import bcrypt from 'bcryptjs';
import {
  generateRegistrationOptions,
  verifyRegistrationResponse,
  generateAuthenticationOptions,
  verifyAuthenticationResponse,
  type AuthenticatorTransportFuture,
} from '@simplewebauthn/server';
import { db } from '../db/database';
import { resolveWebauthnConfig } from './webauthnConfig';
import { generateToken, stripUserForClient, avatarUrl } from './authService';
import type { User } from '../types';

// ---------------------------------------------------------------------------
// Constants
// ---------------------------------------------------------------------------

// Short single-use challenge lifetime — a ceremony is a few seconds of user
// interaction. Kept tight so a stray row can't be replayed and the table can't
// accumulate. Mirrors the spirit of the OIDC state TTL.
const CHALLENGE_TTL_MS = 5 * 60 * 1000;

// Pinned COSE algorithms: EdDSA (-8), ES256 (-7), RS256 (-257). We never want a
// future library default to silently widen what we accept.
const SUPPORTED_ALGORITHM_IDS = [-8, -7, -257];

const NOT_CONFIGURED = { error: 'Passkey login is not configured for this server.', status: 400 } as const;
// One generic message for every authentication failure so the endpoint can't be
// used to tell "no such credential" apart from "bad signature" (CWE-203).
const AUTH_FAILED = { error: 'Authentication failed', status: 401 } as const;

interface CredentialRow {
  id: number;
  user_id: number;
  credential_id: string;
  public_key: Buffer;
  counter: number;
  transports: string | null;
  device_type: string | null;
  backed_up: number;
  name: string | null;
  aaguid: string | null;
  created_at: string;
  last_used_at: string | null;
}

// ---------------------------------------------------------------------------
// Challenge store (DB-backed, single-use, TTL'd)
// ---------------------------------------------------------------------------

function purgeExpiredChallenges(now: number): void {
  db.prepare('DELETE FROM webauthn_challenges WHERE expires_at < ?').run(now);
}

function storeChallenge(challenge: string, userId: number | null, type: 'registration' | 'authentication', now: number): void {
  db.prepare('INSERT INTO webauthn_challenges (challenge, user_id, type, expires_at) VALUES (?, ?, ?, ?)')
    .run(challenge, userId, type, now + CHALLENGE_TTL_MS);
}

/**
 * Atomically claim a challenge by its EXACT bytes + type. This is a single
 * DELETE ... RETURNING statement that runs BEFORE any async verification, so a
 * concurrent double-submit of the same assertion can never spend one challenge
 * twice (the replay window a SELECT→await→DELETE ordering would open).
 */
function claimChallenge(challenge: string, type: 'registration' | 'authentication', now: number): { user_id: number | null } | null {
  const row = db.prepare(
    'DELETE FROM webauthn_challenges WHERE challenge = ? AND type = ? AND expires_at > ? RETURNING user_id',
  ).get(challenge, type, now) as { user_id: number | null } | undefined;
  return row ?? null;
}

/** Decode the challenge the authenticator echoed back inside clientDataJSON. */
function challengeFromResponse(resp: unknown): string | null {
  try {
    const cdj = (resp as { response?: { clientDataJSON?: unknown } })?.response?.clientDataJSON;
    if (typeof cdj !== 'string') return null;
    const parsed = JSON.parse(Buffer.from(cdj, 'base64url').toString('utf8')) as { challenge?: unknown };
    return typeof parsed.challenge === 'string' ? parsed.challenge : null;
  } catch {
    return null;
  }
}

function parseTransports(raw: string | null): AuthenticatorTransportFuture[] | undefined {
  if (!raw) return undefined;
  try {
    const parsed = JSON.parse(raw);
    return Array.isArray(parsed) ? (parsed as AuthenticatorTransportFuture[]) : undefined;
  } catch {
    return undefined;
  }
}

function sanitizeName(raw: unknown): string | null {
  if (typeof raw !== 'string') return null;
  const trimmed = raw.trim().slice(0, 60);
  return trimmed || null;
}

function defaultCredentialName(deviceType: string | undefined): string {
  return deviceType === 'multiDevice' ? 'Passkey (synced)' : 'Passkey';
}

