using System.Text.Json;
using Fleet.Core;
using Fleet.Server;

namespace MoShiro.Backend.Application;

/// <summary>CI 发布公钥（PEM）：验节点握手时带来的签名清单。由 Api 层提供（它就是内嵌在程序里的那一把）。</summary>
public interface IReleaseKey
{
    string Pem { get; }
}

/// <summary>
/// 节点二进制的绑定：节点第一次握手成功的那一刻，把它正在运行的二进制的 SHA-256 和这个节点绑在一起；之后哈希对不上，就不让它继续运行。
/// <para>
/// 合法的升级：新哈希出现在一份 <b>CI 签名的清单</b>里（节点握手时带着宿主机更新器验过的清单，这里用内嵌的 CI 公钥再验一遍，
/// 所以不依赖面板有没有收到过这次发布），并且清单的 seq 不低于绑定时的——不许回退到更旧的版本。其余情况（文件被换掉、降级、没人签过的二进制、
/// 手工替换了二进制的非容器节点）都算不符；管理员确认过之后可以清除绑定，下一次握手重新绑定。
/// </para>
/// <para>
/// 边界：哈希是节点自己报的。一个被换进来、故意撒谎的恶意二进制可以照抄原来的哈希；这一层抓的是文件被换、版本被改、降级和起了不对的二进制。
/// 容器节点要堵住撒谎，需要宿主机更新器背书（容器之外），见 docs/access.md。
/// </para>
/// </summary>
public sealed class BinaryBindingService : IBinaryAttestor
{
    public const string Enforce = "enforce";
    public const string Warn = "warn";
    public const string Off = "off";

    private readonly INodeBindingStore _store;
    private readonly ISettingsStore _settings;
    private readonly IReleaseKey _key;
    private readonly BackendOptions _options;
    private readonly TimeProvider _time;

    public BinaryBindingService(INodeBindingStore store, ISettingsStore settings, IReleaseKey key, BackendOptions options, TimeProvider time)
    {
        _settings = settings;
        _store = store;
        _key = key;
        _options = options;
        _time = time;
    }

    public ValueTask<IReadOnlyList<NodeBinding>> ListAsync(CancellationToken ct) => _store.ListAsync(ct);

    /// <summary>管理员确认新的二进制是自己要的（比如手工升级了非容器节点）：清除绑定，下一次握手重新绑定。</summary>
    public ValueTask<bool> ClearAsync(string nodeId, CancellationToken ct) => _store.DeleteAsync(nodeId, ct);

    /// <summary>节点删除之后顺手清掉它的绑定。</summary>
    public async ValueTask ForgetAsync(string nodeId, CancellationToken ct) => await _store.DeleteAsync(nodeId, ct);

    public async ValueTask<BinaryDecision> CheckAsync(NodeRecord node, BinaryEvidence evidence, CancellationToken ct)
    {
        string policy = _options.BinaryPolicy;
        if (policy == Off || ReleaseService.ComponentOf(node.Id) is not { } component)
        {
            return new BinaryDecision(true);
        }

        long now = _time.GetUtcNow().ToUnixTimeMilliseconds();
        NodeBinding? binding = await _store.GetAsync(node.Id.Value, ct);

        if (evidence.Sha256 is null)
        {
            // 旧节点不上报：还没绑定过就放行（未绑定）；绑定过的不许退回去，否则换个旧版本就绕过了
            return binding is null ? new BinaryDecision(true) : await ViolationAsync(binding, "the node stopped reporting its binary hash", policy, now, ct);
        }

        string hash = evidence.Sha256;
        if (!IsHash(hash))
        {
            return new BinaryDecision(policy != Enforce, "the reported binary hash is malformed");
        }

