/*
    * Licensed to The Apereo Foundation under one or more contributor license
    * agreements. See the NOTICE file distributed with this work for additional
    * information regarding copyright ownership.
    *
    *
    * The Apereo Foundation licenses this file to you under the Educational
    * Community 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://opensource.org/licenses/ecl2.txt
   *
   * 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.opencastproject.oaipmh.server;
  
  import static org.opencastproject.oaipmh.util.OsgiUtil.checkDictionary;
  import static org.opencastproject.oaipmh.util.OsgiUtil.getCfg;
  import static org.opencastproject.oaipmh.util.OsgiUtil.getContextProperty;
  import static org.opencastproject.util.data.Collections.map;
  import static org.opencastproject.util.data.functions.Strings.trimToNil;
  
  import org.opencastproject.oaipmh.util.XmlGen;
  import org.opencastproject.security.api.SecurityService;
  import org.opencastproject.util.OsgiUtil;
  import org.opencastproject.util.UrlSupport;
  
  import org.apache.commons.lang3.StringUtils;
  import org.osgi.framework.ServiceRegistration;
  import org.osgi.service.cm.ConfigurationException;
  import org.osgi.service.component.ComponentContext;
  import org.osgi.service.component.annotations.Activate;
  import org.osgi.service.component.annotations.Component;
  import org.osgi.service.component.annotations.Deactivate;
  import org.osgi.service.component.annotations.Modified;
  import org.osgi.service.component.annotations.Reference;
  import org.osgi.service.component.annotations.ReferenceCardinality;
  import org.osgi.service.component.annotations.ReferencePolicy;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.IOException;
  import java.util.Arrays;
  import java.util.Dictionary;
  import java.util.Map;
  import java.util.Optional;
  
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  /** The OAI-PMH server. Backed by an arbitrary amount of OAI-PMH repositories. */
  @Component(
      immediate = true,
      service = { OaiPmhServerInfo.class, OaiPmhServer.class },
      property = {
          "service.description=OAI-PMH server"
      }
  )
  public final class OaiPmhServer extends HttpServlet implements OaiPmhServerInfo {
  
    private static final long serialVersionUID = -7536526468920288612L;
  
    private static final Logger logger = LoggerFactory.getLogger(OaiPmhServer.class);
  
    private static final String CFG_DEFAULT_REPOSITORY = "default-repository";
    private static final String CFG_OAIPMH_MOUNTPOINT = "org.opencastproject.oaipmh.mountpoint";
    private static final String CFG_DEFAULT_OAIPMH_MOUNTPOINT = "/oaipmh";
  
    private SecurityService securityService;
  
    private final Map<String, OaiPmhRepository> repositories = map();
  
    private ComponentContext componentContext;
  
    private String defaultRepo;
  
    /**
     * The alias under which the servlet is currently registered.
     */
    private String mountPoint;
  
    private ServiceRegistration<?> serviceRegistration;
  
    /** OSGi DI. */
    @Reference(
        cardinality = ReferenceCardinality.MULTIPLE,
        policy = ReferencePolicy.DYNAMIC,
        unbind = "unsetRepository"
    )
    public void setRepository(final OaiPmhRepository r) {
      synchronized (repositories) {
       final String rId = r.getRepositoryId();
       if (repositories.containsKey(rId)) {
         logger.error("A repository with id {} has already been registered", rId);
       } else {
         // lazy creation since 'baseUrl' is not available at this time
         repositories.put(rId, r);
         logger.info("Registered repository " + rId);
       }
     }
   }
 
   /** OSGi DI. */
   public void unsetRepository(OaiPmhRepository r) {
     synchronized (repositories) {
       repositories.remove(r.getRepositoryId());
       logger.info("Unregistered repository " + r.getRepositoryId());
     }
   }
 
   /** OSGi DI. */
   @Reference
   public void setSecurityService(SecurityService securityService) {
     this.securityService = securityService;
   }
 
   /** OSGi component activation. */
   @Activate
   public void activate(ComponentContext cc) throws ConfigurationException {
     logger.info("Activate");
     this.componentContext = cc;
     // get mount point
     try {
       mountPoint = UrlSupport.concat("/",
           StringUtils.trimToNull(getContextProperty(componentContext, CFG_OAIPMH_MOUNTPOINT)));
     } catch (RuntimeException e) {
       mountPoint = CFG_DEFAULT_OAIPMH_MOUNTPOINT;
     }
     updated(cc.getProperties());
   }
 
   @Modified
   public void modified(ComponentContext cc) throws ConfigurationException {
     logger.info("Updated");
     updated(cc.getProperties());
   }
 
