using System.Security.Cryptography;
using System.Text;
using System.Runtime.InteropServices;

namespace CredentialManager.Services;

/// <summary>
/// Interfaccia per il servizio di crittografia
/// </summary>
public interface IEncryptionService
{
    string Encrypt(string plainText);
    string Decrypt(string encryptedText);
}

/// <summary>
/// Servizio per la crittografia delle password cross-platform
/// </summary>
public class EncryptionService : IEncryptionService
{
    private readonly byte[] _key;
    private readonly byte[] _iv;

    public EncryptionService()
    {
        // Chiave e IV derivati da una stringa fissa (in produzione dovrebbero essere configurabili)
        var keySource = "CredentialManager2025KeyForEncryption!";
        var ivSource = "CredMgr2025IV!";
        
        using var sha256 = SHA256.Create();
        _key = sha256.ComputeHash(Encoding.UTF8.GetBytes(keySource));
        _iv = new byte[16];
        Array.Copy(Encoding.UTF8.GetBytes(ivSource), _iv, Math.Min(16, ivSource.Length));
    }

    public string Encrypt(string plainText)
    {
        if (string.IsNullOrEmpty(plainText))
            return string.Empty;

        try
        {
            // Su Windows, usa ProtectedData se disponibile
            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            {
                return EncryptWithProtectedData(plainText);
            }
            
            // Su altre piattaforme, usa AES
            return EncryptWithAes(plainText);
        }
        catch (Exception ex)
        {
            throw new InvalidOperationException("Errore durante la crittografia", ex);
        }
    }

    public string Decrypt(string encryptedText)
    {
        if (string.IsNullOrEmpty(encryptedText))
            return string.Empty;

        try
        {
            // Su Windows, usa ProtectedData se disponibile
            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            {
                return DecryptWithProtectedData(encryptedText);
            }
            
            // Su altre piattaforme, usa AES
            return DecryptWithAes(encryptedText);
        }
        catch (Exception ex)
        {
            throw new InvalidOperationException("Errore durante la decrittografia", ex);
        }
    }    private string EncryptWithProtectedData(string plainText)
    {
        byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);
        byte[] entropy = Encoding.UTF8.GetBytes("CredentialManager2025");
        
        if (OperatingSystem.IsWindows())
        {
            byte[] encryptedBytes = ProtectedData.Protect(plainTextBytes, entropy, DataProtectionScope.CurrentUser);
            return Convert.ToBase64String(encryptedBytes);
        }
        
        // Fallback ad AES se non su Windows
        return EncryptWithAes(plainText);
    }

    private string DecryptWithProtectedData(string encryptedText)
    {
        if (OperatingSystem.IsWindows())
        {
            byte[] encryptedBytes = Convert.FromBase64String(encryptedText);
            byte[] entropy = Encoding.UTF8.GetBytes("CredentialManager2025");
            byte[] decryptedBytes = ProtectedData.Unprotect(encryptedBytes, entropy, DataProtectionScope.CurrentUser);
            return Encoding.UTF8.GetString(decryptedBytes);
        }
        
        // Fallback ad AES se non su Windows
        return DecryptWithAes(encryptedText);
    }

    private string EncryptWithAes(string plainText)
    {
        using var aes = Aes.Create();
        aes.Key = _key;
        aes.IV = _iv;

        using var encryptor = aes.CreateEncryptor();
        using var msEncrypt = new MemoryStream();
        using var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write);
        using var swEncrypt = new StreamWriter(csEncrypt);
        
        swEncrypt.Write(plainText);
        swEncrypt.Close();
        
        return Convert.ToBase64String(msEncrypt.ToArray());
    }

    private string DecryptWithAes(string encryptedText)
    {
        byte[] cipherBytes = Convert.FromBase64String(encryptedText);
        
        using var aes = Aes.Create();
        aes.Key = _key;
        aes.IV = _iv;

        using var decryptor = aes.CreateDecryptor();
        using var msDecrypt = new MemoryStream(cipherBytes);
        using var csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read);
        using var srDecrypt = new StreamReader(csDecrypt);
        
        return srDecrypt.ReadToEnd();
    }
}