/*******************************************************************************
    * Copyright (c) 2011 Michael Mimo Moratti.
    *  
    * Michael Mimo Moratti licenses this file to you 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 ch.mimo.netty.handler.codec.icap;
  
  import java.util.LinkedHashSet;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * Icap Headers
   * 
   * This class provides a linked list implementation in order to store Icap headers.
   * 
   * @author Michael Mimo Moratti (mimo@mimo.ch)
   *
   */
  // TODO add setDateheader format: "Fri, 20 May 2011 15:36:30 GMT"
  public final class IcapHeaders {
  	
  	private Entry base;
  	private Entry head;
  	
  	/**
  	 * The most common Icap Header names.
  	 * 
  	 * @author Michael Mimo Moratti (mimo@mimo.ch)
  	 *
  	 */
  	public static final class Names {
          /**
           * {@code "Cache-Control"}
           */
  		public static final String CACHE_CONTROL = "Cache-Control";
          /**
           * {@code "Connection"}
           */
  		public static final String CONNECTION = "Connection";
          /**
           * {@code "Date"}
           */
  		public static final String DATE = "Date";	
          /**
           * {@code "Expires"}
           */
  		public static final String EXPIRES = "Expires";
          /**
           * {@code "Pragma"}
           */
  		public static final String PRAGMA = "Pragma";
          /**
           * {@code "Trailer"}
           */
  		public static final String TRAILER = "Trailer";
          /**
           * {@code "Upgrade"}
           */
  		public static final String UPGRADE = "Upgrade";
          /**
           * {@code "Encapsulated"}
           */
  		public static final String ENCAPSULATED = "Encapsulated";
          /**
           * {@code "Authorization"}
           */
  		public static final String AUTHORIZATION = "Authorization";
          /**
           * {@code "Allow"}
           */
  		public static final String ALLOW = "Allow";
          /**
           * {@code "From"}
           */
  		public static final String FROM = "From";
          /**
           * {@code "Host"}
           */
  		public static final String HOST = "Host";
          /**
           * {@code "Referer"}
           */
  		public static final String REFERER = "Referer";
          /**
           * {@code "User-Agent"}
           */
  		public static final String USER_AGENT = "User-Agent";
          /**
           * {@code "Preview"}
           */
 		public static final String PREVIEW = "Preview";
 		
 		/**
 		 * {@code "ISTag"}
 		 */
 		public static final String ISTAG = "ISTag";
 	}
 	
 	public IcapHeaders() {
 	}
 	
 	public void clearHeaders() {
 		base = null;
 		head = null;
 	}
 	
 	/**
 	 * Adds a header key,value combination to the list
 	 * The existence of such a header name will have no impact. The header is simply added
 	 * to the end of the linked list. 
 	 * 
 	 * @param name Icap message header name
 	 * @param value Icap message header value. Can also be null
 	 */
 	public void addHeader(String name, Object value) {
 		Entry entry = new Entry(name,value);
 		if(base == null) {
 			base = entry;
 			head = entry;
 		} else {
 			Entry currentHead = head;
 			head = entry;
 			entry.before = currentHead;
 			currentHead.after = entry;
 		}
 	}
 	
 	/**
 	 * Sets one header at the end of the list.
 	 * Headers with the same name that are already in the list will be removed first!
 	 * 
 	 * @param name Icap message header name
 	 * @param value Icap message header value. Can also be null
 	 */
 	public void setHeader(String name, Object value) {
 		removeHeader(name);
 		addHeader(name,value);
 	}
 	
 	/**
 	 * Sets one header with many values.
 	 * Headers with the same name that are already in the list will be removed first!
 	 * 
 	 * @param name Icap message header name
 	 * @param values Icap message header value. Can also be null
 	 */
 	public void setHeader(String name, Iterable<?> values) {
 		removeHeader(name);
 		for(Object value : values) {
 			addHeader(name,value);
 		}
 	}
 	
 	/**
 	 * retrieves a header value from the list.
 	 * If no header exists with the given name null is returned.
 	 *
 	 * If there are multiple headers with the same name only the first occurence in the
 	 * list is returned.
 	 * 
 	 * @param name Icap message header name
 	 * @return String value or null
 	 */
 	public String getHeader(String name) {
 		Entry entry = base;
 		while(entry != null) {
 			if(identicalKeys(entry.getKey(),name)) {
 				return entry.getValue();
 			}
 			entry = entry.after;
 		}
 		return null;
 	}
 	
