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

import java.util.*;
import org.xwt.js.*;
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 Trap {

    // Static Data //////////////////////////////////////////////////////////////

    private static Function cascadeHelper = null;
    private static String cascadeHelperText =
        "return function(q) { var ret = arguments.doTrap;" +
        "if (ret != false && !arguments.didCascade) arguments.cascade = q; };";
    static {
        try {
            cascadeHelper = JS.parse("cascadeHelper", 1, new StringReader(cascadeHelperText));
            cascadeHelper = (Function)new JS.Context(cascadeHelper, null).resume();
        } catch (Exception e) {
            Log.log(Trap.class, e);
        }
    }

    /** List of properties that cannot be trapped */
    private static final Hash PROHIBITED = new Hash(120, 3);

    static {
        String[] p = new String[] {
            "shrink", "hshrink", "vshrink", "x", "y",
            "width", "height", "flex", "colspan", "rowspan", "cols",
            "rows", "align", "invisible", "absolute", "globalx",
            "globaly", "minwidth", "minheight", "height", "width",
            "maxwidth", "maxheight", "numchildren", "hpad", "vpad",
            "buffered", "cursor", "mousex", "mousey",
            "mouseinside", "thisbox", "indexof", "path", "font", "fontsize"
        };
        for(int i=0; i<p.length; i++) PROHIBITED.put(p[i], Boolean.TRUE);
    };


    // Instance Members ////////////////////////////////////////////////////////

    /** the box on which this trap was placed */
    private Box trapee = null;

    /** the function for this trap */
    Function f = null;

    /** the next trap down the trap stack */
    private Trap next = null;

    /** the property that the trap was placed on */
    private Object name = null;


    // Static Methods //////////////////////////////////////////////////////////////////////////

    /**
     *  adds a trap.
     *  @param trapee the box to place the trap on
     *  @param name the name of the property to trap on
     *  @param f the function to place as a trap
     */
    static void addTrap(Box trapee, Object name, Function f) {

        // check if this script has already placed a trap on this property
        for(Trap t = (Trap)trapee.get(name, Trap.class); t != null; t = t.next)
            if (t.f == f) return;
        
        // actually place the trap
        trapee.put2(name, Trap.class, new Trap(trapee, name.toString(), f, (Trap)trapee.get(name, Trap.class)));
    }


    /**
     *  deletes a trap.
     *  @param trapee the box to remove the trap from
     *  @param name the name of the property to trap on
     *  @param f the function to remove
     */
    static void delTrap(Box trapee, Object name, Function f) {
        Trap t = (Trap)trapee.get(name, Trap.class);
        if (t.f == f) { trapee.put2(name, Trap.class, t.next); return; }
        for(; t.next != null; t = t.next)
            if (t.next.f == f) { t.next = t.next.next; return; }
        Log.logJS("warning: tried to remove a trap that had not been placed");
    }


    // Instance Methods //////////////////////////////////////////////////////////////////////////

    private Trap(Box b, String n, Function f, Trap nx)
    { trapee = b; name = n; this.f = f; this.next = nx; }

    // Read Traps //////////////////////////////////////////////////////////////////////

    public Object perform() {
        if (f.getNumFormalArgs() > 0) return cascade();
        else return new JS.TailCall().set(f, new TrapArgs(this));
    }

    public Object cascade() {
        if (next != null) return next.perform();
        else return trapee.get(name, true);
    }

    // Write Traps //////////////////////////////////////////////////////////////////////

    public Object perform(Object val) {
        if (f.getNumFormalArgs() == 0) return cascade(val);
        else return new JS.TailCall().set(cascadeHelper, new TrapArgs(this, val));
    }
    
    public Object cascade(Object val) {
        if (next != null) return next.perform(val);
        else return trapee.put(name, val, true);
    }

    // Args ///////////////////////////////////////////////////////////////////////////

    private static class TrapArgs extends JS.Array {
        private Trap t;
        public boolean cascadeHappened = false;
        public TrapArgs(Trap t) { this.t = t; }
        public TrapArgs(Trap t, Object value) { this.t = t; addElement(value); }
        
        public Object put(Object key, Object val) {
            if (key.equals("cascade")) { cascadeHappened = true; return t.cascade(val); }
            else return super.put(key, val);
        }

        public Object get(Object key) {
            // common case
            if(!(key instanceof String)) return super.get(key);
            if (key.equals("trapee")) return t.trapee;
            if (key.equals("doTrap")) return new JS.TailCall().set(t.f, this);
            if (key.equals("didCascade")) return cascadeHappened ? Boolean.TRUE : Boolean.FALSE;
            if (key.equals("trapname")) return t.name;
            if (key.equals("cascade")) return t.cascade();
            if (key.equals("callee")) return t.f;
            return super.get(key);
        }
    }
}