/*
    * 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.userdirectory.studip;
  
  import org.opencastproject.security.api.CachingUserProviderMXBean;
  import org.opencastproject.security.api.Group;
  import org.opencastproject.security.api.JaxbOrganization;
  import org.opencastproject.security.api.JaxbRole;
  import org.opencastproject.security.api.JaxbUser;
  import org.opencastproject.security.api.Organization;
  import org.opencastproject.security.api.Role;
  import org.opencastproject.security.api.RoleProvider;
  import org.opencastproject.security.api.User;
  import org.opencastproject.security.api.UserProvider;
  
  import com.google.common.cache.CacheBuilder;
  import com.google.common.cache.CacheLoader;
  import com.google.common.cache.LoadingCache;
  import com.google.common.util.concurrent.ExecutionError;
  import com.google.common.util.concurrent.UncheckedExecutionException;
  
  import org.apache.http.client.config.RequestConfig;
  import org.apache.http.client.methods.CloseableHttpResponse;
  import org.apache.http.client.methods.HttpGet;
  import org.apache.http.client.utils.URIBuilder;
  import org.apache.http.impl.client.CloseableHttpClient;
  import org.apache.http.impl.client.HttpClientBuilder;
  import org.json.simple.JSONArray;
  import org.json.simple.JSONObject;
  import org.json.simple.parser.JSONParser;
  import org.json.simple.parser.ParseException;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.lang.management.ManagementFactory;
  import java.net.URI;
  import java.net.URISyntaxException;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Objects;
  import java.util.Set;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicLong;
  
  import javax.management.InstanceNotFoundException;
  import javax.management.MBeanServer;
  import javax.management.ObjectName;
  
  /**
   * A UserProvider that reads user roles from Studip.
   */
  public class StudipUserProviderInstance implements UserProvider, RoleProvider, CachingUserProviderMXBean {
  
    public static final String PROVIDER_NAME = "studip";
  
    private static final String OC_USERAGENT = "Opencast";
    private static final String STUDIP_GROUP = Group.ROLE_PREFIX + "STUDIP";
  
    /** The logger */
    private static final Logger logger = LoggerFactory.getLogger(StudipUserProviderInstance.class);
  
    /** The organization */
    private Organization organization = null;
  
    /** Total number of requests made to load users */
    private AtomicLong requests = null;
  
    /** The number of requests made to Studip */
    private AtomicLong studipLoads = null;
  
    /** A cache of users, which lightens the load on Studip */
    private LoadingCache<String, Object> cache = null;
  
   /** A token to store in the miss cache */
   protected Object nullToken = new Object();
 
   /** The URL of the Studip instance */
   private URI studipUrl;
 
   /** The URL of the Studip instance */
   private String studipToken = null;
 
   /**
    * Constructs an Studip user provider with the needed settings.
    *
    * @param pid
    *          the pid of this service
    * @param organization
    *          the organization
    * @param url
    *          the url of the Studip server
    * @param token
    *          the token to authenticate with
    * @param cacheSize
    *          the number of users to cache
    * @param cacheExpiration
    *          the number of minutes to cache users
    */
   public StudipUserProviderInstance(
       String pid,
       Organization organization,
       URI url,
       String token,
 
       int cacheSize,
       int cacheExpiration
   ) {
 
     this.organization = organization;
     this.studipUrl = url;
     this.studipToken = token;
 
     logger.info("Creating new StudipUserProviderInstance(pid={}, url={}, cacheSize={}, cacheExpiration={})",
                  pid, url, cacheSize, cacheExpiration);
 
     // Setup the caches
     cache = CacheBuilder.newBuilder().maximumSize(cacheSize).expireAfterWrite(cacheExpiration, TimeUnit.MINUTES)
         .build(new CacheLoader<String, Object>() {
           @Override
           public Object load(String id) throws Exception {
             User user = loadUserFromStudip(id);
             return user == null ? nullToken : user;
           }
         });
 
     registerMBean(pid);
   }
 
   @Override
   public String getName() {
     return PROVIDER_NAME;
   }
 
   /**
    * Registers an MXBean.
    */
   protected void registerMBean(String pid) {
     // register with jmx
     requests = new AtomicLong();
     studipLoads = new AtomicLong();
     try {
       ObjectName name;
       name = StudipUserProviderFactory.getObjectName(pid);
       Object mbean = this;
       MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
       try {
         mbs.unregisterMBean(name);
       } catch (InstanceNotFoundException e) {
         logger.debug("{} was not registered before", name);
       }
       mbs.registerMBean(mbean, name);
     } catch (Exception e) {
       logger.error("Unable to register {} as an mbean", this, e);
     }
   }
 
