using System;
using System.Net;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

namespace HikvisionAttendanceService;

/// <summary>Exponential backoff retries for transient HTTP / network failures.</summary>
internal static class UserSyncRetryHelper
{
    /// <summary>0-based attempt index: delays 1s, 2s, 4s, ... capped at 30s.</summary>
    public static int GetBackoffDelayMilliseconds(int zeroBasedAttemptIndex)
    {
        if (zeroBasedAttemptIndex < 0)
            zeroBasedAttemptIndex = 0;
        double seconds = Math.Pow(2, zeroBasedAttemptIndex);
        var ms = (int)(seconds * 1000);
        return Math.Min(ms, 30_000);
    }

    /// <summary>Returns true if the HTTP status may succeed on retry.</summary>
    public static bool IsTransientHttpStatus(HttpStatusCode code)
    {
        var n = (int)code;
        if (n == 408 || n == 429)
            return true;
        if (n >= 500 && n <= 599)
            return true;
        return false;
    }

    public static bool ShouldRetryException(Exception ex)
    {
        if (ex is HttpRequestException || ex is TaskCanceledException)
            return true;
        return false;
    }

    public static void SleepBackoff(int zeroBasedAttemptIndex, CancellationToken ct)
    {
        ct.ThrowIfCancellationRequested();
        var delay = GetBackoffDelayMilliseconds(zeroBasedAttemptIndex);
        Thread.Sleep(delay);
        ct.ThrowIfCancellationRequested();
    }

    public static async Task DelayBackoffAsync(int zeroBasedAttemptIndex, CancellationToken ct)
    {
        var delay = GetBackoffDelayMilliseconds(zeroBasedAttemptIndex);
        await Task.Delay(delay, ct).ConfigureAwait(false);
    }
}