<?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;
      }
  }