/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you 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
    *
   *   https://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.Const;
  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.InstructionHandle;
  import org.apache.bcel.generic.JsrInstruction;
  import org.apache.bcel.generic.MethodGen;
  import org.apache.bcel.generic.ObjectType;
  import org.apache.bcel.generic.RET;
  import org.apache.bcel.generic.ReferenceType;
  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.
   * <p>
   * The system property {@code org.apache.bcel.verifier.maxFrameSlots} bounds the size of the pass 3b data flow analysis, measured in frame slots:
   * {@code (max_locals + max_stack) * instruction count} of the method under verification. Methods above the bound are rejected instead of analyzed. The default
   * is 100,000,000; a value of zero or less disables the bound.
   * </p>
   *
   * @see #do_verify()
   */
  public final class Pass3bVerifier extends PassVerifier {
      /*
       * TODO: Throughout pass 3b, upper halves of LONG and DOUBLE are represented by Type.UNKNOWN. This should be changed in
       * favor 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 --- for example 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 {
          // The following two fields together represent the queue.
  
          /** The first elements from pairs in the queue. */
          private final List<InstructionContext> ics = new Vector<>();
  
          /** The second elements from pairs in the queue. */
          private final List<ArrayList<InstructionContext>> ecs = new Vector<>();
  
          /**
           * Adds an (InstructionContext, ExecutionChain) pair to this queue.
           *
           * @param ic The InstructionContext.
           * @param executionChain The ExecutionChain.
           */
          public void add(final InstructionContext ic, final ArrayList<InstructionContext> executionChain) {
              ics.add(ic);
              ecs.add(executionChain);
          }
  
          /**
           * Gets a specific ExecutionChain from the queue.
           *
           * @param i The index of the item to be fetched.
           * @return The indicated ExecutionChain.
           */
         public ArrayList<InstructionContext> getEC(final int i) {
             return ecs.get(i);
         }
 
         /**
          * Gets a specific InstructionContext from the queue.
          *
          * @param i The index of the item to be fetched.
          * @return The indicated InstructionContext.
          */
         public InstructionContext getIC(final int i) {
             return ics.get(i);
         }
 
         /**
          * Tests if InstructionContext queue is empty.
          *
          * @return true if the InstructionContext queue is empty.
          */
         public boolean isEmpty() {
             return ics.isEmpty();
         }
 
         /**
          * Removes a specific (InstructionContext, ExecutionChain) pair from their respective queues.
          *
          * @param i The index of the items to be removed.
          */
         public void remove(final int i) {
             ics.remove(i);
             ecs.remove(i);
         }
 
         /**
          * Gets the size of the InstructionContext queue.
          *
          * @return The size of the InstructionQueue.
          */
         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;
 
     /**
      * The name of the system property bounding the size of the pass 3b data flow analysis, measured in frame slots:
      * {@code (max_locals + max_stack) * instruction count} of the method under verification. Methods above the bound
      * are rejected instead of analyzed. The default is 100,000,000; a value of zero or less disables the bound.
      */
     private static final String MAX_FRAME_SLOTS_PROPERTY = "org.apache.bcel.verifier.maxFrameSlots";
 
     private static final long MAX_FRAME_SLOTS = Long.getLong(MAX_FRAME_SLOTS_PROPERTY, 100_000_000L).longValue();
 
     /** The Verifier that created this. */
     private final Verifier myOwner;
 
     /** The method number to verify. */
     private final int methodNo;
 
     /**
      * This class should only be instantiated by a Verifier.
      *
      * @param myOwner The verifier that owns this Pass3bVerifier.
      * @param methodNo The method number.
      * @see org.apache.bcel.verifier.Verifier
      */
     public Pass3bVerifier(final Verifier myOwner, final int methodNo) {
         this.myOwner = myOwner;
         this.methodNo = methodNo;
     }
 
     /**
      * 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(final MethodGen m, final ControlFlowGraph cfg, final InstructionContext start, final Frame vanillaFrame,
         final InstConstraintVisitor icv, final ExecutionVisitor ev) {
         final Random random = new Random();
         final 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()) {
             final InstructionContext u;
             final ArrayList<InstructionContext> ec;
             if (!DEBUG) {
                 final 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);
             }
 
