namespace MoShiro.Agent;

/// <summary>Reconnect cadence for the control connection of a single dialer-to-listener path: 1, 2, 4, 8, 16, then five 32-second waits, then once per minute.</summary>
public sealed class ControlBackoff
{
    private static readonly TimeSpan[] s_delays =
    [
        TimeSpan.FromSeconds(1),
        TimeSpan.FromSeconds(2),
        TimeSpan.FromSeconds(4),
        TimeSpan.FromSeconds(8),
        TimeSpan.FromSeconds(16),
        TimeSpan.FromSeconds(32),
        TimeSpan.FromSeconds(32),
        TimeSpan.FromSeconds(32),
        TimeSpan.FromSeconds(32),
        TimeSpan.FromSeconds(32),
    ];

    private const int MaxMinutes = 10;

    private int _attempt;

    public int Attempts => Volatile.Read(ref _attempt);

    public TimeSpan Next()
    {
        int attempt = Interlocked.Increment(ref _attempt) - 1;
        if (attempt < s_delays.Length)
        {
            return s_delays[attempt];
        }

        // 表走完还连不上（对端关了、这台机器没有这条路由）：一分钟起继续翻倍，最长十分钟，不再每分钟白白重试一次、写三条日志
        return TimeSpan.FromMinutes(Math.Min(MaxMinutes, 1 << Math.Min(attempt - s_delays.Length, 4)));
    }

    public void Reset() => Interlocked.Exchange(ref _attempt, 0);
}