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The core HTTP and composition mechanisms of Ratpack
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/*
 * Copyright 2013 the original author or authors.
 *
 * 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 ratpack.http.internal;

import java.text.ParsePosition;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

/**
 * This DateFormat decodes 3 formats of {@link Date}, but only encodes the one,
 * the first:
 * 
 * Sun, 06 Nov 1994 08:49:37 GMT: standard specification, the only one with
 * valid generation
 * Sun, 06 Nov 1994 08:49:37 GMT: obsolete specification
 * Sun Nov 6 08:49:37 1994: obsolete specification
 * 
 */
public class HttpHeaderDateFormat extends SimpleDateFormat {
  private static final long serialVersionUID = -925286159755905325L;

  private final SimpleDateFormat format1 = new HttpHeaderDateFormatObsolete1();
  private final SimpleDateFormat format2 = new HttpHeaderDateFormatObsolete2();

  private static final ThreadLocal DATE_FORMAT_THREAD_LOCAL =
    new ThreadLocal() {
      @Override
      protected HttpHeaderDateFormat initialValue() {
        return new HttpHeaderDateFormat();
      }
    };

  public static HttpHeaderDateFormat get() {
    return DATE_FORMAT_THREAD_LOCAL.get();
  }

  /**
   * Standard date format
   * Sun, 06 Nov 1994 08:49:37 GMT -> E, d MMM yyyy HH:mm:ss z
   */
  private HttpHeaderDateFormat() {
    super("E, dd MMM yyyy HH:mm:ss z", Locale.ENGLISH);
    setTimeZone(TimeZone.getTimeZone("GMT"));
  }

  @Override
  public Date parse(String text, ParsePosition pos) {
    Date date = super.parse(text, pos);
    if (date == null) {
      date = format1.parse(text, pos);
    }
    if (date == null) {
      date = format2.parse(text, pos);
    }
    return date;
  }

  /**
   * First obsolete format

   * Sunday, 06-Nov-94 08:49:37 GMT -> E, d-MMM-y HH:mm:ss z
   */
  private static final class HttpHeaderDateFormatObsolete1 extends SimpleDateFormat {
    private static final long serialVersionUID = -3178072504225114298L;

    HttpHeaderDateFormatObsolete1() {
      super("E, dd-MMM-yy HH:mm:ss z", Locale.ENGLISH);
      setTimeZone(TimeZone.getTimeZone("GMT"));
    }
  }

  /**
   * Second obsolete format
   * 
   * Sun Nov 6 08:49:37 1994 -> EEE, MMM d HH:mm:ss yyyy
   */
  private static final class HttpHeaderDateFormatObsolete2 extends SimpleDateFormat {
    private static final long serialVersionUID = 3010674519968303714L;

    HttpHeaderDateFormatObsolete2() {
      super("E MMM d HH:mm:ss yyyy", Locale.ENGLISH);
      setTimeZone(TimeZone.getTimeZone("GMT"));
    }
  }
}