"use strict";

const dns2 = require("dns2");
const { default: Resolution } = require("@unstoppabledomains/resolution");

const LISTEN_HOST = process.env.ZILDNS_LISTEN_HOST || "0.0.0.0";
const LISTEN_PORT = Number(process.env.ZILDNS_LISTEN_PORT || "53");
const DEFAULT_TTL = Number(process.env.ZILDNS_TTL || "120");
const CACHE_SECONDS = Number(process.env.ZILDNS_CACHE_SECONDS || "30");

const ZNS_URL = process.env.ZILDNS_ZNS_URL || "https://api.zilliqa.com";
const ZNS_NETWORK = process.env.ZILDNS_ZNS_NETWORK || "mainnet";
const PREWARM_DOMAIN = normalizePrewarmDomain(process.env.ZILDNS_PREWARM_DOMAIN || "brad.zil");

const { Packet, UDPServer, TCPServer } = dns2;
const RCODE = {
  NOERROR: 0,
  SERVFAIL: 2,
  NXDOMAIN: 3,
};

const resolution = new Resolution({
  sourceConfig: {
    zns: {
      url: ZNS_URL,
      network: ZNS_NETWORK,
    },
  },
});

const cache = new Map();

function normalizeName(name) {
  return String(name || "").replace(/\.$/, "").toLowerCase();
}

function normalizePrewarmDomain(name) {
  const normalized = normalizeName(name);
  return normalized.endsWith(".zil") ? normalized : "";
}

function cacheGet(key) {
  const entry = cache.get(key);
  if (!entry) {
    return null;
  }
  if (Date.now() > entry.expiresAt) {
    cache.delete(key);
    return null;
  }
  return entry.value;
}

function cacheSet(key, value) {
  cache.set(key, {
    value,
    expiresAt: Date.now() + CACHE_SECONDS * 1000,
  });
}

function withTimeout(promise, ms) {
  return Promise.race([
    promise,
    new Promise((_, reject) => 
      setTimeout(() => reject(new Error(`Timeout after ${ms}ms`)), ms)
    )
  ]);
}

async function resolveZilDomain(domain) {
  const cached = cacheGet(domain);
  if (cached !== null) {
    return cached;
  }

  try {
    const [zilResult, ipfsResult] = await withTimeout(
      Promise.allSettled([
        resolution.addr(domain, "ZIL"),
        resolution.ipfsHash(domain),
      ]),
      5000 // 5 second timeout
    );

    const result = {
      zilAddress: zilResult.status === "fulfilled" && zilResult.value ? zilResult.value : null,
      ipfsHash: ipfsResult.status === "fulfilled" && ipfsResult.value ? ipfsResult.value : null,
    };

    const hasData = Boolean(result.zilAddress || result.ipfsHash);
    const resolved = hasData ? result : null;
    cacheSet(domain, resolved);
    return resolved;
  } catch (err) {
    console.error(`[zildns] API failed for ${domain}:`, err.message);
    // Cache negative result for a short time to avoid repeated API failures
    cacheSet(domain, null);
    return null;
  }
}

function makeResponse(request) {
  const response = Packet.createResponseFromRequest(request);
  response.header.aa = 1;
  response.header.ra = 1;
  response.header.z = 0;
  response.header.tc = 0;
  return response;
}

function addTxtAnswers(response, name, resolved) {
  if (resolved.zilAddress) {
    response.answers.push({
      name,
      type: Packet.TYPE.TXT,
      class: Packet.CLASS.IN,
      ttl: DEFAULT_TTL,
      data: `zil_address=${resolved.zilAddress}`,
    });
  }

  if (resolved.ipfsHash) {
    response.answers.push({
      name,
      type: Packet.TYPE.TXT,
      class: Packet.CLASS.IN,
      ttl: DEFAULT_TTL,
      data: `ipfs_hash=${resolved.ipfsHash}`,
    });
  }
}

function addCnameAnswer(response, name, resolved) {
  if (!resolved.ipfsHash) {
    return;
  }

  response.answers.push({
    name,
    type: Packet.TYPE.CNAME,
    class: Packet.CLASS.IN,
    ttl: DEFAULT_TTL,
    domain: `${resolved.ipfsHash}.ipfs.dweb.link.`,
  });
}

async function buildResponse(request) {
  const response = makeResponse(request);
  const question = request.questions && request.questions[0];

  if (!question) {
    return response;
  }

  const qname = normalizeName(question.name);
  const qtype = question.type;
  const isType = (name) => qtype === name || qtype === Packet.TYPE[name];

  if (!qname.endsWith(".zil")) {
    response.header.rcode = RCODE.NXDOMAIN;
    return response;
  }

  const resolved = await resolveZilDomain(qname);
  if (!resolved) {
    response.header.rcode = RCODE.NXDOMAIN;
    return response;
  }

  if (isType("TXT") || isType("ANY")) {
    addTxtAnswers(response, question.name, resolved);
  }

  if (isType("CNAME") || isType("A") || isType("AAAA") || isType("ANY")) {
    addCnameAnswer(response, question.name, resolved);
  }

  return response;
}

async function maybePrewarm() {
  if (!PREWARM_DOMAIN) {
    console.log("[zildns] prewarm disabled");
    return;
  }

  const started = Date.now();
  try {
    await resolveZilDomain(PREWARM_DOMAIN);
    console.log(`[zildns] prewarm complete for ${PREWARM_DOMAIN} in ${Date.now() - started}ms`);
  } catch (err) {
    console.warn(
      `[zildns] prewarm failed for ${PREWARM_DOMAIN}:`,
      err && err.message ? err.message : String(err),
    );
  }
}

async function start() {
  await maybePrewarm();
  
  const udpServer = new UDPServer((request, send) => {
    buildResponse(request)
      .then((response) => {
        send(response);
      })
      .catch((err) => {
        console.error("[zildns] request failed:", err.message);
        const response = makeResponse(request);
        response.header.rcode = RCODE.SERVFAIL;
        send(response);
      });
  });

  const tcpServer = new TCPServer((request, send) => {
    buildResponse(request)
      .then((response) => {
        send(response);
      })
      .catch((err) => {
        console.error("[zildns] request failed:", err.message);
        const response = makeResponse(request);
        response.header.rcode = RCODE.SERVFAIL;
        send(response);
      });
  });

  udpServer.on("error", (err) => {
    console.error("[zildns] udp error:", err);
  });

  tcpServer.on("error", (err) => {
    console.error("[zildns] tcp error:", err);
  });

  udpServer.listen(LISTEN_PORT, LISTEN_HOST);
  tcpServer.listen(LISTEN_PORT, LISTEN_HOST);
  
  console.log(`[zildns] listening on ${LISTEN_HOST}:${LISTEN_PORT} (udp/tcp)`);
  console.log(`[zildns] zns provider ${ZNS_URL} (${ZNS_NETWORK})`);
  
  return { udpServer, tcpServer };
}

start().catch((err) => {
  console.error("[zildns] startup failed:", err);
  process.exit(1);
});