/*
 * Copyright  2000-2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); 
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License. 
 *
 */ 
package org.apache.bcel.verifier.structurals;


import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.Vector;

import org.apache.bcel.Constants;
import org.apache.bcel.Repository;
import org.apache.bcel.classfile.JavaClass;
import org.apache.bcel.classfile.Method;
import org.apache.bcel.generic.ConstantPoolGen;
import org.apache.bcel.generic.GETFIELD;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.InvokeInstruction;
import org.apache.bcel.generic.JsrInstruction;
import org.apache.bcel.generic.LoadInstruction;
import org.apache.bcel.generic.MethodGen;
import org.apache.bcel.generic.ObjectType;
import org.apache.bcel.generic.RET;
import org.apache.bcel.generic.ReturnInstruction;
import org.apache.bcel.generic.ReturnaddressType;
import org.apache.bcel.generic.Type;
import org.apache.bcel.verifier.PassVerifier;
import org.apache.bcel.verifier.VerificationResult;
import org.apache.bcel.verifier.Verifier;
import org.apache.bcel.verifier.exc.AssertionViolatedException;
import org.apache.bcel.verifier.exc.StructuralCodeConstraintException;
import org.apache.bcel.verifier.exc.VerifierConstraintViolatedException;

/**
 * This PassVerifier verifies a method of class file according to pass 3,
 * so-called structural verification as described in The Java Virtual Machine
 * Specification, 2nd edition.
 * More detailed information is to be found at the do_verify() method's
 * documentation. 
 *
 * @version $Id: ModifiedPass3bVerifier.java,v 1.3 2007-11-08 17:22:56 ebruneton Exp $
 * @author Enver Haase
 * @see #do_verify()
 */

public final class ModifiedPass3bVerifier extends PassVerifier{
    /* TODO:    Throughout pass 3b, upper halves of LONG and DOUBLE
                        are represented by Type.UNKNOWN. This should be changed
                        in favour of LONG_Upper and DOUBLE_Upper as in pass 2. */

    /**
     * An InstructionContextQueue is a utility class that holds
     * (InstructionContext, ArrayList) pairs in a Queue data structure.
     * This is used to hold information about InstructionContext objects
     * externally --- i.e. that information is not saved inside the
     * InstructionContext object itself. This is useful to save the
     * execution path of the symbolic execution of the
     * Pass3bVerifier - this is not information
     * that belongs into the InstructionContext object itself.
     * Only at "execute()"ing
     * time, an InstructionContext object will get the current information
     * we have about its symbolic execution predecessors.
     */
    private static final class InstructionContextQueue{
        private List ics = new Vector(); // Type: InstructionContext
        private List ecs = new Vector(); // Type: ArrayList (of InstructionContext)
        public void add(InstructionContext ic, ArrayList executionChain){
            ics.add(ic);
            ecs.add(executionChain);
        }
        public boolean isEmpty(){
            return ics.isEmpty();
        }
        public void remove(){
            this.remove(0);
        }
        public void remove(int i){
            ics.remove(i);
            ecs.remove(i);
        }
        public InstructionContext getIC(int i){
            return (InstructionContext) ics.get(i);
        }
        public ArrayList getEC(int i){
            return (ArrayList) ecs.get(i);
        }
        public int size(){
            return ics.size();
        }
    } // end Inner Class InstructionContextQueue

    /** In DEBUG mode, the verification algorithm is not randomized. */
    private static final boolean DEBUG = true;

    private JavaClass jc;

    /** The method number to verify. */
    private int method_no;

    /**
     * This class should only be instantiated by a Verifier.
     *
     * @see org.apache.bcel.verifier.Verifier
     */
    public ModifiedPass3bVerifier(JavaClass jc, int method_no){
        this.jc = jc;
        this.method_no = method_no;
    }

