/*
 * 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.beam.runners.samza.runtime;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NavigableSet;
import java.util.TreeSet;
import javax.annotation.Nullable;
import org.apache.beam.runners.core.StateNamespace;
import org.apache.beam.runners.core.StateNamespaces;
import org.apache.beam.runners.core.StateTags;
import org.apache.beam.runners.core.TimerInternals;
import org.apache.beam.runners.core.TimerInternalsFactory;
import org.apache.beam.runners.samza.SamzaPipelineOptions;
import org.apache.beam.runners.samza.SamzaRunner;
import org.apache.beam.runners.samza.state.SamzaMapState;
import org.apache.beam.sdk.coders.Coder;
import org.apache.beam.sdk.coders.CoderException;
import org.apache.beam.sdk.coders.StringUtf8Coder;
import org.apache.beam.sdk.coders.StructuredCoder;
import org.apache.beam.sdk.coders.VarLongCoder;
import org.apache.beam.sdk.state.TimeDomain;
import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
import org.apache.beam.sdk.transforms.windowing.GlobalWindow;
import org.apache.beam.sdk.values.PCollection.IsBounded;
import org.apache.beam.sdk.values.WindowingStrategy;
import org.apache.samza.operators.Scheduler;
import org.joda.time.Instant;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * {@link TimerInternalsFactory} that creates Samza {@link TimerInternals}. This class keeps track
 * of the {@link org.apache.beam.runners.core.TimerInternals.TimerData} added to the sorted timer
 * set, and removes the ready timers when the watermark is advanced.
 */
public class SamzaTimerInternalsFactory<K> implements TimerInternalsFactory<K> {
  private static final Logger LOG = LoggerFactory.getLogger(SamzaTimerInternalsFactory.class);

  private final NavigableSet<KeyedTimerData<K>> eventTimeTimers;
  private final Coder<K> keyCoder;
  private final Scheduler<KeyedTimerData<K>> timerRegistry;
  private final SamzaTimerState state;
  private final IsBounded isBounded;

  private Instant inputWatermark = BoundedWindow.TIMESTAMP_MIN_VALUE;
  private Instant outputWatermark = BoundedWindow.TIMESTAMP_MIN_VALUE;

  private SamzaTimerInternalsFactory(
      Coder<K> keyCoder,
      Scheduler<KeyedTimerData<K>> timerRegistry,
      String timerStateId,
      SamzaStoreStateInternals.Factory<?> nonKeyedStateInternalsFactory,
      Coder<BoundedWindow> windowCoder,
      IsBounded isBounded) {
    this.keyCoder = keyCoder;
    this.timerRegistry = timerRegistry;
    this.eventTimeTimers = new TreeSet<>();
    this.state = new SamzaTimerState(timerStateId, nonKeyedStateInternalsFactory, windowCoder);
    this.isBounded = isBounded;
  }

  static <K> SamzaTimerInternalsFactory<K> createTimerInternalFactory(
      Coder<K> keyCoder,
      Scheduler<KeyedTimerData<K>> timerRegistry,
      String timerStateId,
      SamzaStoreStateInternals.Factory<?> nonKeyedStateInternalsFactory,
      WindowingStrategy<?, BoundedWindow> windowingStrategy,
      IsBounded isBounded,
      SamzaPipelineOptions pipelineOptions) {

    final Coder<BoundedWindow> windowCoder = windowingStrategy.getWindowFn().windowCoder();

    return new SamzaTimerInternalsFactory<>(
        keyCoder,
        timerRegistry,
        timerStateId,
        nonKeyedStateInternalsFactory,
        windowCoder,
        isBounded);
  }

  @Override
  public TimerInternals timerInternalsForKey(@Nullable K key) {
    final byte[] keyBytes;

    if (keyCoder == null) {
      if (key != null) {
        throw new IllegalArgumentException(
            String.format("Received non-null key for unkeyed timer factory. Key: %s", key));
      }
      keyBytes = null;
    } else {
      final ByteArrayOutputStream baos = new ByteArrayOutputStream();
      try {
        keyCoder.encode(key, baos);
      } catch (IOException e) {
        throw new RuntimeException("Could not encode key: " + key, e);
      }
      keyBytes = baos.toByteArray();
    }

    return new SamzaTimerInternals(keyBytes, key);
  }

  public void setInputWatermark(Instant watermark) {
    if (watermark.isBefore(inputWatermark)) {
      throw new IllegalArgumentException("New input watermark is before current watermark");
    }
    LOG.debug("Advancing input watermark from {} to {}.", inputWatermark, watermark);
    inputWatermark = watermark;
  }

  public void setOutputWatermark(Instant watermark) {
    if (watermark.isAfter(inputWatermark)) {
      LOG.debug("Clipping new output watermark from {} to {}.", watermark, inputWatermark);
      watermark = inputWatermark;
    }

    if (watermark.isBefore(outputWatermark)) {
      throw new IllegalArgumentException("New output watermark is before current watermark");
    }
    LOG.debug("Advancing output watermark from {} to {}.", outputWatermark, watermark);
    outputWatermark = watermark;
  }

