/*
 * Copyright 2008,  Unitils.org
 *
 * 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 org.unitils.reflectionassert;

import org.unitils.core.UnitilsException;
import org.unitils.reflectionassert.comparator.Comparator;
import org.unitils.reflectionassert.difference.Difference;

import java.util.IdentityHashMap;
import java.util.List;
import java.util.Map;


/**
 * A comparator for comparing two values by reflection.
 * <p/>
 * The actual comparison of the values is implemented as a comparator chain. The chain is passed as an argument
 * during the construction. Each of the comparators in the chain is able to compare some types of values. E.g.
 * a CollectionComparator is able to compare collections, simple values such as integers are compared by the
 * SimpleCasesComparator...  A number of 'leniency levels' can also be added to the chain: e.g. the
 * LenientOrderCollectionComparator ignores the actual ordering of 2 collections.
 * <p/>
 * The preferred way of creating new instances is by using the ReflectionComparatorFactory. This factory will make
 * sure that a correct comparator chain is assembled.
 * <p/>
 * A readable report differences can be created using the DifferenceReport.
 *
 * @author Tim Ducheyne
 * @author Filip Neven
 */
public class ReflectionComparator {

    /**
     * The comparator chain.
     */
    protected List<Comparator> comparators;

    /**
     * A cache of results, so that comparisons are only performed once and infinite loops because of cycles are avoided
     * A different cache is used dependent on whether only the first difference is required or whether we need all
     * differences, since the resulting {@link Difference} objects differ. 
     */
    protected Map<Object, Map<Object, Difference>> firstDifferenceCachedResults = new IdentityHashMap<Object, Map<Object, Difference>>();
    protected Map<Object, Map<Object, Difference>> allDifferencesCachedResults = new IdentityHashMap<Object, Map<Object, Difference>>();


    /**
     * Creates a comparator that will use the given chain.
     *
     * @param comparators The comparator chain, not null
     */
    public ReflectionComparator(List<Comparator> comparators) {
        this.comparators = comparators;
    }


    /**
     * Checks whether there is no difference between the left and right objects.
     *
     * @param left  the left instance
     * @param right the right instance
     * @return true if there is no difference, false otherwise
     */
    public boolean isEqual(Object left, Object right) {
        Difference difference = getDifference(left, right, true);
        return difference == null;
    }


    /**
     * Checks whether there is a difference between the left and right objects.
     *
     * @param left  the left instance
     * @param right the right instance
     * @return the difference, null if there is no difference
     */
    public Difference getDifference(Object left, Object right) {
        return getDifference(left, right, false);
    }


    /**
     * Checks whether there are differences between the left and right objects. This will return the root difference
     * of the whole difference tree containing all the differences between the objects.
     *
     * @param left                the left instance
     * @param right               the right instance
     * @param onlyFirstDifference True if the comparison should stop at the first differnece
     * @return the root difference, null if there is no difference
     */
    public Difference getDifference(Object left, Object right, boolean onlyFirstDifference) {
        // check whether difference is available in cache
        Map<Object, Difference> cachedResult = getCachedDifference(left, onlyFirstDifference);
        if (cachedResult != null) {
            if (cachedResult.containsKey(right)) {
                // found difference in cache, return cached value
                return cachedResult.get(right);
            }
        } else {
            cachedResult = new IdentityHashMap<Object, Difference>();
            saveResultInCache(left, cachedResult, onlyFirstDifference);
        }
        cachedResult.put(right, null);

        // perform actual comparison by iterating over the comparators
        boolean compared = false;
        Difference result = null;
        for (Comparator comparator : comparators) {
            if (comparator.canCompare(left, right)) {
                result = comparator.compare(left, right, onlyFirstDifference, this);
                compared = true;
                break;
            }
        }

        // check whether a suitable comparator was found
        if (!compared) {
            throw new UnitilsException("Could not determine differences. No comparator found that is able to compare the values. Left: " + left + ", right " + right);
        }

        // register outcome in cache
        cachedResult.put(right, result);
        return result;
    }

    protected void saveResultInCache(Object left, Map<Object, Difference> cachedResult, boolean onlyFirstDifference) {
        if (onlyFirstDifference) {
            firstDifferenceCachedResults.put(left, cachedResult);
        } else {
            allDifferencesCachedResults.put(left, cachedResult);
        }
    }

    protected Map<Object, Difference> getCachedDifference(Object left, boolean onlyFirstDifference) {
        if (onlyFirstDifference) {
            return firstDifferenceCachedResults.get(left);
        } else {
            return allDifferencesCachedResults.get(left);
        }
    }
}