Billing/Billing.Shared/Views/AccountPage.xaml.cs

using System.Collections.Generic;
using System.Linq;
using Billing.Models;
using Billing.UI;
using Xamarin.Forms;

namespace Billing.Views
{
    public partial class AccountPage : BillingPage
    {
        private static readonly BindableProperty BalanceProperty = BindableProperty.Create(nameof(Balance), typeof(decimal), typeof(AccountPage));
        private static readonly BindableProperty AssetProperty = BindableProperty.Create(nameof(Asset), typeof(decimal), typeof(AccountPage));
        private static readonly BindableProperty LiabilityProperty = BindableProperty.Create(nameof(Liability), typeof(decimal), typeof(AccountPage));
        private static readonly BindableProperty AccountsProperty = BindableProperty.Create(nameof(Accounts), typeof(List<AccountGrouping>), typeof(AccountPage));

        public decimal Balance => (decimal)GetValue(BalanceProperty);
        public decimal Asset => (decimal)GetValue(AssetProperty);
        public decimal Liability => (decimal)GetValue(LiabilityProperty);
        public List<AccountGrouping> Accounts => (List<AccountGrouping>)GetValue(AccountsProperty);

        public Command AddAccount { get; }

        private readonly List<AccountGrouping> accounts;

        public AccountPage()
        {
            AddAccount = new Command(OnAddAccount);
            accounts = new List<AccountGrouping>();
            SetValue(AccountsProperty, accounts);

            InitializeComponent();
        }

        private async void OnAddAccount()
        {
            if (Tap.IsBusy)
            {
                return;
            }
            using (Tap.Start())
            {
                var page = new AddAccountPage();
                page.AccountChecked += AccountChecked;
                await Navigation.PushAsync(page);
            }
        }

        private void AccountChecked(object sender, AccountEventArgs e)
        {
            Helper.Debug(e.Account.ToString());
            var group = accounts.FirstOrDefault(g => g.Key == e.Account.Category);
            if (group == null)
            {
                group = new AccountGrouping(e.Account.Category)
                {
                    e.Account
                };
                accounts.Add(group);
            }
            else
            {
                group.Add(e.Account);
            }
            groupLayout.Refresh(accounts);
        }
    }

    public class AccountGrouping : List<Account>, IGrouping<AccountCategory, Account>
    {
        public AccountGrouping(AccountCategory key) : base() => Key = key;
        public AccountCategory Key { get; }
        public decimal Balance { get; set; }
    }
}