  public Collection<KeyedTimerData<K>> removeReadyTimers() {
    final Collection<KeyedTimerData<K>> readyTimers = new ArrayList<>();

    while (!eventTimeTimers.isEmpty()
        && eventTimeTimers.first().getTimerData().getTimestamp().isBefore(inputWatermark)) {
      final KeyedTimerData<K> keyedTimerData = eventTimeTimers.pollFirst();
      readyTimers.add(keyedTimerData);
      state.deletePersisted(keyedTimerData);
    }

    return readyTimers;
  }

  public void removeProcessingTimer(KeyedTimerData<K> keyedTimerData) {
    state.deletePersisted(keyedTimerData);
  }

  public Instant getInputWatermark() {
    return inputWatermark;
  }

  public Instant getOutputWatermark() {
    return outputWatermark;
  }

  private class SamzaTimerInternals implements TimerInternals {
    private final byte[] keyBytes;
    private final K key;

    public SamzaTimerInternals(byte[] keyBytes, K key) {
      this.keyBytes = keyBytes;
      this.key = key;
    }

    @Override
    public void setTimer(
        StateNamespace namespace, String timerId, Instant target, TimeDomain timeDomain) {
      setTimer(TimerData.of(timerId, namespace, target, timeDomain));
    }

    @Override
    public void setTimer(TimerData timerData) {
      if (isBounded == IsBounded.UNBOUNDED
          && timerData.getTimestamp().getMillis()
              >= GlobalWindow.INSTANCE.maxTimestamp().getMillis()) {
        // No need to register a timer of max timestamp if the input is unbounded
        return;
      }

      final KeyedTimerData<K> keyedTimerData = new KeyedTimerData<>(keyBytes, key, timerData);
      if (eventTimeTimers.contains(keyedTimerData)) {
        return;
      }

      final Long lastTimestamp = state.get(keyedTimerData);
      final Long newTimestamp = timerData.getTimestamp().getMillis();

      if (!newTimestamp.equals(lastTimestamp)) {
        if (lastTimestamp != null) {
          final TimerData lastTimerData =
              TimerData.of(
                  timerData.getTimerId(),
                  timerData.getNamespace(),
                  new Instant(lastTimestamp),
                  timerData.getDomain());
          deleteTimer(lastTimerData, false);
        }

        // persist it first
        state.persist(keyedTimerData);

        switch (timerData.getDomain()) {
          case EVENT_TIME:
            eventTimeTimers.add(keyedTimerData);
            break;

          case PROCESSING_TIME:
            timerRegistry.schedule(keyedTimerData, timerData.getTimestamp().getMillis());
            break;

          default:
            throw new UnsupportedOperationException(
                String.format(
                    "%s currently only supports even time or processing time", SamzaRunner.class));
        }
      }
    }

    @Override
    public void deleteTimer(StateNamespace namespace, String timerId, TimeDomain timeDomain) {
      deleteTimer(TimerData.of(timerId, namespace, Instant.now(), timeDomain));
    }

    @Override
    public void deleteTimer(StateNamespace namespace, String timerId) {
      deleteTimer(TimerData.of(timerId, namespace, Instant.now(), TimeDomain.EVENT_TIME));
    }

    @Override
    public void deleteTimer(TimerData timerData) {
      deleteTimer(timerData, true);
    }

    private void deleteTimer(TimerData timerData, boolean updateState) {
      final KeyedTimerData<K> keyedTimerData = new KeyedTimerData<>(keyBytes, key, timerData);
      if (updateState) {
        state.deletePersisted(keyedTimerData);
      }

      switch (timerData.getDomain()) {
        case EVENT_TIME:
          eventTimeTimers.remove(keyedTimerData);
          break;

        case PROCESSING_TIME:
          timerRegistry.delete(keyedTimerData);
          break;

        default:
          throw new UnsupportedOperationException(
              String.format("%s currently only supports event time", SamzaRunner.class));
      }
    }

    @Override
    public Instant currentProcessingTime() {
      return new Instant();
    }

    @Override
    public Instant currentSynchronizedProcessingTime() {
      throw new UnsupportedOperationException(
          String.format(
              "%s does not currently support synchronized processing time", SamzaRunner.class));
    }

    @Override
    public Instant currentInputWatermarkTime() {
      return inputWatermark;
    }

    @Override
    public Instant currentOutputWatermarkTime() {
      return outputWatermark;
    }
  }

  private class SamzaTimerState {
    private final SamzaMapState<TimerKey<K>, Long> eventTimerTimerState;
    private final SamzaMapState<TimerKey<K>, Long> processingTimerTimerState;

