using System.Security.Cryptography;
using Fleet.Core;

namespace MoShiro.Backend.Application;

/// <summary>一把发布公钥的指纹（SPKI 的 SHA-256，小写十六进制）和 PEM。</summary>
public sealed record ReleaseKeyInfo(string Fingerprint, string PublicKey);

/// <summary>可信资产来源：官方 CI 发布密钥（内嵌，始终信任）和可选的自有发布公钥（默认没有）。</summary>
public sealed record ReleaseKeys(ReleaseKeyInfo Official, ReleaseKeyInfo? Custom);

/// <summary>
/// 面板信任哪些发布密钥：内嵌的官方 CI 公钥始终信任，不能关；部署的人可以另外导入<b>自己的发布公钥</b>（默认没有），
/// 用自己的私钥给自己构建的清单签名。验签（登记清单、取镜像仓库里的清单）通过官方或自有任意一把即可。
/// 私钥只在部署的人手里，面板只存公钥，拒绝带私钥的 PEM。
/// </summary>
public sealed class ReleaseKeyService
{
    internal const string SettingKey = "release.custom_key";
    private const int MaxPemBytes = 1024;
    private const string P256Oid = "1.2.840.10045.3.1.7";

    private readonly IReleaseKey _official;
    private readonly ISettingsStore _settings;

    public ReleaseKeyService(IReleaseKey official, ISettingsStore settings)
    {
        _official = official;
        _settings = settings;
    }

    public async ValueTask<ReleaseKeys> GetAsync(CancellationToken ct) =>
        new(Describe(_official.Pem)!, Describe(await CustomAsync(ct)));

    /// <summary>清单的签名由官方密钥或自有密钥（开启时）验过。</summary>
    public async ValueTask<bool> VerifyAsync(string manifest, string signature, CancellationToken ct) =>
        ReleaseSignature.Verify(_official.Pem, manifest, signature)
        || (await CustomAsync(ct) is { } custom && ReleaseSignature.Verify(custom, manifest, signature));

    public async ValueTask<Result<ReleaseKeys>> SetCustomAsync(string? publicKey, CancellationToken ct)
    {
        if (!TryNormalize(publicKey, out string? pem, out string? problem))
        {
            return ValidationError.Fail<ReleaseKeys>("public_key", problem);
        }

        await _settings.SetAsync(SettingKey, pem, ct);
        return Result<ReleaseKeys>.Ok(await GetAsync(ct));
    }

    public async ValueTask ClearCustomAsync(CancellationToken ct) => await _settings.SetAsync(SettingKey, string.Empty, ct);

    private async ValueTask<string?> CustomAsync(CancellationToken ct) =>
        await _settings.GetAsync(SettingKey, ct) is { Length: > 0 } pem ? pem : null;

    private static ReleaseKeyInfo? Describe(string? pem)
    {
        if (pem is null)
        {
            return null;
        }

        using var key = ECDsa.Create();
        key.ImportFromPem(pem);
        return new ReleaseKeyInfo(Convert.ToHexStringLower(SHA256.HashData(key.ExportSubjectPublicKeyInfo())), key.ExportSubjectPublicKeyInfoPem().Trim());
    }

    /// <summary>只收 P-256 的公钥：带私钥的 PEM 直接拒绝（私钥不该离开你的机器）。</summary>
    private static bool TryNormalize(string? text, [System.Diagnostics.CodeAnalysis.NotNullWhen(true)] out string? pem, [System.Diagnostics.CodeAnalysis.NotNullWhen(false)] out string? problem)
    {
        pem = null;
        problem = null;
        string trimmed = (text ?? string.Empty).Trim();
        if (trimmed.Length is 0 or > MaxPemBytes)
        {
            problem = "must be a PEM public key";
            return false;
        }

        if (trimmed.Contains("PRIVATE", StringComparison.OrdinalIgnoreCase))
        {
            problem = "must be a public key: never upload the private key, keep it on your own machine";
            return false;
        }

        try
        {
            using var key = ECDsa.Create();
            key.ImportFromPem(trimmed);
            if (key.ExportParameters(false).Curve.Oid.Value != P256Oid)
            {
                problem = "must be an ECDSA P-256 public key";
                return false;
            }

            pem = key.ExportSubjectPublicKeyInfoPem().Trim();
            return true;
        }
        catch (Exception ex) when (ex is CryptographicException or ArgumentException)
        {
            problem = "is not a valid PEM public key";
            return false;
        }
    }
}