using System;
using System.Windows.Forms;
using System.Data;
using System.Data.OleDb;
using System.Text;

namespace Database {
    static public class OleDBHandler {
        static private OleDbConnection connection;
        static public OleDbConnection Connection {
            get {
                if (connection == null) {
                    InitializeConnection();
                }
                return connection;
            }
        }
        static private void InitializeConnection() {
            try {
                using (var ofDlg = new OpenFileDialog()) {
                    ofDlg.InitialDirectory = "c:\\";
                    ofDlg.Filter = "Access database files (*.accdb;*.mdb)|*.accdb;*.mdb";
                    ofDlg.RestoreDirectory = true;
                    ofDlg.CheckFileExists = true;

                    if (ofDlg.ShowDialog() == DialogResult.OK) {
                        connection = new OleDbConnection(string.Format(
                            "Provider = Microsoft.ACE.Oledb.12.0; Data Source = {0}"
                            , ofDlg.FileName
                        ));
                    }
                    else {
                        Environment.Exit(0);
                    }
                }
                connection.Open();
            }
            catch (Exception e) {
                MessageBox.Show(
                    e.Message
                    , "Database connection error"
                    , MessageBoxButtons.OK
                    , MessageBoxIcon.Error
                );
                Environment.Exit(e.HResult);
            }
        }
        public enum ExecuteType { NonQuery, Scalar };
        public static object Execute(string command, ExecuteType type)
        {
            using (var statement = new OleDbCommand(command, Connection))
            {
                switch (type)
                {
                    case ExecuteType.NonQuery:
                        return statement.ExecuteNonQuery();
                    case ExecuteType.Scalar:
                        return statement.ExecuteScalar();
                    default:
                        throw new ArgumentException("An unsupported method is specified");
                }
            }
        }
        public static OleDbCommand SelectCommand(string tableName, string fields)
        {
            var command = $"SELECT {fields} FROM [{tableName}];";
            return new OleDbCommand(command, Connection);
        }
        public static bool Delete(string tableName, int id) {
            string command = $"DELETE FROM [{tableName}] WHERE [id] = {id};";
            var result = Execute(command, ExecuteType.NonQuery);
            return Convert.ToBoolean(result);
        }
        private static string UpdatePart(params (string, object)[] listPairColumnNameValue) {
            StringBuilder result = new StringBuilder(string.Empty);
            var size = listPairColumnNameValue.Length;
            if (size < 1)
                return result.ToString();
            foreach (var pair in listPairColumnNameValue)
                if(pair.Item2 is string)
                  result.Append($"[{pair.Item1}]='{pair.Item2}',");
                else
                    result.Append($"[{pair.Item1}]={pair.Item2},");

            return result.ToString().TrimEnd(',');
        }
        public static bool Update(string tableName, int id, params (string, object)[] listPairColumnNameValue)
        {
            string partCommand = UpdatePart(listPairColumnNameValue);
            if (partCommand.Length < 1)
                return true;
            string command = $"UPDATE [{tableName}] SET {partCommand} WHERE [id] = {id};";
            var result = Execute(command, ExecuteType.NonQuery);
            return Convert.ToBoolean(result);
        }
        private static string InsertPart(params (string, object)[] listPairColumnNameValue)
        {
            var size = listPairColumnNameValue.Length;
            if (size < 1)
                return string.Empty;

            StringBuilder left = new StringBuilder("(");
            StringBuilder right = new StringBuilder("VALUES (");
            foreach (var pair in listPairColumnNameValue) {
                left.Append('[');
                left.Append(pair.Item1);
                left.Append("],");
                if (pair.Item2 is string)
                    right.Append('\'' + pair.Item2.ToString() + '\'' + ',');
                else
                    right.Append(pair.Item2.ToString() + ',');
            }
            var leftResult = left.ToString().TrimEnd(',') + ')';
            var rightResult = right.ToString().TrimEnd(',') + ')';
            return leftResult + rightResult;
        }
            public static bool Insert(string tableName, params (string, object)[] listPairColumnNameValue)
        {
            string partCommand = InsertPart(listPairColumnNameValue);
            if (partCommand.Length < 1)
                return true;
            string command = $"INSERT INTO [{tableName}] {partCommand};";
            var result = Execute(command, ExecuteType.NonQuery);
            return Convert.ToBoolean(result);
        }
    }
}