using StellaOps.Zastava.Observer.Configuration;

namespace StellaOps.Zastava.Observer.Worker;

internal static class BackoffCalculator
{
    public static TimeSpan ComputeDelay(ObserverBackoffOptions options, int attempt, Random random)
    {
        ArgumentNullException.ThrowIfNull(options);
        ArgumentNullException.ThrowIfNull(random);

        var cappedAttempt = Math.Max(1, attempt);
        var baseDelayMs = options.Initial.TotalMilliseconds * Math.Pow(2, cappedAttempt - 1);
        baseDelayMs = Math.Min(baseDelayMs, options.Max.TotalMilliseconds);

        if (options.JitterRatio <= 0)
        {
            return TimeSpan.FromMilliseconds(baseDelayMs);
        }

        var jitterWindow = baseDelayMs * options.JitterRatio;
        var jitter = (random.NextDouble() * 2 - 1) * jitterWindow;
        var jittered = Math.Clamp(baseDelayMs + jitter, options.Initial.TotalMilliseconds, options.Max.TotalMilliseconds);
        return TimeSpan.FromMilliseconds(jittered);
    }
}