             @SuppressWarnings("unchecked") // ec is of type ArrayList<InstructionContext>
             final ArrayList<InstructionContext> oldchain = (ArrayList<InstructionContext>) ec.clone();
             @SuppressWarnings("unchecked") // ec is of type ArrayList<InstructionContext>
             final ArrayList<InstructionContext> newchain = (ArrayList<InstructionContext>) 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.
                 final RET ret = (RET) u.getInstruction().getInstruction();
                 final ReturnaddressType t = (ReturnaddressType) u.getOutFrame(oldchain).getLocals().get(ret.getIndex());
                 final InstructionContext theSuccessor = cfg.contextOf(t.getTarget());
 
                 // Sanity check
                 InstructionContext lastJSR = null;
                 int skipJsr = 0;
                 for (int ss = oldchain.size() - 1; ss >= 0; ss--) {
                     if (skipJsr < 0) {
                         throw new AssertionViolatedException("More RET than JSR in execution chain?.");
                     }
 //System.err.println("+"+oldchain.get(ss));
                     if (oldchain.get(ss).getInstruction().getInstruction() instanceof JsrInstruction) {
                         if (skipJsr == 0) {
                             lastJSR = oldchain.get(ss);
                             break;
                         }
                         skipJsr--;
                     }
                     if (oldchain.get(ss).getInstruction().getInstruction() instanceof RET) {
                         skipJsr++;
                     }
                 }
                 if (lastJSR == null) {
                     throw new AssertionViolatedException("RET without a JSR before in ExecutionChain?! EC: '" + oldchain + "'.");
                 }
                 final 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)) {
                     @SuppressWarnings("unchecked") // newchain is already of type ArrayList<InstructionContext>
                     final ArrayList<InstructionContext> newchainClone = (ArrayList<InstructionContext>) newchain.clone();
                     icq.add(theSuccessor, newchainClone);
                 }
             } else { // "not a ret"
 
                 // Normal successors. Add them to the queue of successors.
                 final InstructionContext[] succs = u.getSuccessors();
                 for (final InstructionContext v : succs) {
                     if (v.execute(u.getOutFrame(oldchain), newchain, icv, ev)) {
                         @SuppressWarnings("unchecked") // newchain is already of type ArrayList<InstructionContext>
                         final ArrayList<InstructionContext> newchainClone = (ArrayList<InstructionContext>) newchain.clone();
                         icq.add(v, newchainClone);
                     }
                 }
             } // end "not a ret"
 
             // Exception Handlers. Add them to the queue of successors.
             // [subroutines are never protected; mandated by JustIce]
             final ExceptionHandler[] excHds = u.getExceptionHandlers();
             for (final ExceptionHandler excHd : excHds) {
                 final InstructionContext v = cfg.contextOf(excHd.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(),
                     excHd.getExceptionType() == null ? Type.THROWABLE : excHd.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)) {
                 final InstructionContext ic = cfg.contextOf(ih);
                 // 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?
                 final Frame f = ic.getOutFrame(new ArrayList<>());
                 final LocalVariables lvs = f.getLocals();
                 for (int i = 0; i < lvs.maxLocals(); i++) {
                     if (lvs.get(i) instanceof UninitializedObjectType) {
                         addMessage("Warning: ReturnInstruction '" + ic + "' may leave method with an uninitialized object in the local variables array '"
                             + lvs + "'.");
                     }
                 }
                 final OperandStack os = f.getStack();
                 for (int i = 0; i < os.size(); i++) {
                     if (os.peek(i) instanceof UninitializedObjectType) {
                         addMessage(
                             "Warning: ReturnInstruction '" + ic + "' may leave method with an uninitialized object on the operand stack '" + os + "'.");
                     }
                 }
                 // see JVM $4.8.2
                 Type returnedType = null;
                 final OperandStack inStack = ic.getInFrame().getStack();
                 if (inStack.size() >= 1) {
                     returnedType = inStack.peek();
                 } else {
                     returnedType = Type.VOID;
                 }
 
                 if (returnedType != null) {
                     if (returnedType instanceof ReferenceType) {
                         try {
                             if (!((ReferenceType) returnedType).isCastableTo(m.getReturnType())) {
                                 invalidReturnTypeError(returnedType, m);
                             }
                         } catch (final ClassNotFoundException e) {
                             // Don't know what to do now, so raise RuntimeException
                             throw new IllegalArgumentException(e);
                         }
                     } else if (!returnedType.equals(m.getReturnType().normalizeForStackOrLocal())) {
                         invalidReturnTypeError(returnedType, m);
                     }
                 }
             }
         } 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)
      */
     @Override
     public VerificationResult do_verify() {
         if (!myOwner.doPass3a(methodNo).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.
         final JavaClass jc;
         try {
             jc = Repository.lookupClass(myOwner.getClassName());
         } catch (final ClassNotFoundException e) {
             // FIXME: maybe not the best way to handle this
             throw new AssertionViolatedException("Missing class: " + e, e);
         }
 
