/**
 * Two-device handoff payload.
 *
 * The NEW device publishes a key package to the coordinator and shows this
 * compact code as a QR. An EXISTING member scans it, consumes the key package
 * by ref, and the coordinator stores the Welcome for the new device. The
 * private key never leaves the new device, and the code is short enough for a
 * normal QR.
 */
export interface CordnDeviceLink {
  gid: string;
  kpRef: string;
  pubkey: string;
  coordinatorPubkey: string;
  relays: string[];
}

const PREFIX = 'cordn-device:';
const HEX64 = /^[0-9a-f]{64}$/;

function b64urlEncode(value: string): string {
  return btoa(value).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/g, '');
}

function b64urlDecode(value: string): string {
  const padded = value.replace(/-/g, '+').replace(/_/g, '/');
  const pad = padded.length % 4 === 0 ? '' : '='.repeat(4 - (padded.length % 4));
  return atob(padded + pad);
}

export function encodeDeviceLink(link: CordnDeviceLink): string {
  const json = JSON.stringify({
    g: link.gid,
    k: link.kpRef,
    p: link.pubkey,
    c: link.coordinatorPubkey,
    r: link.relays,
  });
  return `${PREFIX}${b64urlEncode(json)}`;
}

export function decodeDeviceLink(raw: string | undefined | null): CordnDeviceLink | null {
  if (!raw || !raw.startsWith(PREFIX)) return null;
  try {
    const parsed = JSON.parse(b64urlDecode(raw.slice(PREFIX.length))) as {
      g?: unknown;
      k?: unknown;
      p?: unknown;
      c?: unknown;
      r?: unknown;
    };
    if (
      typeof parsed.g !== 'string' ||
      !parsed.g ||
      typeof parsed.k !== 'string' ||
      !parsed.k ||
      typeof parsed.p !== 'string' ||
      !HEX64.test(parsed.p) ||
      typeof parsed.c !== 'string' ||
      !HEX64.test(parsed.c) ||
      !Array.isArray(parsed.r) ||
      parsed.r.length === 0
    ) {
      return null;
    }
    const relays = parsed.r.filter(
      (relay): relay is string =>
        typeof relay === 'string' && /^wss?:\/\/[^\s]+$/i.test(relay),
    );
    if (relays.length === 0) return null;
    return {
      gid: parsed.g,
      kpRef: parsed.k,
      pubkey: parsed.p,
      coordinatorPubkey: parsed.c,
      relays,
    };
  } catch {
    return null;
  }
}