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

using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
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 = new();
        private bool initialized;

        public AccountPage()
        {
            AddAccount = new Command(OnAddAccount);
            SetValue(AccountsProperty, accounts);

            InitializeComponent();
        }

        protected override void OnAppearing()
        {
            if (!initialized)
            {
                initialized = true;
                accounts.Clear();
                foreach (var account in App.Accounts)
                {
                    AddToAccountGroup(account);
                }
            }
            groupLayout.Refresh(accounts);
        }

        private void AddToAccountGroup(Account account)
        {
            int maxId;
            if (accounts.Count > 0)
            {
                maxId = accounts.Max(g => g.Max(a => a.Id));
            }
            else
            {
                maxId = -1;
            }
            account.Id = maxId + 1;

            var group = accounts.FirstOrDefault(g => g.Key == account.Category);
            if (group == null)
            {
                group = new AccountGrouping(account.Category, account.Balance) { account };
                accounts.Add(group);
            }
            else
            {
                group.Add(account);
                group.Balance += account.Balance;
            }
        }

        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)
        {
            App.Accounts.Add(e.Account);
            AddToAccountGroup(e.Account);
            groupLayout.Refresh(accounts);

            Task.Run(App.WriteAccounts);
        }
    }

    public class AccountGrouping : List<Account>, IGrouping<AccountCategory, Account>
    {
        public AccountCategory Key { get; }
        public decimal Balance { get; set; }

        public AccountGrouping(AccountCategory key, decimal balance) : base()
        {
            Key = key;
            Balance = balance;
        }
    }
}