// ---------------------------------------------------------------------------
// Registration (authenticated — from Settings, password re-auth required)
// ---------------------------------------------------------------------------

export async function passkeyRegisterOptions(
  userId: number,
  password: string | undefined,
): Promise<{ error?: string; status?: number; options?: Awaited<ReturnType<typeof generateRegistrationOptions>> }> {
  const cfg = resolveWebauthnConfig();
  if (!cfg) return { ...NOT_CONFIGURED };

  const user = db.prepare('SELECT * FROM users WHERE id = ?').get(userId) as User | undefined;
  if (!user) return { error: 'User not found', status: 404 };

  // Re-authentication: a hijacked session must not be able to silently plant an
  // attacker-controlled passkey. Require the current password (parity with the
  // change-password / disable-MFA step-up).
  if (!password || !user.password_hash || !bcrypt.compareSync(password, user.password_hash)) {
    return { error: 'Incorrect password', status: 401 };
  }

  const existing = db.prepare('SELECT credential_id, transports FROM webauthn_credentials WHERE user_id = ?')
    .all(userId) as { credential_id: string; transports: string | null }[];

  const now = Date.now();
  purgeExpiredChallenges(now);

  const options = await generateRegistrationOptions({
    rpName: cfg.rpName,
    rpID: cfg.rpID,
    userName: user.email,
    userDisplayName: user.username,
    userID: new TextEncoder().encode(String(user.id)),
    attestationType: 'none',
    // Stop the same authenticator from enrolling twice on this account.
    excludeCredentials: existing.map((c) => ({ id: c.credential_id, transports: parseTransports(c.transports) })),
    authenticatorSelection: { residentKey: 'preferred', userVerification: 'required' },
    supportedAlgorithmIDs: SUPPORTED_ALGORITHM_IDS,
  });

  storeChallenge(options.challenge, userId, 'registration', now);
  return { options };
}

export async function passkeyRegisterVerify(
  userId: number,
  body: { attestationResponse?: unknown; name?: unknown },
): Promise<{ error?: string; status?: number; success?: boolean; credential?: unknown }> {
  const cfg = resolveWebauthnConfig();
  if (!cfg) return { ...NOT_CONFIGURED };

  const resp = body?.attestationResponse;
  if (!resp) return { error: 'Invalid registration response', status: 400 };

  const challenge = challengeFromResponse(resp);
  if (!challenge) return { error: 'Invalid registration response', status: 400 };

  const now = Date.now();
  const claimed = claimChallenge(challenge, 'registration', now);
  if (!claimed || claimed.user_id !== userId) {
    return { error: 'Registration challenge expired. Please try again.', status: 400 };
  }

  let verification;
  try {
    verification = await verifyRegistrationResponse({
      response: resp as Parameters<typeof verifyRegistrationResponse>[0]['response'],
      expectedChallenge: challenge,
      expectedOrigin: cfg.origins,
      expectedRPID: cfg.rpID,
      requireUserVerification: true,
    });
  } catch {
    return { error: 'Could not register this passkey.', status: 400 };
  }

  if (!verification.verified || !verification.registrationInfo) {
    return { error: 'Could not register this passkey.', status: 400 };
  }

