/**
 * Copyright (c) 2014, University of Warsaw
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this list of
 * conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
 * conditions and the following disclaimer in the documentation and/or other materials provided
 * with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
 * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package pl.edu.mimuw.cloudatlas.model;

import pl.edu.mimuw.cloudatlas.model.Value;
import pl.edu.mimuw.cloudatlas.model.ValueNull;

/**
 * A special null value of an unknown type. This class is a singleton.
 *
 * @see TypePrimitve#NULL
 * @see Type#isCompatible(Value)
 */
public class ValueNull extends Value {
    private static ValueNull instance = null;

    private ValueNull() {}

    /**
     * Gets a singleton instance of the <code>ValueNull</code> class. Every call to this method returns the same
     * reference.
     *
     * @return an instance of <code>ValueNull</code>
     */
    public static ValueNull getInstance() {
        if(instance == null)
            instance = new ValueNull();
        return instance;
    }

    @Override
    public Value getDefaultValue() {
        return instance;
    }

    @Override
    public Value convertTo(Type type) {
        switch(type.getPrimaryType()) {
            case STRING:
                return ValueString.NULL_STRING;
            default:
                return this;
        }
    }

    @Override
    public Type getType() {
        return TypePrimitive.NULL;
    }

    @Override
    public boolean isNull() {
        return true;
    }

    @Override
    public Value isEqual(Value value) {
        return new ValueBoolean(isNull() && value.isNull());
    }

    @Override
    public Value isLowerThan(Value value) {
        if(value == getInstance())
            return this;
        return value.isLowerThan(this);
    }

    @Override
    public Value addValue(Value value) {
        if(value == getInstance())
            return this;
        return value.addValue(this);
    }

    @Override
    public Value subtract(Value value) {
        if(value == getInstance())
            return this;
        return value.subtract(this);
    }

    @Override
    public Value multiply(Value value) {
        if(value == getInstance())
            return this;
        return value.multiply(this);
    }

    @Override
    public Value divide(Value value) {
        if(value == getInstance())
            return this;
        return value.divide(this);
    }

    @Override
    public Value modulo(Value value) {
        if(value == getInstance())
            return this;
        return value.modulo(this);
    }

    @Override
    public Value and(Value value) {
        if(value == getInstance())
            return this;
        return value.and(this);
    }

    @Override
    public Value or(Value value) {
        if(value == getInstance())
            return this;
        return value.or(this);
    }

    @Override
    public Value regExpr(Value value) {
        if(value == getInstance())
            return this;
        return value.regExpr(this);
    }

    @Override
    public Value negate() {
        return this;
    }

    @Override
    public Value valueSize() {
        return this;
    }
}