    const addon = Math.random() < 0.5 ? 'ь' : 'ъ';
    const toEnd = Math.random() < 0.5;
    const isLower = Math.random() < 0.5;
    const reverse = Math.random() < 0.5;

    if (reverse) {
        captcha.value = Array.from(captcha.value).reverse().join('');
    }

    if (hasAddon) {
        if (toEnd) {
            captcha.value += addon;
        } else {
            captcha.value = addon + captcha.value;
        }
    }

    captcha.value = isLower ? captcha.value.toLocaleLowerCase() : captcha.value.toLocaleUpperCase();

    captcha.instructionImg = await textToImage.generate(
        `Напиши этот текст ${isLower ? 'маленькими' : 'большими'
        } буквами ${reverse ? 'наоборот ' : ''
        }и ${hasAddon ? 'добавь' : 'не добавляй'
        } в ${toEnd ? 'конец' : 'начало'
        } ${addon === 'ъ' ? 'твёрдый' : 'мягкий'
        } знак:`,
        {
            fontSize: 16,
            bgColor: '#222',
            textColor: '#fff',
            margin: 0,
            fontPath: chooseFont(),
            maxWidth: 720,
        });

    captchasPool.add(captcha);

    return captcha;
};

const expire = () => {
    const expired = [];
    const nowMinusTime = Date.now() - 20000;

    for (const captcha of captchasPool) {
        if (captcha.createdAt < nowMinusTime) {
            expired.push(captcha);
        }
    }

    expired.forEach(c => captchasPool.delete(c));
}

const check = (key: string | undefined, value: string | undefined) => {
    if (!key || !value) return false;

    expire();

    for (const captcha of captchasPool) {
        if (captcha.key === key && captcha.value === value) {
            captchasPool.delete(captcha);
            return true;
        }
    }

    return false;
}

export const captchas = {
    generate,
    check,
    encodeString,
};