        // 节点自己带来的清单（宿主机更新器验过的那份）；没有更新器的节点（一键容器安装、二进制安装）没有，就用面板自己手里的：
        // 面板登记它们时已经验过 CI 签名，这里再验一遍。只有节点自带的清单才能因为「不在清单里」而被拒绝，面板手里的只用来把绑定标成已签名。
        Official? official = VerifyManifest(evidence.Manifest, evidence.Signature, component);
        bool carried = official is not null;
        official ??= await StoredOfficialAsync(component, ct);
        bool listed = official is not null && official.Binaries.Contains(hash);

        if (binding is null)
        {
            if (carried && !listed)
            {
                // 带着一份有效的签名清单，自己的哈希却不在里面：它不是这份清单对应的官方二进制
                return new BinaryDecision(policy != Enforce, "this binary is not in the CI-signed manifest it was installed from");
            }

            await _store.UpsertAsync(new NodeBinding(node.Id.Value, hash, listed ? official!.Seq : 0, listed, now, null, null), ct);
            return new BinaryDecision(true);
        }

        if (binding.Sha256 == hash)
        {
            if (listed && (official!.Seq > binding.Seq || !binding.Signed || binding.Violation is not null))
            {
                await _store.UpsertAsync(binding with { Seq = Math.Max(binding.Seq, official!.Seq), Signed = true, Violation = null, ViolationAtMs = null }, ct);
            }
            else if (binding.Violation is not null)
            {
                await _store.UpsertAsync(binding with { Violation = null, ViolationAtMs = null }, ct);
            }

            return new BinaryDecision(true);
        }

        // 哈希变了：必须是一份不低于绑定时 seq 的 CI 签名清单里的官方二进制（合法升级），否则不符
        if (listed && official!.Seq >= binding.Seq)
        {
            await _store.UpsertAsync(new NodeBinding(node.Id.Value, hash, official.Seq, true, now, null, null), ct);
            return new BinaryDecision(true);
        }

        return await ViolationAsync(binding, $"the running binary changed (bound {Short(binding.Sha256)}, now {Short(hash)}) and is not in a newer CI-signed manifest", policy, now, ct);
    }

    private async ValueTask<BinaryDecision> ViolationAsync(NodeBinding binding, string reason, string policy, long now, CancellationToken ct)
    {
        await _store.UpsertAsync(binding with { Violation = reason, ViolationAtMs = now }, ct);
        return new BinaryDecision(policy != Enforce, reason);
    }

    private sealed record Official(long Seq, HashSet<string> Binaries);

    /// <summary>用内嵌的 CI 公钥验清单；验过且是这个组件的才返回它列出的官方二进制哈希。</summary>
    private async ValueTask<Official?> StoredOfficialAsync(string component, CancellationToken ct) =>
        VerifyManifest(await _settings.GetAsync(ReleaseService.Key(component, "manifest"), ct), await _settings.GetAsync(ReleaseService.Key(component, "signature"), ct), component);

    private Official? VerifyManifest(string? manifestText, string? signatureText, string component)
    {
        if (manifestText is not { Length: > 0 and <= ReleaseService.MaxManifestBytes } manifest
            || signatureText is not { Length: > 0 and <= ReleaseService.MaxSignatureBytes } signature
            || !ReleaseSignature.Verify(_key.Pem, manifest, signature))
        {
            return null;
        }

        try
        {
            using JsonDocument document = JsonDocument.Parse(manifest);
            JsonElement root = document.RootElement;
            if (root.ValueKind != JsonValueKind.Object
                || !root.TryGetProperty("component", out JsonElement c) || c.GetString() != component
                || !root.TryGetProperty("seq", out JsonElement s) || !s.TryGetInt64(out long seq) || seq <= 0)
            {
                return null;
            }

            var binaries = new HashSet<string>(StringComparer.Ordinal);
            if (root.TryGetProperty("binaries", out JsonElement list) && list.ValueKind == JsonValueKind.String)
            {
                foreach (string item in (list.GetString() ?? "").Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries))
                {
                    if (IsHash(item))
                    {
                        binaries.Add(item);
                    }
                }
            }

            return new Official(seq, binaries);
        }
        catch (JsonException)
        {
            return null;
        }
    }

    private static bool IsHash(string value) => value.Length == 64 && value.All(ch => ch is (>= '0' and <= '9') or (>= 'a' and <= 'f'));

    private static string Short(string hash) => hash.Length > 12 ? hash[..12] : hash;
}