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    /*****************************************************************
 *   Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you 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.apache.cayenne.query;

import java.io.PrintWriter;
import java.io.Serializable;
import java.io.StringWriter;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import org.apache.cayenne.exp.Expression;
import org.apache.cayenne.exp.ExpressionException;
import org.apache.cayenne.exp.parser.ASTDbPath;
import org.apache.cayenne.exp.parser.ASTObjPath;
import org.apache.cayenne.util.ConversionUtil;
import org.apache.cayenne.util.Util;
import org.apache.cayenne.util.XMLEncoder;
import org.apache.cayenne.util.XMLSerializable;
import org.apache.commons.collections.ComparatorUtils;

/**
 * Defines object sorting criteria, used either for in-memory sorting of object lists or
 * as a specification for building ORDER BY clause of a SelectQuery query. Note
 * that in case of in-memory sorting, Ordering can be used with any JavaBeans, not just
 * DataObjects.
 */
public class Ordering implements Comparator, Serializable, XMLSerializable {

    protected String sortSpecString;
    protected transient Expression sortSpec;
    protected SortOrder sortOrder;
    protected boolean pathExceptionSuppressed = false;
    protected boolean nullSortedFirst = true;

    /**
     * Orders a given list of objects, using a List of Orderings applied according the
     * default iteration order of the Orderings list. I.e. each Ordering with lower index
     * is more significant than any other Ordering with higher index. List being ordered
     * is modified in place.
     */
    public static void orderList(List objects, List orderings) {
        Collections.sort(objects, ComparatorUtils.chainedComparator(orderings));
    }

    public Ordering() {
    }

    /**
     * @since 3.0
     */
    public Ordering(String sortPathSpec, SortOrder sortOrder) {
        setSortSpecString(sortPathSpec);
        setSortOrder(sortOrder);
    }

    /**
     * Sets sortSpec to be an expression represented by string argument.
     * 
     * @since 1.1
     */
    public void setSortSpecString(String sortSpecString) {
        if (!Util.nullSafeEquals(this.sortSpecString, sortSpecString)) {
            this.sortSpecString = sortSpecString;
            this.sortSpec = null;
        }
    }

    /**
     * Sets sort order for whether nulls are at the top or bottom of the resulting list.
     * Default is true.
     * 
     * @param nullSortedFirst true sorts nulls to the top of the list, false sorts nulls
     *            to the bottom
     */
    public void setNullSortedFirst(boolean nullSortedFirst) {
        this.nullSortedFirst = nullSortedFirst;
    }

    /**
     * Get sort order for nulls.
     * 
     * @return true if nulls are sorted to the top of the list, false if sorted to the
     *         bottom
     */
    public boolean isNullSortedFirst() {
        return nullSortedFirst;
    }

    /**
     * Sets whether a path with a null in the middle is ignored. For example, a sort from
     * painting on artist.name would by default throw an
     * exception if the artist was null. If set to true, then this is treated just like a
     * null value. Default is false.
     * 
     * @param pathExceptionSuppressed true to suppress exceptions and sort as null
     */
    public void setPathExceptionSupressed(boolean pathExceptionSuppressed) {
        this.pathExceptionSuppressed = pathExceptionSuppressed;
    }

    /**
     * Is a path with a null in the middle is ignored.
     * 
     * @return true is exception is suppressed and sorted as null
     */
    public boolean isPathExceptionSuppressed() {
        return pathExceptionSuppressed;
    }

    /**
     * Returns sortSpec string representation.
     * 
     * @since 1.1
     */
    public String getSortSpecString() {
        return sortSpecString;
    }

    /**
     * Sets the sort order for this ordering.
     * 
     * @since 3.0
     */
    public void setSortOrder(SortOrder order) {
        this.sortOrder = order;
    }

    /** Returns true if sorting is done in ascending order. */
    public boolean isAscending() {
        return sortOrder == null
                || sortOrder == SortOrder.ASCENDING
                || sortOrder == SortOrder.ASCENDING_INSENSITIVE;
    }

    /**
     * Returns true if the sorting is done in descending order.
     * 
     * @since 3.0
     */
    public boolean isDescending() {
        return !isAscending();
    }

    /**
     * If the sort order is DESCENDING or DESCENDING_INSENSITIVE, sets the sort order to
     * ASCENDING or ASCENDING_INSENSITIVE, respectively.
     * 
     * @since 3.0
     */
    public void setAscending() {
        if (sortOrder == null || sortOrder == SortOrder.DESCENDING)
            setSortOrder(SortOrder.ASCENDING);
        else if (sortOrder == SortOrder.DESCENDING_INSENSITIVE)
            setSortOrder(SortOrder.ASCENDING_INSENSITIVE);
    }

    /**
     * If the sort order is ASCENDING or ASCENDING_INSENSITIVE, sets the sort order to
     * DESCENDING or DESCENDING_INSENSITIVE, respectively.
     * 
     * @since 3.0
     */
    public void setDescending() {
        if (sortOrder == null || sortOrder == SortOrder.ASCENDING)
            setSortOrder(SortOrder.DESCENDING);
        else if (sortOrder == SortOrder.ASCENDING_INSENSITIVE)
            setSortOrder(SortOrder.DESCENDING_INSENSITIVE);
    }

