using System;
using System.Data;
using System.Configuration;
using System.Data.SqlClient;

namespace DAL
{
    /// <summary>
    /// 資料庫幫助類
    /// </summary>
    public abstract class DatabaseHelper
    {
        # region 成員變數

        /// <summary>
        /// 資料庫連線字串
        /// </summary>
 

        private static string m_ConnectionString = null;

        # endregion

        # region 屬性

        /// <summary>
        /// 獲取資料庫連線字串
        /// </summary>
        /// <returns></returns>
        public string ConnectionString
        {
            get
            {
                if
 
 (m_ConnectionString == null)
                {
                    m_ConnectionString = ReadConnectionString("ConnectionString");
                }

                return m_ConnectionString;
            }
        }

        # endregion

        # region 建構函式

        public DatabaseHelper()
        {
            m_ConnectionString = ReadConnectionString("ConnectionString"
 
);
        }

        public DatabaseHelper(string connectionString)
        {
            m_ConnectionString = connectionString;
        }

        # endregion

        # region 靜態方法

        /// <summary>
        /// 從配置檔案讀取資料庫連線字串
        /// </summary>
        /// <param name="configKeyName"></param>
        /// <returns></returns>
        private static string ReadConnectionString(string configKeyName)
        {
            string connectionString = "";

            object obj = ConfigurationManager.ConnectionStrings[configKeyName];
            if (obj != null)
            {
                connectionString = obj.ToString();
            }

            return connectionString;
        }

        /// <summary>
        /// 獲取資料庫連線字串
        /// </summary>
        /// <returns></returns>
        public static string GetConnectionString()
        {
            if (m_ConnectionString == null)
            {
                m_ConnectionString = ReadConnectionString("ConnectionString");
            }

            return m_ConnectionString;
        }

        #endregion

        #region 抽象方法

        protected abstract object DataReaderToEntity(IDataReader dataReader);

        #endregion

        #region 資料庫操作方法

        /// <summary>
        /// 構造資料庫操作命令
        /// </summary>
        /// <param name="conn">資料庫連線物件</param>
        /// <param name="cmdString">sql語句</param>
        private SqlCommand CreateCommand(SqlConnection conn, string cmdString)
        {
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = cmdString;

            return cmd;
        }

        /// <summary>
        /// 清空引數，釋放SqlCommand資源
        /// </summary>
        /// <param name="cmd"></param>
        private void DisposeCommand(SqlCommand cmd)
        {
            if (cmd != null)
            {
                cmd.Parameters.Clear();
                cmd.Dispose();
            }
        }

        /// <summary>
        /// 繫結SqlCommand引數，引數值為空時不新增
        /// </summary>
        /// <param name="cmd"></param>
        /// <param name="parameters"></param>
        private void AttachParameters(SqlCommand cmd, params SqlParameter[] parameters)
        {
            if (parameters != null)
            {
                foreach (SqlParameter para in parameters)
                {
                    if (para != null)
                    {
                        if (para.Direction == ParameterDirection.InputOutput ||
                            (para.Direction == ParameterDirection.Input && para.Value == null))
                        {
                            para.Value = DBNull.Value;
                        }
                        cmd.Parameters.Add(para);
                    }
                }
            }
        }

        /// <summary>
        /// 執行一個查詢，返回查詢的結果集
        /// </summary>
        /// <param name="sqlString">sql語句</param>
        /// <param name="parameters">引數化引數</param>
        /// <returns>查詢的結果集</returns>
        public DataTable ExecuteDataTable(string sqlString, params SqlParameter[] parameters)
        {
            DataTable dataTable = new DataTable();

            using (SqlConnection conn = new SqlConnection(m_ConnectionString))
            {
                conn.Open();

                SqlCommand cmd = CreateCommand(conn, sqlString);
                AttachParameters(cmd, parameters);
                SqlDataAdapter adapter = new SqlDataAdapter(cmd);
                adapter.Fill(dataTable);

                DisposeCommand(cmd);
            }

            return dataTable;
        }

        /// <summary>
        /// 執行sql操作，返回受影響的行數
        /// </summary>
        /// <param name="sqlString">sql語句</param>
        /// <param name="parameters">引數化引數</param>
        /// <returns>受影響的行數</returns>
        public int ExecuteNonQuery(string sqlString, params SqlParameter[] parameters)
        {
            int num = 0;

            using (SqlConnection conn = new SqlConnection(m_ConnectionString))
            {
                conn.Open();

                SqlCommand cmd = CreateCommand(conn, sqlString);
                AttachParameters(cmd, parameters);
                num = cmd.ExecuteNonQuery();
                DisposeCommand(cmd);
            }

            return num;
        }

        /// <summary>
        /// 執行查詢，並返回查詢所返回的結果集中第一行的第一列。忽略其他列或行。
        /// </summary>
        /// <param name="sqlString">sql語句</param>
        /// <param name="parameters">引數化引數</param>
        /// <returns>結果集中第一行的第一列；如果結果集為空，則為空引用</returns>
        public object ExecuteScalar(string sqlString, params SqlParameter[] parameters)
        {
            object obj = new object();

            using (SqlConnection conn = new SqlConnection(m_ConnectionString))
            {
                conn.Open();

                SqlCommand cmd = CreateCommand(conn, sqlString);
                AttachParameters(cmd, parameters);
                obj = cmd.ExecuteScalar();
                DisposeCommand(cmd);
            }

            return obj;
        }

        public SqlDataReader ExecuteReader(string sqlString, params SqlParameter[] parameters)
        {
            SqlDataReader reader = null;

            SqlConnection conn = new SqlConnection(m_ConnectionString);
            conn.Open();
            SqlCommand cmd = CreateCommand(conn, sqlString);
            AttachParameters(cmd, parameters);
            reader = cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
            DisposeCommand(cmd);

            return reader;
        }

        # endregion
    }
}