  // Persist ONLY the values the verifier vouches for — never anything parsed
  // from the raw client payload.
  const { credential, credentialDeviceType, credentialBackedUp, aaguid } = verification.registrationInfo;

  if (db.prepare('SELECT id FROM webauthn_credentials WHERE credential_id = ?').get(credential.id)) {
    return { error: 'This passkey is already registered.', status: 409 };
  }

  const name = sanitizeName(body?.name) || defaultCredentialName(credentialDeviceType);
  try {
    db.prepare(
      `INSERT INTO webauthn_credentials
         (user_id, credential_id, public_key, counter, transports, device_type, backed_up, name, aaguid, last_used_at)
       VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, NULL)`,
    ).run(
      userId,
      credential.id,
      Buffer.from(credential.publicKey),
      credential.counter ?? 0,
      credential.transports ? JSON.stringify(credential.transports) : null,
      credentialDeviceType ?? null,
      credentialBackedUp ? 1 : 0,
      name,
      aaguid ?? null,
    );
  } catch {
    return { error: 'Could not register this passkey.', status: 400 };
  }

  const created = db.prepare(
    'SELECT id, name, device_type, backed_up, created_at, last_used_at FROM webauthn_credentials WHERE credential_id = ?',
  ).get(credential.id) as { backed_up: number } & Record<string, unknown>;
  return { success: true, credential: { ...created, backed_up: created.backed_up === 1 } };
}

// ---------------------------------------------------------------------------
// Authentication (public — primary, discoverable-credential login)
// ---------------------------------------------------------------------------

export async function passkeyLoginOptions(): Promise<{
  error?: string;
  status?: number;
  options?: Awaited<ReturnType<typeof generateAuthenticationOptions>>;
}> {
  const cfg = resolveWebauthnConfig();
  if (!cfg) return { ...NOT_CONFIGURED };

  const now = Date.now();
  purgeExpiredChallenges(now);

  const options = await generateAuthenticationOptions({
    rpID: cfg.rpID,
    userVerification: 'required',
    // Empty allowCredentials → discoverable flow. The server never echoes which
    // accounts have passkeys, so the endpoint can't be used to enumerate users.
  });

  storeChallenge(options.challenge, null, 'authentication', now);
  return { options };
}

export async function passkeyLoginVerify(body: { assertionResponse?: unknown }): Promise<{
  error?: string;
  status?: number;
  token?: string;
  user?: Record<string, unknown>;
  auditUserId?: number | null;
  auditAction?: string;
}> {
  const cfg = resolveWebauthnConfig();
  if (!cfg) return { ...NOT_CONFIGURED };

  const resp = body?.assertionResponse;
  if (!resp) return { ...AUTH_FAILED };

  const challenge = challengeFromResponse(resp);
  if (!challenge) return { ...AUTH_FAILED };

  // Claim the challenge (single-use) BEFORE looking anything up or verifying.
  const now = Date.now();
  if (!claimChallenge(challenge, 'authentication', now)) return { ...AUTH_FAILED };

  const credId = (resp as { id?: unknown; rawId?: unknown }).id ?? (resp as { rawId?: unknown }).rawId;
  if (typeof credId !== 'string') return { ...AUTH_FAILED };

  const cred = db.prepare('SELECT * FROM webauthn_credentials WHERE credential_id = ?').get(credId) as CredentialRow | undefined;
  if (!cred) return { ...AUTH_FAILED };

  let verification;
  try {
    verification = await verifyAuthenticationResponse({
      response: resp as Parameters<typeof verifyAuthenticationResponse>[0]['response'],
      expectedChallenge: challenge,
      expectedOrigin: cfg.origins,
      expectedRPID: cfg.rpID,
      requireUserVerification: true,
      credential: {
        id: cred.credential_id,
        publicKey: new Uint8Array(cred.public_key),
        counter: cred.counter,
        transports: parseTransports(cred.transports),
      },
    });
  } catch {
    return { ...AUTH_FAILED };
  }

  if (!verification.verified) return { ...AUTH_FAILED };

  const { newCounter } = verification.authenticationInfo;
  // Clone detection only makes sense for authenticators that actually increment.
  // Synced passkeys legitimately report a counter that stays 0 — never treat
  // that as a clone. A regression from a previously NON-ZERO counter rejects
  // THIS assertion (and is audited) but does not disable the credential.
  if (cred.counter > 0 && newCounter <= cred.counter) {
    return { ...AUTH_FAILED, auditUserId: cred.user_id, auditAction: 'user.passkey_clone_suspected' };
  }

  const user = db.prepare('SELECT * FROM users WHERE id = ?').get(cred.user_id) as User | undefined;
  if (!user) return { ...AUTH_FAILED };

