-- File graphg.adb
--  This is a generic graph package with an active iterator. The package
--  will be used in a larger program that performs graph traversals using
--  the iterator (lab6). For this purpose the iterator is not sufficient,
--  in that the *iterator* marks nodes as visited when they are returned. 
--  This makes it impossible to correctly perform depth-first traversals.
--  The flaws will be fixed in a subsequent version that students
--  implement as a child package of this package.


package body Graphg is

   procedure Clear (AGraph: in out Graph) is
      begin
         for i in 1..AGraph.Size loop
            AGraph.InGraph (i) := False;
            AGraph.Visited (i) := False;
            for j in 1..AGraph.Size loop
               AGraph.Edges (i, j) := False;
            end loop;
         end loop;
      end Clear;

   procedure Add (ANode: in positive;
                  WithValue: in Element;
                  ToGraph: in out Graph) is
      begin
         ToGraph.InGraph (ANode) := True;
         ToGraph.Values (ANode) := WithValue;
      end Add;

   procedure InsertEdge (FromNode: in positive; 
                         ToNode: in positive;
                         InGraph: in out Graph) is
      begin
         InGraph.Edges (FromNode, ToNode) := True;
      end InsertEdge;

   procedure Initialize (AnIterator: out Iterator;
                         ForGraph: in out Graph;
                         ToNode: in positive) is
      begin
         for i in 1..ForGraph.Size loop
            ForGraph.Visited (i) := False;
         end loop;
         ForGraph.Visited (ToNode) := True;
         AnIterator := Iterator (ToNode);
      end Initialize;

   procedure GetNext (IteratorNode: in out Iterator;
                      ForGraph: in out Graph) is
      row: positive := integer (IteratorNode);
      begin
         for i in 1..ForGraph.Size loop
            if ForGraph.Edges (row, i) then
               if not ForGraph.Visited (i) then
                  ForGraph.Visited (i) := True;
                  IteratorNode := Iterator (i);
                  return;
               end if;
            end if;
         end loop;
      end GetNext;

   function ValueOf (IteratorNode: in Iterator;
                     ForGraph: in Graph) return Element is
      begin
         return ForGraph.Values (integer (IteratorNode));
      end ValueOf;

   function Done (IteratorNode: in Iterator;
                  ForGraph: in Graph) return Boolean is
     -- return True if all nodes adjacent to that specified by
     -- IteratorNode have been visited
     row: positive := integer (IteratorNode);
     begin
        for i in 1..ForGraph.Size loop
           if ForGraph.Edges (row, i) then
              if not ForGraph.Visited (i) then
                 return False;
              end if;
           end if;
        end loop;
        return True;
     end Done;

end graphg;