/*
  SCOPE.hpp  -  nested search scope for properties of placement
 
  Copyright (C)         Lumiera.org
    2009,               Hermann Vosseler <Ichthyostega@web.de>
 
  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License as
  published by the Free Software Foundation; either version 2 of the
  License, or (at your option) any later version.
 
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
 
  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 
*/


#ifndef MOBJECT_SESSION_SCOPE_H
#define MOBJECT_SESSION_SCOPE_H

#include "proc/mobject/placement.hpp"
#include "proc/mobject/placement-ref.hpp"
#include "lib/error.hpp"


namespace mobject {
namespace session {
  
  LUMIERA_ERROR_DECLARE (NO_PARENT_SCOPE); ///< Parent scope of root not accessible
  LUMIERA_ERROR_DECLARE (INVALID_SCOPE);  ///<  Placement scope invalid and not locatable within model
  
  
  
  /**
   * A Placement scope within the high-level-model.
   * Within the Session/Model, Placements are used to attach
   * MObjects; but beyond that, each Placement can \em contain
   * other Placements, effectively forming a scope. Thus Scope
   * is basically another view on Placements <i>which are attached
   * to the session.</i> This (hidden) link to the session is utilised
   * to establish the nesting of scopes and allow querying and navigating.
   * 
   * Actually, Scope is implemented through a PlacementRef pointing to
   * the Placement which \em constitutes this Scope. We call this Placement
   * the "scope top". A track e.g. can \em contain several clips, but also
   * nested sub tracks, all of which would be within the scope of this track.
   * This scoping relation plays an important role when it comes to \em resolving
   * properties of placement, like e.g. the output designation, overlay mode,
   * sound pan position etc -- properties from enclosing scopes will be 
   * inherited unless \em shaded by local definitions, similar to the
   * behaviour known from most programming languages when referring
   * to local variables. 
   * @note Scope is a passive entity,
   *       basically just wrapping up a Scope-top Placement.
   *       Contrast this to QueryFocus, which actively
   *       maintains the current focus location
   *       and exposes query facilities.
   */
  class Scope
    {
      RefPlacement anchor_;
      
    public:
      Scope (PlacementMO const& constitutingPlacement);
      Scope (); ///< unlocated NIL scope
      
      Scope (Scope const&);
      Scope& operator= (Scope const&);
            
      static const Scope INVALID;

      static Scope containing (PlacementMO const& aPlacement);
      static Scope containing (RefPlacement const& refPlacement);
      
      Scope getParent()      const;
      PlacementMO& getTop()  const;
      bool isValid() const;
      bool isRoot()  const;
      
      friend bool operator== (Scope const&, Scope const&);
      friend bool operator!= (Scope const&, Scope const&);
    };
  
  
  
  
  
  /** as scopes are constituted by a "scope top" element (placement)
   *  registered within the PlacementIndex of the current session,
   *  equality is defined in terms of this defining placement.
   */
  inline bool
  operator== (Scope const& scope1, Scope const& scope2)
  {
    return scope1.anchor_ == scope2.anchor_;
  }
  
  inline bool
  operator!= (Scope const& scope1, Scope const& scope2)
  {
    return scope1.anchor_ != scope2.anchor_;
  }
  
  
  
  
}} // namespace mobject::session
#endif