/*
    * 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.sakai;
  
  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 org.opencastproject.util.XmlSafeParser;
  
  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.commons.codec.binary.Base64;
  import org.apache.commons.io.IOUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  import org.w3c.dom.Document;
  import org.w3c.dom.Element;
  import org.w3c.dom.Node;
  import org.w3c.dom.NodeList;
  
  import java.io.BufferedInputStream;
  import java.io.FileNotFoundException;
  import java.io.StringReader;
  import java.net.HttpURLConnection;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Set;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicLong;
  import java.util.regex.PatternSyntaxException;
  
  import javax.xml.parsers.DocumentBuilder;
  
  /**
   * A UserProvider that reads user roles from Sakai.
   */
  public class SakaiUserProviderInstance implements UserProvider, RoleProvider {
  
    private static final String LTI_LEARNER_ROLE = "Learner";
  
    private static final String LTI_INSTRUCTOR_ROLE = "Instructor";
  
    public static final String PROVIDER_NAME = "sakai";
  
    private static final String OC_USERAGENT = "Opencast";
  
    /** The logger */
    private static final Logger logger = LoggerFactory.getLogger(SakaiUserProviderInstance.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 Sakai */
    private AtomicLong sakaiLoads = null;
  
    /** A cache of users, which lightens the load on Sakai */
    private LoadingCache<String, Object> cache = null;
  
    /** A token to store in the miss cache */
    protected Object nullToken = new Object();
  
   /** The URL of the Sakai instance */
   private String sakaiUrl = null;
 
   /** The username used to call Sakai REST webservices */
   private String sakaiUsername = null;
 
   /** The password of the user used to call Sakai REST webservices */
   private String sakaiPassword = null;
 
   /** Regular expression for matching valid sites */
   private String sitePattern;
 
   /** Regular expression for matching valid users */
   private String userPattern;
 
   /** A map of roles which are regarded as Instructor roles */
   private Set<String> instructorRoles;
 
   /**
    * Constructs an Sakai user provider with the needed settings.
    *
    * @param pid
    *          the pid of this service
    * @param organization
    *          the organization
    * @param url
    *          the url of the Sakai server
    * @param userName
    *          the user to authenticate as
    * @param password
    *          the user credentials
    * @param cacheSize
    *          the number of users to cache
    * @param cacheExpiration
    *          the number of minutes to cache users
    */
   public SakaiUserProviderInstance(
       String pid,
       Organization organization,
       String url,
       String userName,
       String password,
       String sitePattern,
       String userPattern,
       Set<String> instructorRoles,
       int cacheSize,
       int cacheExpiration
   ) {
 
     this.organization = organization;
     this.sakaiUrl = url;
     this.sakaiUsername = userName;
     this.sakaiPassword = password;
     this.sitePattern = sitePattern;
     this.userPattern = userPattern;
     this.instructorRoles = instructorRoles;
 
     logger.info("Creating new SakaiUserProviderInstance(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 = loadUserFromSakai(id);
             return user == null ? nullToken : user;
           }
         });
   }
 
   @Override
   public String getName() {
     return PROVIDER_NAME;
   }
 
   // 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 + ")");
 
     try {
       if ((userPattern != null) && !userName.matches(userPattern)) {
         logger.debug("load user {} failed regexp {}", userName, userPattern);
         return null;
       }
     } catch (PatternSyntaxException e) {
       logger.warn("Invalid regular expression for user pattern {} - disabling checks", userPattern);
       userPattern = null;
     }
 
     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 " + userName + " from cache");
         return (JaxbUser) user;
       }
     } catch (ExecutionError e) {
       logger.warn("Exception while loading user {}", userName, e);
       return null;
     } catch (UncheckedExecutionException e) {
       logger.warn("Exception while loading user {}", userName, e);
       return null;
     }
   }
 
   /**
    * Loads a user from Sakai.
    * 
    * @param userName
    *          the username
    * @return the user
    */
   protected User loadUserFromSakai(String userName) {
 
     if (cache == null) {
       throw new IllegalStateException("The Sakai 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 loadUserFromSakai, currently processing user : {}", userName);
 
     JaxbOrganization jaxbOrganization = JaxbOrganization.fromOrganization(organization);
 
     // update cache statistics
     sakaiLoads.incrementAndGet();
 
