// Copyright 2017 The Nomulus Authors. 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 google.registry.whois;

import static com.google.common.base.Strings.nullToEmpty;
import static com.google.common.base.Verify.verify;
import static com.google.common.net.HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN;
import static com.google.common.net.HttpHeaders.CACHE_CONTROL;
import static com.google.common.net.HttpHeaders.EXPIRES;
import static com.google.common.net.HttpHeaders.LAST_MODIFIED;
import static com.google.common.net.HttpHeaders.X_CONTENT_TYPE_OPTIONS;
import static com.google.common.net.MediaType.PLAIN_TEXT_UTF_8;
import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;
import static javax.servlet.http.HttpServletResponse.SC_OK;

import com.google.common.base.Joiner;
import com.google.common.base.Splitter;
import google.registry.config.RegistryConfig.Config;
import google.registry.request.Action;
import google.registry.request.RequestPath;
import google.registry.request.Response;
import google.registry.util.Clock;
import google.registry.util.FormattingLogger;
import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;
import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import javax.inject.Inject;
import org.joda.time.DateTime;
import org.joda.time.Duration;

/**
 * Human-Friendly HTTP WHOIS API
 *
 * <p>This API uses easy to understand paths rather than {@link WhoisServer} which
 * requires a POST request containing a WHOIS command. Because the typical WHOIS command is
 * along the lines of {@code "domain google.lol"} or the equivalent {@code "google.lol}, this
 * servlet is just going to replace the slashes with spaces and let {@link WhoisReader}
 * figure out what to do.
 *
 * <p>This servlet accepts requests from any origin.
 *
 * <p>You can send AJAX requests to our WHOIS API from your <em>very own</em> website using the
 * following embed code:
 *
 * <pre>
 *   <p>
 *     <input id="query-input" placeholder="Domain, Nameserver, IP, etc." autofocus>
 *     <button id="search-button">Lookup</button>
 *   <p>
 *     <pre id="whois-results"></pre>
 *   <script>
 *    (function() {
 *      var WHOIS_API_URL = 'https://domain-registry-alpha.appspot.com/whois/';
 *      function OnKeyPressQueryInput(ev) {
 *        if (typeof ev == 'undefined' && window.event) {
 *          ev = window.event;
 *        }
 *        if (ev.keyCode == 13) {
 *          document.getElementById('search-button').click();
 *        }
 *      }
 *      function OnClickSearchButton() {
 *        var query = document.getElementById('query-input').value;
 *        var req = new XMLHttpRequest();
 *        req.onreadystatechange = function() {
 *          if (req.readyState == 4) {
 *            var results = document.getElementById('whois-results');
 *            results.textContent = req.responseText;
 *          }
 *        };
 *        req.open('GET', WHOIS_API_URL + escape(query), true);
 *        req.send();
 *      }
 *      document.getElementById('search-button').onclick = OnClickSearchButton;
 *      document.getElementById('query-input').onkeypress = OnKeyPressQueryInput;
 *    })();
 *   </script>
 * </pre>
 *
 * @see WhoisServer
 */
@Action(path = WhoisHttpServer.PATH, isPrefix = true)
public final class WhoisHttpServer implements Runnable {

  public static final String PATH = "/whois/";

  private static final FormattingLogger logger = FormattingLogger.getLoggerForCallerClass();

  /**
   * Cross-origin resource sharing (CORS) allowed origins policy.
   *
   * <p>This field specifies the value of the {@code Access-Control-Allow-Origin} response header.
   * Without this header, other domains such as charlestonroadregistry.com would not be able to
   * send requests to our WHOIS interface.
   *
   * <p>Our policy shall be to allow requests from pretty much anywhere using a wildcard policy.
   * The reason this is safe is because our WHOIS interface doesn't allow clients to modify data,
   * nor does it allow them to fetch user data. Only publicly available information is returned.
   *
   * @see <a href="http://www.w3.org/TR/cors/#access-control-allow-origin-response-header">
   *        W3C CORS § 5.1 Access-Control-Allow-Origin Response Header</a>
   */
  private static final String CORS_ALLOW_ORIGIN = "*";

  /** We're going to let any HTTP proxy in the world cache our responses. */
  private static final String CACHE_CONTROL_VALUE = "public";

  /** Responses may be cached for up to a day. */
  private static final String X_CONTENT_NO_SNIFF = "nosniff";

  /** Splitter that turns information on HTTP into a list of tokens. */
  private static final Splitter SLASHER = Splitter.on('/').trimResults().omitEmptyStrings();

  /** Joiner that turns {@link #SLASHER} tokens into a normal WHOIS query. */
  private static final Joiner JOINER = Joiner.on(' ');

  @Inject Clock clock;
  @Inject Response response;
  @Inject @Config("whoisDisclaimer") String disclaimer;
  @Inject @Config("whoisHttpExpires") Duration expires;
  @Inject @Config("whoisCommandFactory") WhoisCommandFactory commandFactory;
  @Inject @RequestPath String requestPath;
  @Inject WhoisHttpServer() {}

  @Override
  public void run() {
    verify(requestPath.startsWith(PATH));
    String path = nullToEmpty(requestPath);
    try {
      // Extremely permissive parsing that turns stuff like "/hello/world/" into "hello world".
      String command = decode(JOINER.join(SLASHER.split(path.substring(PATH.length())))) + "\r\n";
      Reader reader = new StringReader(command);
      DateTime now = clock.nowUtc();
      sendResponse(
          SC_OK, new WhoisReader(reader, commandFactory, now).readCommand().executeQuery(now));
    } catch (WhoisException e) {
      sendResponse(e.getStatus(), e);
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }

  private void sendResponse(int status, WhoisResponse whoisResponse) {
    response.setStatus(status);
    response.setDateHeader(LAST_MODIFIED, whoisResponse.getTimestamp());
    response.setDateHeader(EXPIRES, whoisResponse.getTimestamp().plus(expires));
    response.setHeader(CACHE_CONTROL, CACHE_CONTROL_VALUE);
    response.setHeader(ACCESS_CONTROL_ALLOW_ORIGIN, CORS_ALLOW_ORIGIN);
    response.setHeader(X_CONTENT_TYPE_OPTIONS, X_CONTENT_NO_SNIFF);
    response.setContentType(PLAIN_TEXT_UTF_8);
    response.setPayload(whoisResponse.getPlainTextOutput(true, disclaimer));
  }

  /** Removes {@code %xx} escape codes from request path components. */
  private String decode(String pathData)
      throws UnsupportedEncodingException, WhoisException {
    try {
      return URLDecoder.decode(pathData, "UTF-8");
    } catch (IllegalArgumentException e) {
      logger.infofmt("Malformed WHOIS request path: %s (%s)", requestPath, pathData);
      throw new WhoisException(clock.nowUtc(), SC_BAD_REQUEST, "Malformed path query.");
    }
  }
}