FreemarkerLimit.java

/*
   Copyright 2014 base2Services

   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 com.base2.kagura.core.report.freemarker;

import com.base2.kagura.core.report.connectors.FreemarkerSQLDataReportConnector;
import freemarker.core.Environment;
import freemarker.template.*;

import java.io.IOException;
import java.util.List;
import java.util.Map;

/**
 * Simple Freemaker custom tag to insert the appropriate query (page) limit and offset (page number) for the query being run. Takes 1 optional
 * parameter called "sql" which execpts the SQL engine to be there, defaults to mysql. Outputs the appropriate style
 * LIMIT tag depending on input. Currently only supports mysql and postgres.
 * @author aubels
 *         Date: 13/09/13
 */
public class FreemarkerLimit implements TemplateDirectiveModel {
    private final Boolean[] limitExists;
    private List<String> errors;
    private FreemarkerSQLDataReportConnector freemarkerSQLDataReportConnector;

    /**
     * Constructor
     * @param limitExists A reference to an array of boolean to store if the limit has been used. In a sql statement
     *                    that is a query it is required and can only be used once. Other times it is optional
     * @param errors A reference to a list of errors, this is something to populate if there are any errors encountered
     * @param freemarkerSQLDataReportConnector A reference back to the report connector.
     */
    public FreemarkerLimit(Boolean[] limitExists, List<String> errors, FreemarkerSQLDataReportConnector freemarkerSQLDataReportConnector) {
        this.limitExists = limitExists;
        this.errors = errors;
        this.freemarkerSQLDataReportConnector = freemarkerSQLDataReportConnector;
    }

    /**
     * Inserts the appropriate LIMIT .. OFFSET .. statement into the query.
     * {@inheritDoc}
     */
    @Override
    public void execute(Environment env, Map params, TemplateModel[] loopVars, TemplateDirectiveBody body) throws TemplateException, IOException {
        if (params.size() > 1)
        {
            String message = "This directive doesn't allow multiple parameters.";
            errors.add(message);
            throw new TemplateModelException(message);
        }
        if (params.size() == 1 && !((Map.Entry)params.entrySet().toArray()[0]).getKey().equals("sql")) {
            String message = "This directive only takes 'sql', which you specify the type of engine, ie mysql, postgres, etc.";
            errors.add(message);
            throw new TemplateModelException(message);
        }
        Object sqlParam = params.get("sql");
        String engine = "mysql";
        if (sqlParam == null) { } else
        if (sqlParam instanceof TemplateScalarModel)
        {
            TemplateScalarModel engineParam = (TemplateScalarModel) sqlParam;
            engine = engineParam.getAsString();
        } else {
            String message = "This directive only accepts string values for 'sql'.";
            errors.add(message);
            throw new TemplateModelException(message);
        }
        if (loopVars.length != 0) throw new TemplateModelException("This directive doesn't allow loop variables.");
        limitExists[0] = true;
        int limit = freemarkerSQLDataReportConnector.getPageLimit();
        int offset = freemarkerSQLDataReportConnector.getPage() * limit;
        if (engine.equalsIgnoreCase("mysql") || engine.equalsIgnoreCase("postgres"))
        {
            env.getOut().write(" LIMIT " + limit + " OFFSET " + offset + " ");
        } else
        {
            String message = "Unknown SQL Engine " + engine + ".";
            errors.add(message);
            throw new TemplateModelException(message);
        }
    }
}