/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at
 * docs/licenses/cddl.txt
 * or http://www.opensource.org/licenses/cddl1.php.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at
 * docs/licenses/cddl.txt.  If applicable,
 * add the following below this CDDL HEADER, with the fields enclosed
 * by brackets "[]" replaced with your own identifying information:
 *      Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 *
 *
 *      Copyright 2011-2016 UnboundID Corp.
 */
package com.unboundid.directory.sdk.http.api;



import java.util.Collections;
import java.util.List;
import java.util.Map;

import javax.servlet.Filter;
import javax.servlet.http.HttpServlet;

import com.unboundid.directory.sdk.broker.internal.BrokerExtension;
import com.unboundid.directory.sdk.common.internal.ExampleUsageProvider;
import com.unboundid.directory.sdk.common.internal.Reconfigurable;
import com.unboundid.directory.sdk.common.internal.UnboundIDExtension;
import com.unboundid.directory.sdk.ds.internal.DirectoryServerExtension;
import com.unboundid.directory.sdk.http.config.HTTPServletExtensionConfig;
import com.unboundid.directory.sdk.http.types.HTTPServerContext;
import com.unboundid.directory.sdk.metrics.internal.MetricsEngineExtension;
import com.unboundid.directory.sdk.proxy.internal.DirectoryProxyServerExtension;
import com.unboundid.ldap.sdk.LDAPException;
import com.unboundid.ldap.sdk.ResultCode;
import com.unboundid.util.Extensible;
import com.unboundid.util.ThreadSafety;
import com.unboundid.util.ThreadSafetyLevel;
import com.unboundid.util.args.ArgumentException;
import com.unboundid.util.args.ArgumentParser;



/**
 * This class defines an API that must be implemented by extensions which create
 * servlets for use with an HTTP connection handler.
 * <BR>
 * <H2>Configuring HTTP Servlet Extensions</H2>
 * In order to configure an HTTP servlet extension created using this API, use a
 * command like:
 * <PRE>
 *      dsconfig create-http-servlet-extension \
 *           --extension-name "<I>{extension-name}</I>" \
 *           --type third-party \
 *           --set "extension-class:<I>{class-name}</I>" \
 *           --set "extension-argument:<I>{name=value}</I>"
 * </PRE>
 * where "<I>{extension-name}</I>" is the name to use for the HTTP servlet
 * extension instance, "<I>{class-name}</I>" is the fully-qualified name of the
 * Java class that extends
 * {@code com.unboundid.directory.sdk.ds.api.HTTPServletExtension},
 * and "<I>{name=value}</I>" represents name-value pairs for any arguments to
 * provide to the HTTP servlet extension.  If multiple arguments should be
 * provided to the HTTP servlet extension, then the
 * "<CODE>--set extension-argument:<I>{name=value}</I></CODE>" option should be
 * provided multiple times.
 * <BR><BR>
 * Note that the server also provides the ability to run full web applications,
 * by creating a Web Application Extension and specifying the necessary
 * properties.  If that web application needs to perform internal operations or
 * interact with the server in any way, then the
 * {@link com.unboundid.directory.sdk.http.types.WebAppServerContextFactory}
 * class may be called from the web application in order to obtain a server
 * context.
 *
 * @see  com.unboundid.directory.sdk.http.scripting.ScriptedHTTPServletExtension
 */
@Extensible()
@DirectoryServerExtension()
@DirectoryProxyServerExtension(appliesToLocalContent=true,
     appliesToRemoteContent=true)
@MetricsEngineExtension()
@BrokerExtension()
@ThreadSafety(level=ThreadSafetyLevel.INTERFACE_THREADSAFE)
public abstract class HTTPServletExtension
       implements UnboundIDExtension,
                  Reconfigurable<HTTPServletExtensionConfig>,
                  ExampleUsageProvider
{
  /**
   * Creates a new instance of this HTTP servlet extension.  All HTTP servlet
   * extension implementations must include a default constructor, but any
   * initialization should generally be done in the
   * {@code createServlet} method.
   */
  public HTTPServletExtension()
  {
    // No implementation is required.
  }



  /**
   * {@inheritDoc}
   */
  public abstract String getExtensionName();



  /**
   * {@inheritDoc}
   */
  public abstract String[] getExtensionDescription();



  /**
   * {@inheritDoc}
   */
  public void defineConfigArguments(final ArgumentParser parser)
         throws ArgumentException
  {
    // No arguments will be allowed by default.
  }



