/*
    * 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.commons.javaflow.bytecode.transformation.bcel.analyser;
  
  import org.apache.bcel.generic.ASTORE;
  import org.apache.bcel.generic.ATHROW;
  import org.apache.bcel.generic.BranchInstruction;
  import org.apache.bcel.generic.CodeExceptionGen;
  import org.apache.bcel.generic.GotoInstruction;
  import org.apache.bcel.generic.IndexedInstruction;
  import org.apache.bcel.generic.Instruction;
  import org.apache.bcel.generic.InstructionHandle;
  import org.apache.bcel.generic.JsrInstruction;
  import org.apache.bcel.generic.LocalVariableInstruction;
  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;
  
  import java.util.ArrayList;
  import java.util.HashSet;
  import java.util.Hashtable;
  import java.util.Iterator;
  import java.util.Set;
  
  /**
   * Instances of this class contain information about the subroutines
   * found in a code array of a method.
   * This implementation considers the top-level (the instructions
   * reachable without a JSR or JSR_W starting off from the first
   * instruction in a code array of a method) being a special subroutine;
   * see getTopLevel() for that.
   * Please note that the definition of subroutines in the Java Virtual
   * Machine Specification, Second Edition is somewhat incomplete.
   * Therefore, JustIce uses an own, more rigid notion.
   * Basically, a subroutine is a piece of code that starts at the target
   * of a JSR of JSR_W instruction and ends at a corresponding RET
   * instruction. Note also that the control flow of a subroutine
   * may be complex and non-linear; and that subroutines may be nested.
   *
   * WARNING! These classes are a fork of the bcel verifier.
   *
   * @version $Id: Subroutines.java 480487 2006-11-29 08:54:42Z bayard $
   * @author <A HREF="http://www.inf.fu-berlin.de/~ehaase"/>Enver Haase</A>
   * @see #getTopLevel()
   */
  public class Subroutines{
  	/**
  	 * This inner class implements the Subroutine interface.
  	 */
  	private class SubroutineImpl implements Subroutine{
  		/**
  		 * UNSET, a symbol for an uninitialized localVariable
  		 * field. This is used for the "top-level" Subroutine;
  		 * i.e. no subroutine.
  		 */
  		private final int UNSET = -1;
  
  		/**
  		 * The Local Variable slot where the first
  		 * instruction of this subroutine (an ASTORE) stores
  		 * the JsrInstruction's ReturnAddress in and
  		 * the RET of this subroutine operates on.
  		 */
  		private int localVariable = UNSET;
  
  		/** The instructions that belong to this subroutine. */
  		private Set instructions;
  
  		/*
  		 * Refer to the Subroutine interface for documentation.
  		 */
  		public boolean contains(InstructionHandle inst){
  			return instructions.contains(inst);
  		}
  
  		/**
  		 * The JSR or JSR_W instructions that define this
  		 * subroutine by targeting it.
  		 */
  		private HashSet theJSRs = new HashSet();
  
  		/**
 		 * The RET instruction that leaves this subroutine.
 		 */
 		private InstructionHandle theRET;
 
 		/**
 		 * Returns a String representation of this object, merely
 		 * for debugging purposes.
 		 * (Internal) Warning: Verbosity on a problematic subroutine may cause
 		 * stack overflow errors due to recursive subSubs() calls.
 		 * Don't use this, then.
 		 */
 		public String toString(){
 			String ret = "Subroutine: Local variable is '"+localVariable+"', JSRs are '"+theJSRs+"', RET is '"+theRET+"', Instructions: '"+instructions.toString()+"'.";
 
 			ret += " Accessed local variable slots: '";
 			int[] alv = getAccessedLocalsIndices();
 			for (int i=0; i<alv.length; i++){
 				ret += alv[i]+" ";
 			}
 			ret+="'.";
 
 			ret += " Recursively (via subsub...routines) accessed local variable slots: '";
 			alv = getRecursivelyAccessedLocalsIndices();
 			for (int i=0; i<alv.length; i++){
 				ret += alv[i]+" ";
 			}
 			ret+="'.";
 
