/*
    * Copyright 2002-2014 the original author or authors.
    *
    * Licensed under the Apache 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://www.apache.org/licenses/LICENSE-2.0
    *
   * 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.springframework.web.servlet;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.List;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  import org.springframework.util.CollectionUtils;
  import org.springframework.util.ObjectUtils;
  
  /**
   * Handler execution chain, consisting of handler object and any handler interceptors.
   * Returned by HandlerMapping's {@link HandlerMapping#getHandler} method.
   *
   * @author Juergen Hoeller
   * @since 20.06.2003
   * @see HandlerInterceptor
   */
  public class HandlerExecutionChain {
  
  	private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
  
  	private final Object handler;
  
  	private HandlerInterceptor[] interceptors;
  
  	private List<HandlerInterceptor> interceptorList;
  
  	private int interceptorIndex = -1;
  
  
  	/**
  	 * Create a new HandlerExecutionChain.
  	 * @param handler the handler object to execute
  	 */
  	public HandlerExecutionChain(Object handler) {
  		this(handler, (HandlerInterceptor[]) null);
  	}
  
  	/**
  	 * Create a new HandlerExecutionChain.
  	 * @param handler the handler object to execute
  	 * @param interceptors the array of interceptors to apply
  	 * (in the given order) before the handler itself executes
  	 */
  	public HandlerExecutionChain(Object handler, HandlerInterceptor... interceptors) {
  		if (handler instanceof HandlerExecutionChain) {
  			HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
  			this.handler = originalChain.getHandler();
  			this.interceptorList = new ArrayList<HandlerInterceptor>();
  			CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
  			CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
  		}
  		else {
  			this.handler = handler;
  			this.interceptors = interceptors;
  		}
  	}
  
  
  	/**
  	 * Return the handler object to execute.
  	 * @return the handler object
  	 */
  	public Object getHandler() {
  		return this.handler;
  	}
  
  	public void addInterceptor(HandlerInterceptor interceptor) {
  		initInterceptorList().add(interceptor);
  	}
  
  	public void addInterceptors(HandlerInterceptor... interceptors) {
  		if (!ObjectUtils.isEmpty(interceptors)) {
  			initInterceptorList().addAll(Arrays.asList(interceptors));
  		}
  	}
  
  	private List<HandlerInterceptor> initInterceptorList() {
 		if (this.interceptorList == null) {
 			this.interceptorList = new ArrayList<HandlerInterceptor>();
 			if (this.interceptors != null) {
 				// An interceptor array specified through the constructor
 				this.interceptorList.addAll(Arrays.asList(this.interceptors));
 			}
 		}
 		this.interceptors = null;
 		return this.interceptorList;
 	}
 
 	/**
 	 * Return the array of interceptors to apply (in the given order).
 	 * @return the array of HandlerInterceptors instances (may be {@code null})
 	 */
 	public HandlerInterceptor[] getInterceptors() {
 		if (this.interceptors == null && this.interceptorList != null) {
 			this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[this.interceptorList.size()]);
 		}
 		return this.interceptors;
 	}
 
 
 	/**
 	 * Apply preHandle methods of registered interceptors.
 	 * @return {@code true} if the execution chain should proceed with the
 	 * next interceptor or the handler itself. Else, DispatcherServlet assumes
 	 * that this interceptor has already dealt with the response itself.
 	 */
 	boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
 		HandlerInterceptor[] interceptors = getInterceptors();
 		if (!ObjectUtils.isEmpty(interceptors)) {
 			for (int i = 0; i < interceptors.length; i++) {
 				HandlerInterceptor interceptor = interceptors[i];
 				if (!interceptor.preHandle(request, response, this.handler)) {
 					triggerAfterCompletion(request, response, null);
 					return false;
 				}
 				this.interceptorIndex = i;
 			}
 		}
 		return true;
 	}
 
 	/**
 	 * Apply postHandle methods of registered interceptors.
 	 */
 	void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
 		HandlerInterceptor[] interceptors = getInterceptors();
 		if (!ObjectUtils.isEmpty(interceptors)) {
 			for (int i = interceptors.length - 1; i >= 0; i--) {
 				HandlerInterceptor interceptor = interceptors[i];
 				interceptor.postHandle(request, response, this.handler, mv);
 			}
 		}
 	}
 
 	/**
 	 * Trigger afterCompletion callbacks on the mapped HandlerInterceptors.
 	 * Will just invoke afterCompletion for all interceptors whose preHandle invocation
 	 * has successfully completed and returned true.
 	 */
 	void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
 			throws Exception {
 
 		HandlerInterceptor[] interceptors = getInterceptors();
 		if (!ObjectUtils.isEmpty(interceptors)) {
 			for (int i = this.interceptorIndex; i >= 0; i--) {
 				HandlerInterceptor interceptor = interceptors[i];
 				try {
 					interceptor.afterCompletion(request, response, this.handler, ex);
 				}
 				catch (Throwable ex2) {
 					logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
 				}
 			}
 		}
 	}
 
 	/**
 	 * Apply afterConcurrentHandlerStarted callback on mapped AsyncHandlerInterceptors.
 	 */
 	void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
 		HandlerInterceptor[] interceptors = getInterceptors();
 		if (!ObjectUtils.isEmpty(interceptors)) {
 			for (int i = interceptors.length - 1; i >= 0; i--) {
 				if (interceptors[i] instanceof AsyncHandlerInterceptor) {
 					try {
 						AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) interceptors[i];
 						asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
 					}
 					catch (Throwable ex) {
 						logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", ex);
 					}
 				}
 			}
 		}
 	}
 
 
 	/**
 	 * Delegates to the handler's {@code toString()}.
 	 */
 	@Override
 	public String toString() {
 		if (this.handler == null) {
 			return "HandlerExecutionChain with no handler";
 		}
 		StringBuilder sb = new StringBuilder();
 		sb.append("HandlerExecutionChain with handler [").append(this.handler).append("]");
 		if (!CollectionUtils.isEmpty(this.interceptorList)) {
 			sb.append(" and ").append(this.interceptorList.size()).append(" interceptor");
 			if (this.interceptorList.size() > 1) {
 				sb.append("s");
 			}
 		}
 		return sb.toString();
 	}
 
 }