###########################################
 Add food
###########################################
package com.example.valii.restaurantapp;

import android.content.Intent;
import android.media.Image;
import android.net.Uri;
import android.provider.ContactsContract;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.Toast;

import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.StorageReference;
import com.google.firebase.storage.UploadTask;

public class AddFood extends AppCompatActivity {

    private ImageButton foodImage;
    private static final int GALLREQ = 1;
    private EditText name,desc,price,gramaj;
    private Uri uri = null;
    private StorageReference storageReference = null;
    private DatabaseReference mRef;
    private FirebaseDatabase firebaseDatabase;


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

        name = (EditText) findViewById(R.id.itemName);
        desc = (EditText) findViewById(R.id.itemDesc);
        price = (EditText) findViewById(R.id.itemPrice);
        gramaj = (EditText) findViewById(R.id.itemGramaj);
        storageReference = FirebaseStorage.getInstance().getReference();
        mRef = FirebaseDatabase.getInstance().getReference("Item");
    }

    public void imageButtonClicked(View view){
        Intent galleryIntent = new Intent(Intent.ACTION_GET_CONTENT);

        galleryIntent.setType("image/*");
        startActivityForResult(galleryIntent,GALLREQ);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if(requestCode == GALLREQ && resultCode == RESULT_OK){
            uri = data.getData();
            foodImage = (ImageButton) findViewById(R.id.foodImageButton);
            foodImage.setImageURI(uri);
        }
    }

    public void addItemButtonClicked(View view){
        final String name_text = name.getText().toString().trim();
        final String desc_text = desc.getText().toString().trim();
        final String price_text = price.getText().toString().trim();
        final String gramaj_text = price.getText().toString().trim();

        if(!TextUtils.isEmpty(name_text) && !TextUtils.isEmpty(desc_text) && !TextUtils.isEmpty(price_text)){
            StorageReference filepath = storageReference.child(uri.getLastPathSegment());
            filepath.putFile(uri).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
                @Override
                public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
                    final Uri downloadurl = taskSnapshot.getDownloadUrl();
                    Toast.makeText(AddFood.this,"Item added successfully",Toast.LENGTH_LONG).show();
                    final DatabaseReference newPost = mRef.push();
                    newPost.child("name").setValue(name_text);
                    newPost.child("desc").setValue(desc_text);
                    newPost.child("price").setValue(price_text);
                    newPost.child("gramaj").setValue(gramaj_text);
                    newPost.child("image").setValue(downloadurl.toString());

                }
            });

        }
    }
}

############################################
Admin activity
############################################
package com.example.valii.restaurantapp;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;

public class AdminActivity extends AppCompatActivity {

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

    public void addFoodButtonClicked(View view){
        Intent addFoodIntent = new Intent(AdminActivity.this,AddFood.class);
        startActivity(addFoodIntent);
    }

    public void viewOrders(View view){
        startActivity(new Intent(AdminActivity.this,OpenOrders.class));
    }
}

#####################################
Login Activity
#####################################

package com.example.valii.restaurantapp;

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
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;

public class LoginActivity extends AppCompatActivity {

    private EditText userEmail, userPass;
    private String access;
    private FirebaseAuth mAuth;
    private DatabaseReference mDatabase;
    private String access0 ="0";
    private String access1 ="1";

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

        userEmail = (EditText) findViewById(R.id.userEmail);
        userPass = (EditText)findViewById(R.id.userPass);
        mAuth = FirebaseAuth.getInstance();
        mDatabase = FirebaseDatabase.getInstance().getReference().child("users");

    }

    public void signinButtonClicked(View view){
        String email = userEmail.getText().toString().trim();
        String pass = userPass.getText().toString().trim();

        if(!TextUtils.isEmpty(email) && !TextUtils.isEmpty(pass)){
            mAuth.signInWithEmailAndPassword(email,pass).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if(task.isSuccessful()){
                        checkAccess();
                        checkUserExists();
                    }
                    else{
                        Toast.makeText(LoginActivity.this,"Username or Password invalid!",Toast.LENGTH_LONG).show();
                    }
                }
            });
        }
        else{
            Toast.makeText(LoginActivity.this,"Fill in all the blanks!",Toast.LENGTH_LONG).show();
        }

