#include "structures.h"

extern SystemCallDescriptor sys_preds[];
extern int SysCount;

/*
============================================================
|                    GetSysDescriptor()                    |
|----------------------------------------------------------|
| Params : 1)a functor                                     |
|                                                          |
| Returns: The pointer to the descriptor of the system     |
|          predicate, if functor is a system predicate.    |
|          NULL otherwise                                  |
|==========================================================|
*/
SystemCallDescriptor *GetSysDescriptor(int functor)
{
   int k,i=0,j=SysCount;
   SystemCallDescriptor *res=NULL;
   while(j-i>0 && res==NULL)
   {
      k=i+(j-i)/2;
      if(sys_preds[k].functor==functor)
         res=&sys_preds[k];
      else if (sys_preds[k].functor<functor)
         i=k+1;
      else
         j=k;
   }
   return res;
}

/*
============================================================
|                       system_call()                      |
|----------------------------------------------------------|
| Params : 1)The pointer to the system call descriptor     |
|          2)The pointer to the system call                |
|          3)The vars-list for the term                    |
|          4) the garbage list                             |
|                                                          |
| Desc   : calls the function corresponding to the system  |
|          call, and returns the results as a new vars     |
|          list. If system call has two argument, the first|
|          argument is input and second output. If it has
           one argument, that argument is output.
| Returns: A list of bindings                              |
|==========================================================|
*/
struct list *system_call(SystemCallDescriptor *d,
                         struct term *call_t,
                         var_array *vars,
                         garbage_lists *g)
{
   struct term *input=eval_deref(call_t->argument_array[0],
                                  vars);
   struct list *result=NULL;
   struct term *res=(d->funct)(input);
   if(res!=NULL)
   {
      var_array *local_vars=create_vars(vars->length);
      int match_status;
      g->garbage_vars=cons(local_vars,g->garbage_vars);
      copy_vars(vars,local_vars);
      match_status=match(res,
                         call_t->argument_array[call_t->arity-1],
                         local_vars);
      
      if (match_status==SUCCESS)
         result=g_cons(local_vars,NULL,g);
      else result=NULL;
   }
   else
      result=NULL;
   free(input);
   return result;
}