/*

 * Copyright (c) 2015, 2018, 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

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package java.net.http;

import java.util.ArrayList;

import java.util.List;

import java.util.Locale;

import java.util.Map;

import java.util.Optional;

import java.util.OptionalLong;

import java.util.TreeMap;

import java.util.TreeSet;

import java.util.function.BiPredicate;

import static java.lang.String.CASE_INSENSITIVE_ORDER;

import static java.util.Collections.unmodifiableMap;

import static java.util.Objects.requireNonNull;

/**

 * A read-only view of a set of HTTP headers.

 *

 * <p> An {@code HttpHeaders} is not typically created directly, but rather

 * returned from an {@link HttpRequest#headers() HttpRequest} or an

 * {@link HttpResponse#headers() HttpResponse}. Specific HTTP headers can be

 * set for a {@linkplain HttpRequest request} through one of the request

 * builder's {@link HttpRequest.Builder#header(String, String) headers} methods.

 *

 * <p> The methods of this class ( that accept a String header name ), and the

 * {@code Map} returned by the {@link #map() map} method, operate without regard

 * to case when retrieving the header value(s).

 *

 * <p> An HTTP header name may appear more than once in the HTTP protocol. As

 * such, headers are represented as a name and a list of values. Each occurrence

 * of a header value is added verbatim, to the appropriate header name list,

 * without interpreting its value. In particular, {@code HttpHeaders} does not

 * perform any splitting or joining of comma separated header value strings. The

 * order of elements in a header value list is preserved when {@link

 * HttpRequest.Builder#header(String, String) building} a request. For

 * responses, the order of elements in a header value list is the order in which

 * they were received. The {@code Map} returned by the {@code map} method,

 * however, does not provide any guarantee with regard to the ordering of its

 * entries.

 *

 * <p> {@code HttpHeaders} instances are immutable.

 *

 * @since 11

 */

public final class HttpHeaders {

    /**

     * Returns an {@link Optional} containing the first header string value of

     * the given named (and possibly multi-valued) header. If the header is not

     * present, then the returned {@code Optional} is empty.

     *

     * @param name the header name

     * @return an {@code Optional<String>} containing the first named header

     *         string value, if present

     */

    public Optional<String> firstValue(String name) {

        return allValues(name).stream().findFirst();

    }

    /**

     * Returns an {@link OptionalLong} containing the first header string value

     * of the named header field. If the header is not present, then the

     * Optional is empty. If the header is present but contains a value that

     * does not parse as a {@code Long} value, then an exception is thrown.

     *

     * @param name the header name

     * @return  an {@code OptionalLong}

     * @throws NumberFormatException if a value is found, but does not parse as

     *                               a Long

     */

    public OptionalLong firstValueAsLong(String name) {

        return allValues(name).stream().mapToLong(Long::valueOf).findFirst();

    }

    /**

     * Returns an unmodifiable List of all of the header string values of the

     * given named header. Always returns a List, which may be empty if the

     * header is not present.

     *

     * @param name the header name

     * @return a List of headers string values

     */

    public List<String> allValues(String name) {

        requireNonNull(name);

        List<String> values = map().get(name);

        // Making unmodifiable list out of empty in order to make a list which

        // throws UOE unconditionally

        return values != null ? values : List.of();

    }

    /**

     * Returns an unmodifiable multi Map view of this HttpHeaders.

     *

     * @return the Map

     */

    public Map<String,List<String>> map() {

        return headers;

    }

    /**

     * Tests this HTTP headers instance for equality with the given object.

     *

     * <p> If the given object is not an {@code HttpHeaders} then this

     * method returns {@code false}. Two HTTP headers are equal if each

     * of their corresponding {@linkplain #map() maps} are equal.

     *

     * <p> This method satisfies the general contract of the {@link

     * Object#equals(Object) Object.equals} method.

     *

     * @param obj the object to which this object is to be compared

     * @return {@code true} if, and only if, the given object is an {@code

     *         HttpHeaders} that is equal to this HTTP headers

     */

    public final boolean equals(Object obj) {

        if (!(obj instanceof HttpHeaders))

            return false;

        HttpHeaders that = (HttpHeaders)obj;

        return this.map().equals(that.map());

    }

    /**

     * Computes a hash code for this HTTP headers instance.

     *

     * <p> The hash code is based upon the components of the HTTP headers

     * {@link #map() map}, and satisfies the general contract of the

     * {@link Object#hashCode Object.hashCode} method.

