guardia-messenger/hooks/useBiometric.ts

import * as LocalAuth from 'expo-local-authentication'

export async function isBiometricAvailable(): Promise<boolean> {
  const hasHardware = await LocalAuth.hasHardwareAsync()
  const isEnrolled  = await LocalAuth.isEnrolledAsync()
  return hasHardware && isEnrolled
}

export async function authenticateWithBiometric(
  promptMessage = 'GUARDiA 로그인'
): Promise<{ success: boolean; error?: string }> {
  const available = await isBiometricAvailable()
  if (!available) return { success: false, error: '생체인증을 사용할 수 없습니다.' }

  const result = await LocalAuth.authenticateAsync({
    promptMessage,
    cancelLabel:   '취소',
    fallbackLabel: '비밀번호 사용',
    disableDeviceFallback: false,
  })

  return result.success
    ? { success: true }
    : { success: false, error: result.error ?? '인증 실패' }
}