object FirebaseManager {
    fun sendOTP(phone: String, activity: Activity, callback: (Boolean, String?) -> Unit) {
        val options = PhoneAuthOptions.newBuilder(FirebaseAuth.getInstance())
            .setPhoneNumber("+91$phone")
            .setTimeout(120L, TimeUnit.SECONDS)
            .setActivity(activity)
            .setCallbacks(object : PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
                override fun onVerificationCompleted(credential: PhoneAuthCredential) {
                    signInWithCredential(credential, callback)
                }
                override fun onVerificationFailed(e: FirebaseException) {
                    callback(false, e.message)
                }
                override fun onCodeSent(verificationId: String, token: PhoneAuthProvider.ForceResendingToken) {
                    PrefsManager.saveVerificationId(verificationId)
                    callback(true, verificationId)
                }
            }).build()
        PhoneAuthProvider.verifyPhoneNumber(options)
    }

    fun verifyOTP(verificationId: String, otp: String, callback: (Boolean, String?) -> Unit) {
        val credential = PhoneAuthProvider.getCredential(verificationId, otp)
        signInWithCredential(credential, callback)
    }

    private fun signInWithCredential(credential: PhoneAuthCredential, callback: (Boolean, String?) -> Unit) {
        FirebaseAuth.getInstance().signInWithCredential(credential)
            .addOnSuccessListener { result ->
                result.user?.getIdToken(true)
                    ?.addOnSuccessListener { tokenResult ->
                        callback(true, tokenResult.token)
                    }
                    ?.addOnFailureListener { callback(false, it.message) }
            }
            .addOnFailureListener { callback(false, it.message) }
    }
}