Simplifying the overall implementation when signing in a User using Firebase Authentication

FirebaseAuthHelper.kt

/*
 * Copyright (c) 2020, Shashank Verma <shashank.verma2002@gmail.com> [@shank03]
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 */

import android.content.Context
import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import com.google.android.gms.auth.api.signin.GoogleSignIn
import com.google.android.gms.auth.api.signin.GoogleSignInAccount
import com.google.android.gms.auth.api.signin.GoogleSignInClient
import com.google.android.gms.auth.api.signin.GoogleSignInOptions
import com.google.android.gms.common.api.ApiException
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.auth.FirebaseUser
import com.google.firebase.auth.GoogleAuthProvider

/**
 * FirebaseAuthHelper
 *
 * Simplifying the overall implementation when signing in a User
 *
 * @param activity Used for startingActivity for result and handling result
 * @param defaultWebClientId Base implementation requirement
 * @param auth [FirebaseAuth] for final sign in
 * @param onStart Block to be executed before starting sign in
 * @param onSignInComplete Block to be executed when sign in complete
 * @param onSignInFailed Block to be executed when sign in failed or cancelled
 *
 * IMPORTANT ! You have to create instance of this class on OnCreate, else get ready for crashes
 */
class FirebaseAuthHelper(private val activity: AppCompatActivity, defaultWebClientId: String, private val auth: FirebaseAuth,
                         val onStart: () -> Unit = {},
                         val onSignInComplete: (account: GoogleSignInAccount, user: FirebaseUser) -> Unit = { _, _ -> },
                         val onSignInFailed: (err: String?) -> Unit = {}) {

    companion object {
        // Request Code for auth
        private const val RC_SIGN_IN = 111

        // Signing out user
        @JvmStatic
        fun signOutUser(context: Context, defaultWebClientId: String) {
            getSignInClient(context, defaultWebClientId).signOut()
        }

        private fun getSignInClient(context: Context, defaultWebClientId: String): GoogleSignInClient = GoogleSignIn.getClient(context, GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestIdToken(defaultWebClientId)
                .requestEmail()
                .build())
    }

    private val googleSignInClient = getSignInClient(activity, defaultWebClientId)

    /**
     * Call this when you need to start sign in process
     * Such as onClick
     */
    fun signIn() {
        onStart()
        googleSignInClient.signOut()
        activity.startActivityForResult(googleSignInClient.signInIntent, RC_SIGN_IN)
    }

    /**
     * This method should be called on [AppCompatActivity.onActivityResult] in your activity, to handle the result
     * Otherwise nothing will happen.
     *
     * @param requestCode It's the requestCode param from [AppCompatActivity.onActivityResult]
     * @param data It's the [Intent] param from [AppCompatActivity.onActivityResult]
     */
    fun passOnActivityResult(requestCode: Int, data: Intent?) {
        if (requestCode == RC_SIGN_IN) {
            val task = GoogleSignIn.getSignedInAccountFromIntent(data)
            try {
                val account = task.getResult(ApiException::class.java)
                if (account != null) {
                    auth.signInWithCredential(GoogleAuthProvider.getCredential(account.idToken, null)).addOnCompleteListener {
                        if (task.isSuccessful) {
                            val user = auth.currentUser
                            if (user != null) onSignInComplete(account, user)
                        } else onSignInFailed(task.exception?.message)
                    }
                }
            } catch (e: ApiException) {
                e.printStackTrace()
                onSignInFailed(e.message)
            }
        }
    }
}