    }

    public void checkAccess() {
        final String user_id = mAuth.getCurrentUser().getUid();
        mDatabase.child(user_id).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                access = (String) dataSnapshot.child("Access").getValue();
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }

    public void checkUserExists() {
        final String user_id = mAuth.getCurrentUser().getUid();
        mDatabase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.hasChild(user_id)) {
                    if (access.equals(access0)) {
                        Intent menuIntent = new Intent(LoginActivity.this, MenuActivity.class);
                        startActivity(menuIntent);
                    }
                    else if(access.equals(access1)){
                        Intent adminIntent = new Intent(LoginActivity.this, AdminActivity.class);
                        startActivity(adminIntent);
                    }
                    else{
                        Toast.makeText(LoginActivity.this,"Oops something went wrong!",Toast.LENGTH_LONG).show();
                    }
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }

    public void signupButtonClicked(View view) {
        Intent loginIntent = new Intent(LoginActivity.this,MainActivity.class);
        startActivity(loginIntent);
    }
}

######################################
Main activity
######################################
package com.example.valii.restaurantapp;

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextUtils;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

public class MainActivity extends AppCompatActivity {

    private EditText email,pass,pass2,phone;
    private String access;
    private DatabaseReference mDatabase;
    private FirebaseAuth mAuth;


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

        email = (EditText) findViewById(R.id.editEmail);
        pass = (EditText) findViewById(R.id.editPass);
        pass2 =(EditText) findViewById(R.id.editPass2);
        phone = (EditText) findViewById(R.id.editPhone);
        access = "0";
        mAuth = FirebaseAuth.getInstance();
        mDatabase = FirebaseDatabase.getInstance().getReference().child("users");

    }

    public void signupButtonClicked(View view){
        final String email_text = email.getText().toString().trim();
        String pass_text = pass.getText().toString().trim();
        String pass2_text = pass2.getText().toString().trim();
        final String phone_text = phone.getText().toString().trim();

        if(!TextUtils.isEmpty(email_text) && !TextUtils.isEmpty(pass_text) && !TextUtils.isEmpty(pass2_text)){
            if( pass_text.equals(pass2_text)) {
                mAuth.createUserWithEmailAndPassword(email_text, pass_text).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            String user_id = mAuth.getCurrentUser().getUid();
                            DatabaseReference current_user = mDatabase.child(user_id);
                            current_user.child("Name").setValue(email_text);
                            current_user.child("Access").setValue(access);
                            current_user.child("Phone").setValue(phone_text);

                            Intent login = new Intent(MainActivity.this, LoginActivity.class);
                            startActivity(login);
                        }
                        else{
                            Toast.makeText(MainActivity.this,"Email already in use!!",Toast.LENGTH_LONG).show();
                        }
                    }
                });
            }
            else{
                Toast.makeText(MainActivity.this,"Passwords do not match!",Toast.LENGTH_LONG).show();
            }
        }
        else{
            Toast.makeText(MainActivity.this,"Fill in all the blanks!",Toast.LENGTH_LONG).show();
        }
    }

    public void signinButtonClicked(View view){
        Intent loginIntent = new Intent(MainActivity.this,LoginActivity.class);
        startActivity(loginIntent);
    }
}

#######################################
Menu Acrivity
#######################################

package com.example.valii.restaurantapp;

import android.content.Context;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.text.method.SingleLineTransformationMethod;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;

import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.squareup.picasso.Picasso;

import org.w3c.dom.Text;

public class MenuActivity extends AppCompatActivity {

    private RecyclerView mFoodList;
    private DatabaseReference mDatabase;
    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;

