import { parseIpv4, parseIpv6 } from "@add-ideas/toolbox-helpers";

export type DnsRecordType =
  "A" | "AAAA" | "CAA" | "CNAME" | "MX" | "SRV" | "TXT";

export interface DnsRecordInput {
  owner: string;
  ttl: number;
  type: DnsRecordType;
  value: string;
  priority?: number;
  weight?: number;
  port?: number;
  flag?: number;
  tag?: "issue" | "issuewild" | "iodef";
}

const LABEL =
  /^(?:[A-Za-z0-9_](?:[A-Za-z0-9_-]{0,61}[A-Za-z0-9_])?)(?:\.(?:[A-Za-z0-9_](?:[A-Za-z0-9_-]{0,61}[A-Za-z0-9_])?))*\.?$/u;
function integer(
  value: number | undefined,
  name: string,
  maximum = 65_535,
): number {
  if (!Number.isInteger(value) || value! < 0 || value! > maximum)
    throw new Error(`${name} must be an integer from 0 to ${maximum}.`);
  return value!;
}

function domain(value: string, name: string): string {
  const candidate = value.trim();
  if (candidate === "@") return candidate;
  if (!candidate || candidate.length > 253 || !LABEL.test(candidate))
    throw new Error(`${name} must be a valid ASCII DNS name.`);
  return candidate;
}

function quoteTxt(value: string): string {
  const bytes = new TextEncoder().encode(value);
  if (bytes.length > 255)
    throw new Error("A TXT character-string is limited to 255 UTF-8 bytes.");
  return `"${value.replaceAll("\\", "\\\\").replaceAll('"', '\\"')}"`;
}

export function buildDnsRecord(input: DnsRecordInput): string {
  const owner = domain(input.owner, "Owner");
  const ttl = integer(input.ttl, "TTL", 2_147_483_647);
  const value = input.value.trim();
  if (!value) throw new Error("Record value is required.");

  let data: string;
  switch (input.type) {
    case "A":
      try {
        data = parseIpv4(value).canonical;
      } catch {
        throw new Error("A records require a dotted-decimal IPv4 address.");
      }
      break;
    case "AAAA":
      try {
        data = parseIpv6(value).canonical;
      } catch {
        throw new Error("AAAA records require an IPv6 address.");
      }
      break;
    case "CNAME":
      data = domain(value, "Target");
      break;
    case "MX":
      data = `${integer(input.priority, "Priority")} ${domain(value, "Mail exchanger")}`;
      break;
    case "SRV":
      data = `${integer(input.priority, "Priority")} ${integer(input.weight, "Weight")} ${integer(input.port, "Port")} ${domain(value, "Target")}`;
      break;
    case "CAA": {
      const tag = input.tag ?? "issue";
      data = `${integer(input.flag ?? 0, "Flag", 255)} ${tag} ${quoteTxt(value)}`;
      break;
    }
    case "TXT":
      data = quoteTxt(value);
      break;
  }
  return `${owner} ${ttl} IN ${input.type} ${data}`;
}