using DodoSSH.Api.Features.Relay;
using Microsoft.AspNetCore.DataProtection;
using Microsoft.AspNetCore.DataProtection.KeyManagement;
using Microsoft.AspNetCore.DataProtection.Repositories;
using Microsoft.Extensions.Options;

namespace DodoSSH.Api.Setup;

/// <summary>The relay's services. See ADR 0004.</summary>
internal static class RelaySetup
{
    /// <summary>
    /// How much longer than the drain the host waits before it stops regardless.
    /// </summary>
    /// <remarks>
    /// Room for the close handshakes and the audit rows' final writes once the drain has run out, which
    /// is the part of a shutdown an operator would otherwise lose without noticing.
    /// </remarks>
    private static readonly TimeSpan ShutdownMargin = TimeSpan.FromSeconds(10);

    internal static IServiceCollection AddDodoRelay(this IServiceCollection services)
    {
        // Singletons: a session outlives the request that opened it, a protector is safe to share, and
        // the network seam holds no state.
        services.AddSingleton<RelayTicketCodec>();
        services.AddSingleton<RelaySessionRegistry>();
        services.AddSingleton<RelayAccessWatch>();
        services.AddSingleton<IRelayNetwork, SystemRelayNetwork>();

        // The application name isolates this deployment's payloads from any other ASP.NET application
        // sharing a key directory, and — unlike the default, which is derived from the content root —
        // is the same on every node, which is what lets any node verify any node's ticket.
        services.AddDataProtection().SetApplicationName("DodoSSH");

        services.AddOptions<KeyManagementOptions>()
            .Configure<IOptions<RelayOptions>, ILoggerFactory>((keys, relay, loggers) =>
            {
                if (relay.Value.KeyRingDirectory is { Length: > 0 } directory)
                {
                    keys.XmlRepository = new FileSystemXmlRepository(new DirectoryInfo(directory), loggers);
                }
            });

        // Longer than the drain, or the host would stop waiting for live sessions before the drain ADR 0004
        // promises them had run. Harmless with the relay off: nothing else holds a request open that long,
        // and the host stops as soon as the last request has.
        services.AddOptions<HostOptions>()
            .Configure<IOptions<RelayOptions>>((host, relay) =>
            {
                var wanted = relay.Value.DrainTimeout + ShutdownMargin;

                if (wanted > host.ShutdownTimeout)
                {
                    host.ShutdownTimeout = wanted;
                }
            });

        return services;
    }
}