// The dialling half of code pairing — shared by device pairing and vault
// adoption.
//
// Both flows are identical up to the point where they diverge: decode a
// pairing code, dial the address inside it, present the token in a plaintext
// hello, and run Noise NK as the INITIATOR against the ephemeral key the
// listener returns. What they then say over the encrypted channel differs
// (PAIR_IDENTITY vs ADOPT_REQUEST); how they get there does not.
//
// The browser is always the dialler. It cannot listen, so it is always the NK
// initiator and the listener's `ephemeralPublicKeyHex` is the responder static.
//
// Nothing here touches chrome, the vault, or a real WebSocket — the socket is
// injected — because vault adoption runs before a vault exists at all.

import { noiseNKInitiator } from "./noise-js";
import { derivePairingSAS, type PairingTransport } from "./chirp-handshake";
import { parsePairingCode } from "./pairing-code";

/** The pairing-only port a legacy helper code implies. */
export const PAIRING_PORT = 49142;

export type PairingDialError =
  | "invalid_code" // socket closed before PEACH_HELLO_ACK (wrong/expired)
  | "no_host_found" // nothing answered at the endpoint
  | "handshake_failed"; // Noise NK failed or the ACK was malformed

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

export interface PairingDialDeps {
  /**
   * Legacy 6-digit codes carry no address, so a host has to be found. Omit it
   * where only pairing codes are accepted — a code without an address then
   * simply has nowhere to go.
   */
  findHost?(port: number): Promise<string | null>;
  openSocket(ip: string, port: number): Promise<PairingSocket>;
}

export interface DialledPairingChannel {
  /** Encrypted channel — everything written to it is Noise-protected. */
  channel: PairingTransport;
  /** The 6-digit code the user must confirm matches the listener's screen. */
  sas: string;
  /** The address actually connected to, for the reconnect cache. */
  host: string;
  socket: PairingSocket;
}

export type DialResult =
  | { ok: true; dialled: DialledPairingChannel }
  | { ok: false; error: PairingDialError };

/**
 * Dial a pairing code and bring up the encrypted channel behind it.
 *
 * On success the socket is left OPEN and owned by the caller, which must close
 * it. On failure it is closed here.
 */
export async function dialPairingChannel(
  code: string,
  deps: PairingDialDeps,
): Promise<DialResult> {
  const pairing = parsePairingCode(code);

  // A pairing code already carries an endpoint; a legacy helper code does not,
  // so the /24 has to be probed for it.
  const port = pairing?.port ?? PAIRING_PORT;
  const host = pairing?.ip ?? (await deps.findHost?.(PAIRING_PORT)) ?? null;
  if (!host) return { ok: false, error: "no_host_found" };

  let sock: PairingSocket;
  try {
    sock = await deps.openSocket(host, port);
  } catch {
    return { ok: false, error: "no_host_found" };
  }

  try {
    // 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) },
    ));

    // A wrong or expired code gets NO error frame — the listener silently
    // closes and rotates. That silence IS the wrong-code signal.
    let ackBytes: Uint8Array;
    try {
      ackBytes = await sock.receive();
    } catch {
      sock.close();
      return { ok: false, error: "invalid_code" };
    }
    if (sock.closedBeforeFrame() || ackBytes.length === 0) {
      sock.close();
      return { ok: false, error: "invalid_code" };
    }

    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 a missing
        // ACK exactly like a wrong code.
        sock.close();
        return { ok: false, error: "invalid_code" };
      }
      ephemeralPublicKeyHex = ack.ephemeralPublicKeyHex;
    } catch {
      sock.close();
      return { ok: false, error: "invalid_code" };
    }

    const session = await noiseNKInitiator(
      hexToBytes32(ephemeralPublicKeyHex),
      async (msg) => sock.send(msg),
      () => sock.receive(),
    );

    const channel: PairingTransport = {
      async send(plaintext) { sock.send(session.encrypt(plaintext)); },
      async receive() { return session.decrypt(await sock.receive()); },
    };

    return {
      ok: true,
      dialled: {
        channel,
        sas: derivePairingSAS(session.handshakeHash),
        host,
        socket: sock,
      },
    };
  } catch (err) {
    // Coarse for the UI; log the real cause so a failed dial is diagnosable
    // from the service-worker console.
    if (typeof console !== "undefined") console.error("[pairing-dial] handshake failed:", err);
    sock.close();
    return { ok: false, error: "handshake_failed" };
  }
}

/** Adapt a real `WebSocket` to the `PairingSocket` seam (binary frames). */
export function openPairingSocket(ip: string, port: number): Promise<PairingSocket> {
  return new Promise((resolve, reject) => {
    let ws: WebSocket;
    try {
      ws = new WebSocket(`ws://${ip}:${port}/`);
    } catch (err) {
      reject(err instanceof Error ? err : new Error("websocket open failed"));
      return;
    }
    ws.binaryType = "arraybuffer";

    const inbox: Uint8Array[] = [];
    const readers: Array<{ resolve: (b: Uint8Array) => void; reject: (e: Error) => void }> = [];
    let opened = false;
    let closed = false;
    // True iff the socket closed with no frame delivered for the pending read —
    // the wrong/expired-code signal (the listener sends no error frame).
    let sawCloseBeforeFrame = false;

    ws.onopen = () => {
      opened = true;
      resolve(sock);
    };
    ws.onmessage = (ev: MessageEvent) => {
      const bytes = new Uint8Array(ev.data as ArrayBuffer);
      const r = readers.shift();
      if (r) { sawCloseBeforeFrame = false; r.resolve(bytes); }
      else inbox.push(bytes);
    };
    ws.onerror = () => {
      if (!opened) reject(new Error("websocket connection failed"));
    };
    ws.onclose = () => {
      closed = true;
      if (readers.length) {
        sawCloseBeforeFrame = true;
        while (readers.length) readers.shift()!.reject(new Error("socket closed"));
      }
      if (!opened) reject(new Error("socket closed before open"));
    };

    const sock: PairingSocket = {
      send(bytes: Uint8Array) { ws.send(bytes as Uint8Array<ArrayBuffer>); },
      receive(): Promise<Uint8Array> {
        const queued = inbox.shift();
        if (queued) { sawCloseBeforeFrame = false; return Promise.resolve(queued); }
        if (closed) { sawCloseBeforeFrame = true; return Promise.reject(new Error("socket closed")); }
        return new Promise<Uint8Array>((res, rej) => readers.push({ resolve: res, reject: rej }));
      },
      close() { try { ws.close(); } catch { /* ignore */ } },
      closedBeforeFrame() { return sawCloseBeforeFrame; },
    };
  });
}

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 hexToBytes32(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;
}