using Firebase.Database;
using Firebase.Database.Query;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using XF_CrudFirebase.Models;

namespace XF_CrudFirebase.Services
{
    public class FirebaseService
    {
        FirebaseClient firebase = 
            new FirebaseClient("https://xamarinfirestoreapp.firebaseio.com/");

        public async Task AddContato(int contatoId, string nome, string email)
        {
            await firebase
              .Child("Contatos")
                .PostAsync(new Contato()
                   { ContatoId = contatoId, Nome = nome, Email= email });
        }

        public async Task<List<Contato>> GetContatos()
        {
            return (await firebase
              .Child("Contatos")
              .OnceAsync<Contato>()).Select(item => new Contato
              {
                  Nome = item.Object.Nome,
                  Email = item.Object.Email,
                  ContatoId = item.Object.ContatoId
              }).ToList();
        }

        public async Task<Contato> GetContato(int ContatoId)
        {
            var contatos = await GetContatos();

            await firebase
              .Child("Contatos")
                .OnceAsync<Contato>();

            return contatos.Where(a => a.ContatoId == ContatoId)
                .FirstOrDefault();
        }

        public async Task UpdateContato(int ContatoId, string nome, string email)
        {
            var toUpdateContato = (await firebase
              .Child("Contatos")
                .OnceAsync<Contato>())
                   .Where(a => a.Object.ContatoId == ContatoId).FirstOrDefault();

            await firebase
              .Child("Contatos")
                .Child(toUpdateContato.Key)
                  .PutAsync(new Contato() 
                        { ContatoId = ContatoId, Nome = nome, Email= email });
        }

        public async Task DeleteContato(int ContatoId)
        {
            var toDeleteContato = (await firebase
              .Child("Contatos")
              .OnceAsync<Contato>())
                .Where(a => a.Object.ContatoId == ContatoId).FirstOrDefault();

            await firebase.Child("Contatos")
                    .Child(toDeleteContato.Key)
                        .DeleteAsync();
        }
    }
}

using System;
using System.ComponentModel;
using System.Threading.Tasks;
using Xamarin.Forms;
using XF_CrudFirebase.Services;

namespace XF_CrudFirebase
{
    [DesignTimeVisible(false)]
    public partial class MainPage : ContentPage
    {
        FirebaseService fbService = new FirebaseService();

        public MainPage()
        {
            InitializeComponent();
        }

        protected async override void OnAppearing()
        {
            base.OnAppearing();
            await ExibeContatos();
        }

        private async void BtnIncluir_Clicked(object sender, System.EventArgs e)
        {
            await fbService.AddContato(Convert.ToInt32(txtId.Text), txtNome.Text, txtEmail.Text);
            txtId.Text = string.Empty;
            txtNome.Text = string.Empty;
            txtEmail.Text = string.Empty;

            await DisplayAlert("Success", "Contato incluído com sucesso", "OK");
            await ExibeContatos();
        }

        private async void BtnExibir_Clicked(object sender, System.EventArgs e)
        {
            var contato = await fbService.GetContato(Convert.ToInt32(txtId.Text));
            if (contato != null)
            {
                txtId.Text = contato.ContatoId.ToString();
                txtNome.Text = contato.Nome;
                txtEmail.Text = contato.Email;
            }
            else
            {
                await DisplayAlert("Success", "Não existe contato com esse ID", "OK");
            }
        }

        private async void BtnDeletar_Clicked(object sender, System.EventArgs e)
        {
            await fbService.DeleteContato(Convert.ToInt32(txtId.Text));
            txtId.Text = string.Empty;
            await DisplayAlert("Success", "Contato deletado com sucesso", "OK");
            await ExibeContatos();
        }

        private async void BtnAtualizar_Clicked(object sender, System.EventArgs e)
        {
            await fbService.UpdateContato(Convert.ToInt32(txtId.Text), txtNome.Text, txtEmail.Text);

            txtId.Text = string.Empty;
            txtNome.Text = string.Empty;
            txtEmail.Text = string.Empty;

            await DisplayAlert("Success", "Contato atualizado com sucesso", "OK");
            await ExibeContatos();
        }

        private async Task ExibeContatos()
        {
            var contatos = await fbService.GetContatos();
            listaContatos.ItemsSource = contatos;
        }
    }
}