/*
 * 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
 *
 *      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.apache.logging.log4j.core.util;

import org.apache.logging.log4j.core.time.PreciseClock;
import org.apache.logging.log4j.status.StatusLogger;
import org.apache.logging.log4j.util.PropertiesUtil;
import org.apache.logging.log4j.util.Supplier;

import java.util.HashMap;
import java.util.Map;

Factory for Clock objects. /**
 * Factory for {@code Clock} objects.
 */
public final class ClockFactory {

    
Name of the system property that can be used to specify a Clock implementation class. The value of this property is "log4j.Clock". /**
     * Name of the system property that can be used to specify a {@code Clock}
     * implementation class. The value of this property is {@value}.
     */
    public static final String PROPERTY_NAME = "log4j.Clock";
    private static final StatusLogger LOGGER = StatusLogger.getLogger();

    // private static final Clock clock = createClock();

    private ClockFactory() {
    }

    
Returns a Clock instance depending on the value of system property PROPERTY_NAME. 
 If system property log4j.Clock=CachedClock is specified, this method returns an instance of CachedClock. If system property log4j.Clock=CoarseCachedClock is specified, this method returns an instance of CoarseCachedClock. 
 If another value is specified, this value is taken as the fully qualified class name of a class that implements the Clock interface. An object of this class is instantiated and returned. 
 If no value is specified, or if the specified value could not correctly be instantiated or did not implement the Clock interface, then an instance of SystemClock is returned. 
Returns:
a Clock instance/**
     * Returns a {@code Clock} instance depending on the value of system
     * property {@link #PROPERTY_NAME}.
     * <p>
     * If system property {@code log4j.Clock=CachedClock} is specified,
     * this method returns an instance of {@link CachedClock}. If system
     * property {@code log4j.Clock=CoarseCachedClock} is specified, this
     * method returns an instance of {@link CoarseCachedClock}.
     * </p>
     * <p>
     * If another value is specified, this value is taken as the fully qualified
     * class name of a class that implements the {@code Clock} interface. An
     * object of this class is instantiated and returned.
     * </p>
     * <p>
     * If no value is specified, or if the specified value could not correctly
     * be instantiated or did not implement the {@code Clock} interface, then an
     * instance of {@link SystemClock} is returned.
     * </p>
     *
     * @return a {@code Clock} instance
     */
    public static Clock getClock() {
        return createClock();
    }

    private static Map<String, Supplier<Clock>> aliases() {
        final Map<String, Supplier<Clock>> result = new HashMap<>();
        result.put("SystemClock",       new Supplier<Clock>() { @Override public Clock get() { return new SystemClock(); } });
        result.put("SystemMillisClock", new Supplier<Clock>() { @Override public Clock get() { return new SystemMillisClock(); } });
        result.put("CachedClock",       new Supplier<Clock>() { @Override public Clock get() { return CachedClock.instance(); } });
        result.put("CoarseCachedClock", new Supplier<Clock>() { @Override public Clock get() { return CoarseCachedClock.instance(); } });
        result.put("org.apache.logging.log4j.core.util.CachedClock", new Supplier<Clock>() { @Override public Clock get() { return CachedClock.instance(); } });
        result.put("org.apache.logging.log4j.core.util.CoarseCachedClock", new Supplier<Clock>() { @Override public Clock get() { return CoarseCachedClock.instance(); } });
        return result;
    }

    private static Clock createClock() {
        final String userRequest = PropertiesUtil.getProperties().getStringProperty(PROPERTY_NAME);
        if (userRequest == null) {
            LOGGER.trace("Using default SystemClock for timestamps.");
            return logSupportedPrecision(new SystemClock());
        }
        final Supplier<Clock> specified = aliases().get(userRequest);
        if (specified != null) {
            LOGGER.trace("Using specified {} for timestamps.", userRequest);
            return logSupportedPrecision(specified.get());
        }
        try {
            final Clock result = Loader.newCheckedInstanceOf(userRequest, Clock.class);
            LOGGER.trace("Using {} for timestamps.", result.getClass().getName());
            return logSupportedPrecision(result);
        } catch (final Exception e) {
            final String fmt = "Could not create {}: {}, using default SystemClock for timestamps.";
            LOGGER.error(fmt, userRequest, e);
            return logSupportedPrecision(new SystemClock());
        }
    }

    private static Clock logSupportedPrecision(final Clock clock) {
        final String support = clock instanceof PreciseClock ? "supports" : "does not support";
        LOGGER.debug("{} {} precise timestamps.", clock.getClass().getName(), support);
        return clock;
    }
}