/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * 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 libcore.net.http;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

/**
 * Best-effort parser for HTTP dates.
 */
public final class HttpDate {

    /**
     * Most websites serve cookies in the blessed format. Eagerly create the parser to ensure such
     * cookies are on the fast path.
     */
    private static final ThreadLocal<DateFormat> STANDARD_DATE_FORMAT
            = new ThreadLocal<DateFormat>() {
        @Override protected DateFormat initialValue() {
            DateFormat rfc1123 = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz", Locale.US);
            rfc1123.setTimeZone(TimeZone.getTimeZone("UTC"));
            return rfc1123;
        }
    };

    /**
     * If we fail to parse a date in a non-standard format, try each of these formats in sequence.
     */
    private static final String[] BROWSER_COMPATIBLE_DATE_FORMATS = new String[] {
            /* This list comes from  {@code org.apache.http.impl.cookie.BrowserCompatSpec}. */
            "EEEE, dd-MMM-yy HH:mm:ss zzz", // RFC 1036
            "EEE MMM d HH:mm:ss yyyy", // ANSI C asctime()
            "EEE, dd-MMM-yyyy HH:mm:ss z",
            "EEE, dd-MMM-yyyy HH-mm-ss z",
            "EEE, dd MMM yy HH:mm:ss z",
            "EEE dd-MMM-yyyy HH:mm:ss z",
            "EEE dd MMM yyyy HH:mm:ss z",
            "EEE dd-MMM-yyyy HH-mm-ss z",
            "EEE dd-MMM-yy HH:mm:ss z",
            "EEE dd MMM yy HH:mm:ss z",
            "EEE,dd-MMM-yy HH:mm:ss z",
            "EEE,dd-MMM-yyyy HH:mm:ss z",
            "EEE, dd-MM-yyyy HH:mm:ss z",

            /* RI bug 6641315 claims a cookie of this format was once served by www.yahoo.com */
            "EEE MMM d yyyy HH:mm:ss z",
    };

    /**
     * Returns the date for {@code value}. Returns null if the value couldn't be
     * parsed.
     */
    public static Date parse(String value) {
        try {
            return STANDARD_DATE_FORMAT.get().parse(value);
        } catch (ParseException ignore) {
        }
        for (String formatString : BROWSER_COMPATIBLE_DATE_FORMATS) {
            try {
                return new SimpleDateFormat(formatString, Locale.US).parse(value);
            } catch (ParseException ignore) {
            }
        }
        return null;
    }

    /**
     * Returns the string for {@code value}.
     */
    public static String format(Date value) {
        return STANDARD_DATE_FORMAT.get().format(value);
    }
}