const fs = require("fs");
const path = require("path");
const CleanCSS = require("clean-css");
const { minify } = require("terser");

const ROOT_DIR = path.resolve(__dirname, "..");
const DIST_DIR = path.join(ROOT_DIR, "dist");
const BASE_CSS_DIR = path.join(ROOT_DIR, "css", "base");
const THEMES_DIR = path.join(ROOT_DIR, "css", "themes");
const JS_DIR = path.join(ROOT_DIR, "js");

const BASE_CSS_FILES = ["base.css", "alert.css", "buttons.css"];
const JS_FILES = ["constants.js", "dom.js", "y2k-alert.js", "index.js"];

function ensureDir(dirPath) {
    fs.mkdirSync(dirPath, { recursive: true });
}

function readFiles(folder, files) {
    return files
        .map((file) => fs.readFileSync(path.join(folder, file), "utf8"))
        .join("\n\n");
}

function buildCss() {
    const cssMinifier = new CleanCSS({ level: 2 });
    const baseCss = readFiles(BASE_CSS_DIR, BASE_CSS_FILES);
    const themeFolders = fs
        .readdirSync(THEMES_DIR, { withFileTypes: true })
        .filter((entry) => entry.isDirectory())
        .map((entry) => entry.name)
        .sort();

    themeFolders.forEach((themeName) => {
        const themePath = path.join(THEMES_DIR, themeName);
        const themeFiles = fs
            .readdirSync(themePath)
            .filter((file) => file.endsWith(".css"))
            .sort();

        const themeCss = readFiles(themePath, themeFiles);
        const output = `${baseCss}\n\n${themeCss}`;

        const distFile = path.join(DIST_DIR, `y2k-alerts-${themeName}.css`);
        const distMinFile = path.join(DIST_DIR, `y2k-alerts-${themeName}.min.css`);
        const minified = cssMinifier.minify(output);

        if (minified.errors.length > 0) {
            throw new Error(`CSS minification failed for ${themeName}: ${minified.errors.join(", ")}`);
        }

        fs.writeFileSync(distFile, output, "utf8");
        fs.writeFileSync(distMinFile, minified.styles, "utf8");
    });

    const genericFile = path.join(DIST_DIR, "y2k-alerts-generic.css");
    const genericMinFile = path.join(DIST_DIR, "y2k-alerts-generic.min.css");

    if (fs.existsSync(genericFile)) {
        fs.copyFileSync(genericFile, path.join(DIST_DIR, "y2k-alerts.css"));
    }

    if (fs.existsSync(genericMinFile)) {
        fs.copyFileSync(genericMinFile, path.join(DIST_DIR, "y2k-alerts.min.css"));
    }
}

async function buildJs() {
    const jsBundle = readFiles(JS_DIR, JS_FILES);
    const distFile = path.join(DIST_DIR, "y2k-alerts.js");
    const distMinFile = path.join(DIST_DIR, "y2k-alerts.min.js");
    const minified = await minify(jsBundle, {
        compress: true,
        mangle: true,
        format: {
            comments: false
        }
    });

    if (!minified.code) {
        throw new Error("JS minification failed: terser returned empty output.");
    }

    fs.writeFileSync(distFile, jsBundle, "utf8");
    fs.writeFileSync(distMinFile, minified.code, "utf8");
}

async function build() {
    ensureDir(DIST_DIR);
    buildCss();
    await buildJs();
    console.log("Built y2k-alerts assets in dist/");
}

if (require.main === module) {
    build().catch((error) => {
        console.error(error);
        process.exit(1);
    });
}

module.exports = {
    build
};