/**
 * This is a Janet Compose task for a generic branch & bound algorithm.
 */
package janet.services.tasks;
import  janet.applications.branchandbound.*;
import  janet.services.*;
import  janet.services.shared.*;
import java.rmi.*;

/** A compositional Task, whose inputs & output are Solution objects,
 * used in branch & bound applications.
 */
public final class MinSolution extends Compose
{	
    /** This method returns the Solution Object among its inputs, whose IntUpperBound
     * has minimal intValue, provided that it is at least as low as the Shared
     * objects intValue. Otherwise, it returns null, indicating that none of its
     * input Solution objects is the current best.
     * @param environment The environment's Shared Object defines the currently best known
     * minimal intValue associated with a Solution. It is possible,
     * though unlikely, that the Task's input Solutions contain a better
     * one than the TaskServer knows about, as reflected in the
     * Environment's Shared object's intValue. If this occurs, a side-effect
     * of the execute method is to update the Environment's Shared object accordingly.
     * @return the Solution Object among its inputs, whose IntUpperBound
     * has minimal intValue, provided that it is at least as low as the Shared
     * objects intValue. Otherwise, it returns null, indicating that none of its
     * input Solution objects is the current best.
     */    
    public Object execute ( Environment environment )
    {
        Solution currentBest = null;
        for ( int i = 0; i < numInputs(); i++ ) 
        {
            Solution reportedSolution = (Solution) getInput( i );            
            if ( reportedSolution == null ) 
            {
                continue; // subTask: "No better solution found."
            }        
            int lowerBound = reportedSolution.getLowerBound( environment );
            
            /** The = of <= is needed to return the shared upper bound solution
             * which occurs when that solution is among this task's inputs.
             */
            if ( lowerBound <= sharedUpperBoundValue( environment ) ) 
            {
                environment.setShared( new IntUpperBound( lowerBound ) );
                currentBest = reportedSolution;
            }
        }
        return currentBest;
    }
    
    // return int value of shared IntUpperBound
    private int sharedUpperBoundValue( Environment environment )
    {
        return ( (Integer) environment.getShared().get() ).intValue();     
    }
}