/*
 * 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 2013-2016 UnboundID Corp.
 */
package com.unboundid.directory.sdk.common.api;


import com.unboundid.directory.sdk.broker.internal.BrokerExtension;
import com.unboundid.directory.sdk.common.config.VelocityContextProviderConfig;
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.common.types.ServerContext;
import com.unboundid.directory.sdk.common.types.VelocityContext;
import com.unboundid.directory.sdk.ds.internal.DirectoryServerExtension;
import com.unboundid.directory.sdk.metrics.internal.MetricsEngineExtension;
import com.unboundid.directory.sdk.proxy.internal.DirectoryProxyServerExtension;
import com.unboundid.directory.sdk.sync.internal.SynchronizationServerExtension;
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;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.util.List;

import static com.unboundid.directory.sdk.common.config
        .VelocityContextProviderConfig.ObjectScope;
import static com.unboundid.directory.sdk.common.config
        .VelocityContextProviderConfig.ObjectScope.*;


/**
 * This class defines an API that must be implemented by extensions which
 * contribute content to server pages authored as Velocity templates.
 * These pages are rendered by the Velocity HTTP Servlet Extension included
 * with the server. During rendering of a Velocity page, the template is merged
 * with a 'context' that provides values for variables, properties, and method
 * references in the template.
 * <p>
 * A context provider can be restricted to contributing content for certain
 * pages by specifying one or more included or excluded views names.  A view
 * name is the URL request path to to a template that does not include the
 * HTTP servlet extension's base context path, nor a starting path separator.
 * So for example if a template was accessible by the URL
 * http://localhost:8080/view/path/to/template the view name would be
 * 'path/to/template'.
 * <p>
 * In addition to contributing content for views, a context provider can also
 * be configured to add header fields to HTTP responses using the
 * request-header configuration property.  Header field values specified the
 * by a context provider override values for identical fields names for which
 * the Velocity HTTP Servlet Extension is configured to add to responses.
 * <p>
 * Context providers are restricted to servicing requests for the configured
 * set of HTTP operations.  By default, only the HTTP GET method is enabled
 * though this can be changed by updating the http-method configuration
 * property.  Implementations should abide by the conventions mandated by the
 * HTTP method specification.  For example, an implementation that handles the
 * GET method should be restricted to retrieval only and not introduce any
 * persistent side-effects that would change the state of the server.
 * <H2>Configuring Velocity Context Providers</H2>
 * In order to configure a Velocity context provider created using this API,
 * use a command like:
 * <PRE>
 *      dsconfig create-velocity-context-provider \
 *           --extension-name "<I>{extension}</I>" \
 *           --provider-name "<I>{provider}</I>" \
 *           --type third-party \
 *           --set enabled:true \
 *           --set "extension-class:<I>{class-name}</I>" \
 *           --set "extension-argument:<I>{name=value}</I>"
 * </PRE>
 * where "<I>{extension}</I>" is the name of the Velocity HTTP servlet
 * extension, ("Velocity" by default)
 * "<I>{provider}</I>" is the name to use for the Velocity context provider
 * instance, "<I>{class-name}</I>" is the fully-qualified name of the Java
 * class that extends
 * {@code com.unboundid.directory.sdk.common.api.VelocityContextProvider},
 * and "<I>{name=value}</I>" represents name-value pairs for any arguments to
 * provide to the virtual attribute provider.  If multiple arguments should be
 * provided to the virtual attribute provider, then the
 * "<CODE>--set extension-argument:<I>{name=value}</I></CODE>" option should be
 * provided multiple times.
 */
@Extensible()
@DirectoryServerExtension()
@DirectoryProxyServerExtension(appliesToLocalContent = true,
        appliesToRemoteContent = false)
@SynchronizationServerExtension(appliesToLocalContent = true,
        appliesToSynchronizedContent = false)
@MetricsEngineExtension()
@BrokerExtension()
@ThreadSafety(level = ThreadSafetyLevel.INTERFACE_THREADSAFE)
public abstract class VelocityContextProvider
        implements UnboundIDExtension,
        Reconfigurable<VelocityContextProviderConfig>,
        ExampleUsageProvider
{


