/*
 * Copyright 2010-2016 Amazon.com, Inc. or its affiliates. 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.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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.amazonaws.http;

import com.amazonaws.AmazonClientException;
import com.amazonaws.AmazonWebServiceResponse;
import com.amazonaws.ResponseMetadata;
import com.amazonaws.transform.StaxUnmarshallerContext;
import com.amazonaws.transform.Unmarshaller;
import com.amazonaws.transform.VoidStaxUnmarshaller;
import com.amazonaws.util.StringUtils;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;

import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.util.Map;

/**
 * Default implementation of HttpResponseHandler that handles a successful
 * response from an AWS service and unmarshalls the result using a StAX
 * unmarshaller.
 *
 * @param <T> Indicates the type being unmarshalled by this response handler.
 */
public class StaxResponseHandler<T> implements HttpResponseHandler<AmazonWebServiceResponse<T>> {

    /** The StAX unmarshaller to use when handling the response */
    private Unmarshaller<T, StaxUnmarshallerContext> responseUnmarshaller;

    /** Shared logger for profiling information */
    private static final Log log = LogFactory.getLog("com.amazonaws.request");

    /** Shared factory for creating XML event readers */
    private static final XmlPullParserFactory xmlPullParserFactory;
    static {
        try {
            xmlPullParserFactory = XmlPullParserFactory.newInstance();
        } catch (XmlPullParserException xppe) {
            throw new AmazonClientException("Couldn't initialize XmlPullParserFactory", xppe);
        }
    }

    /**
     * Constructs a new response handler that will use the specified StAX
     * unmarshaller to unmarshall the service response and uses the specified
     * response element path to find the root of the business data in the
     * service's response.
     *
     * @param responseUnmarshaller The StAX unmarshaller to use on the response.
     */
    public StaxResponseHandler(Unmarshaller<T, StaxUnmarshallerContext> responseUnmarshaller) {
        this.responseUnmarshaller = responseUnmarshaller;

        /*
         * Even if the invoked operation just returns null, we still need an
         * unmarshaller to run so we can pull out response metadata. We might
         * want to pass this in through the client class so that we don't have
         * to do this check here.
         */
        if (this.responseUnmarshaller == null) {
            this.responseUnmarshaller = new VoidStaxUnmarshaller<T>();
        }
    }

    /**
     * @see com.amazonaws.http.HttpResponseHandler#handle(com.amazonaws.http.HttpResponse)
     */
    @Override
    public AmazonWebServiceResponse<T> handle(HttpResponse response) throws Exception {
        log.trace("Parsing service response XML");
        InputStream content = response.getContent();
        if (content == null)
            content = new ByteArrayInputStream("<eof/>".getBytes(StringUtils.UTF8));

        XmlPullParser xpp = xmlPullParserFactory.newPullParser();
        xpp.setInput(content, null);

        AmazonWebServiceResponse<T> awsResponse = new AmazonWebServiceResponse<T>();
        StaxUnmarshallerContext unmarshallerContext = new StaxUnmarshallerContext(xpp,
                response.getHeaders());
        unmarshallerContext.registerMetadataExpression("ResponseMetadata/RequestId", 2,
                ResponseMetadata.AWS_REQUEST_ID);
        unmarshallerContext.registerMetadataExpression("requestId", 2,
                ResponseMetadata.AWS_REQUEST_ID);
        registerAdditionalMetadataExpressions(unmarshallerContext);

        T result = responseUnmarshaller.unmarshall(unmarshallerContext);
        awsResponse.setResult(result);

        Map<String, String> metadata = unmarshallerContext.getMetadata();
        Map<String, String> responseHeaders = response.getHeaders();
        if (responseHeaders != null) {
            if (responseHeaders.get("x-amzn-RequestId") != null) {
                metadata.put(ResponseMetadata.AWS_REQUEST_ID,
                        responseHeaders.get("x-amzn-RequestId"));
            }
        }
        awsResponse.setResponseMetadata(new ResponseMetadata(metadata));

        log.trace("Done parsing service response");
        return awsResponse;
    }

    /**
     * Hook for subclasses to override in order to collect additional metadata
     * from service responses.
     *
     * @param unmarshallerContext The unmarshaller context used to process a
     *            service's response data.
     */
    protected void registerAdditionalMetadataExpressions(StaxUnmarshallerContext unmarshallerContext) {
    }

    /**
     * Since this response handler completely consumes all the data from the
     * underlying HTTP connection during the handle method, we don't need to
     * keep the HTTP connection open.
     *
     * @see com.amazonaws.http.HttpResponseHandler#needsConnectionLeftOpen()
     */
    @Override
    public boolean needsConnectionLeftOpen() {
        return false;
    }

}