using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

namespace Fleet.Identity;

/// <summary>
/// 点对点会话的 TLS 证书：自签名的 ECDSA P-256（和身份密钥是两把不同的密钥）。
/// 对端不按证书链校验，而是按 SPKI 的 SHA-256 指纹校验（指纹由服务端经 Agent 列表下发）。
/// </summary>
public static class NodeCertificate
{
    /// <summary>生成自签名证书，返回无口令的 PFX 字节（文件权限由写入方设为 0600）。</summary>
    public static byte[] CreateSelfSignedPfx(string commonName, TimeSpan validity, TimeProvider time)
    {
        using ECDsa key = ECDsa.Create(ECCurve.NamedCurves.nistP256);
        var request = new CertificateRequest("CN=" + commonName, key, HashAlgorithmName.SHA256);
        request.CertificateExtensions.Add(new X509KeyUsageExtension(X509KeyUsageFlags.DigitalSignature, critical: true));
        request.CertificateExtensions.Add(new X509EnhancedKeyUsageExtension(
            [new Oid("1.3.6.1.5.5.7.3.1"), new Oid("1.3.6.1.5.5.7.3.2")], critical: false));
        DateTimeOffset now = time.GetUtcNow();
        using X509Certificate2 certificate = request.CreateSelfSigned(now.AddDays(-1), now.Add(validity));
        return certificate.Export(X509ContentType.Pfx);
    }

    public static X509Certificate2 LoadPfx(byte[] pfx) => X509CertificateLoader.LoadPkcs12(pfx, null, X509KeyStorageFlags.Exportable);

    /// <summary>证书公钥（SPKI）的 SHA-256：对端用它来固定这张证书。</summary>
    public static byte[] SpkiFingerprint(X509Certificate2 certificate) =>
        SHA256.HashData(certificate.PublicKey.ExportSubjectPublicKeyInfo());
}