    /**
     * Whenever the outgoing frame
     * situation of an InstructionContext changes, all its successors are
     * put [back] into the queue [as if they were unvisited].
   * The proof of termination is about the existence of a
   * fix point of frame merging.
     */
    private void circulationPump(MethodGen m,ControlFlowGraph cfg, InstructionContext start, Frame vanillaFrame, InstConstraintVisitor icv, ExecutionVisitor ev){
        final Random random = new Random();
        InstructionContextQueue icq = new InstructionContextQueue();
        
        start.execute(vanillaFrame, new ArrayList(), icv, ev);  // new ArrayList() <=>  no Instruction was executed before
                                                                                                    //                                  => Top-Level routine (no jsr call before)
        icq.add(start, new ArrayList());

        // LOOP!
        while (!icq.isEmpty()){
            InstructionContext u;
            ArrayList ec;
            if (!DEBUG){
                int r = random.nextInt(icq.size());
                u = icq.getIC(r);
                ec = icq.getEC(r);
                icq.remove(r);
            }
            else{
                u  = icq.getIC(0);
                ec = icq.getEC(0);
                icq.remove(0);
            }
            
            ArrayList oldchain = (ArrayList) (ec.clone());
            ArrayList newchain = (ArrayList) (ec.clone());
            newchain.add(u);

            if ((u.getInstruction().getInstruction()) instanceof RET){
//System.err.println(u);
                // We can only follow _one_ successor, the one after the
                // JSR that was recently executed.
                RET ret = (RET) (u.getInstruction().getInstruction());
                ReturnaddressType t = (ReturnaddressType) u.getOutFrame(oldchain).getLocals().get(ret.getIndex());
                InstructionContext theSuccessor = cfg.contextOf(t.getTarget());

                // Sanity check
                InstructionContext lastJSR = null;
                int skip_jsr = 0;
                for (int ss=oldchain.size()-1; ss >= 0; ss--){
                    if (skip_jsr < 0){
                        throw new AssertionViolatedException("More RET than JSR in execution chain?!");
                    }
//System.err.println("+"+oldchain.get(ss));
                    if (((InstructionContext) oldchain.get(ss)).getInstruction().getInstruction() instanceof JsrInstruction){
                        if (skip_jsr == 0){
                            lastJSR = (InstructionContext) oldchain.get(ss);
                            break;
                        }
                        else{
                            skip_jsr--;
                        }
                    }
                    if (((InstructionContext) oldchain.get(ss)).getInstruction().getInstruction() instanceof RET){
                        skip_jsr++;
                    }
                }
                if (lastJSR == null){
                    throw new AssertionViolatedException("RET without a JSR before in ExecutionChain?! EC: '"+oldchain+"'.");
                }
                JsrInstruction jsr = (JsrInstruction) (lastJSR.getInstruction().getInstruction());
                if ( theSuccessor != (cfg.contextOf(jsr.physicalSuccessor())) ){
                    throw new AssertionViolatedException("RET '"+u.getInstruction()+"' info inconsistent: jump back to '"+theSuccessor+"' or '"+cfg.contextOf(jsr.physicalSuccessor())+"'?");
                }
                
                if (theSuccessor.execute(u.getOutFrame(oldchain), newchain, icv, ev)){
                    icq.add(theSuccessor, (ArrayList) newchain.clone());
                }
            }
            else{// "not a ret"
            
                // Normal successors. Add them to the queue of successors.
                InstructionContext[] succs = u.getSuccessors();
                for (int s=0; s<succs.length; s++){
                    InstructionContext v = succs[s];
                    if (v.execute(u.getOutFrame(oldchain), newchain, icv, ev)){
                        icq.add(v, (ArrayList) newchain.clone());
                    }
                }
            }// end "not a ret"