     *

     * @return the hash-code value for this HTTP headers

     */

    public final int hashCode() {

        int h = 0;

        for (Map.Entry<String, List<String>> e : map().entrySet()) {

            h += entryHash(e);

        }

        return h;

    }

    /**

     * Returns this HTTP headers as a string.

     *

     * @return a string describing the HTTP headers

     */

    @Override

    public String toString() {

        StringBuilder sb = new StringBuilder();

        sb.append(super.toString()).append(" { ");

        sb.append(map());

        sb.append(" }");

        return sb.toString();

    }

    /**

     * Returns an HTTP headers from the given map. The given map's key

     * represents the header name, and its value the list of string header

     * values for that header name.

     *

     * <p> An HTTP header name may appear more than once in the HTTP protocol.

     * Such, <i>multi-valued</i>, headers must be represented by a single entry

     * in the given map, whose entry value is a list that represents the

     * multiple header string values. Leading and trailing whitespaces are

     * removed from all string values retrieved from the given map and its lists

     * before processing. Only headers that, after filtering, contain at least

     * one, possibly empty string, value will be added to the HTTP headers.

     *

     * @apiNote The primary purpose of this method is for testing frameworks.

     * Per-request headers can be set through one of the {@code HttpRequest}

     * {@link HttpRequest.Builder#header(String, String) headers} methods.

     *

     * @param headerMap the map containing the header names and values

     * @param filter a filter that can be used to inspect each

     *               header-name-and-value pair in the given map to determine if

     *               it should, or should not, be added to the to the HTTP

     *               headers

     * @return an HTTP headers instance containing the given headers

     * @throws NullPointerException if any of: {@code headerMap}, a key or value

     *        in the given map, or an entry in the map's value list, or

     *        {@code filter}, is {@code null}

     * @throws IllegalArgumentException if the given {@code headerMap} contains

     *         any two keys that are equal ( without regard to case ); or if the

     *         given map contains any key whose length, after trimming

     *         whitespaces, is {@code 0}

     */

    public static HttpHeaders of(Map<String,List<String>> headerMap,

                                 BiPredicate<String,String> filter) {

        requireNonNull(headerMap);

        requireNonNull(filter);

        return headersOf(headerMap, filter);

    }

    // --

    private static final HttpHeaders NO_HEADERS = new HttpHeaders(Map.of());

    private final Map<String,List<String>> headers;

    private HttpHeaders(Map<String,List<String>> headers) {

        this.headers = headers;

    }

    private static final int entryHash(Map.Entry<String, List<String>> e) {

        String key = e.getKey();

        List<String> value = e.getValue();

        // we know that by construction key and values can't be null

        int keyHash = key.toLowerCase(Locale.ROOT).hashCode();

        int valueHash = value.hashCode();

        return keyHash ^ valueHash;

    }

    // Returns a new HTTP headers after performing a structural copy and filtering.

    private static HttpHeaders headersOf(Map<String,List<String>> map,

                                         BiPredicate<String,String> filter) {

        TreeMap<String,List<String>> other = new TreeMap<>(CASE_INSENSITIVE_ORDER);

        TreeSet<String> notAdded = new TreeSet<>(CASE_INSENSITIVE_ORDER);

        ArrayList<String> tempList = new ArrayList<>();

        map.forEach((key, value) -> {

            String headerName = requireNonNull(key).trim();

            if (headerName.isEmpty()) {

                throw new IllegalArgumentException("empty key");

            }

            List<String> headerValues = requireNonNull(value);

            headerValues.forEach(headerValue -> {

                headerValue = requireNonNull(headerValue).trim();

                if (filter.test(headerName, headerValue)) {

                    tempList.add(headerValue);

                }

            });

            if (tempList.isEmpty()) {

                if (other.containsKey(headerName)

                        || notAdded.contains(headerName.toLowerCase(Locale.ROOT)))

                    throw new IllegalArgumentException("duplicate key: " + headerName);

                notAdded.add(headerName.toLowerCase(Locale.ROOT));

            } else if (other.put(headerName, List.copyOf(tempList)) != null) {

                throw new IllegalArgumentException("duplicate key: " + headerName);

            }

            tempList.clear();

        });

        return other.isEmpty() ? NO_HEADERS : new HttpHeaders(unmodifiableMap(other));

    }

}