/*
    * 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
    *
    *      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.util.ArrayList;
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import org.apache.bcel.generic.ATHROW;
  import org.apache.bcel.generic.BranchInstruction;
  import org.apache.bcel.generic.GotoInstruction;
  import org.apache.bcel.generic.Instruction;
  import org.apache.bcel.generic.InstructionHandle;
  import org.apache.bcel.generic.JsrInstruction;
  import org.apache.bcel.generic.MethodGen;
  import org.apache.bcel.generic.RET;
  import org.apache.bcel.generic.ReturnInstruction;
  import org.apache.bcel.generic.Select;
  import org.apache.bcel.verifier.exc.AssertionViolatedException;
  import org.apache.bcel.verifier.exc.StructuralCodeConstraintException;
  
  /**
   * This class represents a control flow graph of a method.
   */
  public class ControlFlowGraph {
  
      /**
       * Objects of this class represent a node in a ControlFlowGraph. These nodes are instructions, not basic blocks.
       */
      private final class InstructionContextImpl implements InstructionContext {
  
          /**
           * The TAG field is here for external temporary flagging, such as graph coloring.
           *
           * @see #getTag()
           * @see #setTag(int)
           */
          private int TAG;
  
          /**
           * The InstructionHandle this InstructionContext is wrapped around.
           */
          private final InstructionHandle instruction;
  
          /**
           * The 'incoming' execution Frames.
           */
          private final Map<InstructionContext, Frame> inFrames; // key: the last-executed JSR
  
          /**
           * The 'outgoing' execution Frames.
           */
          private final Map<InstructionContext, Frame> outFrames; // key: the last-executed JSR
  
          /**
           * The 'execution predecessors' - a list of type InstructionContext of those instances that have been execute()d before
           * in that order.
           */
          private List<InstructionContext> executionPredecessors; // Type: InstructionContext
  
          /**
           * Creates an InstructionHandleImpl object from an InstructionHandle. Creation of one per InstructionHandle suffices.
           * Don't create more.
           */
          public InstructionContextImpl(final InstructionHandle inst) {
              if (inst == null) {
                  throw new AssertionViolatedException("Cannot instantiate InstructionContextImpl from NULL.");
              }
  
              instruction = inst;
              inFrames = new HashMap<>();
              outFrames = new HashMap<>();
          }
  
          /**
           * A utility method that calculates the successors of a given InstructionHandle That means, a RET does have successors
           * as defined here. A JsrInstruction has its target as its successor (opposed to its physical successor) as defined
           * here.
           */
  // TODO: implement caching!
          private InstructionHandle[] _getSuccessors() {
              final InstructionHandle[] single = new InstructionHandle[1];
  
             final Instruction inst = getInstruction().getInstruction();
 
             if (inst instanceof RET) {
                 final Subroutine s = subroutines.subroutineOf(getInstruction());
                 if (s == null) { // return empty;
                     // RET in dead code. "empty" would be the correct answer, but we know something about the surrounding project...
                     throw new AssertionViolatedException("Asking for successors of a RET in dead code?!");
                 }
 
 //TODO: remove. Only JustIce must not use it, but foreign users of the ControlFlowGraph
 //      will want it. Thanks Johannes Wust.
 //throw new AssertionViolatedException("DID YOU REALLY WANT TO ASK FOR RET'S SUCCS?");
 
                 final InstructionHandle[] jsrs = s.getEnteringJsrInstructions();
                 final InstructionHandle[] ret = new InstructionHandle[jsrs.length];
                 Arrays.setAll(ret, i -> jsrs[i].getNext());
                 return ret;
             }
 
             // Terminates method normally.
             // Terminates method abnormally, because JustIce mandates
             // subroutines not to be protected by exception handlers.
             if (inst instanceof ReturnInstruction || inst instanceof ATHROW) {
                 return InstructionHandle.EMPTY_ARRAY;
             }
 
