SoftTraderBackend/ServiceHandler/TrailingPriceEvaluator.cs

using System.Text.Json;
using Backend.DatabaseHandler;
using Backend.Interface;

namespace Backend.ServiceHandler;

public sealed class TrailingPriceEvaluator : IAlertEvaluator
{
	public string AlertType => "trailing_price";

	public Task<AlertEvaluation> EvaluateAsync(AlertRecord alert, MarketDataService marketData)
	{
		var parameters = JsonSerializer.Deserialize<TrailingPriceParameters>(alert.Parameters)
			?? throw new InvalidOperationException($"Invalid parameters for alert {alert.Id}");

		var snapshot = marketData.GetLiveQuote(alert.Symbol);

		if (!snapshot.LastPrice.HasValue)
		{
			return Task.FromResult(new AlertEvaluation { Triggered = false });
		}

		double price = snapshot.LastPrice.Value;
		var state = JsonSerializer.Deserialize<TrailingPriceState>(alert.LastState)
			?? new TrailingPriceState();

		bool triggered;

		if (parameters.Direction.Equals("bullish", StringComparison.OrdinalIgnoreCase))
		{
			if (!state.PeakPrice.HasValue || price > state.PeakPrice.Value)
				state.PeakPrice = price;

			double dropPercent = (state.PeakPrice.Value - price) / state.PeakPrice.Value * 100.0;
			triggered = dropPercent >= parameters.TrailPercent;
		}
		else
		{
			if (!state.TroughPrice.HasValue || price < state.TroughPrice.Value)
				state.TroughPrice = price;

			double risePercent = state.TroughPrice.Value == 0
				? 0
				: (price - state.TroughPrice.Value) / state.TroughPrice.Value * 100.0;
			triggered = risePercent >= parameters.TrailPercent;
		}

		string updatedState = JsonSerializer.Serialize(new
		{
			peakPrice = state.PeakPrice,
			troughPrice = state.TroughPrice,
			lastPrice = price
		});

		return Task.FromResult(new AlertEvaluation
		{
			Triggered = triggered,
			UpdatedLastState = updatedState
		});
	}

	private sealed class TrailingPriceParameters
	{
		public string Direction { get; set; } = string.Empty;
		public double TrailPercent { get; set; }
	}

	private sealed class TrailingPriceState
	{
		public double? PeakPrice { get; set; }
		public double? TroughPrice { get; set; }
	}
}