//  This file is identical to the "taskstub.h" file available before
//    November 20, except for the documentation, which has been updated.

//  The classes below are intended for use in the topological sort
//    algorithm.  Note that it is possible to make classes that you
//    derive from "task_stub" private to classes you derive from
//    "taskset_stub".
//  Although sets of tasks can be implemented simply as linked
//    lists of tasks, without needing a separate class, two classes
//    have been provided to emphasize the abstract difference between
//    the class for which "topsort" is appropriate and the class
//    for which "incr_unmet", etc., are appropriate

#include <string.h>
#include <assert.h>
#include <iostream.h>
#include <fstream.h>


// If your C++ implementation has the ANSI standard "bool", you
//   needn't use "boolean"

typedef int boolean;
#define TRUE 1
#define FALSE 0



// task identifiers are just character strings

typedef char * taskid;


//////////////////////////// CLASSES ////////////////////////////////

// The "task_stub" class has 2 data members -- a task identifier "name"
//   and an integer representing the number of unmet prerequisites
// There are member functions to increment or decrement the
//   number of unmet prerequistes of a task, add an element (or "constraint") to
//   the postrequisite list of a task, and and to decrement the number of
//   unmet prerequisites of each task for which the given task
//   is a prerequisite.



class task_stub							{
  protected:
    taskid name;                     // name of task
    int unmet;                       // # of unmet prereqs
    virtual void incr_unmet()=0;
    virtual void decr_unmet()=0;
    virtual void decr_list_unmet()=0;
    task_stub(taskid taskname)
      {int len=strlen(taskname);
       name=new char[1+len];
       assert(name);
       strcpy(name,taskname);
       unmet=0;              }
						};


// In the "taskset_stub" class is represented as a headed linked
//   list of tasks.  There is no constructor; constructors for
//   derived classes should takes an "istream" as argument.  A
//   "topsort" function applies to tasksets and adds the output
//   sequence of task identifiers to an output stream (ostream).

class taskset_stub						{
  protected:
    virtual boolean bad(void)=0;         // tests for ill-formed taskset
    virtual void topsort(ostream &)=0;					};