index.php

<?php
session_start(); 

if ((isset($_SESSION['auth']) && $_SESSION['auth'] === true)) {
   header("Location: admin.php");
   exit();
}
if (isset($_GET['access'])) {
   $alert_user = true;
}

require 'includes/snippet.php';
require 'includes/db-inc.php';
include "includes/header.php";

echo"<br>";

if(isset($_POST['submit'])){
   $username = sanitize(trim($_POST['username']));
   $password = sanitize(trim($_POST['password']));

   $sql_admin = "SELECT * from admin where username = '$username' and  password = '$password' ";
   $query = mysqli_query($conn, $sql_admin);
   // echo mysqli_error($conn);
   if(mysqli_num_rows($query) > 0){
         
      while($row = mysqli_fetch_assoc($query)){
         $_SESSION['auth'] = true;
         $_SESSION['admin'] = $row['username'];		
         }
         if ($_SESSION['auth'] === true) {
      header("Location: admin.php");
      exit();
         }
   } else {
      echo"<div class='alert alert-success alert-dismissable'>
      <button type='button' class='close' data-dismiss='alert' aria-hidden='true'>&times;</button>
      <strong style='text-align: center'> Wrong Username and Password.</strong>  </div>";
   }		
}
               
?>
<div class="container">
   <div class="col-lg-9 col-md-11 col-sm-12 col-xs-12 col-lg-offset-2 col-md-offset-1 col-sm-offset-0 col-xs-offset-0">
      <div class="jumbotron login col-lg-10 col-md-11 col-sm-12 col-xs-12">
         <p class="page-header" style="text-align: center">ADMIN LOGIN</p>
         <div class="container">
            <form class="form-horizontal" role="form" method="post" action="index.php" enctype="multipart/form-data">
               <div class="form-group">
                  <label for="Username" class="col-sm-2 control-label">Username</label>
                  <div class="col-sm-10">
                     <input type="text" class="form-control" name="username" placeholder="admin" id="username" required>
                  </div>
               </div>
               <div class="form-group">
                  <label for="Password" class="col-sm-2 control-label">Password</label>
                  <div class="col-sm-10">
                     <input type="password" class="form-control" name="password" placeholder="Enter Password(admin)" id="password" required>
                  </div>
               </div>
               <div class="form-group">
                  <div class="col-sm-offset-2 col-sm-10">
                     <input type="submit" class="btn btn-info col-lg-4" name="submit" value="Sign In">
                  </div>
               </div>
            </form>
         </div>
      </div>
   </div>
</div>

<div class="container">
   <div class="col-lg-12 col-md-12 col-sm-6 col-xs-12 col-lg-offset-2 col-md-offset-1 col-sm-offset-0 col-xs-offset-0">
         <a href="bookslist.php"><button class="btn btn-success col-lg-3 col-md-4 col-sm-11 col-xs-11 button" style="margin-left: 15px;margin-bottom: 5px"><span class="glyphicon glyphicon-home"></span>&nbsp&nbspVIEW BOOKS</button></a>
   </div>
</div>
<script type="text/javascript" src="js/jquery.js"></script>
<script type="text/javascript" src="js/bootstrap.js"></script>
<script type="text/javascript" src="js/sweetalert.min.js"> </script> 

<?php if (isset($alert_user)) { ?>
<!-- <script type="text/javascript">
   swal("Oops...", "You are not allowed to view this page directly...!", "error");
</script> --> 
<?php } ?>
</body>
</html>