using System.Collections.Concurrent;
using System.Diagnostics.CodeAnalysis;
using System.Text.Json;
using System.Text.RegularExpressions;
using Fleet.Core;
using MoShiro.Protocol;

namespace MoShiro.Backend.Application;

/// <summary>面板记下的、CI 签名的发布清单（只留每个组件最新的一份）。<c>Manifest</c> 是签名对象的原始文本，面板一个字节也不改。</summary>
public sealed record ReleaseOffer(string Component, long Seq, string Tag, string Version, string Digest, string Manifest, string Signature, string Channel = "release");

/// <summary>
/// 发布清单的分发：CI 签名之后推给面板，面板存下来并原样转给在线的 Agent、Probe（节点连上时再补发一次）。
/// <b>面板不验签、也不决定拉什么</b>：节点宿主机上的更新器用本机的发布公钥验签，并且只认本机配置的镜像仓库；
/// 所以面板即使被攻破，也推不出一个能被装上的假镜像。面板只负责「通知」和「请求更新」，状态由节点随心跳报回来。
/// </summary>
public sealed partial class ReleaseService : IDisposable
{
    public const int MaxManifestBytes = 4096;
    public const int MaxSignatureBytes = 512;
    public const string BackendComponent = "backend";
    private static readonly string[] s_components = [NodeKinds.Agent, NodeKinds.Probe, BackendComponent];

    private readonly ISettingsStore _settings;
    private readonly IAgentGateway _gateway;
    private readonly IBackendUpdateFiles _backendFiles;
    private readonly BackendOptions _options;
    private readonly ConcurrentDictionary<string, UpdateStatus> _status = new();

    public ReleaseService(ISettingsStore settings, IAgentGateway gateway, IBackendUpdateFiles backendFiles, BackendOptions options)
    {
        _settings = settings;
        _gateway = gateway;
        _backendFiles = backendFiles;
        _options = options;
    }

    internal SemaphoreSlim BackendGate { get; } = new(1, 1);

    public void Dispose() => BackendGate.Dispose();

    /// <summary>登记一份新清单并推给在线的同类节点。只要格式对、<c>seq</c> 比现有的新就收下（签名由节点验证）。</summary>
    public async ValueTask<Result<ReleaseOffer>> PublishAsync(string manifest, string signature, CancellationToken ct)
    {
        if (!TryParse(manifest, signature, out ReleaseOffer? offer, out string? problem))
        {
            return ValidationError.Fail<ReleaseOffer>("manifest", problem);
        }

        await BackendGate.WaitAsync(ct);
        try
        {
            bool backend = offer.Component == BackendComponent;
            ReleaseOffer? current = backend ? await GetBackendAsync(offer.Channel, ct) : await GetAsync(offer.Component, ct);
            if (current is not null && offer.Seq <= current.Seq)
            {
                return Result<ReleaseOffer>.Fail(MoShiroErrors.NameConflict, $"a release with seq {current.Seq} or newer is already registered");
            }

            string componentKey = backend ? BackendComponent + "." + offer.Channel : offer.Component;
            await _settings.SetAsync(Key(componentKey, "manifest"), offer.Manifest, ct);
            await _settings.SetAsync(Key(componentKey, "signature"), offer.Signature, ct);
            if (backend)
            {
                if (offer.Channel == BackendUpdates.ChannelOf(_options))
                {
                    await _backendFiles.WriteOfferAsync(offer.Manifest, offer.Signature, ct);
                }
            }
            else
            {
                foreach (NodeId node in OnlineOf(offer.Component))
                {
                    await _gateway.NotifyUpdateOfferAsync(node, offer.Manifest, offer.Signature, ct);
                }
            }

            return Result<ReleaseOffer>.Ok(offer);
        }
        finally
        {
            BackendGate.Release();
        }
    }

    public async ValueTask<ReleaseOffer?> GetAsync(string component, CancellationToken ct)
    {
        string? manifest = await _settings.GetAsync(Key(component, "manifest"), ct);
        string? signature = await _settings.GetAsync(Key(component, "signature"), ct);
        return manifest is not null && signature is not null && TryParse(manifest, signature, out ReleaseOffer? offer, out _) && offer.Component == component ? offer : null;
    }

    public async ValueTask<IReadOnlyList<ReleaseOffer>> ListAsync(CancellationToken ct)
    {
        var list = new List<ReleaseOffer>();
        foreach (string component in s_components)
        {
            ReleaseOffer? offer = component == BackendComponent ? await GetBackendAsync(BackendUpdates.ChannelOf(_options), ct) : await GetAsync(component, ct);
            if (offer is not null)
            {
                list.Add(offer);
            }
        }

