namespace MoShiro.Backend.Application;

/// <summary>
/// 提权窗口的种类（docs/access.md 第 4 节）：加节点（15 分钟）、吊销和删除（5 分钟）、改凭证（60 秒，用一次就没有）。
/// 窗口属于会话，不属于用户：换一台设备、一个浏览器就要重新触碰 passkey。
/// </summary>
public enum ElevationClass
{
    Enroll,
    Revoke,
    Credential,
}

public sealed record ElevationWindow(ElevationClass Class, long ExpiresAtMs);

public static class Elevation
{
    public static string IdOf(ElevationClass elevation) => elevation switch
    {
        ElevationClass.Enroll => "enroll",
        ElevationClass.Revoke => "revoke",
        _ => "credential",
    };

    public static bool TryParse(string? id, out ElevationClass elevation)
    {
        (bool ok, elevation) = id switch
        {
            "enroll" => (true, ElevationClass.Enroll),
            "revoke" => (true, ElevationClass.Revoke),
            "credential" => (true, ElevationClass.Credential),
            _ => (false, default),
        };
        return ok;
    }

    /// <summary>端点要求的能力需要哪一种窗口；不是信任类的能力返回 null。</summary>
    public static ElevationClass? For(string capability) => capability switch
    {
        Capability.FleetRevoke => ElevationClass.Revoke,
        Capability.AccountsManage => ElevationClass.Credential,
        _ => null,
    };
}

/// <summary>
/// 会话的提权窗口，只在内存里：重启之后需要重新触碰 passkey，这正是想要的。API key 不经过这里（它自己带着能力，创建时已经签过）。
/// </summary>
public sealed class ElevationService
{
    private readonly BackendOptions _options;
    private readonly TimeProvider _time;
    private readonly object _gate = new();
    private readonly Dictionary<string, Dictionary<ElevationClass, long>> _windows = [];

    public ElevationService(BackendOptions options, TimeProvider time)
    {
        _options = options;
        _time = time;
    }

    public TimeSpan LifetimeOf(ElevationClass elevation) => elevation switch
    {
        ElevationClass.Enroll => TimeSpan.FromMinutes(_options.ElevationEnrollMinutes),
        ElevationClass.Revoke => TimeSpan.FromMinutes(_options.ElevationRevokeMinutes),
        _ => TimeSpan.FromSeconds(_options.ElevationCredentialSeconds),
    };

    /// <summary>开窗口；已经有的窗口重新计时。返回到期时间。</summary>
    public long Grant(string sessionId, ElevationClass elevation)
    {
        long now = _time.GetUtcNow().ToUnixTimeMilliseconds();
        long expires = now + (long)LifetimeOf(elevation).TotalMilliseconds;
        lock (_gate)
        {
            Prune(now);
            if (!_windows.TryGetValue(sessionId, out Dictionary<ElevationClass, long>? own))
            {
                _windows[sessionId] = own = [];
            }

            own[elevation] = expires;
        }

        return expires;
    }

    /// <summary>窗口是否有效。<paramref name="consume"/> 且是凭证类：同时用掉（一次有效）。</summary>
    public bool Check(string sessionId, ElevationClass elevation, bool consume)
    {
        long now = _time.GetUtcNow().ToUnixTimeMilliseconds();
        lock (_gate)
        {
            if (!_windows.TryGetValue(sessionId, out Dictionary<ElevationClass, long>? own) || !own.TryGetValue(elevation, out long expires) || expires <= now)
            {
                return false;
            }

            if (consume && elevation == ElevationClass.Credential)
            {
                own.Remove(elevation);
            }

            return true;
        }
    }

    public IReadOnlyList<ElevationWindow> Active(string sessionId)
    {
        long now = _time.GetUtcNow().ToUnixTimeMilliseconds();
        lock (_gate)
        {
            return _windows.TryGetValue(sessionId, out Dictionary<ElevationClass, long>? own)
                ? [.. own.Where(w => w.Value > now).OrderBy(w => w.Key).Select(w => new ElevationWindow(w.Key, w.Value))]
                : [];
        }
    }

    /// <summary>主动结束全部窗口（点「结束」或退出登录）。</summary>
    public void End(string sessionId)
    {
        lock (_gate)
        {
            _windows.Remove(sessionId);
        }
    }

    private void Prune(long now)
    {
        foreach (string session in _windows.Where(p => p.Value.All(w => w.Value <= now)).Select(p => p.Key).ToList())
        {
            _windows.Remove(session);
        }
    }
}