/*
 * ====================================================================
 * 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package ch.boye.httpclientandroidlib.protocol;

import java.io.IOException;

import ch.boye.httpclientandroidlib.HttpException;
import ch.boye.httpclientandroidlib.HttpRequest;
import ch.boye.httpclientandroidlib.HttpRequestInterceptor;
import ch.boye.httpclientandroidlib.annotation.Immutable;
import ch.boye.httpclientandroidlib.params.HttpProtocolParams;

/**
 * RequestUserAgent is responsible for adding <code>User-Agent</code> header.
 * This interceptor is recommended for client side protocol processors.
 * <p>
 * The following parameters can be used to customize the behavior of this
 * class:
 * <ul>
 *  <li>{@link ch.boye.httpclientandroidlib.params.CoreProtocolPNames#USER_AGENT}</li>
 * </ul>
 *
 * @since 4.0
 */
@Immutable
public class RequestUserAgent implements HttpRequestInterceptor {

    public RequestUserAgent() {
        super();
    }

    public void process(final HttpRequest request, final HttpContext context)
        throws HttpException, IOException {
        if (request == null) {
            throw new IllegalArgumentException("HTTP request may not be null");
        }
        if (!request.containsHeader(HTTP.USER_AGENT)) {
            String useragent = HttpProtocolParams.getUserAgent(request.getParams());
            if (useragent != null) {
                request.addHeader(HTTP.USER_AGENT, useragent);
            }
        }
    }

}
