/*******************************************************************************
 *******************************************************************************/
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) {
			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(HttpServletRequest request) {
		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(HttpServletRequest request) {
		return getProcessInstance(request).getExecutionContext();
	}

}