Pre-calculate Privacy Suggestions for changeless transaction

[Szpoti]

Alternate of #11496

This PR removes redundant PrivacySuggestionsResult class, and pre-calculates the PrivacyWarnings and PrivacySuggestions, so we don't iterate through the list twice unnecessarily, calling VerifyChangeAsync both times. Instead use OfType on the already calculated PrivacyItems.

[molnard]

tACK, just a nit.

[molnard]

@adamPetho pls check and merge if 👌

[soosr]

This PR reintroduces #11031

[adamPetho]

I have a rather ugly solution to not introduce back that issue. #11512 (review)

PrivacySuggestionsModel.cs

public async IAsyncEnumerable<PrivacyItem> BuildPrivacySuggestionsAsync(TransactionInfo info, BuildTransactionResult transactionResult, [EnumeratorCancellation] CancellationToken cancellationToken)
{
	using CancellationTokenSource singleRunCts = new();

	lock (_lock)
	{
		_singleRunCancellationTokenSource?.Cancel();
		_linkedCancellationTokenSource?.Cancel();
		_singleRunCancellationTokenSource = singleRunCts;
		CancellationTokenSource timeoutCts = new(TimeSpan.FromSeconds(15));
		CancellationTokenSource linkedCts = CancellationTokenSource.CreateLinkedTokenSource(timeoutCts.Token, singleRunCts.Token, cancellationToken);
		_linkedCancellationTokenSource = linkedCts;
	}

	using (await _asyncLock.LockAsync(CancellationToken.None))
	{
		foreach (var item in VerifyLabels(info, transactionResult))
		{
			yield return item;
		}

		foreach (var item in VerifyPrivacyLevel(info, transactionResult))
		{
			yield return item;
		}

		foreach (var item in VerifyConsolidation(transactionResult))
		{
			yield return item;
		}

		foreach (var item in VerifyUnconfirmedInputs(transactionResult))
		{
			yield return item;
		}

		foreach (var item in VerifyCoinjoiningInputs(transactionResult))
		{
			yield return item;
		}

		var changeItems = new List<PrivacyItem>();

		try
		{
			await foreach (var item in VerifyChangeAsync(info, transactionResult, _linkedCancellationTokenSource).ConfigureAwait(false))
			{
				changeItems.Add(item); // Can't yield return in try-catch block
			}
		}
		catch (OperationCanceledException)
		{
			Logger.LogTrace("Operation was cancelled.");
		}
		finally
		{
			lock (_lock)
			{
				_singleRunCancellationTokenSource = null;
			}
		}

		foreach (var item in changeItems)
		{
			yield return item;
		}
	}
}

We can even Concat these foreaches together to have only one foreach.
The Task.Delays are obviously for testing purpose only!!!

Then we can have this inside PrivacySuggestionsFlyoutViewModel.cs

await foreach(var result in _privacySuggestionsModel.BuildPrivacySuggestionsAsync(info, transaction, cancellationToken))
{
	if (result is PrivacyWarning warning)
	{
		Warnings.Add(warning);
	}
	if (result is PrivacySuggestion suggestion)
	{
		Suggestions.Add(suggestion);
	}
}

WDYT @soosr ? I tested it and looks to work well. If it's acceptable, then I can push my changes.

[soosr]

We can even Concat these foreaches together to have only one foreach.
The Task.Delays are obviously for testing purpose only!!!

Please make a final version that you show

[Szpoti]

Check now pls and address

[Szpoti]

I removed this because it's irrelevant, the excpetion was never catched because it was always caught inside.
https://github.com/zkSNACKs/WalletWasabi/blob/33233a26c839aa06771847c6dd8099e61f7df45b/WalletWasabi/Blockchain/TransactionBuilding/ChangelessTransactionCoinSelector.cs#L91-L98

[molnard]

tACK

[adamPetho]

LGTM

[adamPetho]

Note for the future:
if one of these is a heavy operation, it will block all the other results.
This is not the case at the moment.

[soosr]

ACK