/*
 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.net.httpserver;

import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * HTTP request and response headers are represented by this class which
 * implements the interface
 * {@link java.util.Map}{@literal <}{@link java.lang.String},
 * {@link java.util.List} {@literal <}{@link java.lang.String}{@literal >>}.
 * The keys are case-insensitive Strings representing the header names and
 * the value associated with each key is
 * a {@link List}{@literal <}{@link String}{@literal >} with one
 * element for each occurrence of the header name in the request or response.
 *
 * <p> For example, if a response header instance contains
 * one key "HeaderName" with two values "value1 and value2"
 * then this object is output as two header lines:
 *
 * <blockquote><pre>
 * HeaderName: value1
 * HeaderName: value2
 * </pre></blockquote>
 *
 * All the normal {@link java.util.Map} methods are provided, but the
 * following additional convenience methods are most likely to be used:
 *
 * <ul>
 *     <li>{@link #getFirst(String)} returns a single valued header or the first
 *     value of a multi-valued header.
 *     <li>{@link #add(String,String)} adds the given header value to the list
 *     for the given key.
 *     <li>{@link #set(String,String)} sets the given header field to the single
 *     value given overwriting any existing values in the value list.
 * </ul>
 *
 * <p> All methods in this class accept {@code null} values for keys and values.
 * However, {@code null} keys will never will be present in HTTP request
 * headers, and will not be output/sent in response headers. Null values can be
 * represented as either a {@code null} entry for the key (i.e. the list is
 * {@code null}) or where the key has a list, but one (or more) of the list's
 * values is {@code null}. Null values are output as a header line containing
 * the key but no associated value.
 *
 * @since 1.6
 */
public class Headers implements Map<String,List<String>> {

        HashMap<String,List<String>> map;

       /**
        * Creates an empty instance of {@code Headers}.
        */
        public Headers () {map = new HashMap<String,List<String>>(32);}

        /**
         * Normalize the key by converting to following form.
         * First {@code char} upper case, rest lower case.
         * key is presumed to be {@code ASCII}.
         */
        private String normalize (String key) {
            if (key == null) {
                return null;
            }
            int len = key.length();
            if (len == 0) {
                return key;
            }
            char[] b = key.toCharArray();
            if (b[0] >= 'a' && b[0] <= 'z') {
                b[0] = (char)(b[0] - ('a' - 'A'));
            } else if (b[0] == '\r' || b[0] == '\n')
                throw new IllegalArgumentException("illegal character in key");

            for (int i=1; i<len; i++) {
                if (b[i] >= 'A' && b[i] <= 'Z') {
                    b[i] = (char) (b[i] + ('a' - 'A'));
                } else if (b[i] == '\r' || b[i] == '\n')
                    throw new IllegalArgumentException("illegal character in key");
            }
            return new String(b);
        }

        public int size() {return map.size();}

        public boolean isEmpty() {return map.isEmpty();}

        public boolean containsKey(Object key) {
            if (key == null) {
                return false;
            }
            if (!(key instanceof String)) {
                return false;
            }
            return map.containsKey (normalize((String)key));
        }

        public boolean containsValue(Object value) {
            return map.containsValue(value);
        }

        public List<String> get(Object key) {
            return map.get(normalize((String)key));
        }

        /**
         * Returns the first value from the {@link List} of {@code String}
         * values for the given key (if at least one exists).
         *
         * @param key the key to search for
         * @return the first {@code String} value associated with the key
         */
        public String getFirst (String key) {
            List<String> l = map.get(normalize(key));
            if (l == null) {
                return null;
            }
            return l.get(0);
        }

        public List<String> put(String key, List<String> value) {
            for (String v : value)
                checkValue(v);
            return map.put (normalize(key), value);
        }

        /**
         * Adds the given value to the list of headers for the given key. If
         * the mapping does not already exist, then it is created.
         *
         * @param key the header name
         * @param value the value to add to the header
         */
        public void add (String key, String value) {
            checkValue(value);
            String k = normalize(key);
            List<String> l = map.get(k);
            if (l == null) {
                l = new LinkedList<String>();
                map.put(k,l);
            }
            l.add (value);
        }

        private static void checkValue(String value) {
            int len = value.length();
            for (int i=0; i<len; i++) {
                char c = value.charAt(i);
                if (c == '\r') {
                    // is allowed if it is followed by \n and a whitespace char
                    if (i >= len - 2) {
                        throw new IllegalArgumentException("Illegal CR found in header");
                    }
                    char c1 = value.charAt(i+1);
                    char c2 = value.charAt(i+2);
                    if (c1 != '\n') {
                        throw new IllegalArgumentException("Illegal char found after CR in header");
                    }
                    if (c2 != ' ' && c2 != '\t') {
                        throw new IllegalArgumentException("No whitespace found after CRLF in header");
                    }
                    i+=2;
                } else if (c == '\n') {
                    throw new IllegalArgumentException("Illegal LF found in header");
                }
            }
        }

        /**
         * Sets the given value as the sole header value for the given
         * key. If the mapping does not already exist, then it is created.
         *
         * @param key the header name
         * @param value the header value to set
         */
        public void set (String key, String value) {
            LinkedList<String> l = new LinkedList<String>();
            l.add (value);
            put (key, l);
        }


        public List<String> remove(Object key) {
            return map.remove(normalize((String)key));
        }

        public void putAll(Map<? extends String,? extends List<String>> t)  {
            map.putAll (t);
        }

        public void clear() {map.clear();}

        public Set<String> keySet() {return map.keySet();}

        public Collection<List<String>> values() {return map.values();}

        public Set<Map.Entry<String, List<String>>> entrySet() {
            return map.entrySet();
        }

        public boolean equals(Object o) {return map.equals(o);}

        public int hashCode() {return map.hashCode();}
    }
