<?php
 
 namespace Illuminate\View\Engines;
 
 use Closure;
 use InvalidArgumentException;
 
 class EngineResolver
 {
     /**
      * The array of engine resolvers.
      *
      * @var array
      */
     protected $resolvers = [];
 
     /**
      * The resolved engine instances.
      *
      * @var array
      */
     protected $resolved = [];
 
     /**
      * Register a new engine resolver.
      *
      * The engine string typically corresponds to a file extension.
      *
      * @param  string   $engine
      * @param  \Closure  $resolver
      * @return void
      */
     public function register($engine, Closure $resolver)
     {
         unset($this->resolved[$engine]);
 
         $this->resolvers[$engine] = $resolver;
     }
 
     /**
      * Resolve an engine instance by name.
      *
      * @param  string  $engine
      * @return \Illuminate\Contracts\View\Engine
      *
      * @throws \InvalidArgumentException
      */
     public function resolve($engine)
     {
         if (isset($this->resolved[$engine])) {
             return $this->resolved[$engine];
         }
 
         if (isset($this->resolvers[$engine])) {
             return $this->resolved[$engine] = call_user_func($this->resolvers[$engine]);
         }
 
         throw new InvalidArgumentException("Engine [{$engine}] not found.");
     }
 }