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

namespace Backend.ServiceHandler;

public sealed class PriceSpikeEvaluator : IAlertEvaluator
{
	public string AlertType => "price_spike";

	public Task<AlertEvaluation> EvaluateAsync(AlertRecord alert, MarketDataService marketData)
	{
		var parameters = JsonSerializer.Deserialize<PriceSpikeParameters>(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 now = DateTime.UtcNow;

		var state = JsonSerializer.Deserialize<PriceSpikeState>(alert.LastState)
			?? new PriceSpikeState();

		state.Prices ??= new List<PricePoint>();
		state.Prices.Add(new PricePoint { Price = price, Timestamp = now });

		var cutoff = now.AddMinutes(-parameters.WindowMinutes);
		state.Prices.RemoveAll(p => p.Timestamp < cutoff);

		bool triggered = false;
		if (state.Prices.Count >= 2)
		{
			double oldest = state.Prices[0].Price;
			if (oldest != 0)
			{
				double change = Math.Abs((price - oldest) / oldest * 100.0);
				triggered = change >= parameters.PercentChange;
			}
		}

		string updatedState = JsonSerializer.Serialize(state);

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

	private sealed class PriceSpikeParameters
	{
		public double PercentChange { get; set; }
		public int WindowMinutes { get; set; } = 15;
	}

	private sealed class PriceSpikeState
	{
		public List<PricePoint>? Prices { get; set; }
	}

	private sealed class PricePoint
	{
		public double Price { get; set; }
		public DateTime Timestamp { get; set; }
	}
}