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

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

    private string mJpLang;

    public QaManager(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 question, int? excludeId = null)
    {
      using (SqliteConnection conn = new SqliteConnection(mConnectionString))
      {
        conn.Open();
        SqliteCommand com = conn.CreateCommand();
        com.CommandText = @"
          SELECT COUNT(*) FROM Qa
          WHERE UPPER(Website) = UPPER(@website) AND UPPER(Question) = UPPER(@question)";
        com.Parameters.AddWithValue("@website", website);
        com.Parameters.AddWithValue("@question", question);

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

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

    public void AddQa(string website, string question, string answer, string note)
    {
      if (string.IsNullOrWhiteSpace(website) || string.IsNullOrWhiteSpace(question) || string.IsNullOrWhiteSpace(answer))
      {
        string err = mCulture == mJpLang
          ? "ウェブサイト、質問及び、回答を御入力下さい。"
          : "Please fill in the website, question, and answer.";
        throw new ArgumentException(err);
      }

      string encryptedAnswer = EncryptAnswer(answer);

      if (AlreadyExists(website, question))
      {
        string err = mCulture == mJpLang
          ? $"ウェブサイト及び質問「{website}/{question}」向け秘密質問は既に存在します。"
          : $"An secret question with the website and question for '{website}/{question}' already exists.";
        throw new ArgumentException(err);
      }

      using (SqliteConnection conn = new SqliteConnection(mConnectionString))
      {
        conn.Open();
        SqliteCommand com = conn.CreateCommand();
        com.CommandText = @"
          INSERT INTO Qa (Website, Question, Answer, Note)
          VALUES ($website, $question, $answer, $note)";
        com.Parameters.AddWithValue("$website", website);
        com.Parameters.AddWithValue("$question", question);
        com.Parameters.AddWithValue("$answer", encryptedAnswer);
        com.Parameters.AddWithValue("$note", string.IsNullOrEmpty(note) ? DBNull.Value : note);
        com.ExecuteNonQuery();
      }
    }

    public bool EditQa(int id, string website, string question, string answer, string note)
    {
      if (string.IsNullOrWhiteSpace(website) || string.IsNullOrWhiteSpace(question) || string.IsNullOrWhiteSpace(answer))
      {
        string err = mCulture == mJpLang
          ? "ウェブサイト、質問及び、回答を御入力下さい。"
          : "Please fill in the website, question, and answer.";
        throw new ArgumentException(err);
      }

      string encryptedAnswer = EncryptAnswer(answer);

      if (AlreadyExists(website, question, id))
      {
        string err = mCulture == mJpLang
          ? $"ウェブサイト及び質問「{website}/{question}」向け秘密質問は既に存在します。"
          : $"An secret question with the website and question for '{website}/{question}' already exists.";
        throw new ArgumentException(err);
      }

      using (SqliteConnection conn = new SqliteConnection(mConnectionString))
      {
        conn.Open();
        SqliteCommand com = conn.CreateCommand();
        com.CommandText = @"
          UPDATE Qa
          SET Website = $website, Question = $question, Answer = $answer, Note = $note
          WHERE Id = $id";
        com.Parameters.AddWithValue("$id", id);
        com.Parameters.AddWithValue("$website", website);
        com.Parameters.AddWithValue("$question", question);
        com.Parameters.AddWithValue("$answer", encryptedAnswer);
        com.Parameters.AddWithValue("$note", string.IsNullOrEmpty(note) ? DBNull.Value : note);
        return com.ExecuteNonQuery() > 0;
      }
    }

    public bool DeleteQa(int id)
    {
      using (SqliteConnection conn = new SqliteConnection(mConnectionString))
      {
        conn.Open();
        SqliteCommand com = conn.CreateCommand();
        com.CommandText = "DELETE FROM Qa WHERE Id = $id";
        com.Parameters.AddWithValue("$id", id);
        return com.ExecuteNonQuery() > 0;
      }
    }

    public List<(int Id, string Website, string Question, string Answer, string Note)> GetAll(string keyword = "")
    {
      var qas = 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, Question, Answer, Note FROM Qa
          ORDER BY Website ASC";
        }
        else
        {
          com.CommandText = @"
          SELECT Id, Website, Question, Answer, Note FROM Qa
          WHERE Website LIKE @keyword OR Question LIKE @keyword
          ORDER BY Website ASC";
          com.Parameters.AddWithValue("@keyword", $"%{keyword}%");
        }

        using (SqliteDataReader reader = com.ExecuteReader())
        {
          while (reader.Read())
          {
            string encryptedAnswer = reader.GetString(3);
            string decryptedAnswer = DecryptAnswer(encryptedAnswer);
            qas.Add((
              reader.GetInt32(0),
              reader.GetString(1),
              reader.GetString(2),
              decryptedAnswer,
              reader.IsDBNull(4) ? string.Empty : reader.GetString(4)
            ));
          }
        }
      }

      return qas;
    }

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

        using (ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, iv))
        {
          byte[] plainBytes = Encoding.UTF8.GetBytes(answer);
          byte[] encryptedBytes = encryptor.TransformFinalBlock(plainBytes, 0, plainBytes.Length);
          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 DecryptAnswer(string encryptedAnswer)
    {
      byte[] combined = Convert.FromBase64String(encryptedAnswer);
      byte[] iv = new byte[16];
      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 (ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV))
        {
          byte[] decryptedBytes = decryptor.TransformFinalBlock(encryptedBytes, 0, encryptedBytes.Length);
          return Encoding.UTF8.GetString(decryptedBytes);
        }
      }
    }
  }
}