   // UserProvider methods
 
   /**
    * {@inheritDoc}
    * 
    * @see org.opencastproject.security.api.UserProvider#getOrganization()
    */
   @Override
   public String getOrganization() {
     return organization.getId();
   }
 
   /**
    * {@inheritDoc}
    * 
    * @see org.opencastproject.security.api.UserProvider#loadUser(java.lang.String)
    */
   @Override
   public User loadUser(String userName) {
     logger.debug("loaduser({})", userName);
 
     requests.incrementAndGet();
     try {
       Object user = cache.getUnchecked(userName);
       if (user == nullToken) {
         logger.debug("Returning null user from cache");
         return null;
       } else {
         logger.debug("Returning user {} from cache", userName);
         return (JaxbUser) user;
       }
     } catch (ExecutionError | UncheckedExecutionException e) {
       logger.warn("Exception while loading user {}", userName, e);
       return null;
     }
   }
 
   /**
    * Loads a user from Stud.IP.
    * 
    * @param userName
    *          the username
    * @return the user
    */
   protected User loadUserFromStudip(String userName) {
     if (cache == null) {
       throw new IllegalStateException("The Stud.IP user detail service has not yet been configured");
     }
 
     // Don't answer for admin, anonymous or empty user
     if ("admin".equals(userName) || "".equals(userName) || "anonymous".equals(userName)) {
       cache.put(userName, nullToken);
       logger.debug("we don't answer for {}", userName);
       return null;
     }
 
     logger.debug("In loadUserFromStudip, currently processing user : {}", userName);
 
     JaxbOrganization jaxbOrganization = JaxbOrganization.fromOrganization(organization);
 
     // update cache statistics
     studipLoads.incrementAndGet();
 
     Thread currentThread = Thread.currentThread();
     ClassLoader originalClassloader = currentThread.getContextClassLoader();
     try {
       // Stud.IP userId (internal id), email address and display name
       JSONObject userJsonObj = getStudipUser(userName);
       if (userJsonObj == null) {
         return null;
       }
 
       Set<JaxbRole> roles = new HashSet<>();
       if (userJsonObj.containsKey("roles")) {
         JSONArray rolesArray = (JSONArray) userJsonObj.get("roles");
         for (Object r : rolesArray) {
           roles.add(new JaxbRole(r.toString(), jaxbOrganization, "Studip external role", Role.Type.EXTERNAL));
         }
       }
 
       // Group role for all Stud.IP users
       roles.add(new JaxbRole(STUDIP_GROUP, jaxbOrganization, "Studip Users", Role.Type.EXTERNAL_GROUP));
       logger.debug("Returning JaxbRoles: {}", roles);
 
       // Email address
       var email = Objects.toString(userJsonObj.get("email"), null);
       var name = Objects.toString(userJsonObj.get("fullname"), null);
 
       User user = new JaxbUser(userName, null, name, email, PROVIDER_NAME, jaxbOrganization, roles);
 
       cache.put(userName, user);
       logger.debug("Returning user {}", userName);
 
       return user;
 
     } catch (ParseException e) {
       logger.error("Exception while parsing response from provider for user {}", userName, e);
       return null;
     } catch (IOException e) {
       logger.error("Error requesting user data for user `{}`: {}", userName, e.getMessage());
       return null;
     } catch (URISyntaxException e) {
       logger.error("Misspelled URI", e);
       return null;
     } finally {
       currentThread.setContextClassLoader(originalClassloader);
     }
   }
 
   /**
    * Get the internal Stud.IP user Id for the supplied user. If the user exists, set the user's email address.
    * 
    * @param uid Identifier of the user to look for
    * @return JSON object containing user information
    */
   private JSONObject getStudipUser(String uid) throws URISyntaxException, IOException, ParseException {
     // Build URL
     var apiPath = new URIBuilder().setPathSegments("opencast", "user", uid).getPath();
     var url = new URIBuilder(studipUrl)
         .setPath(studipUrl.getPath().replaceAll("/*$", "") + apiPath)
         .addParameter("token", studipToken)
         .build();
 