             // See method comment.
             if (inst instanceof JsrInstruction) {
                 single[0] = ((JsrInstruction) inst).getTarget();
                 return single;
             }
 
             if (inst instanceof GotoInstruction) {
                 single[0] = ((GotoInstruction) inst).getTarget();
                 return single;
             }
 
             if (inst instanceof BranchInstruction) {
                 if (inst instanceof Select) {
                     // BCEL's getTargets() returns only the non-default targets,
                     // thanks to Eli Tilevich for reporting.
                     final InstructionHandle[] matchTargets = ((Select) inst).getTargets();
                     final InstructionHandle[] ret = new InstructionHandle[matchTargets.length + 1];
                     ret[0] = ((Select) inst).getTarget();
                     System.arraycopy(matchTargets, 0, ret, 1, matchTargets.length);
                     return ret;
                 }
                 final InstructionHandle[] pair = new InstructionHandle[2];
                 pair[0] = getInstruction().getNext();
                 pair[1] = ((BranchInstruction) inst).getTarget();
                 return pair;
             }
 
             // default case: Fall through.
             single[0] = getInstruction().getNext();
             return single;
         }
 
         /**
          * "Merges in" (vmspec2, page 146) the "incoming" frame situation; executes the instructions symbolically and therefore
          * calculates the "outgoing" frame situation. Returns: True iff the "incoming" frame situation changed after merging
          * with "inFrame". The execPreds ArrayList must contain the InstructionContext objects executed so far in the correct
          * order. This is just one execution path [out of many]. This is needed to correctly "merge" in the special case of a
          * RET's successor. <B>The InstConstraintVisitor and ExecutionVisitor instances must be set up correctly.</B>
          *
          * @return true - if and only if the "outgoing" frame situation changed from the one before execute()ing.
          */
         @Override
         public boolean execute(final Frame inFrame, final ArrayList<InstructionContext> execPreds, final InstConstraintVisitor icv, final ExecutionVisitor ev) {
 
             @SuppressWarnings("unchecked") // OK because execPreds is compatible type
             final List<InstructionContext> clone = (List<InstructionContext>) execPreds.clone();
             executionPredecessors = clone;
 
             // sanity check
             if (lastExecutionJSR() == null && subroutines.subroutineOf(getInstruction()) != subroutines.getTopLevel()
                 || lastExecutionJSR() != null && subroutines.subroutineOf(getInstruction()) == subroutines.getTopLevel()) {
                 throw new AssertionViolatedException("Huh?! Am I '" + this + "' part of a subroutine or not?");
             }
 
             Frame inF = inFrames.get(lastExecutionJSR());
             if (inF == null) { // no incoming frame was set, so set it.
                 inFrames.put(lastExecutionJSR(), inFrame);
                 inF = inFrame;
             } else if (inF.equals(inFrame) || !mergeInFrames(inFrame)) { // if there was an "old" inFrame
                 return false;
             }
 
             // Now we're sure the inFrame has changed!
 
             // new inFrame is already merged in, see above.
             final Frame workingFrame = inF.getClone();
 
             try {
                 // This verifies the InstructionConstraint for the current
                 // instruction, but does not modify the workingFrame object.
 //InstConstraintVisitor icv = InstConstraintVisitor.getInstance(VerifierFactory.getVerifier(method_gen.getClassName()));
                 icv.setFrame(workingFrame);
                 getInstruction().accept(icv);
             } catch (final StructuralCodeConstraintException ce) {
                 ce.extendMessage("", "\nInstructionHandle: " + getInstruction() + "\n");
                 ce.extendMessage("", "\nExecution Frame:\n" + workingFrame);
                 extendMessageWithFlow(ce);
                 throw ce;
             }
 