         final ConstantPoolGen constantPoolGen = new ConstantPoolGen(jc.getConstantPool());
         // Init Visitors
         final InstConstraintVisitor icv = new InstConstraintVisitor();
         icv.setConstantPoolGen(constantPoolGen);
 
         final ExecutionVisitor ev = new ExecutionVisitor();
         ev.setConstantPoolGen(constantPoolGen);
 
         final Method[] methods = jc.getMethods(); // Method no "methodNo" exists, we ran Pass3a before on it!
 
         try {
 
             final MethodGen mg = new MethodGen(methods[methodNo], myOwner.getClassName(), constantPoolGen);
 
             icv.setMethodGen(mg);
 
             ////////////// DFA BEGINS HERE ////////////////
             if (!(mg.isAbstract() || mg.isNative())) { // IF mg HAS CODE (See pass 2)
 
                 // Reject pathological resource claims before running the data flow analysis: an 'in' and an 'out'
                 // Frame sized max_locals + max_stack is stored for every reachable instruction (and per calling
                 // subroutine), so a small crafted method declaring max_locals = max_stack = 65535 over tens of
                 // thousands of instructions would force tens of gigabytes of allocations before any constraint
                 // could fail. The limit can be changed (or disabled with a value <= 0) via the
                 // MAX_FRAME_SLOTS_PROPERTY system property.
                 final int instructionCount = mg.getInstructionList().getLength();
                 final long frameSlots = ((long) mg.getMaxLocals() + mg.getMaxStack()) * instructionCount;
                 if (MAX_FRAME_SLOTS > 0 && frameSlots > MAX_FRAME_SLOTS) {
                     throw new StructuralCodeConstraintException("Data flow analysis of this method would require more than " + MAX_FRAME_SLOTS
                         + " frame slots: max_locals '" + mg.getMaxLocals() + "' plus max_stack '" + mg.getMaxStack() + "' over '" + instructionCount
                         + "' instructions. Adjust the '" + MAX_FRAME_SLOTS_PROPERTY + "' system property to change this limit.");
                 }
 
                 final ControlFlowGraph cfg = new ControlFlowGraph(mg);
 
                 // Build the initial frame situation for this method.
                 final Frame f = new Frame(mg.getMaxLocals(), mg.getMaxStack());
                 if (!mg.isStatic()) {
                     if (mg.getName().equals(Const.CONSTRUCTOR_NAME)) {
                         Frame.setThis(new UninitializedObjectType(ObjectType.getInstance(jc.getClassName())));
                         f.getLocals().set(0, Frame.getThis());
                     } else {
                         Frame.setThis(null);
                         f.getLocals().set(0, ObjectType.getInstance(jc.getClassName()));
                     }
                 }
                 final 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 (final VerifierConstraintViolatedException ce) {
             ce.extendMessage("Constraint violated in method '" + methods[methodNo] + "':\n", "");
             return new VerificationResult(VerificationResult.VERIFIED_REJECTED, ce.getMessage());
         } catch (final RuntimeException re) {
             // These are internal errors
 
             final StringWriter sw = new StringWriter();
             final PrintWriter pw = new PrintWriter(sw);
             re.printStackTrace(pw);
 
             throw new AssertionViolatedException("Some RuntimeException occurred while verify()ing class '" + jc.getClassName() + "', method '"
                 + methods[methodNo] + "'. Original RuntimeException's stack trace:\n---\n" + sw + "---\n", re);
         }
         return VerificationResult.VR_OK;
     }
 
     /**
      * Returns the method number as supplied when instantiating.
      *
      * @return The method number.
      */
     public int getMethodNo() {
         return methodNo;
     }
 
     /**
      * Throws an exception indicating the returned type is not compatible with the return type of the given method.
      *
      * @param returnedType The type of the returned expression.
      * @param m The method we are processing.
      * @throws StructuralCodeConstraintException Always thrown.
      * @since 6.0
      */
     public void invalidReturnTypeError(final Type returnedType, final MethodGen m) {
         throw new StructuralCodeConstraintException("Returned type " + returnedType + " does not match Method's return type " + m.getReturnType());
     }
 }