/* AccessControlContext.java --- Access Control Context Class
   Copyright (C) 1999, 2004 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
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any later version.

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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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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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terms of your choice, provided that you also meet, for each linked
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this exception to your version of the library, but you are not
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package java.security;

import java.util.HashSet;

/**
 * AccessControlContext makes system resource access decsion 
 * based on permission rights.  
 *
 * It is used for a specific context and has only one method
 * checkPermission. It is similar to AccessController except
 * that it makes decsions based on the current context instead
 * of the the current thread.
 *
 * It is created by call AccessController.getContext method.
 *
 * @author Mark Benvenuto
 * @since 1.2
 */
public final class AccessControlContext
{
  private final ProtectionDomain[] protectionDomains;
  private final DomainCombiner combiner;

  /**
   * Construct a new AccessControlContext with the specified
   * ProtectionDomains. <code>context</code> must not be 
   * null and duplicates will be removed.
   *
   * @param context The ProtectionDomains to use
   */
  public AccessControlContext(ProtectionDomain[] context)
  {
    HashSet domains = new HashSet (context.length);
    for (int i = 0; i < context.length; i++)
      domains.add (context[i]);
    protectionDomains = (ProtectionDomain[])
      domains.toArray (new ProtectionDomain[domains.size()]);
    combiner = null;
  }

  /**
   * Construct a new AccessControlContext with the specified
   * {@link ProtectionDomain}s and {@link DomainCombiner}.
   *
   * <p>Code calling this constructor must have a {@link
   * SecurityPermission} of <i>createAccessControlContext</i>.</p>
   *
   * @throws SecurityException If the caller does not have permission
   * to create an access control context.
   * @since 1.3
   */
  public AccessControlContext(AccessControlContext acc,
			      DomainCombiner combiner)
  {
    AccessControlContext acc2 = null;
    SecurityManager sm = System.getSecurityManager ();
    if (sm != null)
      {
	Permission perm =
	  new SecurityPermission ("createAccessControlContext");

	// The default SecurityManager.checkPermission(perm) just calls 
	// AccessController.checkPermission(perm) which in turn just
	// calls AccessController.getContext().checkPermission(perm).
	// This means AccessController.getContext() is called twice,
	// once for the security check and once by us.  It's a very
	// expensive call (on gcj at least) so if we're using the
	// default security manager we avoid this duplication.
	if (sm.getClass() == SecurityManager.class)
	  {
	    acc2 = AccessController.getContext ();
	    acc2.checkPermission (perm);
	  }
	else
	  sm.checkPermission (perm);
      }
    if (acc2 == null)
      acc2 = AccessController.getContext ();
    protectionDomains = combiner.combine (acc2.protectionDomains,
                                          acc.protectionDomains);
    this.combiner = combiner;
  }

  AccessControlContext (ProtectionDomain[] domains, AccessControlContext acc,
                        DomainCombiner combiner)
  {
    protectionDomains = combiner.combine (domains, acc.protectionDomains);
    this.combiner = combiner;
  }

  /**
   * Returns the Domain Combiner associated with the AccessControlContext
   *
   * @return the DomainCombiner
   */
  public DomainCombiner getDomainCombiner()
  {
    return combiner;
  }

  /**
   * Determines whether or not the specific permission is granted
   * depending on the context it is within. 
   *
   * @param perm a permission to check
   *
   * @throws AccessControlException if the permssion is not permitted
   */
  public void checkPermission(Permission perm) throws AccessControlException
  {
    if (protectionDomains.length == 0)
      throw new AccessControlException ("permission " 
					+ perm 
					+ " not granted: no protection domains");

    for (int i = 0; i < protectionDomains.length; i++)
      {
	final ProtectionDomain domain = protectionDomains[i];
	if (!domain.implies(perm))
	  throw new AccessControlException ("permission " 
					    + perm 
					    + " not granted: " 
					    + domain 
					    + " does not imply it.");
      }
  }

  /**
   * Checks if two AccessControlContexts are equal.
   *
   * It first checks if obj is an AccessControlContext class, and
   * then checks if each ProtectionDomain matches.
   *
   * @param obj The object to compare this class to
   *
   * @return true if equal, false otherwise
   */
  public boolean equals(Object obj)
  {
    if (obj instanceof AccessControlContext)
      {
	AccessControlContext acc = (AccessControlContext) obj;

	if (acc.protectionDomains.length != protectionDomains.length)
	  return false;

        int i, j;
        for (i = 0; i < protectionDomains.length; i++)
          {
            for (j = 0; j < acc.protectionDomains.length; j++)
              {
                if (acc.protectionDomains[j].equals (protectionDomains[i]))
                  break;
              }
            if (j == acc.protectionDomains.length)
              return false;
          }
        return true;
      }
    return false;
  }

  /**
   * Computes a hash code of this class
   *
   * @return a hash code representing this class
   */
  public int hashCode()
  {
    int h = 0;
    for (int i = 0; i < protectionDomains.length; i++)
      h ^= protectionDomains[i].hashCode();

    return h;
  }

  ProtectionDomain[] getProtectionDomains ()
  {
    return protectionDomains;
  }
}