/*
    * Copyright 2017 SPF4J.
    *
    * 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.spf4j.base;
  
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import java.util.function.LongSupplier;
  
  /**
   * Utility method to convert between TimeSource.nanoTime and System.currentTimeMillis
   * @author Zoltan Farkas
   */
  public final class TimeSource {
  
    private static final LongSupplier TIMESUPP;
  
    static {
      String cfgTimeSource = System.getProperty("spf4j.timeSource");
      if (cfgTimeSource == null) {
        TIMESUPP = () -> System.nanoTime();
      } else if ("systemTime".equals(cfgTimeSource)) {
        // System time is about 3 times faster on macOSX (30ns vs 10ns):
        // and worth considering where more than millisecond precission is not needed:
        // JMH benchmarks:
        // TimingBenchmark.getCurrentTimeMillis         thrpt   10  108291306.615 ± 3493136.191  ops/s
        // TimingBenchmark.getNanoTime                  thrpt   10  31056232.360 ± 1804247.295  ops/s
        TIMESUPP = new SystemTimeProvider();
      } else {
        try {
          TIMESUPP = (LongSupplier) Class.forName(cfgTimeSource).newInstance();
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException ex) {
          throw new ExceptionInInitializerError(ex);
        }
      }
  
    }
  
    private TimeSource() { }
  
    /**
     * Get JVM. time source. Default implementation calls System.nanotime.
     *
     * @return
     */
    public static long nanoTime() {
      return TIMESUPP.getAsLong();
    }
  
    public static LongSupplier nanoTimeSupplier() {
      return TIMESUPP;
    }
  
    public static long getDeadlineNanos(final long timeout, final TimeUnit timeUnit) {
      if (timeout < 0) {
        throw new IllegalArgumentException("Invalid timeout " + timeout + " " + timeUnit);
      }
      return nanoTime() + timeUnit.toNanos(timeout);
    }
  
    public static long getDeadlineNanos(final long currentTimeNanos, final long timeout, final TimeUnit timeUnit) {
      if (timeout < 0) {
        throw new IllegalArgumentException("Invalid timeout " + timeout + " " + timeUnit);
      }
      return currentTimeNanos + timeUnit.toNanos(timeout);
    }
  
  
    public static long getTimeToDeadlineStrict(final long deadlineNanos, final TimeUnit timeUnit)
            throws TimeoutException {
      long timeoutNanos = deadlineNanos - nanoTime();
      if (timeoutNanos < 0) {
        throw new TimeoutException("Exceeded deadline " + deadlineNanos + " with " + (-timeoutNanos));
      }
      return timeUnit.convert(timeoutNanos, TimeUnit.NANOSECONDS);
    }
  
    public static long getTimeToDeadline(final long deadlineNanos, final TimeUnit timeUnit) {
      long timeoutNanos = deadlineNanos - nanoTime();
      return timeUnit.convert(timeoutNanos, TimeUnit.NANOSECONDS);
    }
  
    private static final class SystemTimeProvider implements LongSupplier {
  
      private static final long LOCAL_EPOCH = System.currentTimeMillis();
  
      @Override
     public long getAsLong() {
       return TimeUnit.MILLISECONDS.toNanos(System.currentTimeMillis() - LOCAL_EPOCH);
     }
 
   }
 
 
 }