/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  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.  For additional information regarding
 * copyright in this work, please see the NOTICE file in the top level
 * directory of this distribution.
 */
package org.apache.abdera2.ext.json;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import org.apache.abdera2.Abdera;
import org.apache.abdera2.common.misc.Chain;
import org.apache.abdera2.common.misc.Task;
import org.apache.abdera2.common.protocol.RequestContext;
import org.apache.abdera2.common.protocol.ResponseContext;
import org.apache.abdera2.common.protocol.ProviderHelper;
import org.apache.abdera2.model.Document;
import org.apache.abdera2.model.Element;
import org.apache.abdera2.protocol.server.AtompubResponseContext;
import org.apache.abdera2.protocol.server.context.ResponseContextWrapper;
import org.apache.abdera2.writer.Writer;

/**
 * Filter implementation that will convert an Atom document returned by the server into a JSON document if the request
 * specifies a higher preference value for JSON or explicitly requests JSON by including a format=json querystring
 * parameter
 */
public class JSONFilter implements Task<RequestContext,ResponseContext> {

    public ResponseContext apply(RequestContext request, Chain<RequestContext,ResponseContext> chain) {
        AtompubResponseContext resp = (AtompubResponseContext) chain.next(request);
        String format = request.getParameter("format");
        return ((resp.getContentType() != null && jsonPreferred(request, resp.getContentType().toString())) || (format != null && format
            .equalsIgnoreCase("json")) ? new JsonResponseContext(resp, Abdera.getInstance()) : resp);
    }

    private boolean jsonPreferred(RequestContext request, String type) {
        return ProviderHelper.isPreferred(request, "application/json", type);
    }

    private static class JsonResponseContext extends ResponseContextWrapper {

        private final Abdera abdera;

        public JsonResponseContext(AtompubResponseContext response, Abdera abdera) {
            super(response);
            setContentType("application/json");
            this.abdera = abdera;
        }

        public void writeTo(OutputStream out, Writer writer) throws IOException {
            try {
                toJson(out, writer);
            } catch (Exception se) {
                if (se instanceof RuntimeException)
                    throw (RuntimeException)se;
                throw new RuntimeException(se);
            }
        }

        public void writeTo(OutputStream out) throws IOException {
            try {
                toJson(out, null);
            } catch (Exception se) {
                if (se instanceof RuntimeException)
                    throw (RuntimeException)se;
                throw new RuntimeException(se);
            }
        }

        private void toJson(OutputStream aout, Writer writer) throws Exception {
            Document<Element> doc = null;
            try {
                ByteArrayOutputStream out = new ByteArrayOutputStream();
                if (writer == null)
                    super.writeTo(out);
                else
                    super.writeTo(out, writer);
                ByteArrayInputStream in = new ByteArrayInputStream(out.toByteArray());
                doc = abdera.getParser().parse(in);
            } catch (Exception e) {
            }
            if (doc != null) {
                doc.writeTo("json", aout);
            } else {
                throw new RuntimeException("There was an error serializing the entry to JSON");
            }
        }
    }
}