<?php
//signin.php
include 'connect.php';
include 'header.php';

echo '<h3>Sign in</h3>';

//first, check if the user is already signed in. If that is the case, there is no need to display this page
if(isset($_SESSION['signed_in']) && $_SESSION['signed_in'] == true)
{
    echo 'You are already signed in, you can <a href="signout.php">sign out</a> if you want.';
}
else
{
    if($_SERVER['REQUEST_METHOD'] != 'POST')
    {
        /*the form hasn't been posted yet, display it
          note that the action="" will cause the form to post to the same page it is on */
        echo '<form method="post" action="">
            Username: <input type="text" name="user_name" />
            Password: <input type="password" name="user_pass">
            <input type="submit" value="Sign in" />
         </form>';
    }
    else
    {
        /* so, the form has been posted, we'll process the data in three steps:
            1.  Check the data
            2.  Let the user refill the wrong fields (if necessary)
            3.  Varify if the data is correct and return the correct response
        */
        $errors = array(); /* declare the array for later use */

        if(!isset($_POST['user_name']))
        {
            $errors[] = 'The username field must not be empty.';
        }

        if(!isset($_POST['user_pass']))
        {
            $errors[] = 'The password field must not be empty.';
        }

        if(!empty($errors)) /*check for an empty array, if there are errors, they're in this array (note the ! operator)*/
        {
            echo 'Uh-oh.. a couple of fields are not filled in correctly..';
            echo '<ul>';
            foreach($errors as $key => $value) /* walk through the array so all the errors get displayed */
            {
                echo '<li>' . $value . '</li>'; /* this generates a nice error list */
            }
            echo '</ul>';
        }
        else
        {
            include 'connect.php';
            if(!mysqli_connect($server, $username,  $password, $database))
            $sql = "SELECT
                        user_id,
                        user_name,