src/main/java/org/apache/bcel/classfile/DescendingVisitor.java

/*
 * 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.classfile;

import java.util.Objects;
import java.util.Stack;
import java.util.stream.Stream;

import org.apache.commons.lang3.stream.Streams;

/**
 * Traverses a JavaClass with another Visitor object 'piggy-backed' that is applied to all components of a JavaClass
 * object. I.e. this class supplies the traversal strategy, other classes can make use of it.
 */
public class DescendingVisitor implements Visitor {
    private final JavaClass clazz;

    private final Visitor visitor;

    private final Stack<Object> stack = new Stack<>();

    /**
     * Constructs a DescendingVisitor.
     *
     * @param clazz Class to traverse.
     * @param visitor visitor object to apply to all components.
     */
    public DescendingVisitor(final JavaClass clazz, final Visitor visitor) {
        this.clazz = clazz;
        this.visitor = visitor;
    }

    private <E extends Node> void accept(final E[] node) {
        Streams.of(node).forEach(e -> e.accept(this));
    }

    /**
     * Gets the current object.
     *
     * @return current object.
     */
    public Object current() {
        return stack.peek();
    }

    /**
     * Gets the container of current entity, that is, predecessor during traversal.
     *
     * @return container of current entity, that is, predecessor during traversal.
     */
    public Object predecessor() {
        return predecessor(0);
    }

    /**
     * Gets the container of current entity, that is, predecessor during traversal.
     *
     * @param level nesting level, that is, 0 returns the direct predecessor.
     * @return container of current entity, that is, predecessor during traversal.
     */
    public Object predecessor(final int level) {
        final int size = stack.size();
        if (size < 2 || level < 0) {
            return null;
        }
        return stack.elementAt(size - (level + 2)); // size - 1 == current
    }

    /**
     * Start traversal.
     */
    public void visit() {
        clazz.accept(this);
    }

    /**
     * @since 6.0
     */
    @Override
    public void visitAnnotation(final Annotations annotation) {
        stack.push(annotation);
        annotation.accept(visitor);
        accept(annotation.getAnnotationEntries());
        stack.pop();
    }

    /**
     * @since 6.0
     */
    @Override
    public void visitAnnotationDefault(final AnnotationDefault obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /**
     * @since 6.0
     */
    @Override
    public void visitAnnotationEntry(final AnnotationEntry annotationEntry) {
        stack.push(annotationEntry);
        annotationEntry.accept(visitor);
        stack.pop();
    }

    /**
     * @since 6.0
     */
    @Override
    public void visitBootstrapMethods(final BootstrapMethods bm) {
        stack.push(bm);
        bm.accept(visitor);
        // BootstrapMethod[] bms = bm.getBootstrapMethods();
        // for (int i = 0; i < bms.length; i++)
        // {
        // bms[i].accept(this);
        // }
        stack.pop();
    }

    @Override
    public void visitCode(final Code code) {
        stack.push(code);
        code.accept(visitor);
        accept(code.getExceptionTable());
        accept(code.getAttributes());
        stack.pop();
    }

    @Override
    public void visitCodeException(final CodeException ce) {
        stack.push(ce);
        ce.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantClass(final ConstantClass constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantDouble(final ConstantDouble constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    /** @since 6.3 */
    @Override
    public void visitConstantDynamic(final ConstantDynamic obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantFieldref(final ConstantFieldref constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantFloat(final ConstantFloat constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantInteger(final ConstantInteger constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantInterfaceMethodref(final ConstantInterfaceMethodref constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    /**
     * @since 6.0
     */
    @Override
    public void visitConstantInvokeDynamic(final ConstantInvokeDynamic constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantLong(final ConstantLong constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    /** @since 6.0 */
    @Override
    public void visitConstantMethodHandle(final ConstantMethodHandle obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantMethodref(final ConstantMethodref constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    /** @since 6.0 */
    @Override
    public void visitConstantMethodType(final ConstantMethodType obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.1 */
    @Override
    public void visitConstantModule(final ConstantModule obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantNameAndType(final ConstantNameAndType constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    /** @since 6.1 */
    @Override
    public void visitConstantPackage(final ConstantPackage obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantPool(final ConstantPool cp) {
        stack.push(cp);
        cp.accept(visitor);
        Stream.of(cp.getConstantPool()).filter(Objects::nonNull).forEach(e -> e.accept(this));
        stack.pop();
    }

    @Override
    public void visitConstantString(final ConstantString constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantUtf8(final ConstantUtf8 constant) {
        stack.push(constant);
        constant.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitConstantValue(final ConstantValue cv) {
        stack.push(cv);
        cv.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitDeprecated(final Deprecated attribute) {
        stack.push(attribute);
        attribute.accept(visitor);
        stack.pop();
    }