     Thread currentThread = Thread.currentThread();
     ClassLoader originalClassloader = currentThread.getContextClassLoader();
     try {
 
       // Sakai userId (internal id), email address and display name
       String[] sakaiUser = getSakaiUser(userName);
 
       if (sakaiUser == null) {
         // user not known to this provider
         logger.debug("User {} not found in Sakai system", userName);
         cache.put(userName, nullToken);
         return null;
       }
 
       String userId = sakaiUser[0];
       String email = sakaiUser[1];
       String displayName = sakaiUser[2];
 
       // Get the set of Sakai roles for the user
       String[] sakaiRoles = getRolesFromSakai(userId);
 
       // if Sakai doesn't know about this user we need to return
       if (sakaiRoles == null) {
         cache.put(userName, nullToken);
         return null;
       }
 
       logger.debug("Sakai roles for eid " + userName + " id " + userId + ": " + Arrays.toString(sakaiRoles));
 
       Set<JaxbRole> roles = new HashSet<JaxbRole>();
 
       boolean isInstructor = false;
 
       for (String r : sakaiRoles) {
         roles.add(new JaxbRole(r, jaxbOrganization, "Sakai external role", Role.Type.EXTERNAL));
 
         if (r.endsWith(LTI_INSTRUCTOR_ROLE)) {
           isInstructor = true;
         }
       }
 
       // Group role for all Sakai users
       roles.add(new JaxbRole(Group.ROLE_PREFIX + "SAKAI", jaxbOrganization, "Sakai Users", Role.Type.EXTERNAL_GROUP));
 
       // Group role for Sakai users who are an instructor in one more sites
       if (isInstructor) {
         roles.add(new JaxbRole(
             Group.ROLE_PREFIX + "SAKAI_INSTRUCTOR",
             jaxbOrganization,
             "Sakai Instructors",
             Role.Type.EXTERNAL_GROUP
         ));
       }
 
       logger.debug("Returning JaxbRoles: " + roles);
 
       User user = new JaxbUser(userName, null, displayName, email, PROVIDER_NAME, jaxbOrganization, roles);
 
       cache.put(userName, user);
       logger.debug("Returning user {}", userName);
 
       return user;
 
     } finally {
       currentThread.setContextClassLoader(originalClassloader);
     }
 
   }
 
   /*
    ** Verify that the user exists
    ** Query with /direct/user/:ID:/exists
    */
   private boolean verifySakaiUser(String userId) {
 
     logger.debug("verifySakaiUser({})", userId);
 
     try {
       if ((userPattern != null) && !userId.matches(userPattern)) {
         logger.debug("verify user {} failed regexp {}", userId, userPattern);
         return false;
       }
     } catch (PatternSyntaxException e) {
       logger.warn("Invalid regular expression for user pattern {} - disabling checks", userPattern);
       userPattern = null;
     }
 
     int code;
 
     try {
       // This webservice does not require authentication
       URL url = new URL(sakaiUrl + "/direct/user/" + userId + "/exists");
 
       HttpURLConnection connection = (HttpURLConnection) url.openConnection();
       connection.setRequestMethod("GET");
       connection.setRequestProperty("User-Agent", OC_USERAGENT);
 
       connection.connect();
       code = connection.getResponseCode();
     } catch (Exception e) {
       logger.warn("Exception verifying Sakai user " + userId + " at " + sakaiUrl + ": " + e.getMessage());
       return false;
     }
 
     // HTTP OK 200 for site exists, return false for everything else (typically 404 not found)
     return (code == 200);
   }
 
   /*
    ** Verify that the site exists
    ** Query with /direct/site/:ID:/exists
    */
   private boolean verifySakaiSite(String siteId) {
 
     // We could additionally cache positive and negative siteId lookup results here
 
     logger.debug("verifySakaiSite(" + siteId + ")");
 
     try {
       if ((sitePattern != null) && !siteId.matches(sitePattern)) {
         logger.debug("verify site {} failed regexp {}", siteId, sitePattern);
         return false;
       }
     } catch (PatternSyntaxException e) {
       logger.warn("Invalid regular expression for site pattern {} - disabling checks", sitePattern);
       sitePattern = null;
     }
 
     int code;
 
     try {
       // This webservice does not require authentication
       URL url = new URL(sakaiUrl + "/direct/site/" + siteId + "/exists");
 
