/*
 * Copyright 2012-2018 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.boot.logging;

import java.util.ArrayList;
import java.util.List;

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

/**
 * Deferred {@link Log} that can be used to store messages that shouldn't be written until
 * the logging system is fully initialized.
 *
 * @author Phillip Webb
 * @since 1.3.0
 */
public class DeferredLog implements Log {

        private volatile Log destination;

        private final List<Line> lines = new ArrayList<>();

        @Override
        public boolean isTraceEnabled() {
                synchronized (this.lines) {
                        return (this.destination != null) ? this.destination.isTraceEnabled() : true;
                }
        }

        @Override
        public boolean isDebugEnabled() {
                synchronized (this.lines) {
                        return (this.destination != null) ? this.destination.isDebugEnabled() : true;
                }
        }

        @Override
        public boolean isInfoEnabled() {
                synchronized (this.lines) {
                        return (this.destination != null) ? this.destination.isInfoEnabled() : true;
                }
        }

        @Override
        public boolean isWarnEnabled() {
                synchronized (this.lines) {
                        return (this.destination != null) ? this.destination.isWarnEnabled() : true;
                }
        }

        @Override
        public boolean isErrorEnabled() {
                synchronized (this.lines) {
                        return (this.destination != null) ? this.destination.isErrorEnabled() : true;
                }
        }

        @Override
        public boolean isFatalEnabled() {
                synchronized (this.lines) {
                        return (this.destination != null) ? this.destination.isFatalEnabled() : true;
                }
        }

        @Override
        public void trace(Object message) {
                log(LogLevel.TRACE, message, null);
        }

        @Override
        public void trace(Object message, Throwable t) {
                log(LogLevel.TRACE, message, t);
        }

        @Override
        public void debug(Object message) {
                log(LogLevel.DEBUG, message, null);
        }

        @Override
        public void debug(Object message, Throwable t) {
                log(LogLevel.DEBUG, message, t);
        }

        @Override
        public void info(Object message) {
                log(LogLevel.INFO, message, null);
        }

        @Override
        public void info(Object message, Throwable t) {
                log(LogLevel.INFO, message, t);
        }

        @Override
        public void warn(Object message) {
                log(LogLevel.WARN, message, null);
        }

        @Override
        public void warn(Object message, Throwable t) {
                log(LogLevel.WARN, message, t);
        }

        @Override
        public void error(Object message) {
                log(LogLevel.ERROR, message, null);
        }

        @Override
        public void error(Object message, Throwable t) {
                log(LogLevel.ERROR, message, t);
        }

        @Override
        public void fatal(Object message) {
                log(LogLevel.FATAL, message, null);
        }

        @Override
        public void fatal(Object message, Throwable t) {
                log(LogLevel.FATAL, message, t);
        }

        private void log(LogLevel level, Object message, Throwable t) {
                synchronized (this.lines) {
                        if (this.destination != null) {
                                logTo(this.destination, level, message, t);
                        }
                        else {
                                this.lines.add(new Line(level, message, t));
                        }
                }
        }

        /**
         * Switch from deferred logging to immediate logging to the specified destination.
         * @param destination the new log destination
         * @since 2.1.0
         */
        public void switchTo(Class<?> destination) {
                switchTo(LogFactory.getLog(destination));
        }

        /**
         * Switch from deferred logging to immediate logging to the specified destination.
         * @param destination the new log destination
         * @since 2.1.0
         */
        public void switchTo(Log destination) {
                synchronized (this.lines) {
                        replayTo(destination);
                        this.destination = destination;
                }
        }

        /**
         * Replay deferred logging to the specified destination.
         * @param destination the destination for the deferred log messages
         */
        public void replayTo(Class<?> destination) {
                replayTo(LogFactory.getLog(destination));
        }

        /**
         * Replay deferred logging to the specified destination.
         * @param destination the destination for the deferred log messages
         */
        public void replayTo(Log destination) {
                synchronized (this.lines) {
                        for (Line line : this.lines) {
                                logTo(destination, line.getLevel(), line.getMessage(),
                                                line.getThrowable());
                        }
                        this.lines.clear();
                }
        }

        /**
         * Replay from a source log to a destination log when the source is deferred.
         * @param source the source logger
         * @param destination the destination logger class
         * @return the destination
         */
        public static Log replay(Log source, Class<?> destination) {
                return replay(source, LogFactory.getLog(destination));
        }

        /**
         * Replay from a source log to a destination log when the source is deferred.
         * @param source the source logger
         * @param destination the destination logger
         * @return the destination
         */
        public static Log replay(Log source, Log destination) {
                if (source instanceof DeferredLog) {
                        ((DeferredLog) source).replayTo(destination);
                }
                return destination;
        }

        private static void logTo(Log log, LogLevel level, Object message,
                        Throwable throwable) {
                switch (level) {
                case TRACE:
                        log.trace(message, throwable);
                        return;
                case DEBUG:
                        log.debug(message, throwable);
                        return;
                case INFO:
                        log.info(message, throwable);
                        return;
                case WARN:
                        log.warn(message, throwable);
                        return;
                case ERROR:
                        log.error(message, throwable);
                        return;
                case FATAL:
                        log.fatal(message, throwable);
                        return;
                }
        }

        private static class Line {

                private final LogLevel level;

                private final Object message;

                private final Throwable throwable;

                Line(LogLevel level, Object message, Throwable throwable) {
                        this.level = level;
                        this.message = message;
                        this.throwable = throwable;
                }

                public LogLevel getLevel() {
                        return this.level;
                }

                public Object getMessage() {
                        return this.message;
                }

                public Throwable getThrowable() {
                        return this.throwable;
                }

        }

}