/* Provider.java -- 
   Copyright (C) 2002, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath 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 for more details.

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along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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this exception to your version of the library, but you are not
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package gnu.java.nio.charset;

import java.nio.charset.Charset;
import java.nio.charset.spi.CharsetProvider;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;

/**
 * Charset provider for the required charsets.  Used by
 * {@link Charset#charsetForName} and * {@link Charset#availableCharsets}.
 *
 * @author Jesse Rosenstock
 * @author Robert Schuster (thebohemian@gmx.net)
 * @see Charset
 */
public final class Provider extends CharsetProvider
{
  private static Provider singleton;

  static
  {
    synchronized (Provider.class)
      {
        singleton = null;
      }
  }

  /**
   * Map from charset name to charset canonical name. The strings
   * are all lower-case to allow case-insensitive retrieval of
   * Charset instances. 
   */
  private final HashMap canonicalNames;

  /**
   * Map from lower-case canonical name to Charset.
   * TODO: We may want to use soft references.  We would then need to keep
   * track of the class name to regenerate the object.
   */
  private final HashMap charsets;

  private Provider ()
  {
    canonicalNames = new HashMap ();
    charsets = new HashMap ();

    // US-ASCII aka ISO646-US
    addCharset (new US_ASCII ());

    // ISO-8859-1 aka ISO-LATIN-1
    addCharset (new ISO_8859_1 ());

    // UTF-8
    addCharset (new UTF_8 ());

    // UTF-16BE
    addCharset (new UTF_16BE ());

    // UTF-16LE
    addCharset (new UTF_16LE ());

    // UTF-16
    addCharset (new UTF_16 ());
  }

  public Iterator charsets ()
  {
    return Collections.unmodifiableCollection (charsets.values ())
                      .iterator ();
  }

  /**
   * Returns a Charset instance by converting the given
   * name to lower-case, looking up the canonical charset
   * name and finally looking up the Charset with that name.
   * 
   * <p>The lookup is therefore case-insensitive.</p>
   * 
   *  @returns The Charset having <code>charsetName</code>
   *  as its alias or null if no such Charset exist.
   */
  public Charset charsetForName (String charsetName)
  {
    return (Charset) charsets.get(canonicalNames.get(charsetName.toLowerCase()));
  }

  /**
   * Puts a Charset under its canonical name into the 'charsets' map.
   * Then puts a mapping from all its alias names to the canonical name.
   * 
   * <p>All names are converted to lower-case</p>.
   * 
   * @param cs
   */
  private void addCharset (Charset cs)
  {
    String canonicalName = cs.name().toLowerCase();
    charsets.put (canonicalName, cs);
    
    /* Adds a mapping between the canonical name
     * itself making a lookup using that name
     * no special case.
     */  
    canonicalNames.put(canonicalName, canonicalName);

    for (Iterator i = cs.aliases ().iterator (); i.hasNext (); )
      canonicalNames.put (((String) i.next()).toLowerCase(), canonicalName);
  }

  public static synchronized Provider provider ()
  {
    if (singleton == null)
      singleton = new Provider ();
    return singleton;
  }
}