GoogleSignInHelperFragment

AuthenticationFragment.kt

package com.x.y.authentication

import android.os.Bundle
import android.view.View
import androidx.fragment.app.viewModels
import com.x.y.R
import com.x.y.common.BaseFragment
import com.x.y.common.extensions.observeNonNull
import com.x.y.common.viewBinding
import com.x.y.databinding.FragmentAuthenticationBinding
import dagger.hilt.android.AndroidEntryPoint

@AndroidEntryPoint
class AuthenticationFragment : BaseFragment(R.layout.fragment_authentication) {

    val binding: FragmentAuthenticationBinding by viewBinding(FragmentAuthenticationBinding::bind)

    val viewModel: AuthenticationViewModel by viewModels()
    
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.buttonLogin.setOnClickListener {
            GoogleSignInUseHeadlessFragment
                .getSignInFragment(childFragmentManager)
                .signIn()
        }
        GoogleSignInUseHeadlessFragment
            .getSignInFragment(childFragmentManager)
            .apply {
                this.authenticationFailedListener = {
                    viewModel.onAuthenticationFailed(it)
                }
                this.userAuthenticatedListener = { viewModel.onUserAuthenticatedWithGoogle(it) }
            }
    }
}

GoogleSignInHelperFragment.kt

package com.x.y.authentication

import android.content.Intent
import android.os.Bundle
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentManager
import com.x.y.R
import com.google.android.gms.auth.api.signin.GoogleSignIn
import com.google.android.gms.auth.api.signin.GoogleSignInOptions
import com.google.android.gms.common.api.ApiException
import com.google.firebase.auth.FirebaseUser
import com.google.firebase.auth.GoogleAuthProvider
import com.google.firebase.auth.ktx.auth
import com.google.firebase.ktx.Firebase

class GoogleSignInHelperFragment : Fragment() {
    private val RC_SIGN_IN = 42

    var authenticationFailedListener: ((Exception) -> Unit)? = null
    var userAuthenticatedListener: ((FirebaseUser) -> Unit)? = null
    var authenticationCancelledListener: (() -> Unit)? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        retainInstance = true
    }

    fun signIn() {
        val options = GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
            .requestIdToken(requireActivity().getString(R.string.default_web_client_id))
            .requestEmail()
            .build()
        val client = GoogleSignIn.getClient(requireContext(), options)
        val signInIntent = client.signInIntent
        startActivityForResult(signInIntent, RC_SIGN_IN)
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if (requestCode == RC_SIGN_IN) {
            val task = GoogleSignIn.getSignedInAccountFromIntent(data)
            try {
                val account = task.getResult(ApiException::class.java)
                firebaseAuthWithGoogle(requireNotNull(account?.idToken))
            } catch (e: Exception) {
                renderError(e)
            }
        }
    }

    private fun firebaseAuthWithGoogle(idToken: String) {
        val credential = GoogleAuthProvider.getCredential(idToken, null)
        Firebase.auth.signInWithCredential(credential)
            .addOnCompleteListener(requireActivity()) { task ->
                val exception = task.exception
                when {
                    task.isSuccessful -> {
                        onUserAuthenticated(requireNotNull(task.result?.user))
                    }
                    task.isCanceled -> {
                        onAuthenticatedCancelled()
                    }
                    exception != null -> {
                        renderError(exception)
                    }
                }
            }
    }

    private fun renderError(exception: Exception) {
        authenticationFailedListener?.invoke(exception)
    }

    private fun onUserAuthenticated(user: FirebaseUser) {
        userAuthenticatedListener?.invoke(user)
    }

    private fun onAuthenticatedCancelled() {
        authenticationCancelledListener?.invoke()
    }

    companion object {
        private val TAG = "GOOGLE_SIGN_IN_TAG"
        fun getSignInFragment(fragmentManager: FragmentManager): GoogleSignInUseHeadlessFragment {
            return fragmentManager.findFragmentByTag(TAG) as GoogleSignInUseHeadlessFragment?
                ?: GoogleSignInUseHeadlessFragment().apply {
                    fragmentManager
                        .beginTransaction()
                        .add(this, TAG)
                        .commit()
                }
        }
    }

}