/*

 * 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.List;

import java.util.Map;

import java.util.Optional;

import java.util.OptionalLong;

import static java.util.Collections.emptyList;

import static java.util.Collections.unmodifiableList;

import static java.util.Objects.requireNonNull;

/**

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

 *

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

 * an {@link HttpResponse HttpResponse}. Specific HTTP headers can be set for

 * {@linkplain HttpRequest requests} through the 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

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

 * case when retrieving the header value.

 *

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

 *

 * @since 11

 */

public abstract class HttpHeaders {

    /**

     * Creates an HttpHeaders.

     */

    protected HttpHeaders() {}

    /**

     * Returns an {@link Optional} containing the first value of the given named

     * (and possibly multi-valued) header. If the header is not present, then

     * the returned {@code Optional} is empty.

     *

     * @implSpec

     * The default implementation invokes

     * {@code allValues(name).stream().findFirst()}

     *

     * @param name the header name

     * @return an {@code Optional<String>} for the first named value

     */

    public Optional<String> firstValue(String name) {

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

    }

    /**

     * Returns an {@link OptionalLong} containing the first 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.

     *

     * @implSpec

     * The default implementation invokes

     * {@code allValues(name).stream().mapToLong(Long::valueOf).findFirst()}

     *

     * @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 values of the given named

     * header. Always returns a List, which may be empty if the header is not

     * present.

     *

     * @implSpec

     * The default implementation invokes, among other things, the

     * {@code map().get(name)} to retrieve the list of header values.

     *

     * @param name the header name

     * @return a List of 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 : unmodifiableList(emptyList());

    }

    /**

     * Returns an unmodifiable multi Map view of this HttpHeaders.

     *

     * @return the Map

     */

    public abstract Map<String, List<String>> map();

    /**

     * 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() {

        return map().hashCode();

    }

    /**

     * 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();

    }

}