  // The current configuration.
  private VelocityContextProviderConfig config;



  /**
   * {@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.
  }



  /**
   * Initializes this Velocity context provider.
   *
   * @param serverContext A handle to the server context for the server in
   *                      which this extension is running.
   * @param config        The general configuration for this Velocity context
   *                      provider.
   * @param parser        The argument parser which has been initialized from
   *                      the configuration for this Velocity context
   *                      provider.
   * @throws LDAPException If a problem occurs while initializing this context
   *                       provider.
   */
  public void initializeVelocityContextProvider(
          final ServerContext serverContext,
          final VelocityContextProviderConfig config,
          final ArgumentParser parser)
          throws LDAPException
  {
    this.config = config;
  }



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



  /**
   * {@inheritDoc}
   */
  public ResultCode applyConfiguration(
          final VelocityContextProviderConfig 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 Velocity " +
                  "context provider is disabled and re-enabled or until the " +
                  "server is restarted.");
    }

    return ResultCode.SUCCESS;
  }



  /**
   * Performs any cleanup which may be necessary when this virtual attribute
   * provider is to be taken out of service.
   */
  public void finalizeVelocityContextProvider()
  {
    // No implementation is required.
  }



  /**
   * Handle an HTTP DELETE request.  Implementations should be idempotent in
   * the sense that the side-effects of a single call to this method are the
   * same as N > 0 identical requests.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void handleDelete(final VelocityContext context,
                           final HttpServletRequest request,
                           final HttpServletResponse response)
    throws IOException
  {
    response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
  }



  /**
   * Handle an HTTP GET request.  Implementations should be restricted to
   * retrieval operations only, ensuring there are no persistent side-effects
   * generated by the server as a result of this method being called.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void handleGet(final VelocityContext context,
                        final HttpServletRequest request,
                        final HttpServletResponse response)
    throws IOException
  {
    // Do not respond with an error to avoid breaking existing implementations.
  }



  /**
   * Handle an HTTP HEAD request.  Implementations should be restricted to
   * retrieval operations only, ensuring there are no persistent side-effects
   * generated by the server as a result of this method being called.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void handleHead(final VelocityContext context,
                         final HttpServletRequest request,
                         final HttpServletResponse response)
    throws IOException
  {
    response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
  }



  /**
   * Handle an HTTP OPTIONS request.  Implementations should ensure there
   * are no persistent side-effects generated by the server as a result of this
   * method being called.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void handleOptions(final VelocityContext context,
                            final HttpServletRequest request,
                            final HttpServletResponse response)
    throws IOException
  {
    response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
  }



  /**
   * Handle an HTTP PATCH request.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void handlePatch(final VelocityContext context,
                          final HttpServletRequest request,
                          final HttpServletResponse response)
    throws IOException
  {
    response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
  }



  /**
   * Handle an HTTP POST request.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void handlePost(final VelocityContext context,
                         final HttpServletRequest request,
                         final HttpServletResponse response)
    throws IOException
  {
    // Do not respond with an error to avoid breaking existing implementations.
  }



  /**
   * Handle an HTTP PUT request.  Implementations should be idempotent in
   * the sense that the side-effects of a single call to this method are the
   * same as N > 0 identical requests.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void handlePut(final VelocityContext context,
                        final HttpServletRequest request,
                        final HttpServletResponse response)
    throws IOException
  {
    response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
  }



  /**
   * Handle an HTTP TRACE request.  Implementations should ensure there
   * are no persistent side-effects generated by the server as a result of this
   * method being called.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void handleTrace(final VelocityContext context,
                          final HttpServletRequest request,
                          final HttpServletResponse response)
    throws IOException
  {
    response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
  }



  /**
   * Handle an HTTP method not already handled by one of the other
   * {@code handleXXX} methods.  Implementations should check the value
   * of the request's {@code getMethod()} method and take whatever action is
   * necessary to fulfill the request before updating the context.  Unexpected
   * HTTP methods should result in the client sending an HTTP 405 Method Not
   * Allowed response.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void handleAdditionalMethod(final VelocityContext context,
                                     final HttpServletRequest request,
                                     final HttpServletResponse response)
    throws IOException
  {
    response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
  }



