Make a hierarchy in roles

This is more understandable for users.

Security/RoleProvider.php

@@ -32,6 +32,16 @@ class RoleProvider
      */
     private $providers = array();
     
+    /**
+     * an array where keys are the role, and value is the title
+     * for the given role.
+     * 
+     * Null when not initialized.
+     *
+     * @var array|null
+     */
+    private $rolesTitlesCache = null;
+    
     /**
      * Add a role provider
      * 
@@ -75,4 +85,52 @@ class RoleProvider
         return $roles;
     }
     
+    /**
+     * initialize the array for caching role and titles
+     * 
+     */
+    private function initializeRolesTitlesCache()
+    {
+        // break if already initialized
+        if ($this->rolesTitlesCache !== null) {
+            return;
+        }
+        
+        foreach ($this->providers as $provider) {
+            if ($provider instanceof ProvideRoleHierarchyInterface) {
+                foreach ($provider->getRolesWithHierarchy() as $title => $roles) {
+                    foreach($roles as $role) {
+                        $this->rolesTitlesCache[$role] = $title;
+                    }
+                }
+            } else {
+                if ($provider->getRoles() !== null) {
+                    $this->rolesTitlesCache = \array_merge(
+                        $this->rolesTitlesCache, 
+                        \array_fill_keys($provider->getRoles(), null)
+                        );
+                }
+            }
+        }
+    }
+    
+    /**
+     * Get the title for each role.
+     * 
+     * @param string $role
+     * @return string the title of the role
+     */
+    public function getRoleTitle($role)
+    {
+        $this->initializeRolesTitlesCache();
+        
+        if (! \array_key_exists($role, $this->rolesTitlesCache)) {
+            // this case might happens when the role is not described in 
+            // `getRolesWithHierarchy`
+            return null;
+        }
+        
+        return $this->rolesTitlesCache[$role];
+    }
+    
 }