OverviewModel.cs

enum Tab { Summary, Allocation, Transaction }
enum Range { All, YtD, MtD, D }
enum Role { RM, User }

class AssetManager {}
class Account {}

class OverviewModel 
{
	struct FetchRequest 
	{
		public FetchRequest()
		{
			Customer = null;
			Range = Range.All;
			Tab = Tab.Overview;
			AssetManager = null;
			Account = null;
		}

		Customer _customer;
		public Customer Customer 
		{
			get => _customer;
			set 
			{
				if (value != _customer)
				{
					_customer = value;
					AssetManager = null;
					Account = null;
				}
			}
		}

		public Range Range;

		public Tab Tab;

		AssetManager _assetManager;
		public AssetManager AssetManager
		{
			get => _assetManager;
			set
			{
				if (value != _assetManager)
				{
					if (_customer == null) throw new InvalidOperationException();
					_assetManager = value;
				}
			}
		}

		Account _account;
		public Account Account
		{
			get => _account;
			set 
			{
				if (value != _account)
				{
					if (AssetManager == null) throw new InvalidOperationException();
					_account = value;
				}
			}
		}
	}

	struct FetchResult 
	{
		public AssetManager[] Managers;
		public Account[] Accounts;
		public decimal? TotalReturn;
		public decimal? TotalValue;
		public decimal? TotalTransactions;
	}

	FetchRequest _loaded;
	FetchRequest _request;
	FetchResult _data;
	User _user;

	public OverviewModel()
	{
		LoadCommand = new AsyncCommand(Load)
		{
			SerializationPolicy = AsyncCommandSerializationPolicy.Cancel
		};
	}

	public IAsyncCommand LoadCommand { get; }

	private void Load(object arg, CancellationToken token)
	{
		switch (arg)
		{
			case Customer c:
				_request.Customer = c;
				break;
			case AssetManager m:
				_request.AssetManager = m;
				break;
			case Account a:
				_request.Account = a;
				break;
			case Tab t:
				_request.Tab = t;
				break;
			case Range r:
				_request.Range = r;
				break;
		}

		_data = await ProveoContext.SummaryService.Load(_request);

		_loaded = _request;
	}
}