/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed 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.springframework.core;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.util.Collections;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.asm.ClassReader;
import org.springframework.asm.ClassVisitor;
import org.springframework.asm.Label;
import org.springframework.asm.MethodVisitor;
import org.springframework.asm.Opcodes;
import org.springframework.asm.SpringAsmInfo;
import org.springframework.asm.Type;
import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;

Implementation of ParameterNameDiscoverer that uses the LocalVariableTable information in the method attributes to discover parameter names. Returns null if the class file was compiled without debug information. 
Uses ObjectWeb's ASM library for analyzing class files. Each discoverer instance
caches the ASM discovered information for each introspected Class, in a thread-safe
manner. It is recommended to reuse ParameterNameDiscoverer instances as far as possible.
Author:
Adrian Colyer, Costin Leau, Juergen Hoeller, Chris Beams
Since:
2.0/**
 * Implementation of {@link ParameterNameDiscoverer} that uses the LocalVariableTable
 * information in the method attributes to discover parameter names. Returns
 * {@code null} if the class file was compiled without debug information.
 *
 * <p>Uses ObjectWeb's ASM library for analyzing class files. Each discoverer instance
 * caches the ASM discovered information for each introspected Class, in a thread-safe
 * manner. It is recommended to reuse ParameterNameDiscoverer instances as far as possible.
 *
 * @author Adrian Colyer
 * @author Costin Leau
 * @author Juergen Hoeller
 * @author Chris Beams
 * @since 2.0
 */
public class LocalVariableTableParameterNameDiscoverer implements ParameterNameDiscoverer {

	private static final Log logger = LogFactory.getLog(LocalVariableTableParameterNameDiscoverer.class);

	// marker object for classes that do not have any debug info
	private static final Map<Member, String[]> NO_DEBUG_INFO_MAP = Collections.emptyMap();

	// the cache uses a nested index (value is a map) to keep the top level cache relatively small in size
	private final Map<Class<?>, Map<Member, String[]>> parameterNamesCache = new ConcurrentHashMap<>(32);


	@Override
	@Nullable
	public String[] getParameterNames(Method method) {
		Method originalMethod = BridgeMethodResolver.findBridgedMethod(method);
		Class<?> declaringClass = originalMethod.getDeclaringClass();
		Map<Member, String[]> map = this.parameterNamesCache.get(declaringClass);
		if (map == null) {
			map = inspectClass(declaringClass);
			this.parameterNamesCache.put(declaringClass, map);
		}
		if (map != NO_DEBUG_INFO_MAP) {
			return map.get(originalMethod);
		}
		return null;
	}

	@Override
	@Nullable
	public String[] getParameterNames(Constructor<?> ctor) {
		Class<?> declaringClass = ctor.getDeclaringClass();
		Map<Member, String[]> map = this.parameterNamesCache.get(declaringClass);
		if (map == null) {
			map = inspectClass(declaringClass);
			this.parameterNamesCache.put(declaringClass, map);
		}
		if (map != NO_DEBUG_INFO_MAP) {
			return map.get(ctor);
		}
		return null;
	}

	
Inspects the target class. Exceptions will be logged and a maker map returned
to indicate the lack of debug information.
/**
	 * Inspects the target class. Exceptions will be logged and a maker map returned
	 * to indicate the lack of debug information.
	 */
	private Map<Member, String[]> inspectClass(Class<?> clazz) {
		InputStream is = clazz.getResourceAsStream(ClassUtils.getClassFileName(clazz));
		if (is == null) {
			// We couldn't load the class file, which is not fatal as it
			// simply means this method of discovering parameter names won't work.
			if (logger.isDebugEnabled()) {
				logger.debug("Cannot find '.class' file for class [" + clazz +
						"] - unable to determine constructor/method parameter names");
			}
			return NO_DEBUG_INFO_MAP;
		}
		try {
			ClassReader classReader = new ClassReader(is);
			Map<Member, String[]> map = new ConcurrentHashMap<>(32);
			classReader.accept(new ParameterNameDiscoveringVisitor(clazz, map), 0);
			return map;
		}
		catch (IOException ex) {
			if (logger.isDebugEnabled()) {
				logger.debug("Exception thrown while reading '.class' file for class [" + clazz +
						"] - unable to determine constructor/method parameter names", ex);
			}
		}
		catch (IllegalArgumentException ex) {
			if (logger.isDebugEnabled()) {
				logger.debug("ASM ClassReader failed to parse class file [" + clazz +
						"], probably due to a new Java class file version that isn't supported yet " +
						"- unable to determine constructor/method parameter names", ex);
			}
		}
		finally {
			try {
				is.close();
			}
			catch (IOException ex) {
				// ignore
			}
		}
		return NO_DEBUG_INFO_MAP;
	}


