/*
 * 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 com.squareup.okhttp.internal.http;

import java.text.DateFormat;
import java.text.ParsePosition;
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 {

  private static final TimeZone GMT = TimeZone.getTimeZone("GMT");

  /**
   * 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() {
          // RFC 2616 specified: RFC 822, updated by RFC 1123 format with fixed GMT.
          DateFormat rfc1123 = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss 'GMT'", Locale.US);
          rfc1123.setLenient(false);
          rfc1123.setTimeZone(GMT);
          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_FORMAT_STRINGS = new String[] {
      // HTTP formats required by RFC2616 but with any timezone.
      "EEE, dd MMM yyyy HH:mm:ss zzz", // RFC 822, updated by RFC 1123 with any TZ
      "EEEE, dd-MMM-yy HH:mm:ss zzz", // RFC 850, obsoleted by RFC 1036 with any TZ.
      "EEE MMM d HH:mm:ss yyyy", // ANSI C's asctime() format
       // Alternative formats.
      "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",
  };

  private static final DateFormat[] BROWSER_COMPATIBLE_DATE_FORMATS =
      new DateFormat[BROWSER_COMPATIBLE_DATE_FORMAT_STRINGS.length];

  /** Returns the date for {@code value}. Returns null if the value couldn't be parsed. */
  public static Date parse(String value) {
    if (value.length() == 0) {
      return null;
    }

    ParsePosition position = new ParsePosition(0);
    Date result = STANDARD_DATE_FORMAT.get().parse(value, position);
    if (position.getIndex() == value.length()) {
      // STANDARD_DATE_FORMAT must match exactly; all text must be consumed, e.g. no ignored
      // non-standard trailing "+01:00". Those cases are covered below.
      return result;
    }
    synchronized (BROWSER_COMPATIBLE_DATE_FORMAT_STRINGS) {
      for (int i = 0, count = BROWSER_COMPATIBLE_DATE_FORMAT_STRINGS.length; i < count; i++) {
        DateFormat format = BROWSER_COMPATIBLE_DATE_FORMATS[i];
        if (format == null) {
          format = new SimpleDateFormat(BROWSER_COMPATIBLE_DATE_FORMAT_STRINGS[i], Locale.US);
          // Set the timezone to use when interpreting formats that don't have a timezone. GMT is
          // specified by RFC 2616.
          format.setTimeZone(GMT);
          BROWSER_COMPATIBLE_DATE_FORMATS[i] = format;
        }
        position.setIndex(0);
        result = format.parse(value, position);
        if (position.getIndex() != 0) {
          // Something was parsed. It's possible the entire string was not consumed but we ignore
          // that. If any of the BROWSER_COMPATIBLE_DATE_FORMAT_STRINGS ended in "'GMT'" we'd have
          // to also check that position.getIndex() == value.length() otherwise parsing might have
          // terminated early, ignoring things like "+01:00". Leaving this as != 0 means that any
          // trailing junk is ignored.
          return result;
        }
      }
    }
    return null;
  }

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

  private HttpDate() {
  }
}
