//   Copyright 2012 Georg-August-Universität Göttingen, Germany
//
//   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 de.ugoe.cs.autoquest.tasktrees.taskequality;

import java.util.List;

import de.ugoe.cs.autoquest.tasktrees.treeifc.ISelection;
import de.ugoe.cs.autoquest.tasktrees.treeifc.ITask;

/**
 * <p>
 * this task comparison rule is capable of comparing selections. If both selections do not have
 * children, they are treated as lexically equal. If they have children, each child of both
 * selections is compared to each child of the respective other selection. The resulting equality
 * is the most concrete one of all these comparisons. I.e. if all children are at least lexically
 * equal, then the selections are lexically equal. If all children are at least syntactically
 * equal, then the selections are syntactically equal. If all children are at least semantically
 * equal, then the selections are semantically equal. If only one of the selections has children,
 * then the selections are unequal. The comparison is broken up, if only a specific equality is
 * checked for and this equality is ensured.
 * </p>
 * 
 * @version $Revision: $ $Date: 19.02.2012$
 * @author 2012, last modified by $Author: patrick$
 */
public class SelectionComparisonRule implements TaskComparisonRule {

    /** the rule manager for internally comparing tasks */
    private TaskEqualityRuleManager mRuleManager;

    /**
     * <p>
     * simple constructor to provide the rule with the task equality rule manager to be able
     * to perform comparisons of the children of provided tasks
     * </p>
     * 
     * @param ruleManager the rule manager for comparing tasks
     */
    SelectionComparisonRule(TaskEqualityRuleManager ruleManager) {
        super();
        mRuleManager = ruleManager;
    }

    /* (non-Javadoc)
     * @see NodeComparisonRule#isApplicable(ITask, ITask)
     */
    @Override
    public boolean isApplicable(ITask task1, ITask task2) {
        return (task1 instanceof ISelection) && (task2 instanceof ISelection);
    }

    /* (non-Javadoc)
     * @see NodeComparisonRule#areLexicallyEqual(ITask, ITask)
     */
    @Override
    public boolean areLexicallyEqual(ITask task1, ITask task2) {
        TaskEquality equality = getEquality(task1, task2, TaskEquality.LEXICALLY_EQUAL);
        return (equality != null) && (equality.isAtLeast(TaskEquality.LEXICALLY_EQUAL));
    }

    /* (non-Javadoc)
     * @see NodeComparisonRule#areSyntacticallyEqual(ITask, ITask)
     */
    @Override
    public boolean areSyntacticallyEqual(ITask task1, ITask task2) {
        TaskEquality equality = getEquality(task1, task2, TaskEquality.SYNTACTICALLY_EQUAL);
        return (equality != null) && (equality.isAtLeast(TaskEquality.SYNTACTICALLY_EQUAL));
    }

    /* (non-Javadoc)
     * @see NodeComparisonRule#areSemanticallyEqual(ITask, ITask)
     */
    @Override
    public boolean areSemanticallyEqual(ITask task1, ITask task2) {
        TaskEquality equality = getEquality(task1, task2, TaskEquality.SEMANTICALLY_EQUAL);
        return (equality != null) && (equality.isAtLeast(TaskEquality.SEMANTICALLY_EQUAL));
    }

    /* (non-Javadoc)
     * @see NodeComparisonRule#compare(ITask, ITask)
     */
    @Override
    public TaskEquality compare(ITask task1, ITask task2) {
        return getEquality(task1, task2, null);
    }

    /**
     * <p>
     * compares two selections with each other checking for the provided required level of
     * equality. If this level is ensured, the method immediately returns. The more concrete
     * the required equality level, the more checks this method performs.
     * </p>
     * 
     * @param task1                 the first task to be compared
     * @param task2                 the second task to be compared
     * @param requiredEqualityLevel the equality level to be checked for
     * 
     * @return the determined equality.
     */
    private TaskEquality getEquality(ITask task1, ITask task2, TaskEquality requiredEqualityLevel) {
        List<ITask> children1 = ((ISelection) task1).getChildren();
        List<ITask> children2 = ((ISelection) task2).getChildren();

        // if both selections do not have children, they are lexically equal. If only one of them
        // has children, they are unequal.
        if ((children1.size() == 0) && (children2.size() == 0)) {
            return TaskEquality.LEXICALLY_EQUAL;
        }
        else if ((children1.size() == 0) || (children2.size() == 0)) {
            return TaskEquality.UNEQUAL;
        }

