/**
 *
 * Copyright (c) 2006-2017, Speedment, Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); You may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at:
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.speedment.runtime.field.internal.comparator;

import com.speedment.runtime.field.ComparableField;
import com.speedment.runtime.field.comparator.FieldComparator;
import com.speedment.runtime.field.comparator.NullOrder;
import java.util.Objects;
import static java.util.Objects.requireNonNull;

/**
 * The default implementation of the {@link ReferenceFieldComparator} interface.
 * 
 * @param <ENTITY>  the entity type
 * @param <D>       the database type
 * @param <V>       the value type
 * 
 * @author  Per Minborg
 * @author  Emil Forslund
 * @since   2.2.0
 */
public final class ReferenceFieldComparatorImpl
    <ENTITY, D, V extends Comparable<? super V>> 
implements ReferenceFieldComparator<ENTITY, D, V> {

    private final ComparableField<ENTITY, D, V> field;
    private final NullOrder nullOrder;
    private final boolean reversed;
    
    public ReferenceFieldComparatorImpl(
        final ComparableField<ENTITY, D, V> field, 
        final NullOrder nullOrder
    ) {
        this(field, nullOrder, false);
    }

    public ReferenceFieldComparatorImpl(
        final ComparableField<ENTITY, D, V> field, 
        final NullOrder nullOrder,
        final boolean reversed
    ) {
        this.field     = requireNonNull(field);
        this.nullOrder = requireNonNull(nullOrder);
        this.reversed  = reversed;
    }

    @Override
    public ComparableField<ENTITY, D, V> getField() {
        return field;
    }

    @Override
    public NullOrder getNullOrder() {
        return nullOrder;
    }

    @Override
    public boolean isReversed() {
        return reversed;
    }

    @Override
    public FieldComparator<ENTITY, V> reversed() {
        return new ReferenceFieldComparatorImpl<>(field, nullOrder, !reversed);
    }
    
    // TODO: Improve performance of chained comparators.

    @Override
    public int compare(ENTITY o1, ENTITY o2) {
        final V o1Value = field.get(requireNonNull(o1));
        final V o2Value = field.get(requireNonNull(o2));
        
        if (o1Value == null && o2Value == null) {
            if (NullOrder.NONE == nullOrder) {
                throw new NullPointerException(
                    "Both fields were null and null fields not allowed"
                );
            }
            return 0;
        } else if (o1Value == null) {
            return forNull(Parameter.FIRST);
        } else if (o2Value == null) {
            return forNull(Parameter.SECOND);
        }
        
        return applyReversed(o1Value.compareTo(o2Value));
    }
    
    @Override
    public int hashCode() {
        return ((4049 + Objects.hashCode(field.identifier())) * 3109
            + nullOrder.hashCode()) * 1039
            + Boolean.hashCode(reversed);
    }
    
    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (!(obj instanceof FieldComparator)) return false;
        
        @SuppressWarnings("unchecked")
        final FieldComparator<ENTITY, V> casted =
            (FieldComparator<ENTITY, V>) obj;
        
        return reversed  == casted.isReversed()
            && nullOrder == casted.getNullOrder()
            && Objects.equals(
                field.identifier(),
                casted.getField().identifier()
            );
    }
    
    @Override
    public String toString() {
        return "(order by " + field.identifier() + " " +
            (reversed ? "descending" : "ascending") + ")";
    }

    private int forNull(Parameter parameter) {
        final int firstOutcome = Parameter.FIRST.equals(parameter) ? -1 : 1;
        final int lastOutcome  = -firstOutcome;
        
        switch (nullOrder) {
            case FIRST : return applyReversed(firstOutcome);
            case LAST  : return applyReversed(lastOutcome);
            case NONE  : throw new NullPointerException(
                "A field was null and null fields not allowed"
            );
            default : throw new IllegalStateException("Illegal NullOrder");
        }
    }

    private int applyReversed(int compare) {
        return reversed ? -compare : compare;
    }
    
    private enum Parameter {
        FIRST, SECOND
    }
}