/*
    * 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.mvc.condition;
  
  import java.util.Collection;
  import java.util.Collections;
  import javax.servlet.http.HttpServletRequest;
  
  /**
   * A holder for a {@link RequestCondition} useful when the type of the request
   * condition is not known ahead of time, e.g. custom condition. Since this
   * class is also an implementation of {@code RequestCondition}, effectively it
   * decorates the held request condition and allows it to be combined and compared
   * with other request conditions in a type and null safe way.
   *
   * <p>When two {@code RequestConditionHolder} instances are combined or compared
   * with each other, it is expected the conditions they hold are of the same type.
   * If they are not, a {@link ClassCastException} is raised.
   *
   * @author Rossen Stoyanchev
   * @since 3.1
   */
  public final class RequestConditionHolder extends AbstractRequestCondition<RequestConditionHolder> {
  
  	private final RequestCondition<Object> condition;
  
  
  	/**
  	 * Create a new holder to wrap the given request condition.
  	 * @param requestCondition the condition to hold, may be {@code null}
  	 */
  	@SuppressWarnings("unchecked")
  	public RequestConditionHolder(RequestCondition<?> requestCondition) {
  		this.condition = (RequestCondition<Object>) requestCondition;
  	}
  
  
  	/**
  	 * Return the held request condition, or {@code null} if not holding one.
  	 */
  	public RequestCondition<?> getCondition() {
  		return this.condition;
  	}
  
  	@Override
  	protected Collection<?> getContent() {
  		return (this.condition != null ? Collections.singleton(this.condition) : Collections.emptyList());
  	}
  
  	@Override
  	protected String getToStringInfix() {
  		return " ";
  	}
  
  	/**
  	 * Combine the request conditions held by the two RequestConditionHolder
  	 * instances after making sure the conditions are of the same type.
  	 * Or if one holder is empty, the other holder is returned.
  	 */
  	@Override
  	public RequestConditionHolder combine(RequestConditionHolder other) {
  		if (this.condition == null && other.condition == null) {
  			return this;
  		}
  		else if (this.condition == null) {
  			return other;
  		}
  		else if (other.condition == null) {
  			return this;
  		}
  		else {
  			assertEqualConditionTypes(other);
  			RequestCondition<?> combined = (RequestCondition<?>) this.condition.combine(other.condition);
  			return new RequestConditionHolder(combined);
  		}
  	}
  
  	/**
  	 * Ensure the held request conditions are of the same type.
  	 */
  	private void assertEqualConditionTypes(RequestConditionHolder other) {
  		Class<?> clazz = this.condition.getClass();
  		Class<?> otherClazz = other.condition.getClass();
  		if (!clazz.equals(otherClazz)) {
  			throw new ClassCastException("Incompatible request conditions: " + clazz + " and " + otherClazz);
 		}
 	}
 
 	/**
 	 * Get the matching condition for the held request condition wrap it in a
 	 * new RequestConditionHolder instance. Or otherwise if this is an empty
 	 * holder, return the same holder instance.
 	 */
 	@Override
 	public RequestConditionHolder getMatchingCondition(HttpServletRequest request) {
 		if (this.condition == null) {
 			return this;
 		}
 		RequestCondition<?> match = (RequestCondition<?>) this.condition.getMatchingCondition(request);
 		return (match != null ? new RequestConditionHolder(match) : null);
 	}
 
 	/**
 	 * Compare the request conditions held by the two RequestConditionHolder
 	 * instances after making sure the conditions are of the same type.
 	 * Or if one holder is empty, the other holder is preferred.
 	 */
 	@Override
 	public int compareTo(RequestConditionHolder other, HttpServletRequest request) {
 		if (this.condition == null && other.condition == null) {
 			return 0;
 		}
 		else if (this.condition == null) {
 			return 1;
 		}
 		else if (other.condition == null) {
 			return -1;
 		}
 		else {
 			assertEqualConditionTypes(other);
 			return this.condition.compareTo(other.condition, request);
 		}
 	}
 
 }