using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using ZA.CoreService.ESBCertificateManager.Models;

namespace ZA.CoreService.ESBCertificateManager.Services;

public sealed class CertificateProbeService
{
    public static readonly string[] SupportedExtensions =
    [
        ".cer",
        ".crt",
        ".pem",
        ".pfx",
        ".p12"
    ];

    public CertificateProbeResult Probe(
        string certificatePath,
        Func<string?>? passwordPrompt = null)
    {
        string? normalized = NormalizePath(certificatePath);

        if (normalized is null)
        {
            return CertificateProbeResult.Failed(
                "Kein gültiger Zertifikatspfad angegeben.");
        }

        if (!IsSupportedExtension(normalized))
        {
            return CertificateProbeResult.Failed(
                "Nicht unterstütztes Format. Erlaubt: "
                + string.Join(", ", SupportedExtensions));
        }

        PathReachability reachability = AssessPathReachability(normalized);

        if (reachability == PathReachability.AccessDenied)
        {
            return CertificateProbeResult.ForAccessDenied(normalized);
        }

        if (reachability == PathReachability.Unreachable)
        {
            return CertificateProbeResult.Failed(
                "Pfad nicht erreichbar.");
        }

        if (reachability == PathReachability.FileMissing)
        {
            return CertificateProbeResult.Missing(
                normalized,
                "Am Zielpfad liegt noch keine Zertifikatsdatei.");
        }

        try
        {
            CertificateInfo info = ReadCertificate(normalized, password: null);
            return CertificateProbeResult.Found(normalized, info);
        }
        catch (CryptographicException) when (IsPasswordProtected(normalized))
        {
            if (passwordPrompt is null)
            {
                return CertificateProbeResult.PasswordRequired(normalized);
            }

            string? password = passwordPrompt.Invoke();

            if (password is null)
            {
                return CertificateProbeResult.Failed(
                    "Zum Lesen der PFX/P12-Datei wird ein Kennwort benötigt.");
            }

            try
            {
                CertificateInfo info = ReadCertificate(normalized, password);
                return CertificateProbeResult.Found(normalized, info);
            }
            catch (CryptographicException)
            {
                return CertificateProbeResult.Failed(
                    "Das Kennwort ist falsch oder die Datei ist beschädigt.");
            }
        }
        catch (UnauthorizedAccessException)
        {
            return CertificateProbeResult.ForAccessDenied(normalized);
        }
        catch (IOException ex) when (IsAccessOrLogonFailure(ex))
        {
            return CertificateProbeResult.ForAccessDenied(normalized);
        }
        catch (Exception ex)
        {
            return CertificateProbeResult.Failed(
                $"Zertifikat konnte nicht gelesen werden: {ex.Message}");
        }
    }

    public static bool TrySplitTargetPath(
        string fullPath,
        out string directory,
        out string fileName,
        out string? error)
    {
        directory = string.Empty;
        fileName = string.Empty;
        error = null;

        string? normalized = NormalizePath(fullPath);

        if (normalized is null)
        {
            error = "Bitte einen vollständigen Pfad zur Zertifikatsdatei angeben.";
            return false;
        }

        if (!IsSupportedExtension(normalized))
        {
            error =
                "Dateiendung nicht unterstützt. Erlaubt: "
                + string.Join(", ", SupportedExtensions);
            return false;
        }

        string? dir = Path.GetDirectoryName(normalized);
        string file = Path.GetFileName(normalized);

        if (string.IsNullOrWhiteSpace(dir) || string.IsNullOrWhiteSpace(file))
        {
            error =
                "Pfad muss Verzeichnis und Dateiname enthalten, z. B.\n"
                + @"\\server\e$\...\certs\server.p12";
            return false;
        }

        if (Path.GetFileName(file) != file)
        {
            error = "Dateiname darf keinen weiteren Verzeichnisanteil enthalten.";
            return false;
        }

        directory = dir;
        fileName = file;
        return true;
    }

    public static string CombineTargetPath(
        string directory,
        string fileName)
    {
        return Path.Combine(
            directory.Trim().TrimEnd('\\', '/'),
            fileName.Trim());
    }

    public static bool IsSupportedExtension(string path)
    {
        string extension = Path.GetExtension(path);
        return SupportedExtensions.Contains(
            extension,
            StringComparer.OrdinalIgnoreCase);
    }

    private static bool IsPasswordProtected(string path)
    {
        string extension = Path.GetExtension(path);
        return extension.Equals(".pfx", StringComparison.OrdinalIgnoreCase)
            || extension.Equals(".p12", StringComparison.OrdinalIgnoreCase);
    }

    private enum PathReachability
    {
        FileExists,
        FileMissing,
        AccessDenied,
        Unreachable
    }