        TaskEquality selectionEquality;

        if (requiredEqualityLevel == null) {
            // calculate the common equality level for all children of both selections.
            // do it in both directions to ensure commutative comparison
            selectionEquality = getCommonEqualityLevel(children1, children2);
            if (selectionEquality != TaskEquality.UNEQUAL) {
                return selectionEquality.getCommonDenominator
                    (getCommonEqualityLevel(children2, children1));
            }
            else {
                return TaskEquality.UNEQUAL;
            }
        }
        else {
            // we are searching for a specific equality
            if (checkEqualityLevel(children1, children2, requiredEqualityLevel) &&
                checkEqualityLevel(children2, children1, requiredEqualityLevel))
            {
                return requiredEqualityLevel;
            }
            else {
                return TaskEquality.UNEQUAL;
            }
        }
    }

    /**
     * <p>
     * determines the common equality level for all tasks in the first list compared to all
     * tasks in the second list. If for one task in the first list, there is no equal task in the
     * second list, the method return unequality. 
     * </p>
     *
     * @param children1 the first list to be compared
     * @param children2 the second list to be compared
     * 
     * @return the common task equality identified for all tasks in the first list with respect to
     *         the second list
     */
    private TaskEquality getCommonEqualityLevel(List<ITask> children1, List<ITask> children2) {
        TaskEquality listEquality = TaskEquality.LEXICALLY_EQUAL;
        
        TaskEquality childEquality;
        TaskEquality currentEquality;
        for (ITask child1 : children1) {
            childEquality = null;
            for (ITask child2 : children2) {
                currentEquality = callRuleManager(child1, child2, null);
                if ((currentEquality != null) && (currentEquality != TaskEquality.UNEQUAL)) {
                    if (childEquality == null) {
                        childEquality = currentEquality;
                    }
                    else {
                        childEquality = childEquality.getCommonDenominator(currentEquality);
                    }
                    
                    if (childEquality == TaskEquality.SEMANTICALLY_EQUAL) {
                        // as we calculate only the common denominator, we can break up here for
                        // the current child. We will not improve the denominator anymore
                        break;
                    }
                }
            }
            
            if (childEquality == null) {
                // we did not find any child in the second list, that is equal to the searched
                // child
                return TaskEquality.UNEQUAL;
            }
            else {
                listEquality = listEquality.getCommonDenominator(childEquality);
            }
        }

        return listEquality;
    }

    /**
     * <p>
     * ensures for the two given lists, that for each task in the first list there is a task
     * in the second list being on the given level equal to the task in the first list.
     * </p> 
     * 
     * @param children1             the first list to be compared
     * @param children2             the second list to be compared
     * @param requiredEqualityLevel the equality level to be checked for
     * 
     * @return true if each task in the first list has an equal task in the second list when
     *         considering the given equality level, false else.
     */
    private boolean checkEqualityLevel(List<ITask>  children1,
                                       List<ITask>  children2,
                                       TaskEquality requiredEqualityLevel)
    {
        TaskEquality childEquality;
        TaskEquality currentEquality;
        for (ITask child1 : children1) {
            childEquality = null;
            for (ITask child2 : children2) {
                currentEquality = callRuleManager(child1, child2, requiredEqualityLevel);
                if ((currentEquality != null) && (currentEquality.isAtLeast(requiredEqualityLevel)))
                {
                    // we found at least one equal child with sufficient equality in the
                    // second list. So be can break up for this child.
                    childEquality = currentEquality;
                    break;
                }
            }
            
            if (childEquality == null) {
                // we did not find any child in the second list, that is equal to the searched
                // child
                return false;
            }
        }

        // for all children, we found an equality 
        return true;
    }

    /**
     * <p>
     * used to to call the task equality rule manager for the comparison of the two provided
     * children. If no required equality level is provided, than the most concrete equality is
     * returned. Otherwise, the required equality is returned as long as the children are equal
     * on that level.
     * </p> 
     * 
     * @param child1                the first task to be compared
     * @param child2                the second task to be compared
     * @param requiredEqualityLevel the equality level to be checked for
     * 
     * @return the determined equality
     */
    private TaskEquality callRuleManager(ITask        child1,
                                         ITask        child2,
                                         TaskEquality requiredEqualityLevel)
    {
        if (requiredEqualityLevel == null) {
            return mRuleManager.compare(child1, child2);
        }
        else if (mRuleManager.areAtLeastEqual(child1, child2, requiredEqualityLevel)) {
            return requiredEqualityLevel;
        }
        else {
            return TaskEquality.UNEQUAL;
        }
    }

}