 			return ret;
 		}
 
 		/**
 		 * Sets the leaving RET instruction. Must be invoked after all instructions are added.
 		 * Must not be invoked for top-level 'subroutine'.
 		 */
 		void setLeavingRET(){
 			if (localVariable == UNSET){
 				throw new AssertionViolatedException("setLeavingRET() called for top-level 'subroutine' or forgot to set local variable first.");
 			}
 			Iterator iter = instructions.iterator();
 			InstructionHandle ret = null;
 			while(iter.hasNext()){
 				InstructionHandle actual = (InstructionHandle) iter.next();
 				if (actual.getInstruction() instanceof RET){
 					if (ret != null){
 						throw new StructuralCodeConstraintException("Subroutine with more then one RET detected: '"+ret+"' and '"+actual+"'.");
 					}
 					else{
 						ret = actual;
 					}
 				}
 			}
 			if (ret == null){
 				throw new StructuralCodeConstraintException("Subroutine without a RET detected.");
 			}
 			if (((RET) ret.getInstruction()).getIndex() != localVariable){
 				throw new StructuralCodeConstraintException("Subroutine uses '"+ret+"' which does not match the correct local variable '"+localVariable+"'.");
 			}
 			theRET = ret;
 		}
 
 		/*
 		 * Refer to the Subroutine interface for documentation.
 		 */
 		public InstructionHandle[] getEnteringJsrInstructions(){
 			if (this == TOPLEVEL) {
 				throw new AssertionViolatedException("getLeavingRET() called on top level pseudo-subroutine.");
 			}
 			InstructionHandle[] jsrs = new InstructionHandle[theJSRs.size()];
 			return (InstructionHandle[]) (theJSRs.toArray(jsrs));
 		}
 
 		/**
 		 * Adds a new JSR or JSR_W that has this subroutine as its target.
 		 */
 		public void addEnteringJsrInstruction(InstructionHandle jsrInst){
 			if ( (jsrInst == null) || (! (jsrInst.getInstruction() instanceof JsrInstruction))){
 				throw new AssertionViolatedException("Expecting JsrInstruction InstructionHandle.");
 			}
 			if (localVariable == UNSET){
 				throw new AssertionViolatedException("Set the localVariable first!");
 			}
 			else{
 				// Something is wrong when an ASTORE is targeted that does not operate on the same local variable than the rest of the
 				// JsrInstruction-targets and the RET.
 				// (We don't know out leader here so we cannot check if we're really targeted!)
 				if (localVariable != ((ASTORE) (((JsrInstruction) jsrInst.getInstruction()).getTarget().getInstruction())).getIndex()){
 					throw new AssertionViolatedException("Setting a wrong JsrInstruction.");
 				}
 			}
 			theJSRs.add(jsrInst);
 		}
 
 		/*
 		 * Refer to the Subroutine interface for documentation.
 		 */
 		public InstructionHandle getLeavingRET(){
 			if (this == TOPLEVEL) {
 				throw new AssertionViolatedException("getLeavingRET() called on top level pseudo-subroutine.");
 			}
 			return theRET;
 		}
 
 		/*
 		 * Refer to the Subroutine interface for documentation.
 		 */
 		public InstructionHandle[] getInstructions(){
 			InstructionHandle[] ret = new InstructionHandle[instructions.size()];
 			return (InstructionHandle[]) instructions.toArray(ret);
 		}
 
 		/* Satisfies Subroutine.getRecursivelyAccessedLocalsIndices(). */
 		public int[] getRecursivelyAccessedLocalsIndices(){
 			HashSet s = new HashSet();
 			int[] lvs = getAccessedLocalsIndices();
 			for (int j=0; j<lvs.length; j++){
 				s.add(new Integer(lvs[j]));
 			}
 			_getRecursivelyAccessedLocalsIndicesHelper(s, this.subSubs());
 			int[] ret = new int[s.size()];
 			Iterator i = s.iterator();
 			int j=-1;
 			while (i.hasNext()){
 				j++;
 				ret[j] = ((Integer) i.next()).intValue();
 			}
 			return ret;
 		}
 
 		/**
 		 * A recursive helper method for getRecursivelyAccessedLocalsIndices().
 		 * @see #getRecursivelyAccessedLocalsIndices()
 		 */
 		private void _getRecursivelyAccessedLocalsIndicesHelper(HashSet s, Subroutine[] subs){
 			for (int i=0; i<subs.length; i++){
 				int[] lvs = subs[i].getAccessedLocalsIndices();
 				for (int j=0; j<lvs.length; j++){
 					s.add(new Integer(lvs[j]));
 				}
 				if(subs[i].subSubs().length != 0){
 					_getRecursivelyAccessedLocalsIndicesHelper(s, subs[i].subSubs());
 				}
 			}
 		}
 
