/* Soot - a J*va Optimization Framework
 * Copyright (C) 1999 Patrick Lam, Raja Vallee-Rai
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/*
 * Modified by the Sable Research Group and others 1997-1999.  
 * See the 'credits' file distributed with Soot for the complete list of
 * contributors.  (Soot is distributed at http://www.sable.mcgill.ca/soot)
 */

package soot.jimple.toolkits.invoke;

import soot.*;
import soot.jimple.*;
import soot.util.*;
import java.util.*;

/** Utility methods for dealing with traps. */
public class ThrowManager
{
    /** Iterate through the statements in b (starting at the end), returning
     * the last instance of the following pattern:
     *
     *                r928 = new java.lang.NullPointerException;
     *                specialinvoke r928."<init>"();
     *                throw r928;
     *
     * Creates if necessary.
     */
        
    public static Stmt getNullPointerExceptionThrower(JimpleBody b)
    {
        Chain units = b.getUnits();
        Set trappedUnits = TrapManager.getTrappedUnitsOf(b);
        
        for (Stmt s = (Stmt)units.getLast(); s != units.getFirst();
             s = (Stmt)units.getPredOf(s))
        {
            if (trappedUnits.contains(s))
                continue;
            if (s instanceof ThrowStmt)
            {
                Value throwee = ((ThrowStmt)s).getOp();
                if (throwee instanceof Constant)
                    continue;

                if (s == units.getFirst())
                    break;
                Stmt prosInvoke = (Stmt)units.getPredOf(s);

                if (!(prosInvoke instanceof InvokeStmt))
                    continue;

                if (prosInvoke == units.getFirst())
                    break;
                Stmt prosNew = (Stmt)units.getPredOf(prosInvoke);

                if (!(prosNew instanceof AssignStmt))
                    continue;

                InvokeExpr ie = ((InvokeStmt)prosInvoke).getInvokeExpr();
                if (!(ie instanceof SpecialInvokeExpr))
                    continue;

                if (((SpecialInvokeExpr)ie).getBase() != throwee || 
                    !ie.getMethodRef().name().equals("<init>"))
                    continue;

                Value lo = ((AssignStmt)prosNew).getLeftOp();
                Value ro = ((AssignStmt)prosNew).getRightOp();
                if (lo != throwee || !(ro instanceof NewExpr))
                    continue;

                Type newType = ((NewExpr)ro).getBaseType();
                if (!newType.equals(RefType.v("java.lang.NullPointerException")))
                    continue;

                // Whew!
                return prosNew;
            }
        }

        // Create.
        Stmt last = (Stmt)units.getLast();

        return addThrowAfter(b, last);
    }

    static Stmt addThrowAfter(JimpleBody b, Stmt target)
    {
        Chain units = b.getUnits();
        Chain locals = b.getLocals();
        int i = 0;
        
        // Bah!
        boolean canAddI = false;
        do
        {
            canAddI = true;
            Iterator localIt = locals.iterator();
            while (localIt.hasNext())
            {
                Local l = (Local)localIt.next();
                if (l.getName().equals("__throwee"+i))
                    canAddI = false;
            }
            if (!canAddI)
                i++;
        }
        while (!canAddI);

        Local l = Jimple.v().newLocal("__throwee"+i, RefType.v("java.lang.NullPointerException"));
        b.getLocals().add(l);

        Stmt newStmt = Jimple.v().newAssignStmt
            (l, Jimple.v().newNewExpr(RefType.v("java.lang.NullPointerException")));

        Stmt invStmt = Jimple.v().newInvokeStmt
            (Jimple.v().newSpecialInvokeExpr(l, Scene.v().getMethod("<java.lang.NullPointerException: void <init>()>").makeRef()));
        
        Stmt throwStmt = Jimple.v().newThrowStmt(l);

        units.insertAfter(newStmt, target);
        units.insertAfter(invStmt, newStmt);
        units.insertAfter(throwStmt, invStmt);
        return newStmt;
    }

    /** If exception e is caught at stmt s in body b, return the handler;
     * otherwise, return null. */
    static boolean isExceptionCaughtAt(SootClass e, Stmt stmt, Body b)
    {
        /* Look through the traps t of b, checking to see if:
         *  - caught exception is e;
         *  - and, stmt lies between t.beginUnit and t.endUnit */

        Hierarchy h = new Hierarchy();

        Iterator trapsIt = b.getTraps().iterator();

        while (trapsIt.hasNext())
        {
            Trap t = (Trap)trapsIt.next();

            /* Ah ha, we might win. */
            if (h.isClassSubclassOfIncluding(e, t.getException()))
            {
                Iterator it = b.getUnits().iterator(t.getBeginUnit(),
                                                    t.getEndUnit());
                while (it.hasNext())
                    if (stmt.equals(it.next()))
                        return true;
            }
        }

        return false;
    }
}