<?php
  if(isset($_GET['log'])){
    session_start();
    session_destroy();
  }
  $conn = mysqli_connect( "localhost","root","","mydb");
  $username = isset($_POST["username"]) ? $_POST["username"] : '';
  $password = isset($_POST["password"]) ? $_POST["password"] : '';
  $password = md5($password);



  if($username!='' and $password!=''){

    $sql = mysqli_query($conn, "SELECT * from user WHERE username = '$username' AND password = '$password' limit 1");
    $data = mysqli_fetch_assoc($sql);

    if($data){
      session_start();
      $_SESSION['username']     = $data['username'];
      $_SESSION['password']     = $data['password'];
    }

    if(isset($_SESSION["username"])){
      header('Location: index.php');
    }

    else {
      echo "<script type='text/javascript'>
        alert('Gagal login. periksa username dan password anda..!!!');
      </script>";
    }
  }

?>