 	/**
 	 * retrieves all values for one header name.
 	 * If no header exists with that given name an empty set is returned.
 	 * 
 	 * @param name Icap message header name
 	 * @return Set of values from all headers with the same name, or empty set.
 	 */
 	public Set<String> getHeaders(String name) {
 		Set<String> values = new LinkedHashSet<String>();
 		Entry entry = base;
 		while(entry != null) {
 			if(identicalKeys(entry.getKey(),name)) {
 				values.add(entry.getValue());
 			}
 			entry = entry.after;
 		}
 		return values;
 	}
 	
 	/**
 	 * retrieval method for all headers that are currently in this list.
 	 * 
 	 * @return Set of Map Entry instances.
 	 */
 	public Set<Map.Entry<String, String>> getHeaders() {
 		Set<Map.Entry<String, String>> headers = new LinkedHashSet<Map.Entry<String,String>>();
 		Entry entry = base;
 		while(entry != null) {
 			headers.add(entry);
 			entry = entry.after;
 		}
 		return headers;
 	}
 	
 	/**
 	 * check method to validate if a certain header does exists in the list.
 	 * 
 	 * @param name Icap message header name
 	 * @return boolean true if the header exists.
 	 */
 	public boolean containsHeader(String name) {
 		return getHeader(name) != null;
 	}
 	
 	/**
 	 * removes all headers with the same name from the list.
 	 * 
 	 * @param name Icap message header name
 	 */
 	public void removeHeader(String name) {
 		if(base == null) {
 			return;
 		}
 		Entry entry = null;
 		if(base.after == null) {
 			if(identicalKeys(base.getKey(),name)) {
 				base = null;
 				return;
 			}
 		} else {
 			entry = base.after;
 		}
 		while(entry != null) {
 			if(identicalKeys(entry.getKey(),name)) {
 				Entry before = entry.before;
 				Entry after = entry.after;
 				before.after = after;
 				after.before = before;
 				entry = after;
 			} else {
 				entry = entry.after;
 			}
 		}
 		if(identicalKeys(base.getKey(),name)) {
 			base = base.after;
 			base.before = null;
 		}
 	}
 	
 	/**
 	 * retrieval method for all header names.
 	 * this list is unique. If a header name has two entries the name is returned only once.
 	 * 
 	 * @return unique set with all header names in the list.
 	 */
 	public Set<String> getHeaderNames() {
 		Set<String> names = new LinkedHashSet<String>();
 		Entry entry = base;
 		while(entry != null) {
 			names.add(entry.getKey());
 			entry = entry.after;
 		}
 		return names;
 	}
 	
 	/**
 	 * Convenience method to retrieve the @see {@link Integer} value from a Icap Preview header.
 	 * If the header does not exist the value 0 is returned.
 	 * If the header value cannot be parsed into a valid integer a @see {@link IcapDecodingError} is thrown.
 	 * 
 	 * @return int value of preview header.
 	 */
 	public int getPreviewHeaderValue() {
 		String value = getHeader(Names.PREVIEW);
 		int result = 0;
 		try {
 			if(value != null) {
 				result = Integer.parseInt(value);
 			}
 		} catch(NumberFormatException nfe) {
 			throw new IcapDecodingError("Unable to understand the preview amount value [" + value + "]");
 		}
 		return result;
 	}
 	
 	private boolean identicalKeys(String key1, String key2) {
 		if(key1 != null & key2 != null) {
 			return key1.equalsIgnoreCase(key2);
 		}
 		return false;
 	}
 
 	private static final class Entry implements Map.Entry<String, String> {
 		
 		private String key;
 		private String value;
 		
 		private Entry before, after;
 		
 		Entry(String key, Object value) {
 			IcapCodecUtil.validateHeaderName(key);
 			this.key = key;
 			if(value != null) {
 				this.value = value.toString();
 				IcapCodecUtil.validateHeaderValue(this.value);
 			}
 		}
 		
 		public String getKey() {
 			return key;
 		}
 		
 		public String getValue() {
 			return value;
 		}
 		
 		@Override
 		public String setValue(String value) {
 			return null;
 		}
 	}
 	
 	@Override
 	public String toString() {
 		StringBuilder builder = new StringBuilder();
 		for(String name : getHeaderNames()) {
 			builder.append("[" + name + "] = [" + getHeaders(name) + "]");
 		}
 		return builder.toString();
 	}
 }