       HttpURLConnection connection = (HttpURLConnection) url.openConnection();
       connection.setRequestMethod("GET");
       connection.setRequestProperty("User-Agent", OC_USERAGENT);
 
       connection.connect();
       code = connection.getResponseCode();
     } catch (Exception e) {
       logger.warn("Exception verifying Sakai site " + siteId + " at " + sakaiUrl + ": " + e.getMessage());
       return false;
     }
 
     // HTTP OK 200 for site exists, return false for everything else (typically 404 not found)
     return (code == 200);
   }
 
   private String[] getRolesFromSakai(String userId) {
     logger.debug("getRolesFromSakai(" + userId + ")");
     try {
 
       URL url = new URL(sakaiUrl + "/direct/membership/fastroles/" + userId + ".xml" + "?__auth=basic");
       String encoded = Base64.encodeBase64String((sakaiUsername + ":" + sakaiPassword).getBytes("utf8"));
 
       HttpURLConnection connection = (HttpURLConnection) url.openConnection();
       connection.setRequestMethod("GET");
       connection.setDoOutput(true);
       connection.setRequestProperty("Authorization", "Basic " + encoded);
       connection.setRequestProperty("User-Agent", OC_USERAGENT);
 
       String xml = IOUtils.toString(new BufferedInputStream(connection.getInputStream()));
       logger.debug(xml);
 
       DocumentBuilder parser = XmlSafeParser.newDocumentBuilderFactory().newDocumentBuilder();
 
       Document document = parser.parse(new org.xml.sax.InputSource(new StringReader(xml)));
 
       Element root = document.getDocumentElement();
       NodeList nodes = root.getElementsByTagName("membership");
       List<String> roleList = new ArrayList<String>();
       for (int i = 0; i < nodes.getLength(); i++) {
         Element element = (Element) nodes.item(i);
         // The Role in sakai
         String sakaiRole = getTagValue("memberRole", element);
 
         // the location in sakai e.g. /site/admin
         String sakaiLocationReference = getTagValue("locationReference", element);
         // we don't do the sakai admin role
         if ("/site/!admin".equals(sakaiLocationReference)) {
           continue;
         }
 
         String opencastRole = buildOpencastRole(sakaiLocationReference, sakaiRole);
         roleList.add(opencastRole);
       }
 
       return roleList.toArray(new String[0]);
 
     } catch (FileNotFoundException fnf) {
       // if the return is 404 it means the user wasn't found
       logger.debug("user id " + userId + " not found on " + sakaiUrl);
     } catch (Exception e) {
       logger.warn(
           "Exception getting site/role membership for Sakai user {} at {}: {}",
           userId,
           sakaiUrl,
           e.getMessage()
       );
     }
 
     return null;
   }
 
   /**
    * Get the internal Sakai user Id for the supplied user. If the user exists, set the user's email address.
    * 
    * @param eid
    * @return
    */
   private String[] getSakaiUser(String eid) {
 
     try {
 
       URL url = new URL(sakaiUrl + "/direct/user/" + eid + ".xml" + "?__auth=basic");
       logger.debug("Sakai URL: " + sakaiUrl);
       String encoded = Base64.encodeBase64String((sakaiUsername + ":" + sakaiPassword).getBytes("utf8"));
       HttpURLConnection connection = (HttpURLConnection) url.openConnection();
       connection.setRequestMethod("GET");
       connection.setDoOutput(true);
       connection.setRequestProperty("Authorization", "Basic " + encoded);
       connection.setRequestProperty("User-Agent", OC_USERAGENT);
 
       String xml = IOUtils.toString(new BufferedInputStream(connection.getInputStream()));
       logger.debug(xml);
 
       // Parse the document
       DocumentBuilder parser = XmlSafeParser.newDocumentBuilderFactory().newDocumentBuilder();
       Document document = parser.parse(new org.xml.sax.InputSource(new StringReader(xml)));
       Element root = document.getDocumentElement();
 
       String sakaiID = getTagValue("id", root);
       String sakaiEmail = getTagValue("email", root);
       String sakaiDisplayName = getTagValue("displayName", root);
 
       return new String[]{sakaiID, sakaiEmail, sakaiDisplayName};
 
