// Code-pairing client — the browser always dials out, never listens.
//
// Two code formats reach this module, and they differ ONLY in how the
// endpoint is resolved and what the plaintext hello carries:
//
//   - Pairing code (`A74H-48J3-KI32-OEP4`, pairing-code.ts) — the primary
//     path. The phone is the listener and the code carries its IP, port and
//     one-time token, so there is nothing to discover: dial it directly.
//   - Legacy 6-digit helper code — the speculative `peach-sync` desktop
//     helper, which has no address of its own, so the host is probed for.
//
// Everything after the hello is one protocol, shared by both:
//   1. open ws://<host>:<port>
//   2. send PEACH_HELLO { token } (pairing code) or { code } (legacy) in
//      PLAINTEXT
//   3. await PEACH_HELLO_ACK { ephemeralPublicKeyHex } OR socket close
//        (socket close before ACK == wrong/expired code — the listener sends
//         NO error frame; it silently closes and rotates the code)
//   4. run Noise NK as INITIATOR against the listener's ephemeral key
//   5. exchange PAIR_IDENTITY (send ours incl. vault_id, then read theirs)
//   6. derive the SAS, surface it for user confirmation
//   7. on confirm -> persist the PairedDevice; on reject -> abort without
//        persisting
//
// ROLE: the BROWSER is the NK INITIATOR here — the OPPOSITE of the audio
// chirp flow (chirp-handshake.ts), where the extension is the responder.
// The listener's `ephemeralPublicKeyHex` is the NK responder static `s`.
//
// The browser can never accept an incoming connection (MV3 has no listening
// socket), which is why the dialler role is structural and not a choice.

import { noiseNKInitiator } from "../shared/noise-js";
import { parsePairingCode } from "../shared/pairing-code";
import { derivePairingSAS } from "../shared/chirp-handshake";
import type { LocalIdentity } from "../shared/chirp-handshake";
import type { DeviceType, PairedDevice } from "../shared/sync-types";

/** The pairing-only port peach-sync listens on while `peach-sync pair` runs. */
export const DESKTOP_PAIRING_PORT = 49142;
/** Default sync port the helper announces; used when ws_port is absent. */
const DEFAULT_SYNC_PORT = 8765;

export type DesktopPairingError =
  | "invalid_code"      // socket closed before PEACH_HELLO_ACK (wrong/expired)
  | "no_host_found"     // no WebSocket server answered on the pairing port
  | "handshake_failed"  // Noise NK / PAIR_IDENTITY decode failed
  | "sas_mismatch"      // user rejected the SAS
  | "vault_locked";     // no master key available

/**
 * Minimal binary WebSocket transport seam. Production wires the real
 * `WebSocket`; tests inject a fake. One binary message per frame.
 */
export interface DesktopPairingSocket {
  send(bytes: Uint8Array): void;
  /** Resolves with the next inbound binary frame, or rejects on close. */
  receive(): Promise<Uint8Array>;
  close(): void;
  /** Resolves true if the socket closed before the next frame arrived. */
  closedBeforeFrame(): boolean;
}

export interface DesktopPairingDeps {
  /** Change 5 — find a host answering WebSocket on the pairing port. */
  findHost(port: number): Promise<string | null>;
  /** Open a binary WebSocket to ws://<ip>:<port>/ . */
  openSocket(ip: string, port: number): Promise<DesktopPairingSocket>;
  /** Public identity for our outbound PAIR_IDENTITY (incl. vaultId). */
  getLocalIdentity(): Promise<LocalIdentity>;
  /** Persist on user confirm. */
  persistDevice(device: PairedDevice): Promise<void>;
  /** Optional fast-path cache for the next sync round. */
  cacheLastKnownIp?(pubkeyHex: string, ip: string): Promise<void>;
}

export interface PairWithDesktopCallbacks {
  /** Show the 6-digit SAS; the popup must compare against the helper's. */
  onSasReady(sas: string): void;
  /** Pairing succeeded and the device was persisted. */
  onComplete(device: PairedDevice): void;
  /** Pairing failed at some stage. */
  onError(error: DesktopPairingError): void;
}

interface PairingFrame {
  type: "PAIR_IDENTITY";
  device_id: string;
  device_name: string;
  device_type: DeviceType;
  long_term_public_key_hex: string;
  signing_public_key_hex?: string;
  ws_port?: number;
  vault_id?: string; // Change 1 — additive, optional
}

function encodeJson(obj: unknown): Uint8Array {
  return new TextEncoder().encode(JSON.stringify(obj));
}

function decodeJson<T>(bytes: Uint8Array): T {
  return JSON.parse(new TextDecoder().decode(bytes)) as T;
}

function hexToBytes(hex: string): Uint8Array {
  if (!/^[0-9a-f]{64}$/.test(hex)) throw new Error("expected 64-char lowercase hex");
  const out = new Uint8Array(32);
  for (let i = 0; i < 32; i++) out[i] = parseInt(hex.slice(i * 2, i * 2 + 2), 16);
  return out;
}

function decodePairIdentity(bytes: Uint8Array): PairingFrame {
  const p = decodeJson<Record<string, unknown>>(bytes);
  if (p?.type !== "PAIR_IDENTITY") throw new Error("expected PAIR_IDENTITY");
  if (typeof p.device_id !== "string" || !p.device_id) throw new Error("device_id missing");
  if (typeof p.device_name !== "string") throw new Error("device_name missing");
  if (typeof p.device_type !== "string") throw new Error("device_type missing");
  if (typeof p.long_term_public_key_hex !== "string" ||
      !/^[0-9a-f]{64}$/.test(p.long_term_public_key_hex)) {
    throw new Error("long_term_public_key_hex is not 32-byte hex");
  }
  return p as unknown as PairingFrame;
}

