PPT generator using SOLID principles

Question

I want to use SOLID more and more but still learning, I'm improving a PPT generator and would like your help applying SOLID principles in it.

• That generator should print two photos per slide, first one to the left, second to the right;
• If the last photo is a left photo, it should be placed in center;
• Each photo has a text right below it;
• I'll use a third party PPT lib to do the low level stuff.

This is what I came up with, a little bit abstracted just to pass the idea, the sample is in PHP but I'll accept answers in any programming language:

class Controller 
{
 $ppt = new Ppt(Ppt::DEFAULT_RESOLUTION, $background, $header, $footer);
 $ppt->writeSlides($photoCollection);
 $pptFile = $ppt->saveToFile();
 $ppt->deleteLocalTemporaryFiles();
 readfile($pptFile);
 unlink($pptFile);
}
class Ppt extends thirdPartyPptLib
{
 const DEFAULT_RESOLUTION = 'x';
 private $resolution;
 private $background;
 private $header;
 private $footer;
 public function __construct($resolution = null, $background = null, $header = null, $footer = null)
 {
 $this->resolution = $resolution;
 $this->background = $background;
 $this->header = $header;
 $this->footer = $footer;
 }
 public function writeSlides(\Traversable $photoCollection)
 {
 $i = 0;
 $count = count($photoCollection);
 foreach ($photoCollection as $photoInfo) {
 $photoToLeft = $i % 2 == 0;
 $isLastPhoto = $i == ($count - 1);
 if ($isLastPhoto) {
 $slide = $this->newSlide(); 
 $slide->addCenterPhotoInfo($photoInfo); 
 } else if ($photoToLeft) {
 $slide = $this->newSlide(); 
 $slide->addLeftPhotoInfo($photoInfo); 
 } else {
 $slide->addRightPhotoInfo($photoInfo); 
 } 
 $i++; 
 }
 }
 private function newSlide()
 {
 $slide = parent->newSlide();
 if ($this->hasBackground()) {
 $slide->setBackground();
 }
 if ($this->hasHeader()) {
 $slide->setHeader();
 }
 if ($this->hasFooter()) {
 $slide->setFooter();
 } 
 return $slide;
 }
}
class Slide extends thirdPartyPptLibSlide
{
 public function addLeftPhotoInfo($photoInfo)
 {
 $this->addLeftPhoto($photoInfo->getPhoto());
 $this->addUnderlyingText($photoInfo->getText());
 }
 // functions addRightPhotoInfo and addCenterPhotoInfo very similar
}

Should I separate it more into different classes? Or methods? Should I create Interfaces?

Answer 1

You can remove the overloading of properties from constructor. This way you can improve the code maintaning and readability.

An example of improvement:

class Style {
 // Properties here 
}
class Ppt {
 public function __construct(Style $style) {
 }
}

Now you pass just the object of style with all the needed properties.