using Microsoft.Data.Sqlite;
using System.Security.Cryptography;
using System.Text;

namespace SimPas2_Windows.Managers
{
  public class PasswordManager
  {
    private readonly string mConnectionString;
    private readonly byte[] mEncryptionKey;
    private readonly string mCulture;

    private string mJpLang;

    public PasswordManager(string databasePath, byte[] encryptionKey, string culture)
    {
      mConnectionString = $"Data Source={databasePath}";
      mEncryptionKey = encryptionKey ?? throw new ArgumentNullException(nameof(encryptionKey));
      mCulture = culture;

      mJpLang = "ja-JP";
    }

    private bool AlreadyExists(string website, string username, int? excludeId = null)
    {
      using (SqliteConnection conn = new SqliteConnection(mConnectionString))
      {
        conn.Open();
        SqliteCommand com = conn.CreateCommand();
        com.CommandText = @"
          SELECT COUNT(*) FROM Passwords
          WHERE UPPER(Website) = UPPER(@website) AND UPPER(Username) = UPPER(@username)";
        com.Parameters.AddWithValue("@website", website);
        com.Parameters.AddWithValue("@username", username);

        if (excludeId.HasValue)
        {
          com.CommandText += " AND Id != @excludeId";
          com.Parameters.AddWithValue("@excludeId", excludeId.Value);
        }

        return Convert.ToInt32(com.ExecuteScalar()) > 0;
      }
    }

    public void AddPassword(string website, string username, string password, string note)
    {
      if (string.IsNullOrWhiteSpace(website) || string.IsNullOrWhiteSpace(username) || string.IsNullOrWhiteSpace(password))
      {
        string err = mCulture == mJpLang
          ? "ウェブサイト、ユーザー名及び、パスワードを御入力下さい。"
          : "Please fill in the website, user/email, and password.";
        throw new ArgumentException(err);
      }

      if (AlreadyExists(website, username))
      {
        string err = mCulture == mJpLang
          ? $"ウェブサイトとユーザー名「{website}/{username}」付きパスワードは既に存在します。"
          : $"A password with the website and user/email of '{website}/{username}' already exists.";
        throw new ArgumentException(err);
      }

      string encryptedPassword = EncryptPassword(password);
      using (SqliteConnection conn = new SqliteConnection(mConnectionString))
      {
        conn.Open();
        SqliteCommand com = conn.CreateCommand();
        com.CommandText = @"
          INSERT INTO Passwords (Website, Username, Password, Note)
          VALUES ($website, $username, $password, $note)";
        com.Parameters.AddWithValue("$website", website);
        com.Parameters.AddWithValue("$username", username);
        com.Parameters.AddWithValue("$password", encryptedPassword);
        com.Parameters.AddWithValue("$note", string.IsNullOrEmpty(note) ? DBNull.Value : note);
        com.ExecuteNonQuery();
      }
    }

    public bool EditPassword(int id, string website, string username, string password, string note)
    {
      if (string.IsNullOrWhiteSpace(website) || string.IsNullOrWhiteSpace(username) || string.IsNullOrWhiteSpace(password))
      {
        string err = mCulture == "ja-JP"
          ? "ウェブサイト、ユーザー名及び、パスワードを御入力下さい。"
          : "Please fill in the website, user/email, and password.";
        throw new ArgumentException(err);
      }

      if (AlreadyExists(website, username, id))
      {
        string err = mCulture == mJpLang
          ? $"ウェブサイトとユーザー名「{website}/{username}」付きパスワードは既に存在します。"
          : $"A password with the website and user/email of '{website}/{username}' already exists.";
        throw new ArgumentException(err);
      }

