silver-octo-spoon/wolverine/a-frame-architecture/FinancialApi.Application/Handlers/TransferFundsHandler.cs

using FinancialApi.Application.Commands;
using FinancialApi.Application.Events;
using FinancialApi.Application.Queries;
using FinancialApi.Domain;
using Wolverine.Persistence;

namespace FinancialApi.Application.Handlers;

public static class TransferFundsHandler
{
    public static async Task<TransferPair?> LoadAsync(TransferFundsCommand cmd, IAccountQuery query,
        TimeProvider timeProvider)
    {
        var source = await query.FindByIdAsync(cmd.SourceAccountId);
        var dest = await query.FindByIdAsync(cmd.DestinationAccountId);

        if (source == null || dest == null) return null;

        return new TransferPair(source, dest, timeProvider.GetUtcNow());
    }

    public static (
        IStorageAction<Account> SourceWrite,
        IStorageAction<Account> DestWrite,
        IStorageAction<JournalEntry> JournalWrite,
        FundsTransferredEvent Event
        ) Handle(TransferFundsCommand cmd, TransferPair pair)
    {
        var updatedSource = pair.Source.Debit(cmd.Amount);
        var updatedDest = pair.Destination.Credit(cmd.Amount);

        var lines = new List<JournalLine>
        {
            new(pair.Source.Id, cmd.Amount, EntryType.Debit),
            new(pair.Destination.Id, cmd.Amount, EntryType.Credit)
        };

        var journalEntry =
            BalancedJournal.Create(Guid.NewGuid(),
                $"Transfer: {cmd.Amount} from {cmd.SourceAccountId} to {cmd.DestinationAccountId}",
                pair.TimeStamp, lines);

        var @event = new FundsTransferredEvent(cmd.SourceAccountId, cmd.DestinationAccountId, cmd.Amount);

        return (
            Storage.Update(updatedSource),
            Storage.Update(updatedDest),
            Storage.Insert(journalEntry.Entry),
            @event
        );
    }
}