package jrummikub.ai.fdsolver.constraint;

import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;

import jrummikub.ai.fdsolver.Constraint;
import jrummikub.ai.fdsolver.Propagator;
import jrummikub.ai.fdsolver.Satisfiability;
import jrummikub.ai.fdsolver.Var;

public class SameConstraint<T> implements Constraint {
	private Var<T> x, y;
	Propagator propX, propY;

	public SameConstraint(Var<T> x, Var<T> y) {
		this.x = x;
		this.y = y;
		propX = new SameProp<T>(x, y);
		propY = new SameProp<T>(y, x);
	}

	@Override
	public Collection<Var<?>> getWatchedVars() {
		return Arrays.<Var<?>> asList(x, y);
	}
	
	private class SameProp<T> implements Propagator {
		private Var<T> x, y;
		public SameProp(Var<T> x, Var<T> y) {
			this.x = x;
			this.y = y;
		}
		
		@Override
		public Collection<Var<?>> getWatchedVars() {
			return Arrays.<Var<?>>asList(y);
		}

		@Override
		public void propagate() {
			for(Iterator<T> i = x.iterator(); i.hasNext();) {
				if(!y.getRange().contains(i.next())) {
					i.remove();
				}
			}
		}
	}
	

	@Override
	public Collection<Propagator> getPropagators(boolean negate) {
		return Arrays.asList(propX, propY);
	}

	@Override
	public Satisfiability getSatisfiability() {
		HashSet<T> range = new HashSet<T>(x.getRange());
		range.retainAll(y.getRange());
		if (range.isEmpty()) {
			return Satisfiability.UNSAT;
		} else if (x.getRange().size() == 1 && y.getRange().size() == 1) {
			return Satisfiability.TAUT;
		} else {
			return Satisfiability.SAT;
		}
	}

}