	
Helper class that inspects all methods (constructor included) and then
attempts to find the parameter names for that member.
/**
	 * Helper class that inspects all methods (constructor included) and then
	 * attempts to find the parameter names for that member.
	 */
	private static class ParameterNameDiscoveringVisitor extends ClassVisitor {

		private static final String STATIC_CLASS_INIT = "<clinit>";

		private final Class<?> clazz;

		private final Map<Member, String[]> memberMap;

		public ParameterNameDiscoveringVisitor(Class<?> clazz, Map<Member, String[]> memberMap) {
			super(SpringAsmInfo.ASM_VERSION);
			this.clazz = clazz;
			this.memberMap = memberMap;
		}

		@Override
		@Nullable
		public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
			// exclude synthetic + bridged && static class initialization
			if (!isSyntheticOrBridged(access) && !STATIC_CLASS_INIT.equals(name)) {
				return new LocalVariableTableVisitor(this.clazz, this.memberMap, name, desc, isStatic(access));
			}
			return null;
		}

		private static boolean isSyntheticOrBridged(int access) {
			return (((access & Opcodes.ACC_SYNTHETIC) | (access & Opcodes.ACC_BRIDGE)) > 0);
		}

		private static boolean isStatic(int access) {
			return ((access & Opcodes.ACC_STATIC) > 0);
		}
	}


	private static class LocalVariableTableVisitor extends MethodVisitor {

		private static final String CONSTRUCTOR = "<init>";

		private final Class<?> clazz;

		private final Map<Member, String[]> memberMap;

		private final String name;

		private final Type[] args;

		private final String[] parameterNames;

		private final boolean isStatic;

		private boolean hasLvtInfo = false;

		/*
		 * The nth entry contains the slot index of the LVT table entry holding the
		 * argument name for the nth parameter.
		 */
		private final int[] lvtSlotIndex;

		public LocalVariableTableVisitor(Class<?> clazz, Map<Member, String[]> map, String name, String desc, boolean isStatic) {
			super(SpringAsmInfo.ASM_VERSION);
			this.clazz = clazz;
			this.memberMap = map;
			this.name = name;
			this.args = Type.getArgumentTypes(desc);
			this.parameterNames = new String[this.args.length];
			this.isStatic = isStatic;
			this.lvtSlotIndex = computeLvtSlotIndices(isStatic, this.args);
		}

		@Override
		public void visitLocalVariable(String name, String description, String signature, Label start, Label end, int index) {
			this.hasLvtInfo = true;
			for (int i = 0; i < this.lvtSlotIndex.length; i++) {
				if (this.lvtSlotIndex[i] == index) {
					this.parameterNames[i] = name;
				}
			}
		}

		@Override
		public void visitEnd() {
			if (this.hasLvtInfo || (this.isStatic && this.parameterNames.length == 0)) {
				// visitLocalVariable will never be called for static no args methods
				// which doesn't use any local variables.
				// This means that hasLvtInfo could be false for that kind of methods
				// even if the class has local variable info.
				this.memberMap.put(resolveMember(), this.parameterNames);
			}
		}

		private Member resolveMember() {
			ClassLoader loader = this.clazz.getClassLoader();
			Class<?>[] argTypes = new Class<?>[this.args.length];
			for (int i = 0; i < this.args.length; i++) {
				argTypes[i] = ClassUtils.resolveClassName(this.args[i].getClassName(), loader);
			}
			try {
				if (CONSTRUCTOR.equals(this.name)) {
					return this.clazz.getDeclaredConstructor(argTypes);
				}
				return this.clazz.getDeclaredMethod(this.name, argTypes);
			}
			catch (NoSuchMethodException ex) {
				throw new IllegalStateException("Method [" + this.name +
						"] was discovered in the .class file but cannot be resolved in the class object", ex);
			}
		}

		private static int[] computeLvtSlotIndices(boolean isStatic, Type[] paramTypes) {
			int[] lvtIndex = new int[paramTypes.length];
			int nextIndex = (isStatic ? 0 : 1);
			for (int i = 0; i < paramTypes.length; i++) {
				lvtIndex[i] = nextIndex;
				if (isWideType(paramTypes[i])) {
					nextIndex += 2;
				}
				else {
					nextIndex++;
				}
			}
			return lvtIndex;
		}

		private static boolean isWideType(Type aType) {
			// float is not a wide type
			return (aType == Type.LONG_TYPE || aType == Type.DOUBLE_TYPE);
		}
	}

}