            // Exception Handlers. Add them to the queue of successors.
            // [subroutines are never protected; mandated by JustIce]
            ExceptionHandler[] exc_hds = u.getExceptionHandlers();
            for (int s=0; s<exc_hds.length; s++){
                InstructionContext v = cfg.contextOf(exc_hds[s].getHandlerStart());
                // TODO: the "oldchain" and "newchain" is used to determine the subroutine
                // we're in (by searching for the last JSR) by the InstructionContext
                // implementation. Therefore, we should not use this chain mechanism
                // when dealing with exception handlers.
                // Example: a JSR with an exception handler as its successor does not
                // mean we're in a subroutine if we go to the exception handler.
                // We should address this problem later; by now we simply "cut" the chain
                // by using an empty chain for the exception handlers.
                //if (v.execute(new Frame(u.getOutFrame(oldchain).getLocals(), new OperandStack (u.getOutFrame().getStack().maxStack(), (exc_hds[s].getExceptionType()==null? Type.THROWABLE : exc_hds[s].getExceptionType())) ), newchain), icv, ev){
                    //icq.add(v, (ArrayList) newchain.clone());
                if (v.execute(new Frame(u.getOutFrame(oldchain).getLocals(), new OperandStack (u.getOutFrame(oldchain).getStack().maxStack(), (exc_hds[s].getExceptionType()==null? Type.THROWABLE : exc_hds[s].getExceptionType())) ), new ArrayList(), icv, ev)){
                    icq.add(v, new ArrayList());
                }
            }

        }// while (!icq.isEmpty()) END
        
        InstructionHandle ih = start.getInstruction();
        do{
            if ((ih.getInstruction() instanceof ReturnInstruction) && (!(cfg.isDead(ih)))) {
                InstructionContext ic = cfg.contextOf(ih);
                Frame f = ic.getOutFrame(new ArrayList()); // TODO: This is buggy, we check only the top-level return instructions this way. Maybe some maniac returns from a method when in a subroutine?
                LocalVariables lvs = f.getLocals();
                for (int i=0; i<lvs.maxLocals(); i++){
                    if (lvs.get(i) instanceof UninitializedObjectType){
                        this.addMessage("Warning: ReturnInstruction '"+ic+"' may leave method with an uninitialized object in the local variables array '"+lvs+"'.");
                    }
                }
                OperandStack os = f.getStack();
                for (int i=0; i<os.size(); i++){
                    if (os.peek(i) instanceof UninitializedObjectType){
                        this.addMessage("Warning: ReturnInstruction '"+ic+"' may leave method with an uninitialized object on the operand stack '"+os+"'.");
                    }
                }
                //see JVM $4.8.2
                //TODO implement all based on stack 
                Type returnedType = null;
                if( ih.getPrev().getInstruction() instanceof InvokeInstruction )
                {
                    returnedType = ((InvokeInstruction)ih.getPrev().getInstruction()).getType(m.getConstantPool());
                }
                if( ih.getPrev().getInstruction() instanceof LoadInstruction )
                {
                    int index = ((LoadInstruction)ih.getPrev().getInstruction()).getIndex();
                    returnedType = lvs.get(index);
                }
                if( ih.getPrev().getInstruction() instanceof GETFIELD )
                {
                    returnedType = ((GETFIELD)ih.getPrev().getInstruction()).getType(m.getConstantPool());
                }
                if( returnedType != null )
                {
                    if( returnedType instanceof ObjectType )
                    {
                        try
                        {
                            if( !((ObjectType)returnedType).isAssignmentCompatibleWith(m.getReturnType()) )
                            {
                                throw new StructuralCodeConstraintException("Returned type "+returnedType+" does not match Method's return type "+m.getReturnType());
                            }
                        }
                        catch (ClassNotFoundException e)
                        {
                            //dont know what do do now, so raise RuntimeException
                            throw new RuntimeException(e);
                        }
                    }
                    else if( !returnedType.equals(m.getReturnType()) )
                    {
                        throw new StructuralCodeConstraintException("Returned type "+returnedType+" does not match Method's return type "+m.getReturnType());
                    }
                }
            }
        }while ((ih = ih.getNext()) != null);
        
