//
// Slack-Based Heuristics for Constraint Satisfaction Scheduling
// Stephen F. Smith and Cheng-Chung Cheng
// Proceedings AAAI-93
//
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.search.strategy.selectors.values.IntValueSelector;
import java.util.*;

public class FuzzyMinSlackValue implements IntValueSelector {

    Random gen;
    double p; // probability that we accept heuristic advice

    FuzzyMinSlackValue(double p){
	super();
	gen = new Random();
	this.p = p;
    }
    
    @Override
    public int selectValue(IntVar v){
	if (gen.nextDouble() <= p){
	    Decision dec = (Decision) v;
	    int slack_0 = slack(dec.op_i.start,dec.op_i.duration,dec.op_j.start,dec.op_j.duration);
	    int slack_1 = slack(dec.op_j.start,dec.op_j.duration,dec.op_i.start,dec.op_i.duration);
	    if (slack_0 > slack_1) return 1; else return 0;
	}
	else if (gen.nextDouble() < 0.5) return 0; else return 1;
    }
    //
    // decision = 0 -> op_i before op_j
    // decision = 1 -> op_j before op_i
    //

    private int slack(IntVar op_i,int d_i,IntVar op_j,int d_j){
	return op_j.getUB() - Math.max(op_i.getLB() + d_i,op_j.getLB());
    }
    //
    // slack if op_i before op_j 
    // i.e. slack(op_i -> op_j) in S&C AAAI-93 parlance
    //
    // NOTE: we consider earliest and latest start times whereas S&C
    //       consider earliest start and latest finish, but our calculations
    //       are exactly the same
    //
    
}