/*
 * Copyright 2002-2017 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
 *
 *      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.springframework.aop.interceptor;

import java.io.Serializable;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.aop.support.AopUtils;
import org.springframework.lang.Nullable;

/**
 * Base {@code MethodInterceptor} implementation for tracing.
 *
 * <p>By default, log messages are written to the log for the interceptor class,
 * not the class which is being intercepted. Setting the {@code useDynamicLogger}
 * bean property to {@code true} causes all log messages to be written to
 * the {@code Log} for the target class being intercepted.
 *
 * <p>Subclasses must implement the {@code invokeUnderTrace} method, which
 * is invoked by this class ONLY when a particular invocation SHOULD be traced.
 * Subclasses should write to the {@code Log} instance provided.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 1.2
 * @see #setUseDynamicLogger
 * @see #invokeUnderTrace(org.aopalliance.intercept.MethodInvocation, org.apache.commons.logging.Log)
 */
@SuppressWarnings("serial")
public abstract class AbstractTraceInterceptor implements MethodInterceptor, Serializable {

        /**
         * The default {@code Log} instance used to write trace messages.
         * This instance is mapped to the implementing {@code Class}.
         */
        @Nullable
        protected transient Log defaultLogger = LogFactory.getLog(getClass());

        /**
         * Indicates whether or not proxy class names should be hidden when using dynamic loggers.
         * @see #setUseDynamicLogger
         */
        private boolean hideProxyClassNames = false;

        /**
         * Indicates whether to pass an exception to the logger.
         * @see #writeToLog(Log, String, Throwable)
         */
        private boolean logExceptionStackTrace = true;


        /**
         * Set whether to use a dynamic logger or a static logger.
         * Default is a static logger for this trace interceptor.
         * <p>Used to determine which {@code Log} instance should be used to write
         * log messages for a particular method invocation: a dynamic one for the
         * {@code Class} getting called, or a static one for the {@code Class}
         * of the trace interceptor.
         * <p><b>NOTE:</b> Specify either this property or "loggerName", not both.
         * @see #getLoggerForInvocation(org.aopalliance.intercept.MethodInvocation)
         */
        public void setUseDynamicLogger(boolean useDynamicLogger) {
                // Release default logger if it is not being used.
                this.defaultLogger = (useDynamicLogger ? null : LogFactory.getLog(getClass()));
        }

        /**
         * Set the name of the logger to use. The name will be passed to the
         * underlying logger implementation through Commons Logging, getting
         * interpreted as log category according to the logger's configuration.
         * <p>This can be specified to not log into the category of a class
         * (whether this interceptor's class or the class getting called)
         * but rather into a specific named category.
         * <p><b>NOTE:</b> Specify either this property or "useDynamicLogger", not both.
         * @see org.apache.commons.logging.LogFactory#getLog(String)
         * @see java.util.logging.Logger#getLogger(String)
         */
        public void setLoggerName(String loggerName) {
                this.defaultLogger = LogFactory.getLog(loggerName);
        }

        /**
         * Set to "true" to have {@link #setUseDynamicLogger dynamic loggers} hide
         * proxy class names wherever possible. Default is "false".
         */
        public void setHideProxyClassNames(boolean hideProxyClassNames) {
                this.hideProxyClassNames = hideProxyClassNames;
        }

        /**
         * Set whether to pass an exception to the logger, suggesting inclusion
         * of its stack trace into the log. Default is "true"; set this to "false"
         * in order to reduce the log output to just the trace message (which may
         * include the exception class name and exception message, if applicable).
         * @since 4.3.10
         */
        public void setLogExceptionStackTrace(boolean logExceptionStackTrace) {
                this.logExceptionStackTrace = logExceptionStackTrace;
        }


        /**
         * Determines whether or not logging is enabled for the particular {@code MethodInvocation}.
         * If not, the method invocation proceeds as normal, otherwise the method invocation is passed
         * to the {@code invokeUnderTrace} method for handling.
         * @see #invokeUnderTrace(org.aopalliance.intercept.MethodInvocation, org.apache.commons.logging.Log)
         */
        @Override
        @Nullable
        public Object invoke(MethodInvocation invocation) throws Throwable {
                Log logger = getLoggerForInvocation(invocation);
                if (isInterceptorEnabled(invocation, logger)) {
                        return invokeUnderTrace(invocation, logger);
                }
                else {
                        return invocation.proceed();
                }
        }

