One Tap Sign In Handler

GoogleSignInHandler.kt

class GoogleSignInHandler(fragment: Fragment) {
    private val oneTapClient = Identity.getSignInClient(fragment.requireContext())
    private var callback: ActivityResultCallback<ActivityResult> = ActivityResultCallback {
        fragment.toast("Hello!")
    }

    private val launcher: ActivityResultLauncher<IntentSenderRequest> =
        fragment.registerForActivityResult(
            ActivityResultContracts.StartIntentSenderForResult(),
            callback
        )

    private val signInRequest = BeginSignInRequest.builder().setGoogleIdTokenRequestOptions(
        BeginSignInRequest.GoogleIdTokenRequestOptions.builder().setSupported(true)
            .setServerClientId(fragment.getString(R.string.firebase_server_web_client_id))
            .setFilterByAuthorizedAccounts(false).build()
    ).build()

    fun startSignInFlow(onCompleted: (Result<SignInCredential>) -> Unit) {
        callback = ActivityResultCallback {
            val credential = oneTapClient.getSignInCredentialFromIntent(it.data)
            onCompleted(fromSuccess(credential))
        }

        oneTapClient.beginSignIn(signInRequest).addOnSuccessListener { signInResult ->
            try {
                val intentRequest = IntentSenderRequest
                    .Builder(signInResult.pendingIntent.intentSender)
                    .build()
                launcher.launch(intentRequest)
            } catch (error: Exception) {
                onCompleted(fromError(error))
            }
        }.addOnFailureListener {
            onCompleted(fromError(it))
        }
    }
}