Web Browser Bookmarking in PHP

An essential feature of any modern web browser is the ability to bookmark your favorite websites so you can quickly revisit them later. Here, we'll be creating a basic bookmark service that will implement commands for bookmarking the currently visited URL, as well as the ability to undo and redo actions.

Web Browser:

class WebBrowser
{
   private $currentUrl;
   private $bookmarks;

   function __construct()
   {
       $this->currentUrl = "";
       $this->bookmarks = array();
   }

   public function Navigate($url)
   {
       $this->currentUrl = $url;
   }

   public function GetCurrentUrl()
   {
       return $this->currentUrl;
   }

   public function BookmarkCurrentPage()
   {
       if(strlen($this->currentUrl) > 0 
       && !in_array($this->currentUrl, $this->bookmarks))
       {
           $this->bookmarks[] = $this->currentUrl;
       }
   }

   public function RemoveBookmark($url)
   {
       if (($key = array_search($url, $this->bookmarks)) !== false) {
           unset($this->bookmarks[$key]);
       }
   }

   public function PrintBookmarks()
   {
       echo "Bookmarks:\n";
       foreach($this->bookmarks as $bookmark)
       {
           echo "\t" . $bookmark . "\n";
       }
   }
}

IUndoableCommand:

interface IUndoableCommand
{
   public function Execute();
   public function Undo();
   public function Redo();
}

AddBookmarkCommand:

class AddBookmarkCommand implements IUndoableCommand
{
   private $webBrowser;
   private $url;

   function __construct($webBrowser)
   {
       $this->webBrowser = $webBrowser;
       $this->url = "";
   }

   public function Execute()
   {
       $this->url = $this->webBrowser->GetCurrentUrl();
       $this->webBrowser->BookmarkCurrentPage();
   }

   public function Undo()
   {
       $this->webBrowser->RemoveBookmark($this->url);
   }

   public function Redo()
   {
       $this->Execute();
   }

}

With the bookmark command, we'll create our Bookmarker that will hold two stacks for the undo and redo commands.

Bookmarker:

class Bookmarker
{
   private $webBrowser;
   private $undoStack;
   private $redoStack;

   function __construct($webBrowser)
   {
       $this->webBrowser = $webBrowser;
       $this->undoStack = array();
       $this->redoStack = array();
   }

   public function BookmarkCurrentPage()
   {
       $command = new AddBookmarkCommand($this->webBrowser);
       $this->undoStack[] = $command;

       $this->redoStack = array();
       
       $command->Execute();
   }

   public function UndoBookmark()
   {
       if(!empty($this->undoStack))
       {
           $command = array_pop($this->undoStack);
           $this->redoStack[] = $command;
           $command->Undo();
       }
   }

   public function RedoBookmark()
   {
       if(!empty($this->redoStack))
       {
           $command = array_pop($this->redoStack);
           $this->undoStack[] = $command;
           if($command instanceof AddBookmarkCommand)
           {
               $command->Redo();
           }
           
       }
   }
}

Demo:

$memeSurfer = new WebBrowser();
$bookmarker = new Bookmarker($memeSurfer);

$memeSurfer->Navigate("dankMemes.gov");
$bookmarker->BookmarkCurrentPage();

$memeSurfer->PrintBookmarks();

$memeSurfer->Navigate("normieMemes.co");
$bookmarker->BookmarkCurrentPage();

$memeSurfer->PrintBookmarks();

$bookmarker->UndoBookmark();

$memeSurfer->PrintBookmarks();

$bookmarker->RedoBookmark();

$memeSurfer->PrintBookmarks();