        /**
         * Return the appropriate {@code Log} instance to use for the given
         * {@code MethodInvocation}. If the {@code useDynamicLogger} flag
         * is set, the {@code Log} instance will be for the target class of the
         * {@code MethodInvocation}, otherwise the {@code Log} will be the
         * default static logger.
         * @param invocation the {@code MethodInvocation} being traced
         * @return the {@code Log} instance to use
         * @see #setUseDynamicLogger
         */
        protected Log getLoggerForInvocation(MethodInvocation invocation) {
                if (this.defaultLogger != null) {
                        return this.defaultLogger;
                }
                else {
                        Object target = invocation.getThis();
                        return LogFactory.getLog(getClassForLogging(target));
                }
        }

        /**
         * Determine the class to use for logging purposes.
         * @param target the target object to introspect
         * @return the target class for the given object
         * @see #setHideProxyClassNames
         */
        protected Class<?> getClassForLogging(Object target) {
                return (this.hideProxyClassNames ? AopUtils.getTargetClass(target) : target.getClass());
        }

        /**
         * Determine whether the interceptor should kick in, that is,
         * whether the {@code invokeUnderTrace} method should be called.
         * <p>Default behavior is to check whether the given {@code Log}
         * instance is enabled. Subclasses can override this to apply the
         * interceptor in other cases as well.
         * @param invocation the {@code MethodInvocation} being traced
         * @param logger the {@code Log} instance to check
         * @see #invokeUnderTrace
         * @see #isLogEnabled
         */
        protected boolean isInterceptorEnabled(MethodInvocation invocation, Log logger) {
                return isLogEnabled(logger);
        }

        /**
         * Determine whether the given {@link Log} instance is enabled.
         * <p>Default is {@code true} when the "trace" level is enabled.
         * Subclasses can override this to change the level under which 'tracing' occurs.
         * @param logger the {@code Log} instance to check
         */
        protected boolean isLogEnabled(Log logger) {
                return logger.isTraceEnabled();
        }

        /**
         * Write the supplied trace message to the supplied {@code Log} instance.
         * <p>To be called by {@link #invokeUnderTrace} for enter/exit messages.
         * <p>Delegates to {@link #writeToLog(Log, String, Throwable)} as the
         * ultimate delegate that controls the underlying logger invocation.
         * @since 4.3.10
         * @see #writeToLog(Log, String, Throwable)
         */
        protected void writeToLog(Log logger, String message) {
                writeToLog(logger, message, null);
        }

        /**
         * Write the supplied trace message and {@link Throwable} to the
         * supplied {@code Log} instance.
         * <p>To be called by {@link #invokeUnderTrace} for enter/exit outcomes,
         * potentially including an exception. Note that an exception's stack trace
         * won't get logged when {@link #setLogExceptionStackTrace} is "false".
         * <p>By default messages are written at {@code TRACE} level. Subclasses
         * can override this method to control which level the message is written
         * at, typically also overriding {@link #isLogEnabled} accordingly.
         * @since 4.3.10
         * @see #setLogExceptionStackTrace
         * @see #isLogEnabled
         */
        protected void writeToLog(Log logger, String message, @Nullable Throwable ex) {
                if (ex != null && this.logExceptionStackTrace) {
                        logger.trace(message, ex);
                }
                else {
                        logger.trace(message);
                }
        }


        /**
         * Subclasses must override this method to perform any tracing around the
         * supplied {@code MethodInvocation}. Subclasses are responsible for
         * ensuring that the {@code MethodInvocation} actually executes by
         * calling {@code MethodInvocation.proceed()}.
         * <p>By default, the passed-in {@code Log} instance will have log level
         * "trace" enabled. Subclasses do not have to check for this again, unless
         * they overwrite the {@code isInterceptorEnabled} method to modify
         * the default behavior, and may delegate to {@code writeToLog} for actual
         * messages to be written.
         * @param logger the {@code Log} to write trace messages to
         * @return the result of the call to {@code MethodInvocation.proceed()}
         * @throws Throwable if the call to {@code MethodInvocation.proceed()}
         * encountered any errors
         * @see #isLogEnabled
         * @see #writeToLog(Log, String)
         * @see #writeToLog(Log, String, Throwable)
         */
        @Nullable
        protected abstract Object invokeUnderTrace(MethodInvocation invocation, Log logger) throws Throwable;

}