<?php
 
 namespace Illuminate\Support;
 
 class NamespacedItemResolver
 {
     /**
      * A cache of the parsed items.
      *
      * @var array
      */
     protected $parsed = [];
 
     /**
      * Parse a key into namespace, group, and item.
      *
      * @param  string  $key
      * @return array
      */
     public function parseKey($key)
     {
         // If we've already parsed the given key, we'll return the cached version we
         // already have, as this will save us some processing. We cache off every
         // key we parse so we can quickly return it on all subsequent requests.
         if (isset($this->parsed[$key])) {
             return $this->parsed[$key];
         }
 
         // If the key does not contain a double colon, it means the key is not in a
         // namespace, and is just a regular configuration item. Namespaces are a
         // tool for organizing configuration items for things such as modules.
         if (strpos($key, '::') === false) {
             $segments = explode('.', $key);
 
             $parsed = $this->parseBasicSegments($segments);
         } else {
             $parsed = $this->parseNamespacedSegments($key);
         }
 
         // Once we have the parsed array of this key's elements, such as its groups
         // and namespace, we will cache each array inside a simple list that has
         // the key and the parsed array for quick look-ups for later requests.
         return $this->parsed[$key] = $parsed;
     }
 
     /**
      * Parse an array of basic segments.
      *
      * @param  array  $segments
      * @return array
      */
     protected function parseBasicSegments(array $segments)
     {
         // The first segment in a basic array will always be the group, so we can go
         // ahead and grab that segment. If there is only one total segment we are
         // just pulling an entire group out of the array and not a single item.
         $group = $segments[0];
 
         // If there is more than one segment in this group, it means we are pulling
         // a specific item out of a group and will need to return this item name
         // as well as the group so we know which item to pull from the arrays.
         $item = count($segments) === 1
                     ? null
                     : implode('.', array_slice($segments, 1));
 
         return [null, $group, $item];
     }
 
     /**
      * Parse an array of namespaced segments.
      *
      * @param  string  $key
      * @return array
      */
     protected function parseNamespacedSegments($key)
     {
         [$namespace, $item] = explode('::', $key);
 
         // First we'll just explode the first segment to get the namespace and group
         // since the item should be in the remaining segments. Once we have these
         // two pieces of data we can proceed with parsing out the item's value.
         $itemSegments = explode('.', $item);
 
         $groupAndItem = array_slice(
             $this->parseBasicSegments($itemSegments), 1
         );
 
         return array_merge([$namespace], $groupAndItem);
     }
 
     /**
      * Set the parsed value of a key.
      *
      * @param  string  $key
      * @param  array   $parsed
      * @return void
      */
     public function setParsedKey($key, $parsed)
     {
         $this->parsed[$key] = $parsed;
     }
 }