// Copyright 2003 Adam Megacz, see the COPYING file for licensing [GPL]
package org.xwt.js;

import java.util.*;
import org.xwt.util.*;
import java.io.*;

/**
 *  This class encapsulates a single trap placed on a given node. The
 *  traps for a given property name on a given box are maintained as a
 *  linked list stack, with the most recently placed trap at the head
 *  of the list.
 */
public class JSTrap {

    JSTrappable trapee = null;   ///< the box on which this trap was placed
    JSFunction f = null;                 ///< the function for this trap
    JSTrap next = null;          ///< the next trap down the trap stack
    Object name = null;          ///< the property that the trap was placed on

    private JSTrap(JSTrappable b, String n, JSFunction f, JSTrap nx) { trapee = b; name = n; this.f = f; this.next = nx; }

    /** adds a trap, avoiding duplicates */
    public static void addTrap(JSTrappable trapee, Object name, JSFunction f) {
        for(JSTrap t = trapee.getTrap(name); t != null; t = t.next) if (t.f == f) return;
        trapee.putTrap(name, new JSTrap(trapee, name.toString(), f, (JSTrap)trapee.getTrap(name)));
    }

    /** deletes a trap, if present */
    public static void delTrap(JSTrappable trapee, Object name, JSFunction f) {
        JSTrap t = (JSTrap)trapee.getTrap(name);
        if (t == null) return;
        if (t.f == f) { trapee.putTrap(t.name, t.next); return; }
        for(; t.next != null; t = t.next) if (t.next.f == f) { t.next = t.next.next; return; }
    }

    /** objects onto which traps may be placed */
    public static interface JSTrappable {
        public abstract JSTrap getTrap(Object key);
        public abstract void putTrap(Object key, JSTrap trap);
        public abstract void putAndTriggerJSTraps(Object key, Object value);
    }

    static class JSTrapScope extends JSScope {
        JSTrap t;
        Object val = null;
        boolean cascadeHappened = false;
        public JSTrapScope(JSScope parent, JSTrap t, Object val) { super(parent); this.t = t; this.val = val; }
        public Object get(Object key) {
            if (key.equals("trapee")) return t.trapee;
            if (key.equals("trapname")) return t.name;
            return super.get(key);
        }
    }
}