 		/*
 		 * Satisfies Subroutine.getAccessedLocalIndices().
 		 */
 		public int[] getAccessedLocalsIndices(){
 			//TODO: Implement caching.
 			HashSet acc = new HashSet();
 			if (theRET == null && this != TOPLEVEL){
 				throw new AssertionViolatedException("This subroutine object must be built up completely before calculating accessed locals.");
 			}
 			Iterator i = instructions.iterator();
 			while (i.hasNext()){
 				InstructionHandle ih = (InstructionHandle) i.next();
 				// RET is not a LocalVariableInstruction in the current version of BCEL.
 				if (ih.getInstruction() instanceof LocalVariableInstruction || ih.getInstruction() instanceof RET){
 					int idx = ((IndexedInstruction) (ih.getInstruction())).getIndex();
 					acc.add(new Integer(idx));
 					// LONG? DOUBLE?.
 					try{
 						// LocalVariableInstruction instances are typed without the need to look into
 						// the constant pool.
 						if (ih.getInstruction() instanceof LocalVariableInstruction){
 							int s = ((LocalVariableInstruction) ih.getInstruction()).getType(null).getSize();
 							if (s==2) acc.add(new Integer(idx+1));
 						}
 					}
 					catch(RuntimeException re){
 						throw new AssertionViolatedException("Oops. BCEL did not like NULL as a ConstantPoolGen object.");
 					}
 				}
 			}
 
 			int[] ret = new int[acc.size()];
 			i = acc.iterator();
 			int j=-1;
 			while (i.hasNext()){
 				j++;
 				ret[j] = ((Integer) i.next()).intValue();
 			}
 			return ret;
 		}
 
 		/*
 		 * Satisfies Subroutine.subSubs().
 		 */
 		public Subroutine[] subSubs(){
 			HashSet h = new HashSet();
 
 			Iterator i = instructions.iterator();
 			while (i.hasNext()){
 				Instruction inst = ((InstructionHandle) i.next()).getInstruction();
 				if (inst instanceof JsrInstruction){
 					InstructionHandle targ = ((JsrInstruction) inst).getTarget();
 					h.add(getSubroutine(targ));
 				}
 			}
 			Subroutine[] ret = new Subroutine[h.size()];
 			return (Subroutine[]) h.toArray(ret);
 		}
 
 		/*
 		 * Sets the local variable slot the ASTORE that is targeted
 		 * by the JsrInstructions of this subroutine operates on.
 		 * This subroutine's RET operates on that same local variable
 		 * slot, of course.
 		 */
 		void setLocalVariable(int i){
 			if (localVariable != UNSET){
 				throw new AssertionViolatedException("localVariable set twice.");
 			}
 			else{
 				localVariable = i;
 			}
 		}
 
 		/**
 		 * The default constructor.
 		 */
 		public SubroutineImpl(){
 		}
 
         void setInstructions(Set _instructions) {
             this.instructions = _instructions;
         }
     }// end Inner Class SubrouteImpl
 
 	/**
 	 * The Hashtable containing the subroutines found.
 	 * Key: InstructionHandle of the leader of the subroutine.
 	 * Elements: SubroutineImpl objects.
 	 */
 	private Hashtable subroutines = new Hashtable();
 
 	/**
 	 * This is referring to a special subroutine, namely the
 	 * top level. This is not really a subroutine but we use
 	 * it to distinguish between top level instructions and
 	 * unreachable instructions.
 	 */
 	public final Subroutine TOPLEVEL;
 
 	/**
 	 * Constructor.
 	 * @param mg A MethodGen object representing method to
 	 * create the Subroutine objects of.
 	 */
 	public Subroutines(MethodGen mg){
 
 		InstructionHandle[] all = mg.getInstructionList().getInstructionHandles();
 		CodeExceptionGen[] handlers = mg.getExceptionHandlers();
 
 		// Define our "Toplevel" fake subroutine.
 		TOPLEVEL = new SubroutineImpl();
 
 		// Calculate "real" subroutines.
 		HashSet sub_leaders = new HashSet(); // Elements: InstructionHandle
 		for (int i=0; i<all.length; i++){
 			Instruction inst = all[i].getInstruction();
 			if (inst instanceof JsrInstruction){
 				sub_leaders.add(((JsrInstruction) inst).getTarget());
 			}
 		}
 
 		// Build up the database.
 		Iterator iter = sub_leaders.iterator();
 		while (iter.hasNext()){
 			SubroutineImpl sr = new SubroutineImpl();
 			InstructionHandle astore = (InstructionHandle) (iter.next());
 			sr.setLocalVariable( ((ASTORE) (astore.getInstruction())).getIndex() );
 			subroutines.put(astore, sr);
 		}
 