     // Execute request
     HttpGet get = new HttpGet(url);
     get.setHeader("User-Agent", OC_USERAGENT);
 
     // Don't wait for responses indefinitely
     RequestConfig config = RequestConfig.custom()
         .setConnectTimeout(5000)
         .setSocketTimeout(10000).build();
 
     try (CloseableHttpClient client = HttpClientBuilder.create().setDefaultRequestConfig(config).build();) {
       try (CloseableHttpResponse resp = client.execute(get)) {
         var statusCode = resp.getStatusLine().getStatusCode();
         if (statusCode == 404) {
           // Stud.IP does not know about the user
           return null;
         } else if (statusCode / 100 != 2) {
           throw new IOException("HttpRequest unsuccessful, reason: " + resp.getStatusLine().getReasonPhrase());
         }
 
         // Parse response
         BufferedReader reader = new BufferedReader(new InputStreamReader(resp.getEntity().getContent()));
         JSONParser parser = new JSONParser();
         Object obj = parser.parse(reader);
 
         // Check for errors
         if (!(obj instanceof JSONObject)) {
           throw new IOException("StudIP responded in unexpected format");
         }
 
         JSONObject jObj = (JSONObject) obj;
         if (jObj.containsKey("errors")) {
           throw new IOException("Stud.IP returned an error: " + jObj.toJSONString());
         }
 
         return jObj;
       }
     }
   }
 
   /**
    * {@inheritDoc}
    * 
    * @see org.opencastproject.security.api.CachingUserProviderMXBean#getCacheHitRatio()
    */
   @Override
   public float getCacheHitRatio() {
     if (requests.get() == 0) {
       return 0;
     }
     return (float) (requests.get() - studipLoads.get()) / requests.get();
   }
 
   @Override
   public Iterator<User> findUsers(String query, int offset, int limit) {
 
     if (query == null) {
       throw new IllegalArgumentException("Query must be set");
     }
 
     if (query.endsWith("%")) {
       query = query.substring(0, query.length() - 1);
     }
 
     if (query.isEmpty()) {
       return Collections.emptyIterator();
     }
 
     List<User> users = new LinkedList<User>();
     JaxbOrganization jaxbOrganization = JaxbOrganization.fromOrganization(organization);
     JaxbUser queryUser = new JaxbUser(query, PROVIDER_NAME, jaxbOrganization, new HashSet<JaxbRole>());
     users.add(queryUser);
 
     return users.iterator();
   }
 
   @Override
   public Iterator<User> getUsers() {
     // We never enumerate all users
     return Collections.emptyIterator();
   }
 
   @Override
   public void invalidate(String userName) {
     cache.invalidate(userName);
   }
 
   @Override
   public long countUsers() {
     // Not meaningful, as we never enumerate users
     return 0;
   }
 
   // RoleProvider methods
 
   @Override
   public List<Role> getRolesForUser(String userName) {
 
     List<Role> roles = new LinkedList<Role>();
 
     // Don't answer for admin, anonymous or empty user
     if ("admin".equals(userName) || "".equals(userName) || "anonymous".equals(userName)) {
       logger.debug("we don't answer for {}", userName);
       return roles;
     }
 
     logger.debug("getRolesForUser({})", userName);
 
     User user = loadUser(userName);
     if (user != null) {
       logger.debug("Returning cached role set for {}", userName);
       return new ArrayList<Role>(user.getRoles());
     }
 
     // Not found
     logger.debug("Return empty role set for {} - not found on Stud.IP", userName);
     return new LinkedList<>();
   }
 
   @Override
   public Iterator<Role> findRoles(String query, Role.Target target, int offset, int limit) {
     logger.debug("findRoles(query={} offset={} limit={})", query, offset, limit);
 
     // Don't return roles for users or groups
     if (target == Role.Target.USER) {
       return Collections.emptyIterator();
     }
 
     if (query.endsWith("%")) {
       query = query.substring(0, query.length() - 1);
     }
 
     if (query.isEmpty()) {
       return Collections.emptyIterator();
     }
 
     // Roles list
     List<Role> roles = new LinkedList<>();
 
     return roles.iterator();
   }
 
 }