import { mkdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
import path from "node:path";
import { lockSync } from "proper-lockfile";

const STALE_MS = 30_000;

function hasLiveOwner(ownerPath: string): boolean {
	try {
		const pid: unknown = JSON.parse(readFileSync(ownerPath, "utf8")).pid;
		if (typeof pid !== "number" || !Number.isSafeInteger(pid) || pid <= 0) return false;
		try {
			process.kill(pid, 0);
			return true;
		} catch (error) {
			return (error as NodeJS.ErrnoException).code !== "ESRCH";
		}
	} catch {
		return false;
	}
}

/** Reserve durable Chromium storage without opening another process's profile. */
export function reserveInstanceSession(userDataPath: string, primarySessionPath: string) {
	const sessionsPath = path.join(userDataPath, "instance-sessions");
	const locksPath = path.join(sessionsPath, ".locks");
	mkdirSync(locksPath, { recursive: true });
	for (let slot = 0; slot < 128; slot++) {
		const name = slot === 0 ? "primary" : `slot-${slot}`;
		const sessionPath = slot === 0 ? primarySessionPath : path.join(sessionsPath, name);
		const lockfilePath = path.join(locksPath, `${name}.lock`);
		const ownerPath = path.join(locksPath, `${name}.owner.json`);
		// A sleeping Mac pauses heartbeats. Never steal a live owner's profile
		// merely because its lock timestamp has aged beyond the stale threshold.
		if (hasLiveOwner(ownerPath)) continue;
		mkdirSync(sessionPath, { recursive: true });
		let unlock: () => void;
		try {
			unlock = lockSync(sessionPath, { lockfilePath, stale: STALE_MS });
		} catch (error) {
			if ((error as NodeJS.ErrnoException).code === "ELOCKED") continue;
			throw error;
		}
		try {
			writeFileSync(ownerPath, JSON.stringify({ pid: process.pid }), { mode: 0o600 });
		} catch (error) {
			unlock();
			throw error;
		}
		let released = false;
		return {
			sessionPath,
			release() {
				if (released) return;
				released = true;
				// Remove our marker before unlocking; a new owner must not lose its marker.
				rmSync(ownerPath, { force: true });
				unlock();
			},
		};
	}
	throw new Error("No free Recordly session profile is available.");
}