/*
 * Copyright 2017 Graz University of Technology EAAF-Core Components has been developed in a
 * cooperation between EGIZ, A-SIT Plus, A-SIT, and Graz University of Technology.
 *
 * Licensed under the EUPL, Version 1.2 or - as soon they will be approved by the European
 * Commission - subsequent versions of the EUPL (the "Licence"); You may not use this work except in
 * compliance with the Licence. You may obtain a copy of the Licence at:
 * https://joinup.ec.europa.eu/news/understanding-eupl-v12
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the Licence
 * is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the Licence for the specific language governing permissions and limitations under
 * the Licence.
 *
 * This product combines work with different licenses. See the "NOTICE" text file for details on the
 * various modules and licenses. The "NOTICE" text file is part of the distribution. Any derivative
 * works that you distribute must include a readable copy of the "NOTICE" text file.
*/

package at.gv.egiz.eaaf.core.impl.idp.process.springweb;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;

import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.NoUniqueBeanDefinitionException;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

import at.gv.egiz.eaaf.core.api.idp.process.ExecutionContext;
import at.gv.egiz.eaaf.core.api.idp.process.ProcessEngine;
import at.gv.egiz.eaaf.core.impl.idp.process.ProcessInstance;

/**
 * Abstract HttpServlet that provides means for retrieving the process engine
 * (Spring Web required) as well as retrieving the underlying process instance
 * and execution context evaluating a certain request parameter.
 *
 * @author tknall
 *
 */
public abstract class AbstractAuthSourceServlet extends HttpServlet {

  private static final long serialVersionUID = 1L;

  private ProcessEngine processEngine;

  /**
   * Returns the name of the request parameter representing the respective
   * instance id.
   * <p/>
   * Default is {@code processInstanceId}.
   *
   * @return The request parameter name.
   */
  public String getProcessInstanceIdParameterName() {
    return "processInstanceId";
  }

  /**
   * Returns the underlying process engine instance.
   *
   * @return The process engine (never {@code null}).
   * @throws NoSuchBeanDefinitionException   if no {@link ProcessEngine} bean was
   *                                         found.
   * @throws NoUniqueBeanDefinitionException if more than one
   *                                         {@link ProcessEngine} bean was found.
   * @throws BeansException                  if a problem getting the
   *                                         {@link ProcessEngine} bean occurred.
   * @throws IllegalStateException           if the Spring WebApplicationContext
   *                                         was not found, which means that the
   *                                         servlet is used outside a Spring web
   *                                         environment.
   */
  public synchronized ProcessEngine getProcessEngine() {
    if (processEngine == null) {
      final WebApplicationContext ctx =
          WebApplicationContextUtils.getWebApplicationContext(getServletContext());
      if (ctx == null) {
        throw new IllegalStateException(
            "Unable to find Spring WebApplicationContext. "
                + "Servlet needs to be executed within a Spring web environment.");
      }
      processEngine = ctx.getBean(ProcessEngine.class);
    }
    return processEngine;
  }

  /**
   * Retrieves the process instance referenced by the request parameter
   * {@link #getProcessInstanceIdParameterName()}.
   *
   * @param request The HttpServletRequest.
   * @return The process instance (never {@code null}).
   * @throws NoSuchBeanDefinitionException   if no {@link ProcessEngine} bean was
   *                                         found.
   * @throws NoUniqueBeanDefinitionException if more than one
   *                                         {@link ProcessEngine} bean was found.
   * @throws BeansException                  if a problem getting the
   *                                         {@link ProcessEngine} bean occurred.
   * @throws IllegalStateException           if the Spring WebApplicationContext
   *                                         was not found, which means that the
   *                                         servlet is used outside a Spring web
   *                                         environment.
   * @throws IllegalArgumentException        in case the process instance id
   *                                         referenced by the request parameter
   *                                         {@link #getProcessInstanceIdParameterName()}
   *                                         does not exist.
   */
  public ProcessInstance getProcessInstance(final HttpServletRequest request) {
    final String processInstanceId =
        StringUtils.trimToNull(request.getParameter(getProcessInstanceIdParameterName()));
    if (processInstanceId == null) {
      throw new IllegalArgumentException(
          "Missing request parameter '" + getProcessInstanceIdParameterName() + "'.");
    }
    return getProcessEngine().getProcessInstance(processInstanceId);
  }

  /**
   * Retrieves the execution context for the respective process instance
   * referenced by the request parameter
   * {@link #getProcessInstanceIdParameterName()}.
   *
   * @param request The HttpServletRequest.
   * @return The execution context (never {@code null}).
   * @throws NoSuchBeanDefinitionException   if no {@link ProcessEngine} bean was
   *                                         found.
   * @throws NoUniqueBeanDefinitionException if more than one
   *                                         {@link ProcessEngine} bean was found.
   * @throws BeansException                  if a problem getting the
   *                                         {@link ProcessEngine} bean occurred.
   * @throws IllegalStateException           if the Spring WebApplicationContext
   *                                         was not found, which means that the
   *                                         servlet is used outside a Spring web
   *                                         environment.
   * @throws IllegalArgumentException        in case the process instance id
   *                                         referenced by the request parameter
   *                                         {@link #getProcessInstanceIdParameterName()}
   *                                         does not exist.
   */
  public ExecutionContext getExecutionContext(final HttpServletRequest request) {
    return getProcessInstance(request).getExecutionContext();
  }

}