/** Appends timestamped lines to the instance's log, keeping the last few files. */
import { appendFileSync, existsSync, mkdirSync, renameSync, rmSync, statSync } from 'node:fs';
import { dirname } from 'node:path';

const MAX_BYTES = 10 * 1024 * 1024;
const KEEP = 5;

/** Rotation keeps a multi-hour broadcast's log bounded: worker.log, worker.1.log, … */
function rotate(path: string) {
	if (!existsSync(path) || statSync(path).size < MAX_BYTES) return;
	const numbered = (n: number) => path.replace(/\.log$/, `.${n}.log`);
	rmSync(numbered(KEEP), { force: true });
	for (let n = KEEP - 1; n >= 1; n--)
		if (existsSync(numbered(n))) renameSync(numbered(n), numbered(n + 1));
	renameSync(path, numbered(1));
}

export function fileLogger(path: string, alsoConsole = false) {
	mkdirSync(dirname(path), { recursive: true });
	let lines = 0;
	return (...parts: unknown[]) => {
		const text = parts
			.map((part) =>
				part instanceof Error
					? part.message
					: typeof part === 'string'
						? part
						: JSON.stringify(part)
			)
			.join(' ');
		const line = `${new Date().toISOString()} ${text}\n`;
		if (alsoConsole) process.stdout.write(line);
		try {
			if (++lines % 200 === 0) rotate(path);
			appendFileSync(path, line);
		} catch {
			/* a full or locked disk must not stop the broadcast */
		}
	};
}