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 OffsetConstraint implements Constraint {
	private Var<Integer> x, y;
	int offset;
	Propagator propX, propY;

	public OffsetConstraint(int offset, Var<Integer> x, Var<Integer> y) {
		this.offset = offset;
		this.x = x;
		this.y = y;
		propX = new OffsetProp(offset, x, y);
		propY = new OffsetProp(-offset, y, x);
	}

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

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

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

	@Override
	public Satisfiability getSatisfiability() {
		HashSet<Integer> shiftedRange = new HashSet<Integer>();
		for (int val : x.getRange()) {
			shiftedRange.add(val + offset);
		}
		shiftedRange.retainAll(y.getRange());
		if (shiftedRange.isEmpty()) {
			return Satisfiability.UNSAT;
		} else if (x.getRange().size() == 1 && y.getRange().size() == 1) {
			return Satisfiability.TAUT;
		} else {
			return Satisfiability.SAT;
		}
	}

}