/*
 *  Copyright (c) 2015, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
 *
 *  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 org.apache.synapse.util.xpath;

import org.apache.commons.httpclient.URIException;
import org.apache.commons.httpclient.util.URIUtil;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.jaxen.Context;
import org.jaxen.Function;
import org.jaxen.FunctionCallException;
import org.jaxen.function.StringFunction;

import java.util.List;

/**
 * Implements the XPath extension function synapse:url-encode(string)
 */
public class URLEncodeFunction implements Function {

    private static final Log log = LogFactory.getLog(URLEncodeFunction.class);

    /**
     * Returns the url-encoded string value of the first argument.
     *
     * @param context the context at the point in the expression when the function is called
     * @param args  arguments of the functions
     * @return The string value of a property
     * @throws FunctionCallException
     */
    public Object call(Context context, List args) throws FunctionCallException {
        boolean debugOn = log.isDebugEnabled();

        if (args == null || args.size() == 0) {
            if (debugOn) {
                log.debug("Property key value for lookup is not specified");
            }
            return SynapseXPathConstants.NULL_STRING;
        }

        int size = args.size();
        if (size == 1) {
            // get the first argument, it can be a function returning a string as well
            String value = StringFunction.evaluate(args.get(0), context.getNavigator());

            // use the default UTF-8 encoding
            return encode(debugOn, SynapseXPathConstants.DEFAULT_CHARSET, value);
        } else if (size == 2) {
            // get the first argument, it can be a function returning a string as well
            String value = StringFunction.evaluate(args.get(0), context.getNavigator());

            // encoding is in the second argument
            String encoding = StringFunction.evaluate(args.get(1), context.getNavigator());
            
            return encode(debugOn, encoding, value);
        } else if (debugOn) {
            log.debug("url-encode function expects only one argument, returning empty string");
        }
        // return empty string if the arguments are wrong
        return SynapseXPathConstants.NULL_STRING;
    }

    private Object encode(boolean debugOn, String encoding, String value) throws FunctionCallException {
        if (value == null || "".equals(value)) {
            if (debugOn) {
                log.debug("Non empty string value should be provided for encoding");
            }

            return SynapseXPathConstants.NULL_STRING;
        }

        String encodedString;
        try {
            encodedString = URIUtil.encodePathQuery(value, encoding);
        } catch (URIException e) {
            String msg = "Unsupported charset encoding";
            log.error(msg, e);
            throw new FunctionCallException(msg, e);
        }

        if (debugOn) {
            log.debug("Converted string: " + value + " with encoding: " + encoding +
                    " to url encoded value: " + encodedString);
        }

        return encodedString;
    }
}