    /**
     * @since 6.0
     */
    @Override
    public void visitEnclosingMethod(final EnclosingMethod obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitExceptionTable(final ExceptionTable table) {
        stack.push(table);
        table.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitField(final Field field) {
        stack.push(field);
        field.accept(visitor);
        accept(field.getAttributes());
        stack.pop();
    }

    @Override
    public void visitInnerClass(final InnerClass inner) {
        stack.push(inner);
        inner.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitInnerClasses(final InnerClasses ic) {
        stack.push(ic);
        ic.accept(visitor);
        accept(ic.getInnerClasses());
        stack.pop();
    }

    @Override
    public void visitJavaClass(final JavaClass clazz) {
        stack.push(clazz);
        clazz.accept(visitor);
        accept(clazz.getFields());
        accept(clazz.getMethods());
        accept(clazz.getAttributes());
        clazz.getConstantPool().accept(this);
        stack.pop();
    }

    @Override
    public void visitLineNumber(final LineNumber number) {
        stack.push(number);
        number.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitLineNumberTable(final LineNumberTable table) {
        stack.push(table);
        table.accept(visitor);
        accept(table.getLineNumberTable());
        stack.pop();
    }

    @Override
    public void visitLocalVariable(final LocalVariable var) {
        stack.push(var);
        var.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitLocalVariableTable(final LocalVariableTable table) {
        stack.push(table);
        table.accept(visitor);
        accept(table.getLocalVariableTable());
        stack.pop();
    }

    /**
     * @since 6.0
     */
    @Override
    public void visitLocalVariableTypeTable(final LocalVariableTypeTable obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitMethod(final Method method) {
        stack.push(method);
        method.accept(visitor);
        accept(method.getAttributes());
        stack.pop();
    }

    /**
     * @since 6.4.0
     */
    @Override
    public void visitMethodParameter(final MethodParameter obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /**
     * @since 6.0
     */
    @Override
    public void visitMethodParameters(final MethodParameters obj) {
        stack.push(obj);
        obj.accept(visitor);
        Stream.of(obj.getParameters()).forEach(e -> e.accept(this));
        stack.pop();
    }

    /** @since 6.4.0 */
    @Override
    public void visitModule(final Module obj) {
        stack.push(obj);
        obj.accept(visitor);
        accept(obj.getRequiresTable());
        accept(obj.getExportsTable());
        accept(obj.getOpensTable());
        accept(obj.getProvidesTable());
        stack.pop();
    }

    /** @since 6.4.0 */
    @Override
    public void visitModuleExports(final ModuleExports obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.4.0 */
    @Override
    public void visitModuleMainClass(final ModuleMainClass obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.4.0 */
    @Override
    public void visitModuleOpens(final ModuleOpens obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.4.0 */
    @Override
    public void visitModulePackages(final ModulePackages obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.4.0 */
    @Override
    public void visitModuleProvides(final ModuleProvides obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.4.0 */
    @Override
    public void visitModuleRequires(final ModuleRequires obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.4.0 */
    @Override
    public void visitNestHost(final NestHost obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.4.0 */
    @Override
    public void visitNestMembers(final NestMembers obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /**
     * @since 6.0
     */
    @Override
    public void visitParameterAnnotation(final ParameterAnnotations obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.0 */
    @Override
    public void visitParameterAnnotationEntry(final ParameterAnnotationEntry obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    /** @since 6.13.0 */
    @Override
    public void visitPermittedSubclasses(final PermittedSubclasses obj) {
        stack.push(obj);
        obj.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitRecord(final Record record) {
        stack.push(record);
        record.accept(visitor);
        accept(record.getComponents());
        stack.pop();
    }

    @Override
    public void visitRecordComponent(final RecordComponentInfo recordComponentInfo) {
        stack.push(recordComponentInfo);
        recordComponentInfo.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitSignature(final Signature attribute) {
        stack.push(attribute);
        attribute.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitSourceFile(final SourceFile attribute) {
        stack.push(attribute);
        attribute.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitStackMap(final StackMap table) {
        stack.push(table);
        table.accept(visitor);
        accept(table.getStackMap());
        stack.pop();
    }

    @Override
    public void visitStackMapEntry(final StackMapEntry var) {
        stack.push(var);
        var.accept(visitor);
        accept(var.getTypesOfLocals());
        accept(var.getTypesOfStackItems());
        stack.pop();
    }

    /**
     * Visits a {@link StackMapType} object.
     *
     * @param var object to visit.
     * @since 6.8.0
     */
    @Override
    public void visitStackMapType(final StackMapType var) {
        stack.push(var);
        var.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitSynthetic(final Synthetic attribute) {
        stack.push(attribute);
        attribute.accept(visitor);
        stack.pop();
    }

    @Override
    public void visitUnknown(final Unknown attribute) {
        stack.push(attribute);
        attribute.accept(visitor);
        stack.pop();
    }

}