using System;
using System.Collections.Generic;

namespace ytLive.Services;

/// <summary>
/// TASK 32·1: how many times to relaunch the push, and how long to wait between tries.
/// <para><b>Minimum waits, deliberately</b> (creator ruling 2026-11-05): YouTube is not generous about
/// holding a broadcast whose ingest has gone quiet, so every second spent not pushing is grace spent.
/// The first attempt is immediate — there is nothing to wait for when the socket has just died.</para>
/// <para>Pure so the schedule is asserted without waiting on it.</para>
/// </summary>
public sealed class StreamRetryPolicy
{
    /// <summary>Immediate, then +1 s, +2 s, +3 s — four attempts inside about six seconds.</summary>
    public static readonly StreamRetryPolicy Default = new(new[]
    {
        TimeSpan.Zero,
        TimeSpan.FromSeconds(1),
        TimeSpan.FromSeconds(2),
        TimeSpan.FromSeconds(3),
    });

    public IReadOnlyList<TimeSpan> Waits { get; }

    public StreamRetryPolicy(IReadOnlyList<TimeSpan> waits)
    {
        if (waits == null || waits.Count == 0)
            throw new ArgumentException("A retry policy needs at least one attempt.", nameof(waits));
        Waits = waits;
    }

    public int Attempts => Waits.Count;

    /// <summary>The wait BEFORE <paramref name="attemptIndex"/> (0-based).</summary>
    public TimeSpan WaitBefore(int attemptIndex)
        => attemptIndex < 0 || attemptIndex >= Waits.Count ? TimeSpan.Zero : Waits[attemptIndex];
}