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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.
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package org.apache.cayenne.access.translator.select;

import org.apache.cayenne.CayenneRuntimeException;
import org.apache.cayenne.exp.Expression;
import org.apache.cayenne.query.Ordering;
import org.apache.cayenne.query.Query;
import org.apache.cayenne.query.SelectQuery;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * Translates query ordering to SQL.
 */
public class OrderingTranslator extends QueryAssemblerHelper {

	protected List<String> orderByColumnList = new ArrayList<>();

	public OrderingTranslator(QueryAssembler queryAssembler) {
		super(queryAssembler);
	}

	/**
	 * Translates query Ordering list to SQL ORDER BY clause. Ordering list is
	 * obtained from <code>queryAssembler</code>'s query object. In a process of
	 * building of ORDER BY clause, <code>queryAssembler</code> is notified when
	 * a join needs to be added.
	 * 
	 * @since 3.0
	 */
	@Override
	protected void doAppendPart() {

		Query q = queryAssembler.getQuery();

		// only select queries can have ordering...
		if (q == null || !(q instanceof SelectQuery)) {
			return;
		}

		Iterator<Ordering> it = ((SelectQuery<?>) q).getOrderings().iterator();

		StringBuilder mainBuffer = this.out;

		try {
			while (it.hasNext()) {
				Ordering ord = it.next();

				// reset buffer to collect SQL for the single column, that we'll
				// be reusing
				this.out = new StringBuilder();

				if (ord.isCaseInsensitive()) {
					out.append("UPPER(");
				}

				Expression exp = ord.getSortSpec();

				if (exp.getType() == Expression.OBJ_PATH) {
					appendObjPath(exp);
				} else if (exp.getType() == Expression.DB_PATH) {
					appendDbPath(exp);
				} else if (exp.getType() == Expression.FUNCTION_CALL) {
					appendFunction(exp);
				} else {
					throw new CayenneRuntimeException("Unsupported ordering expression: %s", exp);
				}

				// Close UPPER() modifier
				if (ord.isCaseInsensitive()) {
					out.append(")");
				}

				String columnSQL = out.toString();
				mainBuffer.append(columnSQL);
				orderByColumnList.add(columnSQL);

				// "ASC" is a noop, omit it from the query
				if (!ord.isAscending()) {
					mainBuffer.append(" DESC");
				}

				if (it.hasNext()) {
					mainBuffer.append(", ");
				}
			}
		} finally {
			this.out = mainBuffer;
		}
	}

	protected void appendFunction(Expression exp) {
		QualifierTranslator qualifierTranslator = queryAssembler.getAdapter().getQualifierTranslator(queryAssembler);
		qualifierTranslator.setQualifier(exp);
		StringBuilder builder = qualifierTranslator.appendPart(new StringBuilder());
		out.append(builder.toString());
	}

	/**
	 * Returns the column expressions (not Expressions) used in the order by
	 * clause. E.g., in the case of an case-insensitive order by, an element of
	 * the list would be <code>UPPER(<column reference>)</code>
	 */
	public List<String> getOrderByColumnList() {
		return orderByColumnList;
	}
}