<?php
//signin.php
include 'connect.php';
include 'index.htm';

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

//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="username" /><br />
			Password: <input type="password" name="password"><br />
			<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['username']))
		{
			$errors[] = 'The username field must not be empty.';
		}

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

		if(!empty($errors)) /*check for an empty array, if there are errors, they're in this array (note the ! operator)*/
		{
			echo 'Uh-oh.. a couple of fields are not filled in correctly..<br /><br />';
			echo '<ul>';
			foreach($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
		{
			//the form has been posted without errors, so save it
			//notice the use of mysql_real_escape_string, keep everything safe!
			//also notice the sha1 function which hashes the password
			$sql = "SELECT
						id,
						username,
						user_level
					FROM
						users
					WHERE
						username = '" . mysqli_real_escape_string($link, $_POST['username']) . "'
					AND
						password = '" . sha1($_POST['password']) . "'";

			$result = mysqli_query($link, $sql);
			if(!$result)
			{
				//something went wrong, display the error
				echo 'Something went wrong while signing in. Please try again later.';
				echo mysqli_error($link); //debugging purposes, uncomment when needed
			}
			else
			{
				//the query was successfully executed, there are 2 possibilities
				//1. the query returned data, the user can be signed in
				//2. the query returned an empty result set, the credentials were wrong
				if(mysqli_num_rows($result) == 0)
				{
					echo 'You have supplied a wrong user/password combination. Please try again.';
				}
				else
				{
					//set the $_SESSION['signed_in'] variable to TRUE
					$_SESSION['signed_in'] = true;

					//we also put the user_id and user_name values in the $_SESSION, so we can use it at various pages
					while($row = mysqli_fetch_assoc($result))
					{
						$_SESSION['id'] 	= $row['id'];
						$_SESSION['username'] 	= $row['username'];
						$_SESSION['user_level'] = $row['user_level'];
					}

					echo '<META HTTP-EQUIV="Refresh" Content="0; URL=index.php">';
				}
			}
		}
	}
}

?>