 		// Fake it a bit. We want a virtual "TopLevel" subroutine.
 		subroutines.put(all[0], TOPLEVEL);
 		sub_leaders.add(all[0]);
 
 		// Tell the subroutines about their JsrInstructions.
 		// Note that there cannot be a JSR targeting the top-level
 		// since "Jsr 0" is disallowed in Pass 3a.
 		// Instructions shared by a subroutine and the toplevel are
 		// disallowed and checked below, after the BFS.
 		for (int i=0; i<all.length; i++){
 			Instruction inst = all[i].getInstruction();
 			if (inst instanceof JsrInstruction){
 				InstructionHandle leader = ((JsrInstruction) inst).getTarget();
 				((SubroutineImpl) getSubroutine(leader)).addEnteringJsrInstruction(all[i]);
 			}
 		}
 
 		// Now do a closure computation from every subroutine leader to find all the
 		// instructions that belong to a subroutine.
 		HashSet instructions_assigned = new HashSet(); // we don't want to assign an instruction to two or more Subroutine objects.
 
         iter = sub_leaders.iterator();
 		while (iter.hasNext()){
             // set of InstructionHandles reachable from the top
             Set closure = new HashSet();
 
             // Init Queue. Start with the entry point of closure.
             InstructionHandle leader = (InstructionHandle) (iter.next());
 			ArrayList Q = new ArrayList();
 			Q.add(leader);
 
             while (!Q.isEmpty()){
                 while (!Q.isEmpty()){
                     InstructionHandle u = (InstructionHandle) Q.remove(Q.size()-1);
                     if(closure.add(u)) {
                         InstructionHandle[] successors = getSuccessors(u);
                         for (int i=0; i<successors.length; i++){
                             Q.add(successors[i]);
                         }
                     }
                 }
                 // check if exception handlers are reachable from the closure computed thus far.
                 // conceptually, an exception handler is a successor of each instruction inside
                 // the protected region, but the computation works faster if we don't implement it
                 // in a straight-forward way. Instead, we occasionally check if the first instruction
                 // of the protected region is in the closure, and if so, we know that the exception
                 // handler should also be in the closure.
                 //
                 // "one instruction must be always in at-most one subroutine" JVM requirement
                 // guarantees that the entire protected region always belongs to the same closure,
                 // so just checking the start instruction is suffice.
                 for( int i=0; i<handlers.length; i++ ) {
                     if(closure.contains(handlers[i].getStartPC())) {
                         InstructionHandle handlerPC = handlers[i].getHandlerPC();
                         if(!closure.contains(handlerPC)) {
                             Q.add(handlerPC);
                         }
                     }
                 }
             }
             // DFS ended above.
             ((SubroutineImpl) (leader==all[0]?getTopLevel():getSubroutine(leader))).setInstructions(closure);
 
             for (Iterator itr = closure.iterator(); itr.hasNext();) {
                 InstructionHandle h = (InstructionHandle) itr.next();
                 if(!instructions_assigned.add(h)) {
                     throw new StructuralCodeConstraintException("Instruction '"+h+"' is part of more than one subroutine (or of the top level and a subroutine).");
                 }
             }
 
             if (leader != all[0]){// If we don't deal with the top-level 'subroutine'
 				((SubroutineImpl) getSubroutine(leader)).setLeavingRET();
 			}
 		}
 
 		// Now make sure no subroutine is calling a subroutine
 		// that uses the same local variable for the RET as themselves
 		// (recursively).
 		// This includes that subroutines may not call themselves
 		// recursively, even not through intermediate calls to other
 		// subroutines.
 		noRecursiveCalls(getTopLevel(), new HashSet());
 
 	}
 
 	/**
 	 * This (recursive) utility method makes sure that
 	 * no subroutine is calling a subroutine
 	 * that uses the same local variable for the RET as themselves
 	 * (recursively).
 	 * This includes that subroutines may not call themselves
 	 * recursively, even not through intermediate calls to other
 	 * subroutines.
 	 *
 	 * @throws StructuralCodeConstraintException if the above constraint is not satisfied.
 	 */
 	private void noRecursiveCalls(Subroutine sub, HashSet set){
 		Subroutine[] subs = sub.subSubs();
 
 		for (int i=0; i<subs.length; i++){
 			int index = ((RET) (subs[i].getLeavingRET().getInstruction())).getIndex();
 