  /**
   * {@inheritDoc}
   */
  public boolean isConfigurationAcceptable(
                      final HTTPServletExtensionConfig config,
                      final ArgumentParser parser,
                      final List<String> unacceptableReasons)
  {
    // No extended validation will be performed by default.
    return true;
  }



  /**
   * {@inheritDoc}
   */
  public ResultCode applyConfiguration(final HTTPServletExtensionConfig config,
                                       final ArgumentParser parser,
                                       final List<String> adminActionsRequired,
                                       final List<String> messages)
  {
    // By default, no configuration changes will be applied.  If there are any
    // arguments, then add an admin action message indicating that the extension
    // needs to be restarted for any changes to take effect.
    if (! parser.getNamedArguments().isEmpty())
    {
      adminActionsRequired.add(
           "No configuration change has actually been applied.  The new " +
                "configuration will not take effect until this HTTP servlet " +
                "extension is disabled and re-enabled or until the server is " +
                "restarted.");
    }

    return ResultCode.SUCCESS;
  }



  /**
   * {@inheritDoc}
   */
  public Map<List<String>,String> getExamplesArgumentSets()
  {
    return Collections.emptyMap();
  }



  /**
   * Creates an HTTP servlet extension using the provided information.
   *
   * @param  serverContext  A handle to the server context for the server in
   *                        which this extension is running.
   * @param  config         The general configuration for this HTTP servlet
   *                        extension.
   * @param  parser         The argument parser which has been initialized from
   *                        the configuration for this HTTP servlet extension.
   *
   * @return  The HTTP servlet that has been created.
   *
   * @throws  LDAPException  If a problem is encountered while attempting to
   *                         create the HTTP servlet.
   */
  public abstract HttpServlet createServlet(
              final HTTPServerContext serverContext,
              final HTTPServletExtensionConfig config,
              final ArgumentParser parser)
         throws LDAPException;



  /**
   * Retrieves a list of the request paths for which the associated servlet
   * should be invoked.  This method will be called after the
   * {@link #createServlet} method has been used to create the servlet instance.
   *
   * @return  A list of the request paths for which the associated servlet
   *          should be invoked.
   */
  public abstract List<String> getServletPaths();



  /**
   * Retrieves a map of initialization parameters that should be provided to the
   * servlet when it is initialized.
   *
   * @return  A map of initialization parameters that should be provided to the
   *          servlet when it is initialized, or an empty map if no
   *          initialization parameters are needed.
   */
  public Map<String,String> getServletInitParameters()
  {
    return Collections.emptyMap();
  }



  /**
   * Retrieves the order in which the servlet should be started.  A value
   * greater than or equal to zero guarantees that the servlet will be started
   * as soon as the servlet engine has been started, in order of ascending
   * servlet init order values, before the {@code doPostRegistrationProcessing}
   * method has been called.  If the value is less than zero, the servlet may
   * not be started until a request is received for one of its registered paths.
   *
   * @return  The order in which the servlet should be started, or a negative
   *          value if startup order does not matter.
   */
  public int getServletInitOrder()
  {
    return -1;
  }



  /**
   * Retrieves a list of servlet filter instances that should be installed with
   * the created servlet instance, in the order they should be invoked.  If the
   * servlet is to be registered with multiple paths, then these filters will be
   * installed for all of those paths.
   *
   * @return  A list of servlet filter instances that should be installed with
   *          the created servlet instance, in the order that they should be
   *          invoked.  It may be {@code null} or empty if no servlet filters
   *          should be installed.
   */
  public List<Filter> getServletFilters()
  {
    return Collections.emptyList();
  }



  /**
   * Performs any processing that may be needed after the servlet has been
   * registered with the servlet engine.  If the value returned from
   * {@link #getServletInitOrder()} is greater than or equal to zero, then the
   * servlet will have been started before this method is called.  If the value
   * returned from {@code getServletInitOrder()} is negative, then the servlet
   * may or may not have been started by the time this method is called.
   * <BR><BR>
   * Note that the associated servlet can also perform any necessary
   * initialization processing in the {@code init} method provided by the
   * servlet API.
   */
  public void doPostRegistrationProcessing()
  {
    // No implementation required by default.
  }



  /**
   * Performs any processing that may be needed after the servlet has been
   * taken out of service and the associated servlet engine has been shut down.
   * <BR><BR>
   * Note that the associated servlet can also perform any necessary
   * finalization processing in the {@code destroy} method provided by the
   * servlet API.  That method will be called after the servlet has been taken
   * out of service, but before the servlet engine has been shut down.
   */
  public void doPostShutdownProcessing()
  {
    // No implementation required by default.
  }
}