import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.rengwuxian.materialedittext.MaterialEditText;

import sonu.enigma.Common.Common;
import sonu.enigma.Model.User;

import static sonu.enigma.R.drawable.l;

public class MainActivity extends AppCompatActivity {
    MaterialEditText edtNewUser, edtNewPassword, edtNewEmail; //for Sign Up
    MaterialEditText edtUser, edtPassword; //for Sign In
    Button btnSignUp, btnSignIn;
    FirebaseDatabase database;
    DatabaseReference users;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Firebase
        database=FirebaseDatabase.getInstance();
        users=database.getReference("Users");
        edtUser=(MaterialEditText)findViewById(R.id.edtUserName);
        edtPassword=(MaterialEditText)findViewById(R.id.edtPassword);
        btnSignIn=(Button)findViewById(R.id.btn_sign_in);
        btnSignUp=(Button)findViewById(R.id.btn_sign_up);

        btnSignUp.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                showSignUpDialog();
            }
        });
        btnSignIn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                signIn(edtUser.getText().toString(), edtPassword.getText().toString());
            }
        });


    }

    private void signIn(final String user, final String pwd) {
        users.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.child(user).exists()){
                    if (!user.isEmpty()){
                        User login=dataSnapshot.child(user).getValue(User.class);
                        if (login.getPassword().equals(pwd)){
                            Intent homeActivity = new Intent(MainActivity.this, Home.class);

                            Common.CurrentUser=login;

                            startActivity(homeActivity);
                            finish();

                        }
                        else {
                            Toast.makeText(MainActivity.this, "Wrong Password", Toast.LENGTH_SHORT).show();
                        }

                    }
                    else {
                        Toast.makeText(MainActivity.this, "Please enter your User name", Toast.LENGTH_SHORT).show();

                    }
                }
                else{
                    Toast.makeText(MainActivity.this, "User is not exists!", Toast.LENGTH_SHORT).show();

                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

    }

    private void showSignUpDialog() {
        AlertDialog.Builder alertDialog = new AlertDialog.Builder(MainActivity.this);
        alertDialog.setTitle("Sign Up");
        alertDialog.setMessage("Kindly, fill the information!");
        LayoutInflater inflater= this.getLayoutInflater();
        View sign_up_layout= inflater.inflate(R.layout.sign_up_layout, null);
        edtNewUser=(MaterialEditText)sign_up_layout.findViewById(R.id.edtNewUserName);
        edtNewEmail=(MaterialEditText)sign_up_layout.findViewById(R.id.edtNewEmail);
        edtNewPassword=(MaterialEditText)sign_up_layout.findViewById(R.id.edtNewPassword);

        alertDialog.setView(sign_up_layout);
        alertDialog.setIcon(R.drawable.ic_account_circle_black_24dp);

        alertDialog.setNegativeButton("NO", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                dialogInterface.dismiss();

            }
        });

        alertDialog.setPositiveButton("YES", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                final User user= new User(edtNewUser.getText().toString(),
                        edtNewPassword.getText().toString(),
                        edtNewEmail.getText().toString());

                users.addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        if(dataSnapshot.child(user.getUserName()).exists())
                            Toast.makeText(MainActivity.this, "User already exists!", Toast.LENGTH_SHORT).show();
                        else {
                            users.child(user.getUserName())
                                    .setValue(user);
                            Toast.makeText(MainActivity.this, "User Registration Successful!", Toast.LENGTH_SHORT).show();
                        }

                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });
                dialogInterface.dismiss();
            }
        });
        alertDialog.show();
    }
}
`][1]

`package sonu.enigma.Model;

/**
 * Created by PAWAN on 01-10-2017.
 */

public class User {
    private String userName;
    private String password;
    private String email;
    public User(){

    }
    public User(String userName, String password, String email){
        this.userName=userName;
        this.password=password;
        this.email =email;


    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}
`


  [