             // This executes the Instruction.
             // Therefore the workingFrame object is modified.
 //ExecutionVisitor ev = ExecutionVisitor.getInstance(VerifierFactory.getVerifier(method_gen.getClassName()));
             ev.setFrame(workingFrame);
             getInstruction().accept(ev);
             // getInstruction().accept(ExecutionVisitor.withFrame(workingFrame));
             outFrames.put(lastExecutionJSR(), workingFrame);
 
             return true; // new inFrame was different from old inFrame so merging them
                          // yielded a different this.inFrame.
         }
 
         /**
          * Extends the StructuralCodeConstraintException ("e") object with an at-the-end-extended message. This extended message
          * will then reflect the execution flow needed to get to the constraint violation that triggered the throwing of the "e"
          * object.
          */
         private void extendMessageWithFlow(final StructuralCodeConstraintException e) {
             final String s = "Execution flow:\n";
             e.extendMessage("", s + getExecutionChain());
         }
 
         /**
          * Returns the exception handlers of this instruction.
          */
         @Override
         public ExceptionHandler[] getExceptionHandlers() {
             return exceptionhandlers.getExceptionHandlers(getInstruction());
         }
 
         /**
          * Returns the control flow execution chain. This is built while execute(Frame, ArrayList)-ing the code represented by
          * the surrounding ControlFlowGraph.
          */
         private String getExecutionChain() {
             final StringBuilder s = new StringBuilder(this.toString());
             for (int i = executionPredecessors.size() - 1; i >= 0; i--) {
                 s.insert(0, executionPredecessors.get(i) + "\n");
             }
             return s.toString();
         }
 
         @Override
         public Frame getInFrame() {
             Frame org;
 
             final InstructionContext jsr = lastExecutionJSR();
 
             org = inFrames.get(jsr);
 
             if (org == null) {
                 throw new AssertionViolatedException("inFrame not set! This:\n" + this + "\nInFrames: '" + inFrames + "'.");
             }
             return org.getClone();
         }
 
         @Override
         public InstructionHandle getInstruction() {
             return instruction;
         }
 
         /**
          * Returns a clone of the "outgoing" frame situation with respect to the given ExecutionChain.
          */
         @Override
         public Frame getOutFrame(final ArrayList<InstructionContext> execChain) {
             executionPredecessors = execChain;
 
             Frame org;
 
             final InstructionContext jsr = lastExecutionJSR();
 
             org = outFrames.get(jsr);
 
             if (org == null) {
                 throw new AssertionViolatedException(
                     "outFrame not set! This:\n" + this + "\nExecutionChain: " + getExecutionChain() + "\nOutFrames: '" + outFrames + "'.");
             }
             return org.getClone();
         }
 
         @Override
         public InstructionContext[] getSuccessors() {
             return contextsOf(_getSuccessors());
         }
 
         @Override
         public int getTag() {
             return TAG;
         }
 
         /**
          * Returns the InstructionContextImpl with an JSR/JSR_W that was last in the ExecutionChain, without a corresponding
          * RET, i.e. we were called by this one. Returns null if we were called from the top level.
          */
         private InstructionContextImpl lastExecutionJSR() {
 
             final int size = executionPredecessors.size();
             int retcount = 0;
 
             for (int i = size - 1; i >= 0; i--) {
                 final InstructionContextImpl current = (InstructionContextImpl) executionPredecessors.get(i);
                 final Instruction currentlast = current.getInstruction().getInstruction();
                 if (currentlast instanceof RET) {
                     retcount++;
                 }
                 if (currentlast instanceof JsrInstruction) {
                     retcount--;
                     if (retcount == -1) {
                         return current;
                     }
                 }
             }
             return null;
         }
 