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

        mFoodList = (RecyclerView) findViewById(R.id.foodList);
        mFoodList.setHasFixedSize(true);
        mFoodList.setLayoutManager(new LinearLayoutManager(this));
        mDatabase = FirebaseDatabase.getInstance().getReference().child("Item");

        mAuth = FirebaseAuth.getInstance();
        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                if(firebaseAuth.getCurrentUser() == null){
                    Intent loginIntent = new Intent(MenuActivity.this,MainActivity.class);
                    loginIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
                    startActivity(loginIntent);
                }
            }
        };
    }

    @Override
    protected void onStart() {
        super.onStart();
        mAuth.addAuthStateListener(mAuthListener);
        FirebaseRecyclerAdapter <Meniu, FoodViewHolder> FBRA = new FirebaseRecyclerAdapter<Meniu, FoodViewHolder>(
                Meniu.class,
                R.layout.singlemenuitem,
                FoodViewHolder.class,
                mDatabase
        ) {
            @Override
            protected void populateViewHolder(FoodViewHolder viewHolder, Meniu model, int position) {
                viewHolder.setName(model.getName());
                viewHolder.setPrice(model.getPrice());
                viewHolder.setDesc(model.getDesc());
                viewHolder.setImage(getApplicationContext(),model.getImage());

                final String food_key = getRef(position).getKey().toString();
                viewHolder.mView.setOnClickListener(new View.OnClickListener(){
                    @Override
                    public void onClick(View v){
                        Intent singleFoodActivity = new Intent(MenuActivity.this, SingleFoodActivity.class);
                        singleFoodActivity.putExtra("FoodId",food_key);
                        startActivity(singleFoodActivity);
                    }
                });
            }
        };
        mFoodList.setAdapter(FBRA);

    }

    public static class FoodViewHolder extends RecyclerView.ViewHolder{

        View mView;
        public FoodViewHolder(View itemView){
            super(itemView);
            mView = itemView;
        }

        public void setName(String name){
            TextView food_name = (TextView) mView.findViewById(R.id.foodName);
            food_name.setText(name);
        }

        public void setDesc(String desc){
            TextView food_desc = (TextView) mView.findViewById(R.id.foodDesc);
            food_desc.setText(desc);
        }

        public void setPrice(String price){
            TextView food_price = (TextView) mView.findViewById(R.id.foodPrice);
            food_price.setText(price);
        }

        public void setImage(Context ctx, String image){
            ImageView food_image = (ImageView) mView.findViewById(R.id.foodImage);
            Picasso.with(ctx).load(image).into(food_image);

        }
    }
}

###################################
Open Orders
###################################
package com.example.valii.restaurantapp;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.widget.TextView;

import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

public class OpenOrders extends AppCompatActivity {

    private RecyclerView mFoodList;
    private DatabaseReference mDatabase;

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

        mFoodList = (RecyclerView) findViewById(R.id.orderLayout);
        mFoodList.setHasFixedSize(true);
        mFoodList.setLayoutManager(new LinearLayoutManager(this));
        mDatabase = FirebaseDatabase.getInstance().getReference().child("Orders");
    }

    @Override
    protected void onStart() {
        super.onStart();
        FirebaseRecyclerAdapter <Order,OrderViewHolder> FRBA = new FirebaseRecyclerAdapter<Order, OrderViewHolder>(
                Order.class,
                R.layout.singleorderlayout,
                OrderViewHolder.class,
                mDatabase
        ) {
            @Override
            protected void populateViewHolder(OrderViewHolder viewHolder, Order model, int position) {
                viewHolder.setUserName(model.getUsername());
                viewHolder.setItemName(model.getItemname());
            }
        };
        mFoodList.setAdapter(FRBA);
    }

    public static class OrderViewHolder extends RecyclerView.ViewHolder{

        View orderView;
        public OrderViewHolder(View itemView) {
            super(itemView);
            orderView = itemView;
        }

        public void setUserName(String username){
            TextView username_content = (TextView) orderView.findViewById(R.id.orderUserName);
            username_content.setText(username);
        }

        public void setItemName(String itemname){
            TextView itemname_content = (TextView) orderView.findViewById(R.id.orderItemName);
            itemname_content.setText(itemname);
        }