    /** Returns true if the sorting is case insensitive */
    public boolean isCaseInsensitive() {
        return !isCaseSensitive();
    }

    /**
     * Returns true if the sorting is case sensitive.
     * 
     * @since 3.0
     */
    public boolean isCaseSensitive() {
        return sortOrder == null
                || sortOrder == SortOrder.ASCENDING
                || sortOrder == SortOrder.DESCENDING;
    }

    /**
     * If the sort order is ASCENDING or DESCENDING, sets the sort order to
     * ASCENDING_INSENSITIVE or DESCENDING_INSENSITIVE, respectively.
     * 
     * @since 3.0
     */
    public void setCaseInsensitive() {
        if (sortOrder == null || sortOrder == SortOrder.ASCENDING)
            setSortOrder(SortOrder.ASCENDING_INSENSITIVE);
        else if (sortOrder == SortOrder.DESCENDING)
            setSortOrder(SortOrder.DESCENDING_INSENSITIVE);
    }

    /**
     * If the sort order is ASCENDING_INSENSITIVE or DESCENDING_INSENSITIVE, sets the sort
     * order to ASCENDING or DESCENDING, respectively.
     * 
     * @since 3.0
     */
    public void setCaseSensitive() {
        if (sortOrder == null || sortOrder == SortOrder.ASCENDING_INSENSITIVE)
            setSortOrder(SortOrder.ASCENDING);
        else if (sortOrder == SortOrder.DESCENDING_INSENSITIVE)
            setSortOrder(SortOrder.DESCENDING);
    }

    /**
     * Returns the expression defining a ordering Java Bean property.
     */
    public Expression getSortSpec() {
        if (sortSpecString == null) {
            return null;
        }

        // compile on demand .. since orderings can only be paths, avoid the overhead of
        // Expression.fromString, and parse them manually
        if (sortSpec == null) {

            if (sortSpecString.startsWith(ASTDbPath.DB_PREFIX)) {
                sortSpec = new ASTDbPath(sortSpecString.substring(ASTDbPath.DB_PREFIX
                        .length()));
            }
            else if (sortSpecString.startsWith(ASTObjPath.OBJ_PREFIX)) {
                sortSpec = new ASTObjPath(sortSpecString.substring(ASTObjPath.OBJ_PREFIX
                        .length()));
            }
            else {
                sortSpec = new ASTObjPath(sortSpecString);
            }
        }

        return sortSpec;
    }

    /**
     * Sets the expression defining a ordering Java Bean property.
     */
    public void setSortSpec(Expression sortSpec) {
        this.sortSpec = sortSpec;
        this.sortSpecString = (sortSpec != null) ? sortSpec.toString() : null;
    }

    /**
     * Orders the given list of objects according to the ordering that this object
     * specifies. List is modified in-place.
     * 
     * @param objects a List of objects to be sorted
     */
    public void orderList(List objects) {
        Collections.sort(objects, this);
    }

    /**
     * Comparable interface implementation. Can compare two Java Beans based on the stored
     * expression.
     */
    public int compare(Object o1, Object o2) {
        Expression exp = getSortSpec();
        Object value1 = null;
        Object value2 = null;
        try {
            value1 = exp.evaluate(o1);
        }
        catch (ExpressionException e) {
            if (pathExceptionSuppressed
                    && e.getCause() instanceof org.apache.cayenne.reflect.UnresolvablePathException) {
                // do nothing, we expect this
            }
            else {
                // re-throw
                throw e;
            }
        }

        try {
            value2 = exp.evaluate(o2);
        }
        catch (ExpressionException e) {
            if (pathExceptionSuppressed
                    && e.getCause() instanceof org.apache.cayenne.reflect.UnresolvablePathException) {
                // do nothing, we expect this
            }
            else {
                // rethrow
                throw e;
            }
        }

        if (value1 == null && value2 == null) {
            return 0;
        }
        else if (value1 == null) {
            return nullSortedFirst ? -1 : 1;
        }
        else if (value2 == null) {
            return nullSortedFirst ? 1 : -1;
        }

        if (isCaseInsensitive()) {
            // TODO: to upper case should probably be defined as a separate expression
            // type
            value1 = ConversionUtil.toUpperCase(value1);
            value2 = ConversionUtil.toUpperCase(value2);
        }

        int compareResult = ConversionUtil.toComparable(value1).compareTo(
                ConversionUtil.toComparable(value2));
        return (isAscending()) ? compareResult : -compareResult;
    }

    /**
     * Encodes itself as a query ordering.
     * 
     * @since 1.1
     */
    public void encodeAsXML(XMLEncoder encoder) {
        encoder.print("");
        if (getSortSpec() != null) {
            getSortSpec().encodeAsXML(encoder);
        }
        encoder.println("");
    }

    @Override
    public String toString() {
        StringWriter buffer = new StringWriter();
        PrintWriter pw = new PrintWriter(buffer);
        XMLEncoder encoder = new XMLEncoder(pw);
        encodeAsXML(encoder);
        pw.close();
        buffer.flush();
        return buffer.toString();
    }
    
    /**
     * Returns sort order for this ordering
     * @since 3.1
     */
    public SortOrder getSortOrder() {
        return sortOrder;
    }
}
    
    
    
    

    




    
    
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