build.mjs

import * as esbuild from 'esbuild'
import * as fs from "node:fs";
import * as chokidar from 'chokidar';

const tmpPath = 'build/arch-translator.js';
const outWSrcMapPath = 'build/arch-translator.srcmap.user.js';
const outPath = 'build/arch-translator.user.js';
const ctx = await esbuild.context({
    entryPoints: ['src/index.ts'],
    bundle: true,
    outfile: tmpPath,
    sourcemap: 'external',
    loader: {
        '.css': 'text' // TODO: Minify the CSS file
    }
});

const NEW_LINE_ASCII = 0x0A;

function countNewLines(buffer) {
    let count = 0;
    for (let i = 0; i < buffer.length; ++i) {
        if (buffer[i] === NEW_LINE_ASCII) {
            count++;
        }
    }
    return count;
}

async function build() {
    try {
        await ctx.rebuild();
    } catch (e) {
        console.error('Build failed');
        console.error(e);
        return;
    }

    console.log('Prepending userscript header');

    const bundle = fs.readFileSync(tmpPath);
    const header = fs.readFileSync('src/uscript-header.txt');

    const noSrcMapHandle = fs.openSync(outPath, 'w');
    fs.writeSync(noSrcMapHandle, header, 0, header.length, 0);
    fs.writeSync(noSrcMapHandle, bundle, 0, bundle.length, header.length);
    fs.closeSync(noSrcMapHandle);

    const srcMap = JSON.parse(fs.readFileSync(tmpPath + '.map').toString());
    let srcMapOffset = '';
    for (let i = 0; i < countNewLines(header); ++i) {
        srcMapOffset += ';'; // ; represents a newline in the mappings
    }
    srcMap['mappings'] = srcMapOffset + srcMap['mappings'];

    const bundleHandle = fs.openSync(outWSrcMapPath, 'w');
    fs.writeSync(bundleHandle, header, 0, header.length, 0);
    fs.writeSync(bundleHandle, bundle, 0, bundle.length, header.length);

    // inline the modified srcmap
    const srcMapJsonB64 = Buffer.from(JSON.stringify(srcMap), 'utf8');
    const srcMapString = '//# sourceMappingURL=data:application/json;base64,'  + srcMapJsonB64.toString('base64');
    const srcMapBuffer = Buffer.from(srcMapString, 'utf8');
    fs.writeSync(bundleHandle, srcMapBuffer, 0, srcMapBuffer.length, header.length + bundle.length);

    fs.closeSync(bundleHandle);
}

if (process.argv.length < 3) {
    console.error("Usage: node build.mjs <build|watch>");
    process.exit(1);
}

const verb = process.argv[2].toLowerCase();
switch (verb) {
    case 'build':
        build()
            .then(() => {
                ctx.dispose()
                    .then(() => {
                        console.log(`Build done. See ${outPath}`);
                    });
            });
        break;
    case 'watch':
        chokidar.watch('src').on('all', (event, path) => {
            console.log(event, path);
            build()
                .then(() => {
                    console.log('build done');
                });
        });
        break;
    default:
        throw new Error('Invalid verb: ' + verb);
}