import type { ApiErrorCode, DnsJsonResponse, TxtRecord } from './types';

export class DnsLookupError extends Error {
	constructor(message: string) {
		super(message);
		this.name = 'DnsLookupError';
	}
}

function decodeTxtData(value: string): string {
	const parts = value.match(/"((?:\\"|[^"])*)"/g);
	if (parts === null) {
		return value;
	}

	return parts.map((part) => part.slice(1, -1).replaceAll('\\"', '"')).join('');
}

export async function lookupTxtRecords(endpoint: string, name: string): Promise<TxtRecord[]> {
	const url = new URL(endpoint);
	url.searchParams.set('name', name);
	url.searchParams.set('type', 'TXT');

	const response = await fetch(url, { headers: { accept: 'application/dns-json' } });

	if (!response.ok) {
		throw new DnsLookupError(`DNS lookup failed with ${response.status} ${response.statusText}`);
	}

	const body = (await response.json()) as DnsJsonResponse;
	if (body.Status !== 0) {
		return [];
	}

	return (body.Answer ?? [])
		.filter((answer) => answer.type === 16)
		.map((answer) => {
			const record: TxtRecord = { name: answer.name, data: decodeTxtData(answer.data) };

			if (answer.TTL !== undefined) {
				record.ttl = answer.TTL;
			}

			return record;
		});
}

export function findLexiconDid(records: TxtRecord[]): string | null {
	for (const record of records) {
		const value = record.data.trim();
		if (!value.startsWith('did=')) {
			continue;
		}

		const did = value.slice('did='.length);
		if (/^did:[a-z0-9]+:[A-Za-z0-9._:%-]+$/.test(did)) {
			return did;
		}
	}

	return null;
}

export function jsonResponse(body: unknown, init: ResponseInit = {}): Response {
	const headers = new Headers(init.headers);
	headers.set('content-type', 'application/json; charset=utf-8');

	return Response.json(body, { ...init, headers });
}

export function htmlResponse(body: string, init: ResponseInit = {}): Response {
	const headers = new Headers(init.headers);
	headers.set('content-type', 'text/html; charset=utf-8');

	return new Response(body, { ...init, headers });
}

export function apiError(status: number, code: ApiErrorCode, message: string): Response {
	return jsonResponse({ error: { code, message } }, { status });
}