     } catch (FileNotFoundException fnf) {
       logger.debug("user {} does not exist on Sakai system", eid, fnf);
     } catch (Exception e) {
       logger.warn("Exception getting Sakai user information for user {} at {}", eid, sakaiUrl, e);
     }
 
     return null;
   }
 
   /**
    * Build a Opencast role "foo_user" from the given Sakai locations
    * 
    * @param sakaiLocationReference
    * @param sakaiRole
    * @return
    */
   private String buildOpencastRole(String sakaiLocationReference, String sakaiRole) {
 
     // we need to parse the site id from the reference
     String siteId = sakaiLocationReference.substring(sakaiLocationReference.indexOf("/", 2) + 1);
 
     // map Sakai role to LTI role
     String ltiRole = instructorRoles.contains(sakaiRole) ? LTI_INSTRUCTOR_ROLE : LTI_LEARNER_ROLE;
 
     return siteId + "_" + ltiRole;
   }
 
   /**
    * Get a value for for a tag in the element
    * 
    * @param sTag
    * @param eElement
    * @return
    */
   private static String getTagValue(String sTag, Element eElement) {
     if (eElement.getElementsByTagName(sTag) == null) {
       return null;
     }
 
     NodeList nlList = eElement.getElementsByTagName(sTag).item(0).getChildNodes();
     Node nValue = nlList.item(0);
     return (nValue != null) ? nValue.getNodeValue() : null;
   }
 
   @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();
     }
 
     // Verify if a user exists (non-wildcard searches only)
     if (!verifySakaiUser(query)) {
       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 roleset for {}", userName);
       return new ArrayList<Role>(user.getRoles());
     }
 
     // Not found
     logger.debug("Return empty roleset for {} - not found on Sakai", userName);
     return new LinkedList<Role>();
   }
 
   @Override
   public Iterator<Role> findRoles(String query, Role.Target target, int offset, int limit) {
 
     // We search for SITEID, SITEID_Learner, SITEID_Instructor
 
     logger.debug("findRoles(query=" + query + " offset=" + offset + " limit=" + limit + ")");
 
     // Don't return roles for users or groups
     if (target == Role.Target.USER) {
       return Collections.emptyIterator();
     }
 
     boolean exact = true;
     boolean ltirole = false;
 
     if (query.endsWith("%")) {
       exact = false;
       query = query.substring(0, query.length() - 1);
     }
 
     if (query.isEmpty()) {
       return Collections.emptyIterator();
     }
 
     // Verify that role name ends with LTI_LEARNER_ROLE or LTI_INSTRUCTOR_ROLE
     if (exact && !query.endsWith("_" + LTI_LEARNER_ROLE) && !query.endsWith("_" + LTI_INSTRUCTOR_ROLE)) {
       return Collections.emptyIterator();
     }
 
     String sakaiSite = null;
 
     if (query.endsWith("_" + LTI_LEARNER_ROLE)) {
       sakaiSite = query.substring(0, query.lastIndexOf("_" + LTI_LEARNER_ROLE));
       ltirole = true;
     } else if (query.endsWith("_" + LTI_INSTRUCTOR_ROLE)) {
       sakaiSite = query.substring(0, query.lastIndexOf("_" + LTI_INSTRUCTOR_ROLE));
       ltirole = true;
     }
 
     if (!ltirole) {
       sakaiSite = query;
     }
 
     if (!verifySakaiSite(sakaiSite)) {
       return Collections.emptyIterator();
     }
 
     // Roles list
     List<Role> roles = new LinkedList<Role>();
 
     JaxbOrganization jaxbOrganization = JaxbOrganization.fromOrganization(organization);
 
     if (ltirole) {
       // Query is for a Site ID and an LTI role (Instructor/Learner)
       roles.add(new JaxbRole(query, jaxbOrganization, "Sakai Site Role", Role.Type.EXTERNAL));
     } else {
       // Site ID - return both roles
       roles.add(new JaxbRole(
           sakaiSite + "_" + LTI_INSTRUCTOR_ROLE,
           jaxbOrganization,
           "Sakai Site Instructor Role",
           Role.Type.EXTERNAL
       ));
       roles.add(new JaxbRole(
           sakaiSite + "_" + LTI_LEARNER_ROLE,
           jaxbOrganization,
           "Sakai Site Learner Role",
           Role.Type.EXTERNAL
       ));
     }
 
     return roles.iterator();
   }
 
 }