 			if (!set.add(new Integer(index))){
 				// Don't use toString() here because of possibly infinite recursive subSubs() calls then.
 				SubroutineImpl si = (SubroutineImpl) subs[i];
 				throw new StructuralCodeConstraintException("Subroutine with local variable '"+si.localVariable+"', JSRs '"+si.theJSRs+"', RET '"+si.theRET+"' is called by a subroutine which uses the same local variable index as itself; maybe even a recursive call? JustIce's clean definition of a subroutine forbids both.");
 			}
 
 			noRecursiveCalls(subs[i], set);
 
 			set.remove(new Integer(index));
 		}
 	}
 
 	/**
 	 * Returns the Subroutine object associated with the given
 	 * leader (that is, the first instruction of the subroutine).
 	 * You must not use this to get the top-level instructions
 	 * modeled as a Subroutine object.
 	 *
 	 * @see #getTopLevel()
 	 */
 	public Subroutine getSubroutine(InstructionHandle leader){
 		Subroutine ret = (Subroutine) subroutines.get(leader);
 
 		if (ret == null){
 			throw new AssertionViolatedException("Subroutine requested for an InstructionHandle that is not a leader of a subroutine.");
 		}
 
 		if (ret == TOPLEVEL){
 			throw new AssertionViolatedException("TOPLEVEL special subroutine requested; use getTopLevel().");
 		}
 
 		return ret;
 	}
 
 	/**
 	 * Returns the subroutine object associated with the
 	 * given instruction. This is a costly operation, you
 	 * should consider using getSubroutine(InstructionHandle).
 	 * Returns 'null' if the given InstructionHandle lies
 	 * in so-called 'dead code', i.e. code that can never
 	 * be executed.
 	 *
 	 * @see #getSubroutine(InstructionHandle)
 	 * @see #getTopLevel()
 	 */
 	public Subroutine subroutineOf(InstructionHandle any){
 		Iterator i = subroutines.values().iterator();
 		while (i.hasNext()){
 			Subroutine s = (Subroutine) i.next();
 			if (s.contains(any)) return s;
 		}
 System.err.println("DEBUG: Please verify '"+any+"' lies in dead code.");
 		return null;
 		//throw new AssertionViolatedException("No subroutine for InstructionHandle found (DEAD CODE?).");
 	}
 
 	/**
 	 * For easy handling, the piece of code that is <B>not</B> a
 	 * subroutine, the top-level, is also modeled as a Subroutine
 	 * object.
 	 * It is a special Subroutine object where <B>you must not invoke
 	 * getEnteringJsrInstructions() or getLeavingRET()</B>.
 	 *
 	 * @see Subroutine#getEnteringJsrInstructions()
 	 * @see Subroutine#getLeavingRET()
 	 */
 	public Subroutine getTopLevel(){
 		return TOPLEVEL;
 	}
 
     static final InstructionHandle[] empty = new InstructionHandle[0];
 
     /**
 	 * A utility method that calculates the successors of a given InstructionHandle
 	 * <B>in the same subroutine</B>. That means, a RET does not have any successors
 	 * as defined here. A JsrInstruction has its physical successor as its successor
 	 * (opposed to its target) as defined here.
 	 */
 	private static InstructionHandle[] getSuccessors(InstructionHandle instruction){
 		Instruction inst = instruction.getInstruction();
 
         if (inst instanceof RET){
 			return empty;
 		}
 
 		// Terminates method normally.
 		if (inst instanceof ReturnInstruction){
 			return empty;
 		}
 
 		// Terminates method abnormally, because JustIce mandates
 		// subroutines not to be protected by exception handlers.
 		if (inst instanceof ATHROW){
 			return empty;
 		}
 
         final InstructionHandle[] single = new InstructionHandle[1];
 
         // See method comment.
 		if (inst instanceof JsrInstruction){
 			single[0] = instruction.getNext();
 			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.
 				InstructionHandle[] matchTargets = ((Select) inst).getTargets();
 				InstructionHandle[] ret = new InstructionHandle[matchTargets.length+1];
 				ret[0] = ((Select) inst).getTarget();
 				System.arraycopy(matchTargets, 0, ret, 1, matchTargets.length);
 				return ret;
 			}
 			else{
                 final InstructionHandle[] pair = new InstructionHandle[2];
 				pair[0] = instruction.getNext();
 				pair[1] = ((BranchInstruction) inst).getTarget();
 				return pair;
 			}
 		}
 
 		// default case: Fall through.
 		single[0] = instruction.getNext();
 		return single;
 	}
 
 	/**
 	 * Returns a String representation of this object; merely for debugging puposes.
 	 */
 	public String toString(){
 		return "---\n"+subroutines.toString()+"\n---\n";
 	}
 }