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package org.apache.cayenne.access.trans;

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

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;

/** 
 * Translates query ordering to SQL. 
 * 
 * @author Andrei Adamchik
 * @author Craig Miskell
 */
public class OrderingTranslator extends QueryAssemblerHelper {

    protected List orderByColumnList = new ArrayList();
    
    public OrderingTranslator(QueryAssembler queryAssembler) {
        super(queryAssembler);
    }

    /** Translates query Ordering list to SQL ORDER BY clause. 
     *  Ordering list is obtained from queryAssembler's query object. 
     *  In a process of building of ORDER BY clause, queryAssembler 
     *  is notified when a join needs to be added. */
    public String doTranslation() {
        Query q = queryAssembler.getQuery();

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

        StringBuffer buf = new StringBuffer();
        List list = ((SelectQuery) q).getOrderings();
        int len = list.size();

        for (int i = 0; i < len; i++) {
            if (i > 0)
                buf.append(", ");

            StringBuffer ordComp = new StringBuffer();

            Ordering ord = (Ordering) list.get(i);

            //UPPER is (I think) part of the SQL99 standard, and I'm not convinced it's universally available
            // - should the syntax used here be defined by the Db specific adaptor perhaps, or at least
            // possibly specified by the db adaptor (a DB specific OrderingTranslator hook)?
            if (ord.isCaseInsensitive()) {
                ordComp.append("UPPER(");

            }

            Expression exp = ord.getSortSpec();

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

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

            orderByColumnList.add(ordComp.toString());
            
            buf.append(ordComp.toString());

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

        return buf.length() > 0 ? buf.toString() : null;
    }

    /**
     * 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 
     * UPPER(<column reference>)
     */    
    public List getOrderByColumnList() {
        return orderByColumnList;
    }
}