/**
 * Drive a complete desktop-helper code pairing.
 *
 * `confirm` is a function the caller resolves AFTER the user has compared
 * the SAS shown here against the SAS the helper displays. Resolving false
 * (or rejecting) aborts before any device is persisted — this is the
 * out-of-band MITM defence (see SECURITY note in chirp-handshake.ts).
 */
export async function pairWithDesktopHelper(
  code: string,
  cb: PairWithDesktopCallbacks,
  deps: DesktopPairingDeps,
  confirm: (sas: string) => Promise<boolean>,
): Promise<void> {
  const pairing = parsePairingCode(code);

  let identity: LocalIdentity;
  try {
    identity = await deps.getLocalIdentity();
  } catch {
    cb.onError("vault_locked");
    return;
  }

  // 1) Resolve the endpoint. A pairing code already carries one; a legacy
  //    helper code does not, so the /24 has to be probed for it.
  const port = pairing?.port ?? DESKTOP_PAIRING_PORT;
  const host = pairing?.ip ?? (await deps.findHost(DESKTOP_PAIRING_PORT));
  if (!host) {
    cb.onError("no_host_found");
    return;
  }

  // 2) Open the WebSocket.
  let sock: DesktopPairingSocket;
  try {
    sock = await deps.openSocket(host, port);
  } catch {
    cb.onError("no_host_found");
    return;
  }

  try {
    // 3) Send PEACH_HELLO (PLAINTEXT binary frame). The legacy helper compares
    //    the code byte-for-byte against a [6]u8, so that form is normalised to
    //    exactly 6 zero-padded ASCII digits (ground truth §2); a pairing token
    //    is sent as the hex it decoded to.
    sock.send(encodeJson(
      pairing
        ? { type: "PEACH_HELLO", token: pairing.tokenHex }
        : { type: "PEACH_HELLO", code: String(code).replace(/\D/g, "").padStart(6, "0").slice(-6) },
    ));

    // 4) Await PEACH_HELLO_ACK OR socket close.
    //    peach-sync sends NO error frame; a wrong/expired code closes the
    //    socket. So "receive() rejected / closed before a frame" == invalid_code.
    let ackBytes: Uint8Array;
    try {
      ackBytes = await sock.receive();
    } catch {
      cb.onError("invalid_code");
      return;
    }
    if (sock.closedBeforeFrame() || ackBytes.length === 0) {
      cb.onError("invalid_code");
      return;
    }

    let ephemeralPublicKeyHex: string;
    try {
      const ack = decodeJson<{ type?: string; ephemeralPublicKeyHex?: string }>(ackBytes);
      if (ack.type !== "PEACH_HELLO_ACK" || typeof ack.ephemeralPublicKeyHex !== "string") {
        // A non-ACK frame on a matching code should not happen; treat the
        // missing ACK exactly like a wrong code.
        cb.onError("invalid_code");
        return;
      }
      ephemeralPublicKeyHex = ack.ephemeralPublicKeyHex;
    } catch {
      cb.onError("invalid_code");
      return;
    }

    // 5) Noise NK as INITIATOR against the helper's ephemeral static key.
    const responderStatic = hexToBytes(ephemeralPublicKeyHex);
    const session = await noiseNKInitiator(
      responderStatic,
      async (msg) => sock.send(msg),
      () => sock.receive(),
    );

    // 6) Exchange PAIR_IDENTITY — initiator (browser) sends FIRST, then reads.
    const ourFrame: PairingFrame = {
      type: "PAIR_IDENTITY",
      device_id: identity.deviceId,
      device_name: identity.deviceName,
      device_type: identity.deviceType,
      long_term_public_key_hex: identity.longTermPublicKeyHex,
      signing_public_key_hex: identity.signingPublicKeyHex,
      ws_port: identity.wsPort,
      vault_id: identity.vaultId, // Change 1
    };
    sock.send(session.encrypt(encodeJson(ourFrame)));

    const theirCipher = await sock.receive();
    const theirFrame = decodePairIdentity(session.decrypt(theirCipher));

    // 7) Derive the SAS (REUSED — same value the helper computes from the
    //    shared handshake hash) and surface it for user confirmation.
    const sas = derivePairingSAS(session.handshakeHash);
    cb.onSasReady(sas);

    const confirmed = await confirm(sas);
    if (!confirmed) {
      cb.onError("sas_mismatch");
      return;
    }

    // 8) Persist. ws_port comes from the peer frame, defaulting to 8765 (both
    //    peers announce it, but guard it). The device-type fallback follows the
    //    code form so a phone never lands in the registry labelled "desktop".
    const device: PairedDevice = {
      deviceId: theirFrame.device_id,
      deviceName: theirFrame.device_name,
      deviceType: (theirFrame.device_type as DeviceType) || (pairing ? "android" : "desktop"),
      longTermPublicKeyHex: theirFrame.long_term_public_key_hex,
      signingPublicKeyHex: theirFrame.signing_public_key_hex,
      trustSource: "direct",
      wsPort: typeof theirFrame.ws_port === "number" ? theirFrame.ws_port : DEFAULT_SYNC_PORT,
      pairedAt: Date.now(),
    };
    await deps.persistDevice(device);
    if (deps.cacheLastKnownIp && device.longTermPublicKeyHex) {
      await deps.cacheLastKnownIp(device.longTermPublicKeyHex, host).catch(() => undefined);
    }
    cb.onComplete(device);
  } catch (err) {
    // The mapped error is intentionally coarse for the UI; log the real cause
    // so a failed pair is diagnosable from the service-worker console.
    if (typeof console !== "undefined") console.error("[desktop-pairing] handshake failed:", err);
    cb.onError("handshake_failed");
  } finally {
    sock.close();
  }
}