using System.Text.Json;
using Fleet.Core;
using Fleet.Hosting;
using MoShiro.Protocol;

namespace MoShiro.Agent;

/// <summary>
/// 本节点要拨的监听节点列表：由面板作为期望状态（<c>dial_targets</c>）直接下发；面板连不上时用上一次保存的 <c>dial_targets.json</c>。
/// 列表变化时用 <see cref="ConfigStore"/> 写回 <c>agents.json</c>（这是配置，不是测量数据；只在变化时写，保护路由器的闪存）。
/// </summary>
public sealed class DialDirectory
{
    public const string FileName = "dial_targets.json";

    private readonly object _gate = new();
    private readonly ConfigStore _store;
    private readonly INodeLog _log;
    private readonly TrustAnchor _trust;
    private List<DialEndpoint> _targets = [];
    private long _version;

    public DialDirectory(ConfigStore store, string configDirectory, INodeLog log, TrustAnchor? trust = null)
    {
        _trust = trust ?? TrustAnchor.None;
        _store = store;
        _log = log;
        string cache = Path.Combine(configDirectory, FileName);
        if (File.Exists(cache))
        {
            try
            {
                DialCache saved = NodeConfig.Load(cache, AgentConfigContext.Default.DialCache);
                _targets = saved.Targets;
                _version = saved.Version;
            }
            catch (Exception ex) when (ex is IOException or InvalidDataException or JsonException or InvalidOperationException)
            {
                _log.Warn("dial_targets.json is unreadable, waiting for the panel", ("err", ex.Message));
            }
        }
    }

    /// <summary>列表变化（调和连接）。</summary>
    public event Action? Changed;

    public long Version
    {
        get
        {
            lock (_gate)
            {
                return _version;
            }
        }
    }

    public IReadOnlyList<DialEndpoint> Targets
    {
        get
        {
            lock (_gate)
            {
                return [.. _targets];
            }
        }
    }

    /// <summary>应用面板下发的列表。版本不比当前新的忽略（乱序到达的旧推送）。</summary>
    public void Apply(DialTargets result)
    {
        var next = new List<DialEndpoint>();
        _trust.Update(result.TrustChain);
        foreach (DialTarget target in result.Targets)
        {
            if (!string.IsNullOrWhiteSpace(target.Host))
            {
                next.Add(new DialEndpoint { NodeId = target.NodeId.Value, Host = target.Host, TcpPort = target.TcpPort, QuicPorts = [.. target.QuicPorts], PublicKey = target.PublicKey });
            }

            if (!string.IsNullOrWhiteSpace(target.Ipv6Host))
            {
                next.Add(new DialEndpoint { NodeId = target.NodeId.Value, Host = target.Ipv6Host, TcpPort = target.TcpPort, QuicPorts = [.. target.QuicPorts], PublicKey = target.PublicKey, IpVersion = IpVersions.V6 });
            }
        }

        lock (_gate)
        {
            if (result.Version < _version || (result.Version == _version && Same(next, _targets)))
            {
                return;
            }

            _version = result.Version;
            _targets = next;
        }

        try
        {
            _store.Write(FileName, JsonSerializer.SerializeToUtf8Bytes(new DialCache { Version = result.Version, Targets = next }, AgentConfigContext.Default.DialCache));
        }
        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
        {
            _log.Warn("could not save dial_targets.json", ("err", ex.Message));
        }

        _log.Info("dial targets updated", ("version", result.Version), ("targets", next.Count));
        Changed?.Invoke();
    }

    private static bool Same(List<DialEndpoint> a, List<DialEndpoint> b) =>
        a.Count == b.Count && a.Zip(b).All(p => Equal(p.First, p.Second));

    public static bool Equal(DialEndpoint a, DialEndpoint b) =>
        a.NodeId == b.NodeId && a.IpVersion == b.IpVersion && a.Host == b.Host && a.TcpPort == b.TcpPort && a.QuicPorts.SequenceEqual(b.QuicPorts) && a.PublicKey == b.PublicKey;
}