      string encryptedPassword = EncryptPassword(password);
      using (SqliteConnection conn = new SqliteConnection(mConnectionString))
      {
        conn.Open();
        SqliteCommand com = conn.CreateCommand();
        com.CommandText = @"
          UPDATE Passwords
          SET Website = $website, Username = $username, Password = $password, Note = $note
          WHERE Id = $id";
        com.Parameters.AddWithValue("id", id);
        com.Parameters.AddWithValue("$website", website);
        com.Parameters.AddWithValue("$username", username);
        com.Parameters.AddWithValue("$password", encryptedPassword);
        com.Parameters.AddWithValue("$note", string.IsNullOrEmpty(note) ? DBNull.Value : note);

        return com.ExecuteNonQuery() > 0;
      }
    }

    public bool DeletePassword(int id)
    {
      using (SqliteConnection conn = new SqliteConnection(mConnectionString))
      {
        conn.Open();
        SqliteCommand com = conn.CreateCommand();
        com.CommandText = "DELETE FROM Passwords WHERE Id = $id";
        com.Parameters.AddWithValue("$id", id);

        return com.ExecuteNonQuery() > 0;
      }
    }

    public List<(int Id, string Website, string Username, string Password, string Note)> GetAll(string keyword = "")
    {
      var passwords = new List<(int, string, string, string, string)>();
      using (SqliteConnection conn = new SqliteConnection(mConnectionString))
      {
        conn.Open();
        SqliteCommand com = conn.CreateCommand();
        if (string.IsNullOrWhiteSpace(keyword))
        {
          com.CommandText = @"
          SELECT Id, Website, Username, Password, Note FROM Passwords
          ORDER BY Website ASC";
        }
        else
        {
          com.CommandText = @"
          SELECT Id, Website, Username, Password, Note FROM Passwords
          WHERE Website LIKE @keyword OR Username LIKE @keyword
          ORDER BY Website ASC";
          com.Parameters.AddWithValue("@keyword", $"%{keyword}%");
        }

          using (SqliteDataReader reader = com.ExecuteReader())
          {
            while (reader.Read())
            {
              string encryptedPassword = reader.GetString(3);
              string decryptedPassword = DecryptPassword(encryptedPassword);
              passwords.Add((
                reader.GetInt32(0),
                reader.GetString(1),
                reader.GetString(2),
                decryptedPassword,
                reader.IsDBNull(4) ? string.Empty : reader.GetString(4)
              ));
            }
          }
      }

      return passwords;
    }

    private string EncryptPassword(string plainPassword)
    {
      using (Aes aes = Aes.Create())
      {
        aes.Key = mEncryptionKey;
        aes.GenerateIV();
        byte[] iv = aes.IV;

        using (var encryptor = aes.CreateEncryptor(aes.Key, iv))
        {
          byte[] plainBytes = Encoding.UTF8.GetBytes(plainPassword);
          byte[] encryptedBytes = encryptor.TransformFinalBlock(plainBytes, 0, plainBytes.Length);
          // Combine IV and encrypted data for storage
          byte[] result = new byte[iv.Length + encryptedBytes.Length];
          Buffer.BlockCopy(iv, 0, result, 0, iv.Length);
          Buffer.BlockCopy(encryptedBytes, 0, result, iv.Length, encryptedBytes.Length);
          return Convert.ToBase64String(result);
        }
      }
    }

    private string DecryptPassword(string encryptedPassword)
    {
      byte[] combined = Convert.FromBase64String(encryptedPassword);
      byte[] iv = new byte[16]; // AES IV is 16 bytes
      byte[] encryptedBytes = new byte[combined.Length - iv.Length];
      Buffer.BlockCopy(combined, 0, iv, 0, iv.Length);
      Buffer.BlockCopy(combined, iv.Length, encryptedBytes, 0, encryptedBytes.Length);

      using (Aes aes = Aes.Create())
      {
        aes.Key = mEncryptionKey;
        aes.IV = iv;

        using (var decryptor = aes.CreateDecryptor(aes.Key, aes.IV))
        {
          byte[] decryptedBytes = decryptor.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length);
          return Encoding.UTF8.GetString(decryptedBytes);
        }
      }
    }
  }
}