    /// <summary>
    /// Unterscheidet „Datei fehlt“ von „Share/Pfad ohne Admin-Konto nicht erreichbar“.
    /// File.Exists liefert bei fehlenden Credentials oft nur false.
    /// </summary>
    private static PathReachability AssessPathReachability(string filePath)
    {
        try
        {
            if (File.Exists(filePath))
            {
                return PathReachability.FileExists;
            }
        }
        catch (UnauthorizedAccessException)
        {
            return PathReachability.AccessDenied;
        }
        catch (IOException ex) when (IsAccessOrLogonFailure(ex))
        {
            return PathReachability.AccessDenied;
        }
        catch (IOException)
        {
            return PathReachability.Unreachable;
        }

        string? directory = Path.GetDirectoryName(filePath);

        if (string.IsNullOrWhiteSpace(directory))
        {
            return PathReachability.Unreachable;
        }

        return AssessDirectoryReachability(directory);
    }

    private static PathReachability AssessDirectoryReachability(string directory)
    {
        string current = directory.TrimEnd('\\', '/');

        while (!string.IsNullOrWhiteSpace(current))
        {
            try
            {
                if (Directory.Exists(current))
                {
                    // Exists kann bei UNC ohne Rechte „lügen“ – Auflisten erzwingen.
                    _ = Directory.EnumerateFileSystemEntries(current)
                        .Any();
                    return PathReachability.FileMissing;
                }

                if (current.StartsWith(@"\\", StringComparison.Ordinal))
                {
                    // Exists=false: echter Zugriffsfehler oder Ordner fehlt.
                    _ = Directory.GetFileSystemEntries(current);
                    return PathReachability.FileMissing;
                }

                // Lokaler Ordner fehlt → für Erst-Deployment als „Datei fehlt“ werten.
                return PathReachability.FileMissing;
            }
            catch (UnauthorizedAccessException)
            {
                return PathReachability.AccessDenied;
            }
            catch (IOException ex) when (IsAccessOrLogonFailure(ex))
            {
                return PathReachability.AccessDenied;
            }
            catch (DirectoryNotFoundException)
            {
                string? parent = GetParentPath(current);

                if (parent is null || parent == current)
                {
                    return current.StartsWith(@"\\", StringComparison.Ordinal)
                        ? PathReachability.Unreachable
                        : PathReachability.FileMissing;
                }

                current = parent;
                continue;
            }
            catch (IOException)
            {
                return PathReachability.Unreachable;
            }
        }

        return PathReachability.Unreachable;
    }

    private static string? GetParentPath(string path)
    {
        string trimmed = path.TrimEnd('\\', '/');

        if (trimmed.StartsWith(@"\\", StringComparison.Ordinal))
        {
            // \\server\share → Stop; darunter weiter nach oben.
            string withoutPrefix = trimmed[2..];
            int slash = withoutPrefix.IndexOfAny(['\\', '/']);

            if (slash < 0)
            {
                return null;
            }

            int second = withoutPrefix.IndexOfAny(['\\', '/'], slash + 1);

            if (second < 0)
            {
                // Bereits Share-Root \\server\share
                return null;
            }
        }

        string? parent = Path.GetDirectoryName(trimmed);
        return string.IsNullOrWhiteSpace(parent) ? null : parent;
    }

    private static bool IsAccessOrLogonFailure(IOException ex)
    {
        // HRESULT-Lower-Word = Win32-Fehlercode
        int win32 = ex.HResult & 0xFFFF;

        return win32 is
            5 or     // ERROR_ACCESS_DENIED
            53 or    // ERROR_BAD_NETPATH
            67 or    // ERROR_BAD_NET_NAME
            86 or    // ERROR_INVALID_PASSWORD
            1326 or  // ERROR_LOGON_FAILURE
            59 or    // ERROR_UNEXP_NET_ERR
            64 or    // ERROR_NETNAME_DELETED
            1219 or  // ERROR_SESSION_CREDENTIAL_CONFLICT
            1240 or  // ERROR_LOGIN_WKSTA_RESTRICTION
            1245 or  // ERROR_ACCOUNT_RESTRICTION
            1396;    // ERROR_WRONG_TARGET_NAME
    }

