const SYNC_PORT = 44100;
const PROBE_TIMEOUT_MS = 400;

// Detect the local subnet via WebRTC ICE candidate parsing.
// Returns e.g. "192.168.1" or null if unavailable.
export async function getLocalSubnet(): Promise<string | null> {
  return new Promise((resolve) => {
    try {
      const pc = new RTCPeerConnection({ iceServers: [] });
      pc.createDataChannel('');
      pc.onicecandidate = (e) => {
        if (!e.candidate) { pc.close(); resolve(null); return; }
        const m = e.candidate.candidate.match(/(\d+\.\d+\.\d+)\.\d+/);
        if (m) { pc.close(); resolve(m[1]); }
      };
      pc.createOffer().then(o => pc.setLocalDescription(o)).catch(() => { pc.close(); resolve(null); });
      setTimeout(() => { try { pc.close(); } catch { /* ignore */ } resolve(null); }, 2000);
    } catch {
      resolve(null);
    }
  });
}

// Probe a single IP to see if it responds to PEACH_DISCOVER_PROBE with our
// publicKeyHex. Returns true if it's our paired device.
async function probeDiscover(ip: string, publicKeyHex: string): Promise<boolean> {
  return new Promise((resolve) => {
    try {
      const ws = new WebSocket(`ws://${ip}:${SYNC_PORT}`);
      const timer = setTimeout(() => { try { ws.close(); } catch { /* ignore */ } resolve(false); }, PROBE_TIMEOUT_MS);
      ws.onopen = () => ws.send(JSON.stringify({ type: 'PEACH_DISCOVER_PROBE', publicKeyHex }));
      ws.onmessage = (e) => {
        clearTimeout(timer);
        try {
          const msg = JSON.parse(e.data as string);
          resolve(msg?.type === 'PEACH_DISCOVER_ACK' && msg?.publicKeyHex === publicKeyHex);
        } catch { resolve(false); }
        ws.close();
      };
      ws.onerror = () => { clearTimeout(timer); resolve(false); };
      ws.onclose = () => { clearTimeout(timer); };
    } catch {
      resolve(false);
    }
  });
}

// Scan the subnet for a device with the given publicKeyHex.
// Returns the IP if found, null otherwise.
export async function discoverDevice(subnet: string, publicKeyHex: string): Promise<string | null> {
  const batch = 16;
  for (let start = 1; start <= 254; start += batch) {
    const end = Math.min(start + batch - 1, 254);
    const ips = Array.from({ length: end - start + 1 }, (_, i) => `${subnet}.${start + i}`);
    const results = await Promise.all(ips.map(async (ip) => {
      const found = await probeDiscover(ip, publicKeyHex);
      return found ? ip : null;
    }));
    const hit = results.find(r => r !== null);
    if (hit) return hit;
  }
  return null;
}

// Probe a single IP to see if it's a phone in pairing mode with the given token.
// Returns { ip, publicKeyHex } if found, null otherwise.
async function probePair(ip: string, token: string): Promise<{ ip: string; publicKeyHex: string } | null> {
  return new Promise((resolve) => {
    try {
      const ws = new WebSocket(`ws://${ip}:${SYNC_PORT}`);
      const timer = setTimeout(() => { try { ws.close(); } catch { /* ignore */ } resolve(null); }, PROBE_TIMEOUT_MS);
      ws.onopen = () => ws.send(JSON.stringify({ type: 'PEACH_PAIR_PROBE', token }));
      ws.onmessage = (e) => {
        clearTimeout(timer);
        try {
          const msg = JSON.parse(e.data as string);
          if (msg?.type === 'PEACH_PAIR_ACK' && typeof msg?.publicKeyHex === 'string') {
            resolve({ ip, publicKeyHex: msg.publicKeyHex as string });
          } else {
            resolve(null);
          }
        } catch { resolve(null); }
        ws.close();
      };
      ws.onerror = () => { clearTimeout(timer); resolve(null); };
      ws.onclose = () => { clearTimeout(timer); };
    } catch {
      resolve(null);
    }
  });
}

// Scan the subnet for a phone in pairing mode with the given token.
// Returns { ip, publicKeyHex } of the first phone that accepts the token.
export async function scanForPairingPhone(
  subnet: string,
  token: string,
): Promise<{ ip: string; publicKeyHex: string } | null> {
  const batch = 16;
  for (let start = 1; start <= 254; start += batch) {
    const end = Math.min(start + batch - 1, 254);
    const ips = Array.from({ length: end - start + 1 }, (_, i) => `${subnet}.${start + i}`);
    const results = await Promise.all(ips.map(ip => probePair(ip, token)));
    const hit = results.find(r => r !== null);
    if (hit) return hit;
  }
  return null;
}