LoginActivity.kt

package com.example.firebaseAuth

import android.content.Intent
import android.net.Uri
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.util.Log
import android.view.View
import android.widget.Toast
import com.bumptech.glide.Glide
import com.google.android.gms.auth.api.Auth
import com.google.android.gms.auth.api.signin.GoogleSignInAccount
import com.google.android.gms.auth.api.signin.GoogleSignInOptions
import com.google.android.gms.common.ConnectionResult
import com.google.android.gms.common.api.GoogleApiClient
import com.google.android.gms.tasks.OnCompleteListener
import com.google.firebase.auth.AuthResult
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.auth.GoogleAuthProvider
import kotlinx.android.synthetic.main.activity_login.*


class LoginActivity : AppCompatActivity() ,GoogleApiClient.OnConnectionFailedListener {

    private val RC_SIGN_IN = 100
    private lateinit var mAuth: FirebaseAuth
    private lateinit var mGoogleSignInOptions: GoogleSignInOptions
    private lateinit var mGoogleApiClient:GoogleApiClient
    private var isUserLoggedIn = false

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_login)

        // initialise the FirebaseAuth instance
        mAuth = FirebaseAuth.getInstance()

        // Configure Google Sign In
        mGoogleSignInOptions = GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestIdToken(getString(R.string.default_web_client_id))
                .requestEmail()
                .build()

        // configure the GoogleApiClient
        mGoogleApiClient = GoogleApiClient
                .Builder(this)
                .enableAutoManage(this  , this).addApi(Auth.GOOGLE_SIGN_IN_API , mGoogleSignInOptions).build()



        button_login.setOnClickListener {
            if(isUserLoggedIn){
                doLogout()
            }else{
                doLogin()
            }
        }
    }

    public override fun onStart() {
        super.onStart()
        // Check if user is signed in (non-null) and update UI accordingly.
        val currentUser = mAuth.currentUser
        val userName = currentUser?.displayName
        textView_username.text = userName
        if(!userName.isNullOrEmpty()){
            setLoginUIVisible(currentUser?.photoUrl)
        }
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
        if (requestCode == RC_SIGN_IN) {
            val result = Auth.GoogleSignInApi.getSignInResultFromIntent(data)
            if (result.isSuccess) {
                // Google Sign In was successful, authenticate with Firebase
                val account = result.signInAccount
                firebaseAuthWithGoogle(account!!)
            } else {
                // Google Sign In failed
                Log.e("MainActivity", "Google Sign In failed.")
            }
        }
    }

    private fun firebaseAuthWithGoogle(acct: GoogleSignInAccount) {
        Log.d("Login", "firebaseAuthWithGoogle:" + acct.id!!)
        val credential = GoogleAuthProvider.getCredential(acct.idToken, null)
        mAuth.signInWithCredential(credential)
                .addOnCompleteListener(this, OnCompleteListener<AuthResult> { task ->
                    Log.d("Login", "signInWithCredential:onComplete:" + task.isSuccessful)

                    // If sign in fails, display a message to the user. If sign in succeeds
                    // the auth state listener will be notified and logic to handle the
                    // signed in user can be handled in the listener.
                    if (!task.isSuccessful) {
                        Log.d("Login", "signInWithCredential", task.exception)
                        Toast.makeText(this@LoginActivity, "Authentication failed.",
                                Toast.LENGTH_SHORT).show()
                    } else {
                        setLoginUIVisible(task.result?.user?.photoUrl)
                        textView_username.text = task.result?.user?.displayName
//                        textView_username.text = task.result?.user?.photoUrl.toString()
                        Glide.with(this@LoginActivity)
                                .load(task.result?.user?.photoUrl)
                                .into(imageView_profilePic)
                        setLogoutUI()
                    }
                })
    }

    override fun onConnectionFailed(p0: ConnectionResult) {
        Log.d("Login", "onConnectionFailed:$p0")
        Toast.makeText(this, "Google Play Services error.", Toast.LENGTH_SHORT).show()
    }

    private fun doLogin(){
        val signInIntent = Auth.GoogleSignInApi.getSignInIntent(mGoogleApiClient)
        startActivityForResult(signInIntent, RC_SIGN_IN)
    }

    private fun doLogout(){
        mAuth.signOut()
        setLoginUIGone()
        isUserLoggedIn = false
    }

    private fun setLogoutUI(){
        isUserLoggedIn = true
    }

    private fun setLoginUIVisible(photoUrl: Uri?) {
        textView_username.visibility = View.VISIBLE
        imageView_profilePic.visibility = View.VISIBLE
        Glide.with(this@LoginActivity)
                .load(photoUrl)
                .into(imageView_profilePic)
    }

    private fun setLoginUIGone(){
        textView_username.visibility = View.GONE
        imageView_profilePic.visibility = View.GONE
    }
}