/*
    * 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.omid.tso;
  
  import org.apache.phoenix.thirdparty.com.google.common.annotations.VisibleForTesting;
  import org.apache.phoenix.thirdparty.com.google.common.util.concurrent.ThreadFactoryBuilder;
  
  import org.apache.omid.committable.CommitTable;
  import org.apache.omid.metrics.Gauge;
  import org.apache.omid.metrics.MetricsRegistry;
  import org.apache.omid.timestamp.storage.TimestampStorage;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import javax.inject.Inject;
  import javax.inject.Singleton;
  
  import java.io.IOException;
  import java.util.concurrent.Executors;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.TimeUnit;
  
  import static org.apache.omid.metrics.MetricsUtils.name;
  
  /**
   * The Timestamp Oracle that gives monotonically increasing timestamps based on world time
   */
  @Singleton
  public class WorldClockOracleImpl implements TimestampOracle {
  
      private static final Logger LOG = LoggerFactory.getLogger(WorldClockOracleImpl.class);
  
      static final long MAX_TX_PER_MS = 1_000_000; // 1 million
      static final long TIMESTAMP_INTERVAL_MS = 10_000; // 10 seconds interval
      private static final long TIMESTAMP_ALLOCATION_INTERVAL_MS = 7_000; // 7 seconds
  
      private long lastTimestamp;
      private long maxTimestamp;
  
      private TimestampStorage storage;
      private Panicker panicker;
  
      private volatile long maxAllocatedTime;
  
      private final ScheduledExecutorService scheduler =
              Executors.newScheduledThreadPool(1, new ThreadFactoryBuilder().setNameFormat("ts-persist-%d").build());
  
      private Runnable allocateTimestampsBatchTask;
  
      private class AllocateTimestampBatchTask implements Runnable {
          long previousMaxTime;
  
          AllocateTimestampBatchTask(long previousMaxTime) {
              this.previousMaxTime = previousMaxTime;
          }
  
          @Override
          public void run() {
              long newMaxTime = (System.currentTimeMillis() + TIMESTAMP_INTERVAL_MS) * MAX_TX_PER_MS;
              try {
                  storage.updateMaxTimestamp(previousMaxTime, newMaxTime);
                  maxAllocatedTime = newMaxTime;
                  previousMaxTime = newMaxTime;
              } catch (Throwable e) {
                  panicker.panic("Can't store the new max timestamp", e);
              }
          }
      }
  
      @Inject
      public WorldClockOracleImpl(MetricsRegistry metrics,
                                 TimestampStorage tsStorage,
                                 Panicker panicker) throws IOException {
  
          this.storage = tsStorage;
          this.panicker = panicker;
  
          metrics.gauge(name("tso", "maxTimestamp"), new Gauge<Long>() {
              @Override
              public Long getValue() {
                  return maxTimestamp;
              }
          });
  
     }
 
     @Override
     public void initialize() throws IOException {
 
         this.lastTimestamp = this.maxTimestamp = storage.getMaxTimestamp();
 
         this.allocateTimestampsBatchTask = new AllocateTimestampBatchTask(lastTimestamp);
 
         // Trigger first allocation of timestamps
         scheduler.schedule(allocateTimestampsBatchTask, 0, TimeUnit.MILLISECONDS);
 
         // Waiting for the current epoch to start. Occurs in case of failover when the previous TSO allocated the current time frame.
         while ((System.currentTimeMillis() * MAX_TX_PER_MS) < this.lastTimestamp) {
             try {
                 Thread.sleep(1000);
             } catch (InterruptedException e) {
                continue;
             }
         }
 
         // Launch the periodic timestamp interval allocation. In this case, the timestamp interval is extended even though the TSO is idle.
         // Because we are world time based, this guarantees that the first request after a long time does not need to wait for new interval allocation.
         scheduler.scheduleAtFixedRate(allocateTimestampsBatchTask, TIMESTAMP_ALLOCATION_INTERVAL_MS, TIMESTAMP_ALLOCATION_INTERVAL_MS, TimeUnit.MILLISECONDS);
     }
 
     /**
      * Returns the next timestamp if available. Otherwise spins till the ts-persist thread allocates a new timestamp.
      */
     @Override
     public long next() {
 
         long currentMsFirstTimestamp = System.currentTimeMillis() * MAX_TX_PER_MS;
 
         lastTimestamp += CommitTable.MAX_CHECKPOINTS_PER_TXN;
 
         // Return the next timestamp in case we are still in the same millisecond as the previous timestamp was. 
         if (lastTimestamp >= currentMsFirstTimestamp) {
             return lastTimestamp;
         }
 
         if (currentMsFirstTimestamp >= maxTimestamp) { // Intentional race to reduce synchronization overhead in every access to maxTimestamp                                                                                                                       
             while (maxAllocatedTime <= currentMsFirstTimestamp) { // Waiting for the interval allocation
                 try {
                     Thread.sleep(1000);
                 } catch (InterruptedException e) {
                    continue;
                 }
             }
             assert (maxAllocatedTime > maxTimestamp);
             maxTimestamp = maxAllocatedTime;
         }
 
         lastTimestamp = currentMsFirstTimestamp;
 
         return lastTimestamp;
     }
 
     @Override
     public long getLast() {
         return lastTimestamp;
     }
 
     @Override
     public String toString() {
         return String.format("TimestampOracle -> LastTimestamp: %d, MaxTimestamp: %d", lastTimestamp, maxTimestamp);
     }
 
     @VisibleForTesting
     static class InMemoryTimestampStorage implements TimestampStorage {
 
         long maxTime = 0;
 
         @Override
         public void updateMaxTimestamp(long previousMaxTime, long nextMaxTime) {
             maxTime = nextMaxTime;
             LOG.info("Updating max timestamp: (previous:{}, new:{})", previousMaxTime, nextMaxTime);
         }
 
         @Override
         public long getMaxTimestamp() {
             return maxTime;
         }
 
     }
 }