  // Persist the new counter + last-used and bump login bookkeeping atomically.
  db.transaction(() => {
    db.prepare('UPDATE webauthn_credentials SET counter = ?, last_used_at = CURRENT_TIMESTAMP WHERE id = ?').run(newCounter, cred.id);
    db.prepare('UPDATE users SET last_login = CURRENT_TIMESTAMP, login_count = login_count + 1 WHERE id = ?').run(user.id);
  })();

  // A user-verified passkey is phishing-resistant and inherently two-factor
  // (device possession + biometric/PIN), so it mints the real session directly
  // — the SAME path as password and OIDC login (no new token shape).
  const token = generateToken(user);
  const userSafe = stripUserForClient(user) as Record<string, unknown>;
  return { token, user: { ...userSafe, avatar_url: avatarUrl(user) }, auditUserId: Number(user.id) };
}

// ---------------------------------------------------------------------------
// Management (authenticated, owner-scoped)
// ---------------------------------------------------------------------------

export function listPasskeys(userId: number): Array<Record<string, unknown>> {
  const rows = db.prepare(
    'SELECT id, name, device_type, backed_up, created_at, last_used_at FROM webauthn_credentials WHERE user_id = ? ORDER BY created_at DESC',
  ).all(userId) as Array<{ backed_up: number } & Record<string, unknown>>;
  return rows.map((r) => ({ ...r, backed_up: r.backed_up === 1 }));
}

export function renamePasskey(userId: number, id: string, name: unknown): { error?: string; status?: number; success?: boolean } {
  const cleanName = sanitizeName(name);
  if (!cleanName) return { error: 'Name is required', status: 400 };
  // Ownership enforced in SQL (404 on miss, never a 403 that leaks existence).
  const result = db.prepare('UPDATE webauthn_credentials SET name = ? WHERE id = ? AND user_id = ?').run(cleanName, Number(id), userId);
  if (result.changes === 0) return { error: 'Passkey not found', status: 404 };
  return { success: true };
}

export function deletePasskey(
  userId: number,
  id: string,
  password: string | undefined,
): { error?: string; status?: number; success?: boolean } {
  // Re-auth before removing a credential (a hijacked session must not be able to
  // strip the victim's passkeys). Deleting is always allowed because every
  // account keeps a usable password as recovery fallback — losing all passkeys
  // can never lock anyone out.
  const user = db.prepare('SELECT password_hash FROM users WHERE id = ?').get(userId) as { password_hash: string } | undefined;
  if (!user || !user.password_hash || !password || !bcrypt.compareSync(password, user.password_hash)) {
    return { error: 'Incorrect password', status: 401 };
  }
  const result = db.prepare('DELETE FROM webauthn_credentials WHERE id = ? AND user_id = ?').run(Number(id), userId);
  if (result.changes === 0) return { error: 'Passkey not found', status: 404 };
  return { success: true };
}

/** Admin: clear all of a user's passkeys (e.g. on suspected compromise). */
export function adminResetPasskeys(targetUserId: number): { error?: string; status?: number; success?: boolean; deleted?: number; email?: string } {
  const target = db.prepare('SELECT id, email FROM users WHERE id = ?').get(targetUserId) as { id: number; email: string } | undefined;
  if (!target) return { error: 'User not found', status: 404 };
  const result = db.prepare('DELETE FROM webauthn_credentials WHERE user_id = ?').run(targetUserId);
  return { success: true, deleted: result.changes, email: target.email };
}