    }

    /**
     * Pass 3b implements the data flow analysis as described in the Java Virtual
     * Machine Specification, Second Edition.
     * Later versions will use LocalVariablesInfo objects to verify if the
     * verifier-inferred types and the class file's debug information (LocalVariables
     * attributes) match [TODO].
     *
     * @see org.apache.bcel.verifier.statics.LocalVariablesInfo
     * @see org.apache.bcel.verifier.statics.Pass2Verifier#getLocalVariablesInfo(int)
     */
    public VerificationResult do_verify(){
        /*if (! myOwner.doPass3a(method_no).equals(VerificationResult.VR_OK)){
            return VerificationResult.VR_NOTYET;
        }

        // Pass 3a ran before, so it's safe to assume the JavaClass object is
        // in the BCEL repository.
        JavaClass jc;
        try {
            jc = Repository.lookupClass(myOwner.getClassName());
        } catch (ClassNotFoundException e) {
            // FIXME: maybe not the best way to handle this
            throw new AssertionViolatedException("Missing class: " + e.toString());
        }*/

        ConstantPoolGen constantPoolGen = new ConstantPoolGen(jc.getConstantPool());
        // Init Visitors
        InstConstraintVisitor icv = new InstConstraintVisitor();
        icv.setConstantPoolGen(constantPoolGen);
        
        ExecutionVisitor ev = new ExecutionVisitor();
        ev.setConstantPoolGen(constantPoolGen);
        
        Method[] methods = jc.getMethods(); // Method no "method_no" exists, we ran Pass3a before on it!

        try{

            MethodGen mg = new MethodGen(methods[method_no], jc.getClassName(), constantPoolGen);

            icv.setMethodGen(mg);
                
            ////////////// DFA BEGINS HERE ////////////////
            if (! (mg.isAbstract() || mg.isNative()) ){ // IF mg HAS CODE (See pass 2)
                
                ControlFlowGraph cfg = new ControlFlowGraph(mg);

                // Build the initial frame situation for this method.
                Frame f = new Frame(mg.getMaxLocals(),mg.getMaxStack());
                if ( !mg.isStatic() ){
                    if (mg.getName().equals(Constants.CONSTRUCTOR_NAME)){
                        Frame._this = new UninitializedObjectType(new ObjectType(jc.getClassName()));
                        f.getLocals().set(0, Frame._this);
                    }
                    else{
                        Frame._this = null;
                        f.getLocals().set(0, new ObjectType(jc.getClassName()));
                    }
                }
                Type[] argtypes = mg.getArgumentTypes();
                int twoslotoffset = 0;
                for (int j=0; j<argtypes.length; j++){
                    if (argtypes[j] == Type.SHORT || argtypes[j] == Type.BYTE || argtypes[j] == Type.CHAR || argtypes[j] == Type.BOOLEAN){
                        argtypes[j] = Type.INT;
                    }
                    f.getLocals().set(twoslotoffset + j + (mg.isStatic()?0:1), argtypes[j]);
                    if (argtypes[j].getSize() == 2){
                        twoslotoffset++;
                        f.getLocals().set(twoslotoffset + j + (mg.isStatic()?0:1), Type.UNKNOWN);
                    }
                }
                circulationPump(mg,cfg, cfg.contextOf(mg.getInstructionList().getStart()), f, icv, ev);
            }
        }
        catch (VerifierConstraintViolatedException ce){
            ce.extendMessage("Constraint violated in method '"+methods[method_no]+"':\n","");
            return new VerificationResult(VerificationResult.VERIFIED_REJECTED, ce.getMessage());
        }
        catch (RuntimeException re){
            // These are internal errors

            StringWriter sw = new StringWriter();
            PrintWriter pw = new PrintWriter(sw);
            re.printStackTrace(pw);

            throw new AssertionViolatedException("Some RuntimeException occured while verify()ing class '"+jc.getClassName()+"', method '"+methods[method_no]+"'. Original RuntimeException's stack trace:\n---\n"+sw+"---\n");
        }
        return VerificationResult.VR_OK;
    }

    /** Returns the method number as supplied when instantiating. */
    public int getMethodNo(){
        return method_no;
    }
}