using System.Collections.Concurrent;

namespace MoShiro.Backend.Application;

/// <summary>节点的一个属主：它报上来的 passkey 凭证 id，以及面板上对应的 passkey 名称和账户（对不上任何已注册的 passkey 时为空）。</summary>
public sealed record NodeOwner(string CredentialId, string? PasskeyName, string? Username);

/// <summary>
/// 节点的属主：Agent 和 Probe 握手时报上来的、安装时固定在节点本地的 passkey 凭证 id。
/// <b>属主的强制在节点本地</b>（没有属主的节点不运行，见 <c>OwnerGuard</c>），面板这边只是顺着凭证 id 反查出它绑定在哪个账户的哪把 passkey 上——
/// 以后给节点更多的接口和操作（extension 会话、加密内容）时，据此判断谁有资格用。上报的只是自述，真正的授权由节点自己对 passkey 签名的校验把关。
/// 在内存里：节点每次连上来都会重新报。
/// </summary>
public sealed class NodeOwnerService
{
    private const int MaxOwners = 16;
    private const int MaxCredentialIdLength = 256;

    private readonly ConcurrentDictionary<string, string[]> _reported = new(StringComparer.Ordinal);
    private readonly IAuthStore _auth;

    public NodeOwnerService(IAuthStore auth)
    {
        _auth = auth;
    }

    public void Report(string nodeId, IReadOnlyList<string>? credentialIds)
    {
        string[] clean = credentialIds is null ? [] : [.. credentialIds.Where(id => id.Length is > 0 and <= MaxCredentialIdLength).Distinct(StringComparer.Ordinal).Take(MaxOwners)];
        if (clean.Length == 0)
        {
            _reported.TryRemove(nodeId, out _);
        }
        else
        {
            _reported[nodeId] = clean;
        }
    }

    public void Forget(string nodeId) => _reported.TryRemove(nodeId, out _);

    /// <summary>每个节点的属主（只含报过的节点）。</summary>
    public async ValueTask<IReadOnlyDictionary<string, IReadOnlyList<NodeOwner>>> ListAsync(CancellationToken ct)
    {
        var result = new Dictionary<string, IReadOnlyList<NodeOwner>>(StringComparer.Ordinal);
        var users = new Dictionary<string, string?>(StringComparer.Ordinal);
        foreach ((string nodeId, string[] ids) in _reported)
        {
            var owners = new List<NodeOwner>();
            foreach (string id in ids)
            {
                PasskeyRecord? passkey = await _auth.FindPasskeyAsync(id, ct);
                string? username = null;
                if (passkey is not null && !users.TryGetValue(passkey.UserId, out username))
                {
                    username = (await _auth.GetUserAsync(passkey.UserId, ct))?.Username;
                    users[passkey.UserId] = username;
                }

                owners.Add(new NodeOwner(id, passkey?.Name, username));
            }

            result[nodeId] = owners;
        }

        return result;
    }
}