         /**
          * Does the actual merging (vmspec2, page 146). Returns true IFF this.inFrame was changed in course of merging with
          * inFrame.
          */
         private boolean mergeInFrames(final Frame inFrame) {
             // TODO: Can be performance-improved.
             final Frame inF = inFrames.get(lastExecutionJSR());
             final OperandStack oldstack = inF.getStack().getClone();
             final LocalVariables oldlocals = inF.getLocals().getClone();
             try {
                 inF.getStack().merge(inFrame.getStack());
                 inF.getLocals().merge(inFrame.getLocals());
             } catch (final StructuralCodeConstraintException sce) {
                 extendMessageWithFlow(sce);
                 throw sce;
             }
             return !(oldstack.equals(inF.getStack()) && oldlocals.equals(inF.getLocals()));
         }
 
         /* Satisfies InstructionContext.setTag(int). */
         @Override
         public void setTag(final int tag) { // part of InstructionContext interface
             TAG = tag;
         }
 
         /**
          * Returns a simple String representation of this InstructionContext.
          */
         @Override
         public String toString() {
             // TODO: Put information in the brackets, e.g.
             // Is this an ExceptionHandler? Is this a RET? Is this the start of
             // a subroutine?
             return getInstruction().toString(false) + "\t[InstructionContext]";
         }
 
     } // End Inner InstructionContextImpl Class.
 
     /// ** The MethodGen object we're working on. */
     // private final MethodGen method_gen;
 
     /** The Subroutines object for the method whose control flow is represented by this ControlFlowGraph. */
     private final Subroutines subroutines;
 
     /** The ExceptionHandlers object for the method whose control flow is represented by this ControlFlowGraph. */
     private final ExceptionHandlers exceptionhandlers;
 
     /** All InstructionContext instances of this ControlFlowGraph. */
     private final Map<InstructionHandle, InstructionContext> instructionContexts = new HashMap<>();
 
     /**
      * A Control Flow Graph; with additional JustIce checks
      *
      * @param methodGen the method generator instance
      */
     public ControlFlowGraph(final MethodGen methodGen) {
         this(methodGen, true);
     }
 
     /**
      * A Control Flow Graph.
      *
      * @param methodGen the method generator instance
      * @param enableJustIceCheck if true, additional JustIce checks are performed
      * @since 6.0
      */
     public ControlFlowGraph(final MethodGen methodGen, final boolean enableJustIceCheck) {
         subroutines = new Subroutines(methodGen, enableJustIceCheck);
         exceptionhandlers = new ExceptionHandlers(methodGen);
 
         final InstructionHandle[] instructionhandles = methodGen.getInstructionList().getInstructionHandles();
         for (final InstructionHandle instructionhandle : instructionhandles) {
             instructionContexts.put(instructionhandle, new InstructionContextImpl(instructionhandle));
         }
 
         // this.method_gen = method_gen;
     }
 
     /**
      * Returns the InstructionContext of a given instruction.
      */
     public InstructionContext contextOf(final InstructionHandle inst) {
         final InstructionContext ic = instructionContexts.get(inst);
         if (ic == null) {
             throw new AssertionViolatedException("InstructionContext requested for an InstructionHandle that's not known!");
         }
         return ic;
     }
 
     /**
      * Returns the InstructionContext[] of a given InstructionHandle[], in a naturally ordered manner.
      */
     public InstructionContext[] contextsOf(final InstructionHandle[] insts) {
         final InstructionContext[] ret = new InstructionContext[insts.length];
         Arrays.setAll(ret, i -> contextOf(insts[i]));
         return ret;
     }
 
     /**
      * Returns an InstructionContext[] with all the InstructionContext instances for the method whose control flow is
      * represented by this ControlFlowGraph <B>(NOT ORDERED!)</B>.
      */
     public InstructionContext[] getInstructionContexts() {
         final InstructionContext[] ret = new InstructionContext[instructionContexts.size()];
         return instructionContexts.values().toArray(ret);
     }
 
     /**
      * Returns true, if and only if the said instruction is not reachable; that means, if it is not part of this
      * ControlFlowGraph.
      */
     public boolean isDead(final InstructionHandle i) {
         return subroutines.subroutineOf(i) == null;
     }
 }