/*
 * 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.
 */
package org.apache.knox.gateway.jkg;

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.knox.gateway.dispatch.DefaultDispatch;
import org.apache.knox.gateway.filter.rewrite.impl.UrlRewriteRequestStream;
import org.apache.knox.gateway.security.SubjectUtils;


import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.List;
import java.util.Map;


/**
 * This specialized dispatch provides Jupyter Kernel Gateway specific features to the
 * default dispatch.
 */
public class JkgDispatch extends DefaultDispatch {

  @Override
  public void doPost(URI url, HttpServletRequest request, HttpServletResponse response)
      throws IOException, URISyntaxException {
    super.doPost(url, new JkgHttpServletRequest(request), response);
  }

  /**
   * HttpServletRequest that adds or sets the KERNEL_USERNAME parameter on the json body
   */
  private class JkgHttpServletRequest extends HttpServletRequestWrapper {
    private final List<String> kernelEndpoints = Arrays.asList("/kernels");

    JkgHttpServletRequest(HttpServletRequest request) {
      super(request);
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
      ServletInputStream inputStream = super.getInputStream();

      HttpServletRequest request = (HttpServletRequest)getRequest();
      String requestURI = request.getRequestURI();
      if(matchkernelEndpoints(requestURI)) {
        // Parse the json object from the request
        ObjectMapper objectMapper = new ObjectMapper();

        Map<String, Object> jsonMap = objectMapper.readValue(inputStream, new TypeReference<Map<String,Object>>(){});

        Map<String, Object> envMap = objectMapper.convertValue(jsonMap.get("env"), Map.class);
        // Force the KERNEL_USERNAME to be set to the remote user
        envMap.put("KERNEL_USERNAME", SubjectUtils.getCurrentEffectivePrincipalName());

        jsonMap.put("env", envMap);

        // Create the new ServletInputStream with modified json map.
        String s = objectMapper.writeValueAsString(jsonMap);
        return new UrlRewriteRequestStream(new ByteArrayInputStream(s.getBytes(StandardCharsets.UTF_8)));
      }

      return inputStream;
    }

    private boolean matchkernelEndpoints(String requestURI) {
      for(String endpoint : kernelEndpoints) {
        if(requestURI.endsWith(endpoint) || requestURI.endsWith(endpoint + '/')) {
          return true;
        }
      }
      return false;
    }

    @Override
    public BufferedReader getReader() throws IOException {
      return new BufferedReader(new InputStreamReader(getInputStream(), StandardCharsets.UTF_8));
    }
  }
}