    private static string? NormalizePath(string? path)
    {
        if (string.IsNullOrWhiteSpace(path))
        {
            return null;
        }

        string trimmed = path.Trim().Trim('"');

        if (trimmed.Length == 0)
        {
            return null;
        }

        // UNC und absolute lokale Pfade akzeptieren
        if (!Path.IsPathRooted(trimmed)
            && !trimmed.StartsWith(@"\\", StringComparison.Ordinal))
        {
            return null;
        }

        return trimmed;
    }

    private static CertificateInfo ReadCertificate(
        string certificatePath,
        string? password)
    {
        string extension = Path.GetExtension(certificatePath);

        using X509Certificate2 certificate =
            IsPasswordProtected(certificatePath)
                ? new X509Certificate2(
                    certificatePath,
                    password,
                    X509KeyStorageFlags.EphemeralKeySet)
                : new X509Certificate2(certificatePath);

        string subject = certificate.GetNameInfo(
            X509NameType.SimpleName,
            forIssuer: false);

        string issuer = certificate.GetNameInfo(
            X509NameType.SimpleName,
            forIssuer: true);

        if (string.IsNullOrWhiteSpace(subject))
        {
            subject = certificate.Subject;
        }

        if (string.IsNullOrWhiteSpace(issuer))
        {
            issuer = certificate.Issuer;
        }

        string fingerprint = certificate.GetCertHashString(
            HashAlgorithmName.SHA256);

        fingerprint = string.Join(
            ":",
            Enumerable.Range(0, fingerprint.Length / 2)
                .Select(index => fingerprint.Substring(index * 2, 2)));

        DateTimeOffset validFrom = new(certificate.NotBefore);
        DateTimeOffset validUntil = new(certificate.NotAfter);
        DateTimeOffset now = DateTimeOffset.Now;

        return new CertificateInfo
        {
            Subject = subject,
            Issuer = issuer,
            FingerprintSha256 = fingerprint,
            ValidFrom = validFrom,
            ValidUntil = validUntil,
            IsCurrentlyValid = now >= validFrom && now <= validUntil
        };
    }
}

public sealed class CertificateProbeResult
{
    public const string AccessDeniedShortText = "Admin nötig";

    public bool Success { get; init; }

    public bool FileExists { get; init; }

    public bool AccessDenied { get; init; }

    public string Path { get; init; } = string.Empty;

    public string Message { get; init; } = string.Empty;

    public CertificateInfo? Certificate { get; init; }

    public static CertificateProbeResult Found(
        string path,
        CertificateInfo certificate)
    {
        string expiry = certificate.ValidUntil.ToLocalTime()
            .ToString("dd.MM.yyyy HH:mm");

        string validity = certificate.IsCurrentlyValid
            ? "gültig"
            : "abgelaufen / ungültig";

        return new CertificateProbeResult
        {
            Success = true,
            FileExists = true,
            Path = path,
            Certificate = certificate,
            Message =
                $"Zertifikat gefunden · Subject: {certificate.Subject} · "
                + $"Ablauf: {expiry} ({validity})"
        };
    }

    public static CertificateProbeResult Missing(
        string path,
        string message)
    {
        return new CertificateProbeResult
        {
            Success = true,
            FileExists = false,
            Path = path,
            Message = message
        };
    }

    public static CertificateProbeResult Failed(string message)
    {
        return new CertificateProbeResult
        {
            Success = false,
            FileExists = false,
            Message = message
        };
    }

    public static CertificateProbeResult ForAccessDenied(string path)
    {
        return new CertificateProbeResult
        {
            Success = false,
            FileExists = false,
            AccessDenied = true,
            Path = path,
            Message =
                "Kein Zugriff auf den Pfad – Admin-Konto nötig."
        };
    }

    public static CertificateProbeResult PasswordRequired(string path)
    {
        return new CertificateProbeResult
        {
            Success = false,
            FileExists = true,
            Path = path,
            Message = "PFX/P12 vorhanden – Kennwort nötig zum Lesen des Ablaufs"
        };
    }
}