/*
    * 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 java.util.LinkedHashSet;
  import java.util.Set;
  import javax.servlet.http.HttpServletRequest;
  
  import org.springframework.web.bind.annotation.RequestMapping;
  
  /**
   * A logical conjunction (' && ') request condition that matches a request against
   * a set of header expressions with syntax defined in {@link RequestMapping#headers()}.
   *
   * <p>Expressions passed to the constructor with header names 'Accept' or
   * 'Content-Type' are ignored. See {@link ConsumesRequestCondition} and
   * {@link ProducesRequestCondition} for those.
   *
   * @author Arjen Poutsma
   * @author Rossen Stoyanchev
   * @since 3.1
   */
  public final class HeadersRequestCondition extends AbstractRequestCondition<HeadersRequestCondition> {
  
  	private final Set<HeaderExpression> expressions;
  
  
  	/**
  	 * Create a new instance from the given header expressions. Expressions with
  	 * header names 'Accept' or 'Content-Type' are ignored. See {@link ConsumesRequestCondition}
  	 * and {@link ProducesRequestCondition} for those.
  	 * @param headers media type expressions with syntax defined in {@link RequestMapping#headers()};
  	 * if 0, the condition will match to every request
  	 */
  	public HeadersRequestCondition(String... headers) {
  		this(parseExpressions(headers));
  	}
  
  	private HeadersRequestCondition(Collection<HeaderExpression> conditions) {
  		this.expressions = Collections.unmodifiableSet(new LinkedHashSet<HeaderExpression>(conditions));
  	}
  
  
  	private static Collection<HeaderExpression> parseExpressions(String... headers) {
  		Set<HeaderExpression> expressions = new LinkedHashSet<HeaderExpression>();
  		if (headers != null) {
  			for (String header : headers) {
  				HeaderExpression expr = new HeaderExpression(header);
  				if ("Accept".equalsIgnoreCase(expr.name) || "Content-Type".equalsIgnoreCase(expr.name)) {
  					continue;
  				}
  				expressions.add(expr);
  			}
  		}
  		return expressions;
  	}
  
  	/**
  	 * Return the contained request header expressions.
  	 */
  	public Set<NameValueExpression<String>> getExpressions() {
  		return new LinkedHashSet<NameValueExpression<String>>(this.expressions);
  	}
  
  	@Override
  	protected Collection<HeaderExpression> getContent() {
  		return this.expressions;
  	}
  
  	@Override
  	protected String getToStringInfix() {
  		return " && ";
  	}
  
  	/**
  	 * Returns a new instance with the union of the header expressions
  	 * from "this" and the "other" instance.
  	 */
  	@Override
  	public HeadersRequestCondition combine(HeadersRequestCondition other) {
  		Set<HeaderExpression> set = new LinkedHashSet<HeaderExpression>(this.expressions);
  		set.addAll(other.expressions);
  		return new HeadersRequestCondition(set);
 	}
 
 	/**
 	 * Returns "this" instance if the request matches all expressions;
 	 * or {@code null} otherwise.
 	 */
 	@Override
 	public HeadersRequestCondition getMatchingCondition(HttpServletRequest request) {
 		for (HeaderExpression expression : expressions) {
 			if (!expression.match(request)) {
 				return null;
 			}
 		}
 		return this;
 	}
 
 	/**
 	 * Returns:
 	 * <ul>
 	 * <li>0 if the two conditions have the same number of header expressions
 	 * <li>Less than 0 if "this" instance has more header expressions
 	 * <li>Greater than 0 if the "other" instance has more header expressions
 	 * </ul>
 	 * <p>It is assumed that both instances have been obtained via
 	 * {@link #getMatchingCondition(HttpServletRequest)} and each instance
 	 * contains the matching header expression only or is otherwise empty.
 	 */
 	@Override
 	public int compareTo(HeadersRequestCondition other, HttpServletRequest request) {
 		return other.expressions.size() - this.expressions.size();
 	}
 
 
 	/**
 	 * Parses and matches a single header expression to a request.
 	 */
 	static class HeaderExpression extends AbstractNameValueExpression<String> {
 
 		public HeaderExpression(String expression) {
 			super(expression);
 		}
 
 		@Override
 		protected boolean isCaseSensitiveName() {
 			return false;
 		}
 
 		@Override
 		protected String parseValue(String valueExpression) {
 			return valueExpression;
 		}
 
 		@Override
 		protected boolean matchName(HttpServletRequest request) {
 			return request.getHeader(name) != null;
 		}
 
 		@Override
 		protected boolean matchValue(HttpServletRequest request) {
 			return value.equals(request.getHeader(name));
 		}
 	}
 
 }