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/*
 * Copyright 2006-2012 The Scriptella Project Team.
 *
 * 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 scriptella.jdbc;

import scriptella.expression.Expression;
import scriptella.spi.DriverContext;
import scriptella.spi.ParametersCallback;

import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;

/**
 * Parses parameter expressions in SQL statements.
 * This class use {@link Expression} parsing mechanism except the
 * file reference case.
 * The syntax of the file reference is the following:
 * 
?{file <Expression>}
 * 
The result of expression evaluation must be of String or URL type.
 * 
Examples:
 * 

 * ?{file 'http://site.com/img.gif')
 * 
?{file 'file:/path/img.gif')
 * 
?{file 'img.gif') - represents a reference relative to a directory where script file located.
 * 
 *
 * @author Fyodor Kupolov
 * @version 1.0
 * @see Expression
 */
public class ParametersParser {
    private DriverContext driverContext;


    /**
     * Creates a file reference parser.
     *
     * @param driverContext drivers content to use for URL resolution.
     */
    public ParametersParser(DriverContext driverContext) {
        this.driverContext = driverContext;
    }

    /**
     * Parses specified expression and returns the result of evaluation.
     *
     * @param expression expression to parse.
     * @return result of parse.
     */
    public Object evaluate(final String expression, final ParametersCallback parameters) {
        if (expression.startsWith("file ")) {
            //now checking the syntax
            try {
                URL u = getFileUrl(expression.substring(5), parameters);//file prefix removed
                return Lobs.newBlob(u);
            } catch (Expression.ParseException e) {
                //If parsing fails try to evaluate the whole expression not the file reference
            }
        } else if (expression.startsWith("textfile ")) {
            //now checking the syntax
            try {
                URL u = getFileUrl(expression.substring(9), parameters);//textfile prefix removed
                //IMPORTANT NOTE
                //The JVM default encoding is used to create reader,
                //currently we have no way to specify text file encoding.
                return Lobs.newClob(new InputStreamReader(u.openStream()));
            } catch (Expression.ParseException e) {
                //If parsing fails try to evaluate the whole expression not the file reference
            } catch (IOException e) {
                throw new JdbcException("Failed to open reader for expression " + expression, e);
            }
        }
        //Try to eval the whole expression if subexpression is illegal
        return Expression.compile(expression).evaluate(parameters);
    }


    /**
     * Evaluates given expression and resolves specified URL.
     *
     * @param expression expression to evaluate.
     * @param parameters parameters to use for evaluation.
     * @return resolved URL.
     * @throws scriptella.expression.Expression.ParseException
     *          if expression has wrong syntax
     */
    private URL getFileUrl(final String expression, final ParametersCallback parameters) throws Expression.ParseException {
        final Object o = Expression.compile(expression).evaluate(parameters);
        if (o == null) {
            throw new JdbcException("Failed to evaluate file URL", expression);
        }
        if (o instanceof URL) {
            return (URL) o;
        } else {
            try {
                return driverContext.resolve(String.valueOf(o));
            } catch (MalformedURLException e) {
                throw new JdbcException("Wrong file URL \"" + o + "\"", e, expression);
            }
        }
    }

}