import { constants, access, readFile, writeFile } from 'node:fs/promises';
import { setTimeout } from 'node:timers/promises';
import log from '~/utils/log';

export interface DNSRecord {
	type: 'A' | 'AAAA' | (string & {});
	name: string;
	value: string;
}

// This class is solely for DNS records that are out of tree in the main
// Headscale config file. If you are using dns.extra_records_path, it will
// be managed here and not in the main config file.
//
// All DNS insertions and deletions are handled by the main config manager,
// but are passed through to here if the extra file is being used.
export class HeadscaleDNSConfig {
	private records: DNSRecord[];
	private access: 'rw' | 'ro' | 'no';
	private path?: string;
	private writeLock = false;

	constructor(
		access: 'rw' | 'ro' | 'no',
		records?: DNSRecord[],
		path?: string,
	) {
		this.access = access;
		this.records = records ?? [];
		this.path = path;
	}

	readable() {
		return this.access !== 'no';
	}

	writable() {
		return this.access === 'rw';
	}

	get r() {
		return this.records;
	}

	async patch(records: DNSRecord[]) {
		if (!this.path || !this.readable() || !this.writable()) {
			return;
		}

		this.records = records;
		log.debug(
			'config',
			'Patching DNS records (%d -> %d)',
			this.records.length,
			records.length,
		);

		return this.write();
	}

	private async write() {
		if (!this.path || !this.writable()) {
			return;
		}

		while (this.writeLock) {
			await setTimeout(100);
		}

		this.writeLock = true;
		log.debug('config', 'Writing updated DNS configuration to %s', this.path);
		const data = JSON.stringify(this.records, null, 4);
		await writeFile(this.path, data);
		this.writeLock = false;
	}
}

export async function loadHeadscaleDNS(path?: string) {
	if (!path) {
		return;
	}

	log.debug('config', 'Loading Headscale DNS configuration file: %s', path);
	const { w, r } = await validateConfigPath(path);
	if (!r) {
		return new HeadscaleDNSConfig('no');
	}

	const records = await loadConfigFile(path);
	if (!records) {
		return new HeadscaleDNSConfig('no');
	}

	return new HeadscaleDNSConfig(w ? 'rw' : 'ro', records, path);
}

async function validateConfigPath(path: string) {
	try {
		await access(path, constants.F_OK | constants.R_OK);
		log.info('config', 'Found a valid Headscale DNS file at %s', path);
	} catch (error) {
		log.error('config', 'Unable to read a Headscale DNS file at %s', path);
		log.error('config', '%s', error);
		return { w: false, r: false };
	}

	try {
		await access(path, constants.F_OK | constants.W_OK);
		return { w: true, r: true };
	} catch (error) {
		log.warn('config', 'Headscale DNS file at %s is not writable', path);
		return { w: false, r: true };
	}
}

async function loadConfigFile(path: string) {
	log.debug('config', 'Reading Headscale DNS file at %s', path);
	try {
		const data = await readFile(path, 'utf8');
		const records = JSON.parse(data) as DNSRecord[];
		return records;
	} catch (e) {
		log.error('config', 'Error reading Headscale DNS file at %s', path);
		log.error('config', '%s', e);
		return false;
	}
}