/**

  * $Id: hook.h 662 2008-03-02 11:38:08Z nkeynes $

  *

  * This file defines some useful generic macros for hooks

  *

  * Copyright (c) 2008 Nathan Keynes.

  *

  * 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.

  */

 #ifndef lxdream_hook_H

 #define lxdream_hook_H 1

 #include <assert.h>

 /**

  * Hook functions are generally useful, so we'd let to limit the overhead (and 

  * opportunity for stupid bugs) by minimizing the amount of code involved. Glib

  * has GHook (and of course signals), but they don't actually simplify anything

  * at this level.

  * 

  * Hence, the gratuitous macro abuse here.

  * 

  * Usage:

  * 

  * In header file:

  * 

  * DECLARE_HOOK( hook_name, hook_fn_type );

  * 

  * In implementation file:

  * 

  * DEFINE_HOOK( hook_name, hook_fn_type );

  *

  */

 #define DECLARE_HOOK( name, fn_type ) \

     void register_##name( fn_type fn, void *user_data ); \

     void unregister_##name( fn_type fn, void *user_data );

 #define FOREACH_HOOK( h, name ) struct name##_hook_struct *h; for( h = name##_hook_list; h != NULL; h = h->next )

 #define CALL_HOOKS( name, args... ) FOREACH_HOOK(h, name) { h->fn(args, h->user_data); } 

 #define DEFINE_HOOK( name, fn_type ) \

     struct name##_hook_struct { \

         fn_type fn; \

         void *user_data; \

         struct name##_hook_struct *next; \

     } *name##_hook_list = NULL; \

     void register_##name( fn_type fn, void *user_data ) { \

         struct name##_hook_struct *h = malloc(sizeof(struct name##_hook_struct)); \

         assert(h != NULL); \

         h->fn = fn; \

         h->user_data = user_data; \

         h->next = name##_hook_list; \

         name##_hook_list = h; \

     } \

     void unregister_##name( fn_type fn, void *user_data ) { \

         struct name##_hook_struct *last = NULL, *h = name##_hook_list; \

         while( h != NULL )  { \

             if( h->fn == fn && h->user_data == user_data ) { \

                 if( last == NULL ) { \

                     name##_hook_list = h->next; \

                 } else { \

                     last->next = h->next; \

                 } \

                 free( h ); \

             } \

             last = h; \

             h = h->next; \

         }\

     }

 #endif /* !lxdream_hook_H */