namespace ZA.CoreService.ESBCertificateManager.Services;

public sealed class LocalCertificateDeployer
{
    private static readonly HashSet<string> CertificateExtensions =
        new(StringComparer.OrdinalIgnoreCase)
        {
            ".cer",
            ".crt",
            ".pem",
            ".pfx",
            ".p12"
        };

    public async Task<string> DeployAsync(
        string sourceCertificatePath,
        string configuredTargetDirectory,
        string targetFileName,
        bool backupEnabled,
        string backupDirectoryName,
        CancellationToken cancellationToken)
    {
        if (string.IsNullOrWhiteSpace(sourceCertificatePath))
        {
            throw new ArgumentException(
                "Es wurde keine Zertifikatsquelle angegeben.",
                nameof(sourceCertificatePath));
        }

        if (!File.Exists(sourceCertificatePath))
        {
            throw new FileNotFoundException(
                "Die ausgewählte Zertifikatsdatei wurde nicht gefunden.",
                sourceCertificatePath);
        }

        if (string.IsNullOrWhiteSpace(configuredTargetDirectory))
        {
            throw new ArgumentException(
                "Der Zertifikats-Zielordner ist nicht konfiguriert.",
                nameof(configuredTargetDirectory));
        }

        if (string.IsNullOrWhiteSpace(targetFileName))
        {
            throw new ArgumentException(
                "Der Zertifikats-Zieldateiname ist nicht konfiguriert.",
                nameof(targetFileName));
        }

        if (Path.GetFileName(targetFileName) != targetFileName)
        {
            throw new InvalidOperationException(
                "TargetFileName darf keinen Verzeichnispfad enthalten.");
        }

        string targetDirectory = Path.GetFullPath(
            Path.IsPathRooted(configuredTargetDirectory)
                ? configuredTargetDirectory
                : Path.Combine(
                    AppContext.BaseDirectory,
                    configuredTargetDirectory));

        cancellationToken.ThrowIfCancellationRequested();

        Directory.CreateDirectory(targetDirectory);

        string destinationPath = Path.Combine(
            targetDirectory,
            targetFileName);

        string temporaryPath = destinationPath + ".tmp";

        try
        {
            if (backupEnabled)
            {
                BackupExistingCertificates(
                    targetDirectory,
                    backupDirectoryName,
                    cancellationToken);
            }

            await using (FileStream source = new(
                sourceCertificatePath,
                FileMode.Open,
                FileAccess.Read,
                FileShare.Read))
            await using (FileStream temporaryTarget = new(
                temporaryPath,
                FileMode.Create,
                FileAccess.Write,
                FileShare.None))
            {
                await source.CopyToAsync(
                    temporaryTarget,
                    cancellationToken);
            }

            cancellationToken.ThrowIfCancellationRequested();

            File.Move(
                temporaryPath,
                destinationPath,
                overwrite: true);

            return destinationPath;
        }
        catch
        {
            TryDeleteTemporaryFile(temporaryPath);
            throw;
        }
    }

    private static void BackupExistingCertificates(
        string targetDirectory,
        string configuredBackupDirectoryName,
        CancellationToken cancellationToken)
    {
        List<string> filesToBackup = Directory
            .EnumerateFiles(
                targetDirectory,
                "*",
                SearchOption.TopDirectoryOnly)
            .Where(path =>
                CertificateExtensions.Contains(
                    Path.GetExtension(path)))
            .ToList();

        if (filesToBackup.Count == 0)
        {
            return;
        }

        string backupDirectoryName =
            string.IsNullOrWhiteSpace(configuredBackupDirectoryName)
                ? "Backup"
                : configuredBackupDirectoryName.Trim();

        if (Path.GetFileName(backupDirectoryName)
            != backupDirectoryName)
        {
            throw new InvalidOperationException(
                "BackupDirectoryName darf keinen Verzeichnispfad enthalten.");
        }

        string backupDirectory = Path.Combine(
            targetDirectory,
            backupDirectoryName,
            DateTime.Now.ToString("yyyyMMdd_HHmmss_fff"));

        Directory.CreateDirectory(backupDirectory);

        foreach (string certificateFile in filesToBackup)
        {
            cancellationToken.ThrowIfCancellationRequested();

            string backupPath = Path.Combine(
                backupDirectory,
                Path.GetFileName(certificateFile));

            File.Copy(
                certificateFile,
                backupPath,
                overwrite: false);
        }
    }

    private static void TryDeleteTemporaryFile(
        string temporaryPath)
    {
        try
        {
            if (File.Exists(temporaryPath))
            {
                File.Delete(temporaryPath);
            }
        }
        catch
        {
            // Der ursprüngliche Fehler darf nicht verdeckt werden.
            // TODO: Aufräumfehler später separat protokollieren.
        }
    }
}