Undo / redo edits to a PDF file using PHP

<?php
//---------------------------------------------------------------------------------------
// Copyright (c) 2001-2023 by Apryse Software Inc. All Rights Reserved.
// Consult LICENSE.txt regarding license information.
//---------------------------------------------------------------------------------------
if(file_exists("../../../PDFNetC/Lib/PDFNetPHP.php"))
include("../../../PDFNetC/Lib/PDFNetPHP.php");
include("../../LicenseKey/PHP/LicenseKey.php");

// Relative path to the folder containing the test files.
$input_path = getcwd()."/../../TestFiles/";
$output_path = $input_path."Output/";

//---------------------------------------------------------------------------------------
// The following sample illustrates how to use the UndoRedo API.
//---------------------------------------------------------------------------------------
	
	// The first step in every application using PDFNet is to initialize the 
	// library and set the path to common PDF resources. The library is usually 
	// initialized only once, but calling Initialize() multiple times is also fine.
	PDFNet::Initialize($LicenseKey);
	PDFNet::GetSystemFontList();    // Wait for fonts to be loaded if they haven't already. This is done because PHP can run into errors when shutting down if font loading is still in progress.
	
	// Open the PDF document.
	$doc = new PDFDoc($input_path."newsletter.pdf");
	
	$undo_manager = $doc->GetUndoManager();

	// Take a snapshot to which we can undo after making changes.
	$snap0 = $undo_manager->TakeSnapshot();

	$snap0_state = $snap0->CurrentState();
	
	// Start a new page
	$page = $doc->PageCreate();
	
	$builder = new ElementBuilder();	// Used to build new Element objects
	$writer = new ElementWriter();		// Used to write Elements to the page
	
	$page = $doc->PageCreate();		// Start a new page
	$writer->Begin($page);			// Begin writing to this page
	
	// ----------------------------------------------------------
	// Add JPEG image to the output file
	$img = Image::Create($doc->GetSDFDoc(), $input_path."peppers.jpg");
	
	$element = $builder->CreateImage($img, new Matrix2D(200.0,0.0,0.0,250.0,50.0,500.0));
	$writer->WritePlacedElement($element);
	
	// Finish writing to the page
	$writer->End();
	$doc->PagePushFront($page);
	
	// Take a snapshot after making changes, so that we can redo later (after undoing first).
	$snap1 = $undo_manager->TakeSnapshot();
	
	if ($snap1->PreviousState()->Equals($snap0_state))
	{
		echo(nl2br("snap1 previous state equals snap0_state; previous state is correct\n"));
	}

	$snap1_state = $snap1->CurrentState();

	$doc->Save($output_path."addimage.pdf", SDFDoc::e_incremental);

	if ($undo_manager->CanUndo())
	{
		$undo_snap = $undo_manager->Undo();

		$doc->Save($output_path."addimage_undone.pdf", SDFDoc::e_incremental);

		$undo_snap_state = $undo_snap->CurrentState();

		if ($undo_snap_state->Equals($snap0_state))
		{
			echo(nl2br("undo_snap_state equals snap0_state; undo was successful\n"));
		}
		
		if ($undo_manager->CanRedo())
		{
			$redo_snap = $undo_manager->Redo();

			$doc->Save($output_path."addimage_redone.pdf", SDFDoc::e_incremental);

			if ($redo_snap->PreviousState()->Equals($undo_snap_state))
			{
				echo(nl2br("redo_snap previous state equals undo_snap_state; previous state is correct\n"));
			}
			
			$redo_snap_state = $redo_snap->CurrentState();
			
			if ($redo_snap_state->Equals($snap1_state))
			{
				echo(nl2br("Snap1 and redo_snap are equal; redo was successful\n"));
			}
		}
		else
		{
			echo(nl2br("Problem encountered - cannot redo.\n"));
		}
	}
	else
	{
		echo(nl2br("Problem encountered - cannot undo.\n"));
	}
	PDFNet::Terminate();
?>