maraphon-app/src/Marathon.Application/UseCases/CompareStrategiesUseCase.cs

using Marathon.Application.Abstractions;
using Marathon.Application.Storage;
using Marathon.Domain.Backtesting;
using Microsoft.Extensions.Logging;

namespace Marathon.Application.UseCases;

/// <summary>One saved strategy preset paired with its backtest result over a shared window.</summary>
public sealed record StrategyComparison(Guid StrategyId, string Name, BacktestResult Result);

/// <summary>
/// Runs every saved strategy preset over the same anomaly window and returns their
/// backtest results side by side, so the user can see which staking configuration wins.
/// </summary>
/// <remarks>
/// Delegates to <see cref="RunBacktestUseCase"/> once per preset — the anomaly set is
/// re-loaded per run, which is fine for the handful of presets a user keeps. Keeping the
/// composition at the use-case level (rather than re-implementing candidate loading) means
/// the comparison stays bug-for-bug identical to a single backtest run.
/// </remarks>
public sealed class CompareStrategiesUseCase
{
    private readonly ISavedStrategyRepository _strategies;
    private readonly RunBacktestUseCase _backtest;
    private readonly ILogger<CompareStrategiesUseCase> _logger;

    public CompareStrategiesUseCase(
        ISavedStrategyRepository strategies,
        RunBacktestUseCase backtest,
        ILogger<CompareStrategiesUseCase> logger)
    {
        _strategies = strategies ?? throw new ArgumentNullException(nameof(strategies));
        _backtest = backtest ?? throw new ArgumentNullException(nameof(backtest));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    /// <summary>
    /// Backtests each saved preset over <paramref name="dateRange"/> (null = all graded
    /// anomalies). Returns one row per preset in saved (name-ascending) order; empty when
    /// the user has saved no strategies.
    /// </summary>
    public async Task<IReadOnlyList<StrategyComparison>> ExecuteAsync(
        DateRange? dateRange, CancellationToken ct = default)
    {
        var presets = await _strategies.ListAsync(ct).ConfigureAwait(false);
        if (presets.Count == 0)
            return Array.Empty<StrategyComparison>();

        var rows = new List<StrategyComparison>(presets.Count);
        foreach (var preset in presets)
        {
            ct.ThrowIfCancellationRequested();
            var result = await _backtest.ExecuteAsync(preset.Strategy, dateRange, ct).ConfigureAwait(false);
            rows.Add(new StrategyComparison(preset.Id, preset.Name, result));
        }

        _logger.LogInformation("CompareStrategiesUseCase: compared {Count} preset(s)", rows.Count);
        return rows;
    }
}