namespace AvParser.Core.Proxies.Selection;

/// <summary>
/// Holds one proxy until it fails.
/// </summary>
/// <remarks>
/// The default because it is the only strategy that keeps a site's session coherent: rotating on
/// every request changes the apparent client mid-session, which reliably triggers re-logins and
/// captchas on anything that tracks cookies.
/// </remarks>
public sealed class StickyProxySelection : IProxySelectionStrategy
{
    private ProxyEntry? _current;

    /// <inheritdoc />
    public ProxyRotation Kind => ProxyRotation.Sticky;

    /// <inheritdoc />
    public ProxyEntry? Pick(IReadOnlyList<ProxyEntry> candidates)
    {
        ArgumentNullException.ThrowIfNull(candidates);

        // Keep the current pick only while it is still among the available candidates: a refresh
        // or a quarantine may have taken it out from under us.
        if (_current is not null && candidates.Contains(_current))
        {
            return _current;
        }

        _current = candidates.Count > 0 ? candidates[0] : null;
        return _current;
    }

    /// <inheritdoc />
    public void Report(ProxyEntry entry, bool success)
    {
        if (!success && ReferenceEquals(entry, _current))
        {
            _current = null;
        }
    }

    /// <inheritdoc />
    public void Reset() => _current = null;
}