ContentItemMapper.php

<?php

class ContentItemMapper implements MapperInterface
{
    private $isLoaded = false;
    
    // ------------------------------------------------------
    
    public function __construct(MapperCollection $mappers, IdentityMap $idMap, SplFileInfoToContentItem $transformer, $contentPath)
    {
        $mappers->add('contentItems', $this);
        
        $this->mappers      = $mappers;
        $this->idMap        = $idMap;
        $this->transformer  = $transformer;
        $this->contentPath  = $contentPath;
    }
    
    // ------------------------------------------------------
    
    public function getItem($identifier)
    {
        // Be sure we have loaded the items
        if ( ! $this->isLoaded) {
            $this->getItems();
        }
        
        return $this->idMap->get('\Skimpy\Entity\Term', $identifier);
    }
    
    // ------------------------------------------------------

    public function getItems()
    {
        
        foreach ($this->getContentFiles() as $f) {
            
            $obj = $this->transformer->transform($f)
        
            // As we are loading, we need to populate the 'terms' property with
            // Term objects from the TermMapper 
            // (or you could do this in the transformer class...)
            $obj->setTerms(new LazyLoadedCollection('terms', $termSlugsFromFileHere));
        
            // Add it to the identityMap
            $this->idMap->load($obj);
        }
       
        // Set isLoaded is true so we don't read the filesystem for every call to this method
        $this->isLoaded = true;
        
        // Get the items from the identiy map
        return $this->idMap->getType('\Skimpy\Entity\Term');
    }
    
    // ------------------------------------------------------
    
    protected function readItemFiles()
    {
        return (new Finder)->in($this->contentPath)->files();
    }
}

LazyLoadedCollection.php

<?php

/**
 * Lazy Loaded Collection represents a collection of objects
 * that don't exist when the object is constructed, but only loaded
 * when requested
 */
class LazyLoadedCollection implements \IteratorAggregate, \Countable
{
    public function __construct(MapperInterface $mapper, array $identifiers)
    {
        $this->items = [];
        $this->mapper = $mapper;
        $this->ids = $identifiers;
    }
    
    public function getIterator()
    {
        $this->loadEm();
        return new \ArrayIterator($this->items);
    }
    
    public function count()
    {
        $this->loadEm();
        return count($this->items);
    }
    
    protected function loadEm()
    {
        // Only laoad em once
        if ( ! empty($this->items)) {
            return;
        }
        
        foreach ($this->ids as $identifier) {
            $this->items[$identifier] = $this->mapper->getItem($identifier);
        }
    }
}

MapperCollection.php

<?php

class MapperCollection
{
    /**
     * @var array
     */
    private $mappers;
    
    /**
     * Add a mapper
     */
    public function add($mapperName, MapperInterface $mapper);
    
    /**
     * Get a mapper
     * 
     * @return MapperInterface
     * @throws MapperNotFoundException  If could not find that mapper
     */
    public function get($mapperName);
}

MapperInterface.php

<?php

interface MapperInterface
{
    function getItems();
    
    function getItem($identifier);
}