/* SignatureFactory.java -- 
   Copyright (C) 2001, 2002, 2003, 2006 Free Software Foundation, Inc.

This file is a 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
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your option) any later version.

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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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Foundation, Inc., 51 Franklin St, 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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permission to link this library with independent modules to produce an
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package gnu.java.security.sig;

import gnu.java.security.Registry;
import gnu.java.security.sig.dss.DSSSignature;
import gnu.java.security.sig.rsa.RSASignatureFactory;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

/**
 * A Factory to instantiate signature-with-appendix handlers.
 */
public class SignatureFactory
{
  private static Set names;

  /** Trivial constructor to enforce Singleton pattern. */
  private SignatureFactory()
  {
    super();
  }

  /**
   * Returns an instance of a signature-with-appendix scheme given its name.
   * 
   * @param ssa the case-insensitive signature-with-appendix scheme name.
   * @return an instance of the scheme, or <code>null</code> if none found.
   */
  public static final ISignature getInstance(String ssa)
  {
    if (ssa == null)
      return null;

    ssa = ssa.trim();
    ssa = ssa.toLowerCase();
    ISignature result = null;
    if (ssa.equalsIgnoreCase(Registry.DSA_SIG) || ssa.equals(Registry.DSS_SIG))
      result = new DSSSignature();
    else if (ssa.startsWith(Registry.RSA_SIG_PREFIX))
      result = RSASignatureFactory.getInstance(ssa);

    return result;
  }

  /**
   * Returns a {@link Set} of signature-with-appendix scheme names supported by
   * this <i>Factory</i>.
   * 
   * @return a {@link Set} of signature-with-appendix scheme names (Strings).
   */
  public static synchronized final Set getNames()
  {
    if (names == null)
      {
        HashSet hs = new HashSet();
        hs.add(Registry.DSS_SIG);
        hs.addAll(RSASignatureFactory.getNames());
        names = Collections.unmodifiableSet(hs);
      }
    return names;
  }
}