/*
 * 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());
    }
}