const fs = require("node:fs");
const { parse, printParseErrorCode } = require("jsonc-parser");

const exampleFile = process.argv[2];
const targetFile = process.argv[3];

if (!exampleFile || !targetFile) {
	process.exit(1);
}

function deepMerge(target, source) {
	const result = { ...target };
	for (const key of Object.keys(source)) {
		if (
			source[key] !== null &&
			typeof source[key] === "object" &&
			!Array.isArray(source[key])
		) {
			result[key] = deepMerge(target[key] || {}, source[key]);
		} else {
			if (!(key in result)) {
				result[key] = source[key];
			}
		}
	}
	return result;
}

function parseJsonc(file) {
	if (!fs.existsSync(file)) {
		return undefined;
	}
	const content = fs.readFileSync(file, "utf-8");
	const errors = [];
	const value = parse(content, errors, {
		allowTrailingComma: true,
		allowEmptyContent: true,
	});
	if (errors.length > 0) {
		console.error(
			`[merge-config] parse error in ${file}: ${errors
				.map((e) => printParseErrorCode(e.error))
				.join(", ")}`,
		);
		return undefined;
	}
	return value;
}

let example;
try {
	example = parseJsonc(exampleFile);
} catch {
	process.exit(1);
}

if (example === undefined) {
	process.exit(1);
}

let current = {};
try {
	const parsed = parseJsonc(targetFile);
	if (parsed !== undefined && parsed !== null) {
		current = parsed;
	}
} catch {
	current = {};
}

const merged = deepMerge(current, example);
fs.writeFileSync(targetFile, `${JSON.stringify(merged, null, 4)}\n`);