        return list;
    }

    public async ValueTask<ReleaseOffer?> GetBackendAsync(string channel, CancellationToken ct)
    {
        string key = BackendComponent + "." + channel;
        string? manifest = await _settings.GetAsync(Key(key, "manifest"), ct);
        string? signature = await _settings.GetAsync(Key(key, "signature"), ct);
        return manifest is not null && signature is not null && TryParse(manifest, signature, out ReleaseOffer? offer, out _)
            && offer.Component == BackendComponent && offer.Channel == channel ? offer : null;
    }

    /// <summary>节点刚连上：把它这个组件最新的清单补发一份（节点离线时发布的也不会错过）。</summary>
    public async ValueTask OfferToNodeAsync(NodeId node, CancellationToken ct)
    {
        if (ComponentOf(node) is { } component && await GetAsync(component, ct) is { } offer)
        {
            await _gateway.NotifyUpdateOfferAsync(node, offer.Manifest, offer.Signature, ct);
        }
    }

    /// <summary>请求某个节点更新到它手里那份（验过签的）清单。节点不在线返回 false。</summary>
    public ValueTask<bool> RequestUpdateAsync(NodeId node, CancellationToken ct) => _gateway.NotifyUpdateApplyAsync(node, ct);

    public void RecordStatus(NodeId node, UpdateStatus? status)
    {
        if (status is null)
        {
            _status.TryRemove(node.Value, out _);
        }
        else
        {
            _status[node.Value] = status;
        }
    }

    public UpdateStatus? StatusOf(NodeId node) => _status.TryGetValue(node.Value, out UpdateStatus? status) ? status : null;

    public void Forget(NodeId node) => _status.TryRemove(node.Value, out _);

    private IEnumerable<NodeId> OnlineOf(string component) => _gateway.OnlineNodes.Where(n => ComponentOf(n) == component);

    private static string? ComponentOf(NodeId node) =>
        node.Value.StartsWith(AgentIds.Prefix, StringComparison.Ordinal) ? NodeKinds.Agent
        : node.Value.StartsWith(ProbeId.Prefix, StringComparison.Ordinal) ? NodeKinds.Probe
        : null;

    private static string Key(string component, string part) => $"release.{component}.{part}";

    private static bool TryParse(string manifest, string signature, [NotNullWhen(true)] out ReleaseOffer? offer, [NotNullWhen(false)] out string? problem)
    {
        offer = null;
        problem = null;
        if (manifest.Length is 0 or > MaxManifestBytes || signature.Length is 0 or > MaxSignatureBytes || !Base64().IsMatch(signature))
        {
            problem = "manifest or signature has an unexpected size or encoding";
            return false;
        }

        try
        {
            using JsonDocument document = JsonDocument.Parse(manifest);
            JsonElement root = document.RootElement;
            string component = Text(root, "component");
            string digest = Text(root, "digest");
            string channel = Text(root, "channel");
            if (channel.Length == 0)
            {
                channel = "release"; // 老节点的清单没有 channel，保留原来的兼容性
            }

            if (root.ValueKind != JsonValueKind.Object || Array.IndexOf(s_components, component) < 0
                || channel is not ("dev" or "release")
                || !root.TryGetProperty("seq", out JsonElement seq) || !seq.TryGetInt64(out long seqValue) || seqValue <= 0
                || !Digest().IsMatch(digest) || Text(root, "image").Length is 0 or > 200)
            {
                problem = "manifest needs a known component, a positive seq, an image and a sha256 digest";
                return false;
            }

            offer = new ReleaseOffer(component, seqValue, Text(root, "tag"), Text(root, "version"), digest, manifest, signature, channel);
            return true;
        }
        catch (JsonException)
        {
            problem = "manifest is not valid JSON";
            return false;
        }
    }

    private static string Text(JsonElement root, string name) =>
        root.ValueKind == JsonValueKind.Object && root.TryGetProperty(name, out JsonElement value) && value.ValueKind == JsonValueKind.String ? value.GetString() ?? "" : "";

    [GeneratedRegex("^[A-Za-z0-9+/=]+$")]
    private static partial Regex Base64();

    [GeneratedRegex("^sha256:[0-9a-f]{64}$")]
    private static partial Regex Digest();
}