    }

}

###################################
Single Food Activity
###################################
package com.example.valii.restaurantapp;

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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.squareup.picasso.Picasso;

public class SingleFoodActivity extends AppCompatActivity {

    private String food_key = null;
    private DatabaseReference mDatabase, userData;
    private TextView singleFoodTitle,singleFoodDesc,singleFoodPrice;
    private ImageView singleFoodImage;
    private Button orderButton;
    private FirebaseAuth mAuth;
    private FirebaseUser current_user;
    private DatabaseReference mRef;
    private String food_name,food_price,food_desc,food_image;


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

        food_key = getIntent().getExtras().getString("FoodId");
        mDatabase = FirebaseDatabase.getInstance().getReference().child("Item");

        singleFoodDesc = (TextView) findViewById(R.id.singleDesc);
        singleFoodTitle = (TextView) findViewById(R.id.singleTitle);
        singleFoodPrice = (TextView) findViewById(R.id.singlePrice);
        singleFoodImage = (ImageView) findViewById(R.id.singleImageView);

        mAuth = FirebaseAuth.getInstance();

        current_user = mAuth.getCurrentUser();
        userData = FirebaseDatabase.getInstance().getReference().child("users").child(current_user.getUid());
        mRef = FirebaseDatabase.getInstance().getReference().child("Orders");

        mDatabase.child(food_key).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                food_name = (String) dataSnapshot.child("name").getValue();
                food_price = (String) dataSnapshot.child("price").getValue();
                food_desc = (String) dataSnapshot.child("desc").getValue();
                food_image = (String) dataSnapshot.child("image").getValue();

                singleFoodTitle.setText(food_name);
                singleFoodDesc.setText(food_desc);
                singleFoodPrice.setText(food_price);
                Picasso.with(SingleFoodActivity.this).load(food_image).into(singleFoodImage);

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }

    public void orderItemClicked(View view){
        final DatabaseReference newOrder = mRef.push();
        userData.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                newOrder.child("itemname").setValue(food_name);
                newOrder.child("username").setValue(dataSnapshot.child("Name").getValue()).addOnCompleteListener(new OnCompleteListener<Void>() {
                    @Override
                    public void onComplete(@NonNull Task<Void> task) {
                        Toast.makeText(SingleFoodActivity.this,"Order placed!",Toast.LENGTH_LONG).show();
                        startActivity(new Intent(SingleFoodActivity.this,MenuActivity.class));
                    }
                });
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }
}

###################################################
XML - MainActivity
###################################################
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="@drawable/background"
    android:paddingBottom="16dp"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    android:paddingTop="16dp"
    tools:context="com.example.valii.restaurantapp.MainActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textAlignment="center"
        android:textColor="#ffffff"
        android:textSize="20dp"
        android:text="Sign Up"
        />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Enter email"
        android:textColor="#ffffff"
        android:id="@+id/editEmail"
        android:textColorHint="#ffffff"
        />



    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Enter password"
        android:inputType="textPassword"
        android:textColor="#ffffff"
        android:id="@+id/editPass"
        android:textColorHint="#ffffff"
        />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Repeat password"
        android:inputType="textPassword"
        android:textColor="#ffffff"
        android:id="@+id/editPass2"
        android:textColorHint="#ffffff"
        />
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Enter phone number"
        android:textColor="#ffffff"
        android:id="@+id/editPhone"
        android:textColorHint="#ffffff"
        />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Sign Up"
        android:onClick="signupButtonClicked"
        />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Already have an account?"
        android:textColor="#ffffff"
        android:layout_marginTop="150dp"
        />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Sign In"
        android:onClick="signinButtonClicked"
        />

</LinearLayout>