   @Deactivate
   public void deactivate() {
     tryUnregisterServlet();
   }
 
   /** Called by the ConfigurationAdmin service. This method actually sets up the server. */
   public synchronized void updated(Dictionary<String, ?> properties) throws ConfigurationException {
     // Because the OAI-PMH server implementation is technically not a REST service implemented
     // using JAX-RS annotations the Opencast mechanisms for registering REST endpoints do not work.
     // The server has to register itself with the OSGi HTTP service.
     checkDictionary(properties, componentContext);
     defaultRepo = getCfg(properties, CFG_DEFAULT_REPOSITORY);
     // register servlet
     try {
       // ... and unregister first if necessary
       tryUnregisterServlet();
       logger.info("Registering OAI-PMH server under " + mountPoint);
       logger.info("Default repository is " + defaultRepo);
 
       serviceRegistration = OsgiUtil.registerServlet(componentContext.getBundleContext(), this, mountPoint);
     } catch (Exception e) {
       logger.error("Error registering OAI-PMH servlet", e);
       throw new RuntimeException("Error registering OAI-PMH servlet", e);
     }
     logger.info("There are {} repositories registered yet. Watch out for later registration messages.",
             repositories.values().size());
   }
 
   @Override
   protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
     dispatch(req, res);
   }
 
   @Override
   protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
     dispatch(req, res);
   }
 
   private void dispatch(final HttpServletRequest req, final HttpServletResponse res) throws IOException {
     try {
       Optional<String> serverUrl = OaiPmhServerInfoUtil.oaiPmhServerUrlOfCurrentOrganization(securityService);
       if (serverUrl.isPresent()) {
         Optional<String> repositoryId = repositoryId(req, mountPoint);
         if (repositoryId.isPresent()) {
           if (runRepo(repositoryId.get(), serverUrl.get(), req, res)) {
             return;
           } else {
             res.sendError(HttpServletResponse.SC_NOT_FOUND);
             return;
           }
         }
         // no repository id in path, try default repo
         if (runRepo(defaultRepo, serverUrl.get(), req, res)) {
           return;
         }
       }
       res.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
     } catch (Exception e) {
       logger.error("Error handling OAI-PMH request", e);
       res.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e.getMessage());
     }
   }
 
   /**
    * Run repo <code>repoId</code>.
    *
    * @return false if the repo does not exist, true otherwise
    */
   private boolean runRepo(String repoId, String serverUrl, HttpServletRequest req, HttpServletResponse res)
           throws Exception {
     Optional<OaiPmhRepository> repo = getRepoById(repoId);
     if (repo.isPresent()) {
       final String repoUrl = UrlSupport.concat(serverUrl, mountPoint, repoId);
       runRepo(repo.get(), repoUrl, req, res);
       return true;
     }
     return false;
   }
 
   private void runRepo(OaiPmhRepository repo, final String repoUrl, final HttpServletRequest req,
           HttpServletResponse res) throws Exception {
     final Params p = new Params() {
       @Override
       String getParameter(String key) {
         return req.getParameter(key);
       }
 
       @Override
       String getRepositoryUrl() {
         return repoUrl;
       }
     };
     final XmlGen oai = repo.selectVerb(p);
     res.setCharacterEncoding("UTF-8");
     res.setContentType("text/xml;charset=UTF-8");
     oai.generate(res.getOutputStream());
   }
 
   private synchronized void tryUnregisterServlet() {
     if (serviceRegistration != null) {
       serviceRegistration.unregister();
       serviceRegistration = null;
     }
   }
 
   /**
    * Retrieve the repository id from the requested path.
    *
    * @param req
    *          the HTTP request
    * @param mountPoint
    *          the base path of the OAI-PMH server, e.g. /oaipmh
    */
   public static Optional<String> repositoryId(HttpServletRequest req, String mountPoint) {
     String[] parts = StringUtils.removeStart(UrlSupport.removeDoubleSeparator(req.getRequestURI()), mountPoint)
         .split("/");
 
     return Arrays.stream(parts)
         .flatMap(s -> trimToNil(s).stream())
         .findFirst();
   }
 
   /** Get a repository by id. */
   private Optional<OaiPmhRepository> getRepoById(String id) {
     synchronized (repositories) {
       if (hasRepo(id)) {
         return Optional.of(repositories.get(id));
       } else {
         logger.warn("No OAI-PMH repository has been registered with id " + id);
         return Optional.empty();
       }
     }
   }
 
   @Override
   public boolean hasRepo(String id) {
     synchronized (repositories) {
       return repositories.containsKey(id);
     }
   }
 
   @Override
   public String getMountPoint() {
     return mountPoint;
   }
 }