package org.spongycastle.jce.cert;

import java.util.Iterator;
import java.util.Set;

/**
 * An immutable valid policy tree node as defined by the PKIX certification 
 * path validation algorithm.<br />
 * <br />
 * One of the outputs of the PKIX certification path validation 
 * algorithm is a valid policy tree, which includes the policies that
 * were determined to be valid, how this determination was reached,
 * and any policy qualifiers encountered. This tree is of depth
 * <i>n</i>, where <i>n</i> is the length of the certification
 * path that has been validated.<br />
 * <br />
 * Most applications will not need to examine the valid policy tree.
 * They can achieve their policy processing goals by setting the 
 * policy-related parameters in <code>PKIXParameters</code>. However,
 * the valid policy tree is available for more sophisticated applications,
 * especially those that process policy qualifiers.<br />
 * <br />
 * {@link PKIXCertPathValidatorResult#getPolicyTree() 
 * PKIXCertPathValidatorResult.getPolicyTree} returns the root node of the
 * valid policy tree. The tree can be traversed using the 
 * {@link #getChildren getChildren} and {@link #getParent getParent} methods. 
 * Data about a particular node can be retrieved using other methods of 
 * <code>PolicyNode</code>.<br />
 * <br />
 * <b>Concurrent Access</b><br />
 * <br />
 * All <code>PolicyNode</code> objects must be immutable and 
 * thread-safe. Multiple threads may concurrently invoke the methods defined 
 * in this class on a single <code>PolicyNode</code> object (or more than one) 
 * with no ill effects. This stipulation applies to all public fields and 
 * methods of this class and any added or overridden by subclasses.
 **/
public interface PolicyNode
{

    /**
     * Returns the parent of this node, or <code>null</code> if this is the 
     * root node.
     *
     * @return the parent of this node, or <code>null</code> if this is the 
     * root node
     */
    public PolicyNode getParent();

    /**
     * Returns an iterator over the children of this node. Any attempts to 
     * modify the children of this node through the 
     * <code>Iterator</code>'s remove method must throw an
     * <code>UnsupportedOperationException</code>.
     *
     * @return an iterator over the children of this node
     */
    public Iterator getChildren();

    /**
     * Returns the depth of this node in the valid policy tree.
     *
     * @return the depth of this node (0 for the root node, 1 for its
     * children, and so on)
     */
    public int getDepth();

    /**
     * Returns the valid policy represented by this node.
     *
     * @return the <code>String</code> OID of the valid policy
     * represented by this node, or the special value "any-policy". For 
     * the root node, this method always returns the special value "any-policy".
     */
    public String getValidPolicy();

    /**
     * Returns the set of policy qualifiers associated with the
     * valid policy represented by this node.
     *
     * @return an immutable <code>Set</code> of 
     * <code>PolicyQualifierInfo</code>s. For the root node, this
     * is always an empty <code>Set</code>.
     */
    public Set getPolicyQualifiers();

    /**
     * Returns the set of expected policies that would satisfy this
     * node's valid policy in the next certificate to be processed.
     *
     * @return an immutable <code>Set</code> of expected policy 
     * <code>String</code> OIDs, or an immutable <code>Set</code> with
     * the single special value "any-policy". For the root node, this method 
     * always returns a <code>Set</code> with the single value "any-policy".
     */
    public Set getExpectedPolicies();

    /**
     * Returns the criticality indicator of the certificate policy extension
     * in the most recently processed certificate.
     *
     * @return <code>true</code> if extension marked critical, 
     * <code>false</code> otherwise. For the root node, <code>false</code>
     * is always returned.
     */
    public boolean isCritical();
}
