source: trunk/src/org/expeditee/core/EnforcedClipStack.java@ 1097

package org.expeditee.core;

import java.util.Stack;

public class EnforcedClipStack {

        /** The stack of sub-area clips. */
        private Stack<Clip> _clipStack;
        
        /** Default constructor. */
        public EnforcedClipStack()
        {
                _clipStack = new Stack<Clip>();
        }
        
        /** Pushes a new clip onto the stack, ensuring that it is a sub-area of the top of the stack. */
        public EnforcedClipKey push(Clip clip)
        {
                // No null clips allowed
                if (clip == null) return null;
                
                // Leave the given clip unchanged (in case the provider wants to keep using it)
                clip = clip.clone();
                
                // Each clip must be a sub-area of the one below it in the stack
                if (!_clipStack.isEmpty()) {
                        clip.intersectWith(_clipStack.peek());
                }
                
                // Put the new clip on the stack
                _clipStack.push(clip);
                
                // Return the clipped area
                return EnforcedClipKey.get(clip);
        }
        
        /** Pops the top of the stack if there given key corresponds to it. */
        public Clip pop(EnforcedClipKey key)
        {
                if (!_clipStack.isEmpty() && key != null && key.matches(_clipStack.peek())) return _clipStack.pop();
                
                return null;
        }
        
        /** Returns a copy of the current top of the stack. */
        public Clip peek()
        {
                if (!_clipStack.isEmpty()) return _clipStack.peek().clone();
                
                return null;
        }
        
        /** Key class to ensure only the owner of a given pushed clip can pop it again. */
        public static class EnforcedClipKey {
                
                /** The clip this key corresponds to. */
                private Clip _keyedClip;
                
                /** Gets a key for the given clip. */
                public static EnforcedClipKey get(Clip clip)
                {
                        if (clip == null) return null;
                        
                        return new EnforcedClipKey(clip);
                }
                
                /** Private constructor so clip cannot be null. */
                private EnforcedClipKey(Clip clip)
                {
                        _keyedClip = clip;
                }
                
                /** Whether this key corresponds to the given clip. */
                public boolean matches(Clip clip)
                {
                        return clip == _keyedClip;
                }
                
        }
        
}