/* Provider.java -- 
   Copyright (C) 2002, 2005, 2006 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
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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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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package gnu.java.nio.charset;

import java.nio.charset.Charset;
import java.nio.charset.spi.CharsetProvider;
import java.security.AccessController;
import java.security.PrivilegedAction;
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}.
 *
 * Note: This class is a privileged class, because it can be instantiated without
 * requiring the RuntimePermission("charsetProvider"). There is a check in
 * java.nio.charset.spi.CharsetProvider to skip the security check if the provider
 * is an instance of this class.
 *
 * @author Jesse Rosenstock
 * @author Robert Schuster (thebohemian@gmx.net)
 * @see Charset
 */
public final class Provider extends CharsetProvider
{
  private static Provider singleton;

  /**
   * 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;

  /**
   * We don't load all available charsets at the start
   */
  private boolean extendedLoaded;

  // Package private to avoid an accessor method in PrivilegedAction below.
  Provider ()
  {
    extendedLoaded = false;
    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 ());

    // UTF-16LE (marked)
    addCharset (new UnicodeLittle ());

    // Windows-1250 aka cp-1250 (East European)
    addCharset (new Windows1250 ());

    // Windows-1251 (Cyrillic)
    addCharset (new Windows1251 ());

    // Windows-1252 aka cp-1252 (Latin-1)
    addCharset (new Windows1252 ());

    // Windows-1253 (Greek)
    addCharset (new Windows1253 ());

    // Windows-1254 (Turkish)
    addCharset (new Windows1254 ());

    // Windows-1257 (Baltic)
    addCharset (new Windows1257 ());

    // ISO-8859-2 aka ISO-LATIN-2
    addCharset (new ISO_8859_2 ());

    // ISO-8859-4 aka ISO-LATIN-4
    addCharset (new ISO_8859_4 ());

    // ISO-8859-5 (Cyrillic)
    addCharset (new ISO_8859_5 ());

    // ISO-8859-7 (Greek)
    addCharset (new ISO_8859_7 ());

    // ISO-8859-9 aka ISO-LATIN-5
    addCharset (new ISO_8859_9 ());

    // ISO-8859-13 aka ISO-LATIN-7
    addCharset (new ISO_8859_13 ());

    // ISO-8859-15 aka ISO-LATIN-9
    addCharset (new ISO_8859_15 ());

    // KOI8 (Cyrillic)
    addCharset (new KOI_8 ());
  }

 /**
  * Load non-mandatory charsets.
  */
  private void loadExtended ()
  {
    if(extendedLoaded)
      return;

    addCharset (new ISO_8859_3 ());    // ISO-8859-3 aka ISO-LATIN-3
    addCharset (new ISO_8859_6 ());    // ISO-8859-6 (Arabic)
    addCharset (new ISO_8859_8 ());    // ISO-8859-8 (Hebrew)

    // Some more codepages
    addCharset (new Cp855()); // IBM Cyrillic
    addCharset (new Cp857()); // IBM Turkish
    addCharset (new Cp860()); // MSDOS Portugese
    addCharset (new Cp861()); // MSDOS Icelandic
    addCharset (new Cp862()); // PC Hebrew
    addCharset (new Cp863()); // MSDOS Can. French
    addCharset (new Cp864()); // PC Arabic
    addCharset (new Cp865()); // MSDOS Nordic
    addCharset (new Cp866()); // MSDOS Russian
    addCharset (new Cp869()); // IBM modern Greek
    addCharset (new Cp874()); // IBM Thai
    extendedLoaded = true;
  }

  public Iterator charsets ()
  {
    loadExtended();
    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)
  {
    Charset cs = (Charset) charsets.get(canonicalNames.get(charsetName.toLowerCase()));
    if(cs == null && !extendedLoaded)
     {
       loadExtended();
       cs = (Charset) charsets.get(canonicalNames.get(charsetName.toLowerCase()));
     }
    return cs;
  }

  /**
   * 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 ()
  {
    // The default provider is safe to instantiate.
    if (singleton == null)
      singleton = (Provider) AccessController.doPrivileged
	(new PrivilegedAction()
	  {
	    public Object run()
	    {
	      return new Provider();
	    }
	  });
    return singleton;
  }
}