import {
  createHash,
  createPublicKey,
  randomBytes,
  randomUUID,
  verify as verifySignature,
} from 'node:crypto';
import {
  assertVerifiedNodeRegistration,
  type VerifiedNodeRegistration,
} from './node-registration.js';

const CHALLENGE_SCHEMA = 'gh-aios.node-possession-challenge/v1' as const;
const RESPONSE_SCHEMA = 'gh-aios.node-possession-response/v1' as const;
const CHALLENGE_LIFETIME_MS = 60_000;
const IDENTIFIER_PATTERN = /^[A-Z0-9][A-Z0-9._:-]{1,159}$/;
const NONCE_PATTERN = /^[A-Za-z0-9_-]{43}$/;
const issuedChallenges = new WeakSet<object>();
const consumedChallenges = new WeakSet<object>();

export interface NodePossessionChallenge {
  accountId: string;
  challengeId: string;
  claimId: string;
  domainId: string;
  expiresAt: number;
  issuedAt: number;
  nodeId: string;
  nodeKeyFingerprint: string;
  nodeType: VerifiedNodeRegistration['nodeType'];
  nonce: string;
  schema: typeof CHALLENGE_SCHEMA;
}

export interface NodePossessionResponse {
  challengeId: string;
  publicKeyPem: string;
  schema: typeof RESPONSE_SCHEMA;
  signature: string;
}

export interface NodePossessionProofSource {
  prove(challenge: Readonly<NodePossessionChallenge>): Promise<unknown | null>;
}

function invalidProof(): never {
  throw new Error('node_possession_proof_invalid');
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === 'object' && value !== null && !Array.isArray(value);
}

function hasExactKeys(record: Record<string, unknown>, keys: string[]): boolean {
  const expected = [...keys].sort();
  const actual = Object.keys(record).sort();
  return actual.length === expected.length && actual.every((key, index) => key === expected[index]);
}

export function nodePossessionChallengeSigningBytes(challenge: NodePossessionChallenge): Buffer {
  return Buffer.from(JSON.stringify({
    accountId: challenge.accountId,
    challengeId: challenge.challengeId,
    claimId: challenge.claimId,
    domainId: challenge.domainId,
    expiresAt: challenge.expiresAt,
    issuedAt: challenge.issuedAt,
    nodeId: challenge.nodeId,
    nodeKeyFingerprint: challenge.nodeKeyFingerprint,
    nodeType: challenge.nodeType,
    nonce: challenge.nonce,
    schema: challenge.schema,
  }), 'utf8');
}

export function createNodePossessionChallenge(
  registration: VerifiedNodeRegistration,
  now = Date.now(),
  challengeId = `NODE-CHALLENGE-${randomUUID().toUpperCase()}`,
  nonce = randomBytes(32).toString('base64url'),
): Readonly<NodePossessionChallenge> {
  try {
    assertVerifiedNodeRegistration(registration);
  } catch {
    invalidProof();
  }
  if (!Number.isSafeInteger(now)
    || now < registration.issuedAt
    || now >= registration.expiresAt
    || !IDENTIFIER_PATTERN.test(challengeId)
    || !NONCE_PATTERN.test(nonce)) invalidProof();
  const expiresAt = Math.min(now + CHALLENGE_LIFETIME_MS, registration.expiresAt);
  if (expiresAt <= now) invalidProof();
  const challenge = Object.freeze({
    accountId: registration.accountId,
    challengeId,
    claimId: registration.claimId,
    domainId: registration.domainId,
    expiresAt,
    issuedAt: now,
    nodeId: registration.nodeId,
    nodeKeyFingerprint: registration.nodeKeyFingerprint,
    nodeType: registration.nodeType,
    nonce,
    schema: CHALLENGE_SCHEMA,
  });
  issuedChallenges.add(challenge);
  return challenge;
}

export function verifyNodePossessionResponse(
  input: unknown,
  challenge: NodePossessionChallenge,
  registration: VerifiedNodeRegistration,
  now = Date.now(),
): true {
  try {
    assertVerifiedNodeRegistration(registration);
  } catch {
    invalidProof();
  }
  if (!issuedChallenges.has(challenge)
    || consumedChallenges.has(challenge)
    || !Number.isSafeInteger(now)
    || now < challenge.issuedAt
    || now >= challenge.expiresAt
    || registration.expiresAt <= now
    || challenge.accountId !== registration.accountId
    || challenge.claimId !== registration.claimId
    || challenge.domainId !== registration.domainId
    || challenge.nodeId !== registration.nodeId
    || challenge.nodeKeyFingerprint !== registration.nodeKeyFingerprint
    || challenge.nodeType !== registration.nodeType
    || !isRecord(input)
    || !hasExactKeys(input, ['challengeId', 'publicKeyPem', 'schema', 'signature'])
    || input.schema !== RESPONSE_SCHEMA
    || input.challengeId !== challenge.challengeId
    || typeof input.publicKeyPem !== 'string'
    || input.publicKeyPem.length > 4096
    || input.publicKeyPem.includes('PRIVATE KEY')
    || typeof input.signature !== 'string') invalidProof();

  try {
    const publicKey = createPublicKey({ key: input.publicKeyPem, format: 'pem' });
    if (publicKey.asymmetricKeyType !== 'ed25519') invalidProof();
    const fingerprint = createHash('sha256')
      .update(publicKey.export({ format: 'der', type: 'spki' }))
      .digest('hex');
    if (fingerprint !== registration.nodeKeyFingerprint) invalidProof();
    const signature = Buffer.from(input.signature, 'base64');
    if (signature.length !== 64 || signature.toString('base64') !== input.signature) invalidProof();
    if (!verifySignature(null, nodePossessionChallengeSigningBytes(challenge), publicKey, signature)) invalidProof();
  } catch {
    invalidProof();
  }
  consumedChallenges.add(challenge);
  return true;
}