/*
 * 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.Collections;
import java.util.EnumSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

/**
 * Common abstraction over logging systems.
 *
 * @author Phillip Webb
 * @author Dave Syer
 * @author Andy Wilkinson
 * @author Ben Hale
 */
public abstract class LoggingSystem {

        /**
         * A System property that can be used to indicate the {@link LoggingSystem} to use.
         */
        public static final String SYSTEM_PROPERTY = LoggingSystem.class.getName();

        /**
         * The value of the {@link #SYSTEM_PROPERTY} that can be used to indicate that no
         * {@link LoggingSystem} should be used.
         */
        public static final String NONE = "none";

        /**
         * The name used for the root logger. LoggingSystem implementations should ensure that
         * this is the name used to represent the root logger, regardless of the underlying
         * implementation.
         */
        public static final String ROOT_LOGGER_NAME = "ROOT";

        private static final Map<String, String> SYSTEMS;

        static {
                Map<String, String> systems = new LinkedHashMap<>();
                systems.put("ch.qos.logback.core.Appender",
                                "org.springframework.boot.logging.logback.LogbackLoggingSystem");
                systems.put("org.apache.logging.log4j.core.impl.Log4jContextFactory",
                                "org.springframework.boot.logging.log4j2.Log4J2LoggingSystem");
                systems.put("java.util.logging.LogManager",
                                "org.springframework.boot.logging.java.JavaLoggingSystem");
                SYSTEMS = Collections.unmodifiableMap(systems);
        }

        /**
         * Reset the logging system to be limit output. This method may be called before
         * {@link #initialize(LoggingInitializationContext, String, LogFile)} to reduce
         * logging noise until the system has been fully initialized.
         */
        public abstract void beforeInitialize();

        /**
         * Fully initialize the logging system.
         * @param initializationContext the logging initialization context
         * @param configLocation a log configuration location or {@code null} if default
         * initialization is required
         * @param logFile the log output file that should be written or {@code null} for
         * console only output
         */
        public void initialize(LoggingInitializationContext initializationContext,
                        String configLocation, LogFile logFile) {
        }

        /**
         * Clean up the logging system. The default implementation does nothing. Subclasses
         * should override this method to perform any logging system-specific cleanup.
         */
        public void cleanUp() {
        }

        /**
         * Returns a {@link Runnable} that can handle shutdown of this logging system when the
         * JVM exits. The default implementation returns {@code null}, indicating that no
         * shutdown is required.
         * @return the shutdown handler, or {@code null}
         */
        public Runnable getShutdownHandler() {
                return null;
        }

        /**
         * Returns a set of the {@link LogLevel LogLevels} that are actually supported by the
         * logging system.
         * @return the supported levels
         */
        public Set<LogLevel> getSupportedLogLevels() {
                return EnumSet.allOf(LogLevel.class);
        }

        /**
         * Sets the logging level for a given logger.
         * @param loggerName the name of the logger to set ({@code null} can be used for the
         * root logger).
         * @param level the log level ({@code null} can be used to remove any custom level for
         * the logger and use the default configuration instead)
         */
        public void setLogLevel(String loggerName, LogLevel level) {
                throw new UnsupportedOperationException("Unable to set log level");
        }

        /**
         * Returns a collection of the current configuration for all a {@link LoggingSystem}'s
         * loggers.
         * @return the current configurations
         * @since 1.5.0
         */
        public List<LoggerConfiguration> getLoggerConfigurations() {
                throw new UnsupportedOperationException("Unable to get logger configurations");
        }

        /**
         * Returns the current configuration for a {@link LoggingSystem}'s logger.
         * @param loggerName the name of the logger
         * @return the current configuration
         * @since 1.5.0
         */
        public LoggerConfiguration getLoggerConfiguration(String loggerName) {
                throw new UnsupportedOperationException("Unable to get logger configuration");
        }

        /**
         * Detect and return the logging system in use. Supports Logback and Java Logging.
         * @param classLoader the classloader
         * @return the logging system
         */
        public static LoggingSystem get(ClassLoader classLoader) {
                String loggingSystem = System.getProperty(SYSTEM_PROPERTY);
                if (StringUtils.hasLength(loggingSystem)) {
                        if (NONE.equals(loggingSystem)) {
                                return new NoOpLoggingSystem();
                        }
                        return get(classLoader, loggingSystem);
                }
                return SYSTEMS.entrySet().stream()
                                .filter((entry) -> ClassUtils.isPresent(entry.getKey(), classLoader))
                                .map((entry) -> get(classLoader, entry.getValue())).findFirst()
                                .orElseThrow(() -> new IllegalStateException(
                                                "No suitable logging system located"));
        }

        private static LoggingSystem get(ClassLoader classLoader, String loggingSystemClass) {
                try {
                        Class<?> systemClass = ClassUtils.forName(loggingSystemClass, classLoader);
                        return (LoggingSystem) systemClass.getConstructor(ClassLoader.class)
                                        .newInstance(classLoader);
                }
                catch (Exception ex) {
                        throw new IllegalStateException(ex);
                }
        }

        /**
         * {@link LoggingSystem} that does nothing.
         */
        static class NoOpLoggingSystem extends LoggingSystem {

                @Override
                public void beforeInitialize() {

                }

                @Override
                public void setLogLevel(String loggerName, LogLevel level) {

                }

                @Override
                public List<LoggerConfiguration> getLoggerConfigurations() {
                        return Collections.emptyList();
                }

                @Override
                public LoggerConfiguration getLoggerConfiguration(String loggerName) {
                        return null;
                }

        }

}