  /**
   * This method is called following a call to one of the {@code handleXXX}
   * methods and may be used for logic that is independent of the HTTP operation
   * requested.  HTTP method-specific code such as request attribute or form
   * data processing should be restricted to the appropriate {@code handleXXX}
   * method.
   *
   * @param context   to update.
   * @param request   for the view implemented by a template.
   * @param response  to the client.
   *
   * @throws IOException if the provider has a problem related to processing
   *         the response such as sending an error to the client.
   */
  public void updateContext(final VelocityContext context,
                            final HttpServletRequest request,
                            final HttpServletResponse response)
    throws IOException
  {
    // No implementation.
  }



  /**
   * Gets an object from the current user session or servlet context
   * depending on the object scope currently configured for this provider.
   * This method can be used as a convenience for providers the maintain
   * a set of context objects for a particular scope.
   *
   * @param <T>     the type of object to return.  If an object exists in
   *                the current scope with the given name but is not of type
   *                T this method returns {@code null}
   *
   * @param name    of the object.
   * @param request current user request.
   *
   * @return the named object or {@code null} if no object exists by the
   *         provided name or an input parameter is (@code null}.
   */
  protected <T> T getNamedObject(final String name,
                                 final HttpServletRequest request)
  {
    T object = null;
    if (this.config != null)
    {
      object = getNamedObject(name, request, config.getObjectScope());
    }
    return object;
  }



  /**
   * Stores an object in current user request, session or servlet context
   * depending on the object scope currently configured for this provider.
   * This method can be used as a convenience for providers the maintain
   * a set of context objects for a particular scope.
   *
   * @param name    of the object.
   * @param object  to store.
   * @param request current user request.
   */
  protected void setNamedObject(final String name,
                                final Object object,
                                final HttpServletRequest request)
  {
    if (this.config != null)
    {
      setNamedObject(name, object, request, config.getObjectScope());
    }
  }



  /**
   * Gets an object from the current user session or servlet context
   * depending on the object scope currently configured for this provider.
   * This method can be used as a convenience for providers the maintain
   * a set of context objects for a particular scope.
   *
   * @param <T>     the type of object to return.  If an object exists in
   *                the current scope with the given name but is not of type
   *                T this method returns {@code null}
   *
   * @param name    of the object.
   * @param request current user request.
   * @param scope   from which to retrieve the object.
   * @return the named object or {@code null} if no object exists by the
   *         provided name or an input parameter is (@code null}.
   */
  @SuppressWarnings("unchecked")
  public static <T> T getNamedObject(final String name,
                                     final HttpServletRequest request,
                                     final ObjectScope scope)
  {
    T object = null;
    Object o = null;
    if (name != null && request != null)
    {
      if (REQUEST.equals(scope))
      {
        o = request.getAttribute(name);
      }
      else if (SESSION.equals(scope))
      {
        HttpSession session = request.getSession(false);
        if (session != null)
        {
          o = session.getAttribute(name);
        }
      }
      else if (APPLICATION.equals(scope))
      {
        o = request.getServletContext().getAttribute(name);
      }
    }
    try
    {
      object = (T) o;
    }
    catch (ClassCastException cce)
    {
      // ignore
    }
    return object;
  }



  /**
   * Stores an object in current user request, session or servlet context
   * depending on the object scope currently configured for this provider.
   * This method can be used as a convenience for providers the maintain
   * a set of context objects for a particular scope.
   *
   * @param name    of the object.
   * @param object  to store.
   * @param request current user request.
   * @param scope   in which to set the object.
   */
  public static void setNamedObject(final String name,
                                    final Object object,
                                    final HttpServletRequest request,
                                    final ObjectScope scope)
  {
    if (scope != null && request != null && name != null)
    {
      if (REQUEST.equals(scope))
      {
        request.setAttribute(name, object);
      }
      else if (SESSION.equals(scope))
      {
        HttpSession session = request.getSession(true);
        session.setAttribute(name, object);
      }
      else if (APPLICATION.equals(scope))
      {
        request.getServletContext().setAttribute(name, object);
      }
    }
  }

}