/* 
 * Kodkod -- Copyright (c) 2005-2011, Emina Torlak
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package kodkod.engine.bool;

import java.util.Iterator;
import java.util.NoSuchElementException;

import kodkod.util.ints.Ints;


/**
 * A logic NOT gate.
 * 
 * @invariant this.op = Operator.NOT
 * @invariant #inputs = 1 
 * @invariant this.label = -inputs.label
 * @invariant label in (-Integer.MAX_VALUE..-1]
 * @author Emina Torlak
 */
public final class NotGate extends BooleanFormula {

	private final int hashcode;
	
	/**
	 * Constructs a new NotGate with the given formula as its input.
	 * @requires input != null && input !in NotGate
	 * @ensures this.inputs' = 0->input && this.output'.label = -input.label
	 */
	NotGate(BooleanFormula input) {
		super(input);
		this.hashcode = Ints.superFastHash(-input.label());
	}
	
	/**
	 * Returns a hash of this inverter's label.
	 * @return Ints.superFastHash(this.label)
	 */
	@Override
	int hash(Operator op) {
		return hashcode;
	}

	/**
	 * Returns an iterator that returns this gate's single input.
	 * @return an iterator over this.inputs.
	 */
	@Override
	public Iterator<BooleanFormula> iterator() {
		return new Iterator<BooleanFormula>() {
			boolean hasNext = true;
			public boolean hasNext() {
				return hasNext;
			}

			public BooleanFormula next() {
				if (!hasNext) throw new NoSuchElementException();
				hasNext = false;
				return negation();
			}

			public void remove() {
				throw new UnsupportedOperationException();
			}
			
		};
	}
	
	/**
	 * Returns the label for this value. 
	 * @return this.label
	 */
	@Override
	public final int label() { return -negation().label(); }
	
	/**
	 * Returns 1.
	 * @return 1.
	 */
	@Override
	public int size() {
		return 1;
	}
	
	/**
	 * Passes this value and the given
	 * argument value to the visitor, and returns the resulting value.
	 * @return the value produced by the visitor when visiting this node
	 * with the given argument.
	 */
	@Override
	public <T, A> T accept(BooleanVisitor<T,A> visitor, A arg) {
		return visitor.visit(this, arg);
	}
	
	/**
	 * Returns a string representation of this inverter.
	 * @return a string representation of this inverter.
	 */
	public String toString() {
		return "!" + negation().toString();
	}

	/**
	 * Returns Operator.NOT.
	 * @return Operator.NOT
	 */
	@Override
	public kodkod.engine.bool.Operator op() {
		return kodkod.engine.bool.Operator.NOT;
	}

	/**
	 * Returns this.input[i].
	 * @return this.input[i]
	 * @throws IndexOutOfBoundsException  i != 0
	 */
	@Override
	public BooleanFormula input(int i) {
		if (i != 0) throw new IndexOutOfBoundsException();
		return negation();
	}

	/**
	 * Returns a hashcode for this inverter.
	 * @return a hashcode for this inverter.
	 */
	public int hashCode() { 
		return hashcode;
	}
}
