RPG Maker 2k3 Protection Remover in Node

Rm2k3ProtectionRemover.js

/**
 * AUTHOR: Maurycy Zarzycki
 * WEBSITE: www.evidentlycube.com
 * DESCRIPTION:
 * This is a Node script that removes protection from RPG Maker 2000 and 2003
 * games via RM2k3 General Utility Tool.
 * It was not thoroughly tested, I used it so I could fix a very old game of mine,
 * Diamentowa Przygoda, where I "accidentally" released the game with the start
 * position in the wrong place.
 *
 * HOW TO USE:
 *  1. Make sure you have node installed
 *  2. Copy the script to the game's directory
 *  3. Run `node Rm2k3ProtectionRemover.js`
 */

const fs = require('fs');
const { join } = require('path');

const extensionToFirstBytes = {
	'.lmu': [0x0a, 0x4c, 0x63, 0x66, 0x4d, 0x61, 0x70, 0x55, 0x6e, 0x69, 0x74],
	'.ldb': [0x0b, 0x4c, 0x63, 0x66, 0x44, 0x61, 0x74, 0x61, 0x42, 0x61, 0x73, 0x65],
	'.lmt': [0x0a, 0x4c, 0x63, 0x66, 0x4d, 0x61, 0x70, 0x54, 0x72, 0x65, 0x65],
}

const encodedPattern = determinePattern();

fixExe(encodedPattern);

for (const file of fs.readdirSync(__dirname)) {
	const path = join(__dirname, file);
	const stat = fs.statSync(path);
	if (stat.isDirectory()) {
		continue;
	}

	for (const [extension, bytes] of Object.entries(extensionToFirstBytes)) {
		if (!path.endsWith(extension)) {
			continue;
		}

		let changedBytes = 0;

		const data = fs.readFileSync(path);
		for (let i = 0; i < bytes.length; i++) {
			const expectedByte = bytes[i];

			if (data[i] !== expectedByte) {
				changedBytes++;
				data[i] = bytes[i];
			}
		}

		if (changedBytes) {
			console.log(`Fixed ${file}, changed ${changedBytes} byte${changedBytes !== 1 ? 's' : ''}`);
		} else {
			console.log(`Unchanged ${file}`);
		}

		fs.writeFileSync(path, data);
	}
}

function fixExe(encodedPattern) {
	const encodedPatternString = encodedPattern.map(s => String.fromCharCode(s)).join('');
	const data = fs.readFileSync(join(__dirname, 'RPG_RT.exe'));

	const positions = getBufferPositions(data, encodedPatternString.substring(0, 7));

	if (positions.length === 0) {
		console.log("No encoded patterns found in EXE, checking if it has all the expected patterns...");
		if (getBufferPositions(data, 'LcfDataBase').length !== 2) {
			console.error(`Expected 2 'LcfDataBase' but got ${getBufferPositions(data, 'LcfDataBase').length} instead`);
			process.exit(1);
		}
		if (getBufferPositions(data, 'LcfMapTreeItem').length !== 1) {
			console.error(`Expected 1 'LcfMapTreeItem' but got ${getBufferPositions(data, 'LcfMapTreeItem').length} instead`);
			process.exit(1);
		}
		if (getBufferPositions(data, 'LcfMapTree').length !== 3) {
			console.error(`Expected 3 'LcfMapTree' but got ${getBufferPositions(data, 'LcfMapTree').length} instead`);
			process.exit(1);
		}
		if (getBufferPositions(data, 'TestPlay').length !== 3) {
			console.error(`Expected 3 'TestPlay' but got ${getBufferPositions(data, 'TestPlay').length} instead`);
			process.exit(1);
		}
		if (getBufferPositions(data, 'LcfMapUnit').length !== 2) {
			console.error(`Expected 2 'LcfMapUnit' but got ${getBufferPositions(data, 'LcfMapUnit').length} instead`);
			process.exit(1);
		}
		console.log("Valid!");
		return;

	} else if (positions.length !== 8) {
		console.log(`Expected to find 8 encoded patterns but found ${positions.length}`);
		process.exit(1);
	}

	console.log("Fixing EXE");
	replaceStringInBuffer(data, positions[0], 'LcfDataBase');
	replaceStringInBuffer(data, positions[1], 'LcfDataBase');
	replaceStringInBuffer(data, positions[2], 'LcfMapTreeItem');
	replaceStringInBuffer(data, positions[3], 'LcfMapTree');
	replaceStringInBuffer(data, positions[4], 'LcfMapTree');
	replaceStringInBuffer(data, positions[5], 'LcfMapUnit');
	replaceStringInBuffer(data, positions[6], 'LcfMapUnit');
	replaceStringInBuffer(data, positions[7], 'TestPlay');

	console.log("Fixed EXE");
	fs.writeFileSync(join(__dirname, 'RPG_RT.exe'), data);
}

function replaceStringInBuffer(buffer, at, string) {
	for (let i = 0; i < string.length; i++) {
		buffer[at + i] = string.charCodeAt(i);
	}
}

function getBufferPositions(buffer, string) {
	const positions = [];
	let lastPosition = buffer.indexOf(string);
	if (lastPosition === -1) {
		return [];
	}

	do {
		positions.push(lastPosition);
		lastPosition = buffer.indexOf(string, lastPosition + 1);
	} while (lastPosition !== -1);

	return positions;
}

function determinePattern() {
	const data = fs.readFileSync(join(__dirname, 'RPG_RT.ldb'));
	const patternBytes = data.subarray(1, 12);

	return Array.from(patternBytes);
}