    SamzaTimerState(
        String timerStateId,
        SamzaStoreStateInternals.Factory<?> nonKeyedStateInternalsFactory,
        Coder<BoundedWindow> windowCoder) {

      this.eventTimerTimerState =
          (SamzaMapState<TimerKey<K>, Long>)
              nonKeyedStateInternalsFactory
                  .stateInternalsForKey(null)
                  .state(
                      StateNamespaces.global(),
                      StateTags.map(
                          timerStateId + "-et",
                          new TimerKeyCoder<>(keyCoder, windowCoder),
                          VarLongCoder.of()));

      this.processingTimerTimerState =
          (SamzaMapState<TimerKey<K>, Long>)
              nonKeyedStateInternalsFactory
                  .stateInternalsForKey(null)
                  .state(
                      StateNamespaces.global(),
                      StateTags.map(
                          timerStateId + "-pt",
                          new TimerKeyCoder<>(keyCoder, windowCoder),
                          VarLongCoder.of()));

      restore();
    }

    Long get(KeyedTimerData<K> keyedTimerData) {
      final TimerKey<K> timerKey = TimerKey.of(keyedTimerData);
      switch (keyedTimerData.getTimerData().getDomain()) {
        case EVENT_TIME:
          return eventTimerTimerState.get(timerKey).read();

        case PROCESSING_TIME:
          return processingTimerTimerState.get(timerKey).read();

        default:
          throw new UnsupportedOperationException(
              String.format("%s currently only supports event time", SamzaRunner.class));
      }
    }

    void persist(KeyedTimerData<K> keyedTimerData) {
      final TimerKey<K> timerKey = TimerKey.of(keyedTimerData);
      switch (keyedTimerData.getTimerData().getDomain()) {
        case EVENT_TIME:
          eventTimerTimerState.put(
              timerKey, keyedTimerData.getTimerData().getTimestamp().getMillis());
          break;

        case PROCESSING_TIME:
          processingTimerTimerState.put(
              timerKey, keyedTimerData.getTimerData().getTimestamp().getMillis());
          break;

        default:
          throw new UnsupportedOperationException(
              String.format("%s currently only supports event time", SamzaRunner.class));
      }
    }

    void deletePersisted(KeyedTimerData<K> keyedTimerData) {
      final TimerKey<K> timerKey = TimerKey.of(keyedTimerData);
      switch (keyedTimerData.getTimerData().getDomain()) {
        case EVENT_TIME:
          eventTimerTimerState.remove(timerKey);
          break;

        case PROCESSING_TIME:
          processingTimerTimerState.remove(timerKey);
          break;

        default:
          throw new UnsupportedOperationException(
              String.format("%s currently only supports event time", SamzaRunner.class));
      }
    }

    private void loadEventTimeTimers() {
      final Iterator<Map.Entry<TimerKey<K>, Long>> iter =
          eventTimerTimerState.readIterator().read();
      // since the iterator will reach to the end, it will be closed automatically
      while (iter.hasNext()) {
        final Map.Entry<TimerKey<K>, Long> entry = iter.next();
        final KeyedTimerData keyedTimerData =
            TimerKey.toKeyedTimerData(
                entry.getKey(), entry.getValue(), TimeDomain.EVENT_TIME, keyCoder);

        eventTimeTimers.add(keyedTimerData);
      }

      LOG.info("Loaded {} event time timers in memory", eventTimeTimers.size());
    }

    private void loadProcessingTimeTimers() {
      final Iterator<Map.Entry<TimerKey<K>, Long>> iter =
          processingTimerTimerState.readIterator().read();
      // since the iterator will reach to the end, it will be closed automatically
      int count = 0;
      while (iter.hasNext()) {
        final Map.Entry<TimerKey<K>, Long> entry = iter.next();
        final KeyedTimerData keyedTimerData =
            TimerKey.toKeyedTimerData(
                entry.getKey(), entry.getValue(), TimeDomain.PROCESSING_TIME, keyCoder);

        timerRegistry.schedule(
            keyedTimerData, keyedTimerData.getTimerData().getTimestamp().getMillis());
        ++count;
      }

      LOG.info("Loaded {} processing time timers in memory", count);
    }

    private void restore() {
      loadEventTimeTimers();
      loadProcessingTimeTimers();
    }
  }

  private static class TimerKey<K> {
    private final K key;
    private final StateNamespace stateNamespace;
    private final String timerId;

    static <K> TimerKey<K> of(KeyedTimerData<K> keyedTimerData) {
      final TimerInternals.TimerData timerData = keyedTimerData.getTimerData();
      return new TimerKey<>(
          keyedTimerData.getKey(), timerData.getNamespace(), timerData.getTimerId());
    }

    static <K> KeyedTimerData<K> toKeyedTimerData(
        TimerKey<K> timerKey, long timestamp, TimeDomain domain, Coder<K> keyCoder) {
      byte[] keyBytes = null;
      if (keyCoder != null && timerKey.key != null) {
        final ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
          keyCoder.encode(timerKey.key, baos);
        } catch (IOException e) {
          throw new RuntimeException("Could not encode key: " + timerKey.key, e);
        }
        keyBytes = baos.toByteArray();
      }

      return new KeyedTimerData<K>(
          keyBytes,
          timerKey.key,
          TimerInternals.TimerData.of(
              timerKey.timerId, timerKey.stateNamespace, new Instant(timestamp), domain));
    }

    private TimerKey(K key, StateNamespace stateNamespace, String timerId) {
      this.key = key;
      this.stateNamespace = stateNamespace;
      this.timerId = timerId;
    }

    public K getKey() {
      return key;
    }

    public StateNamespace getStateNamespace() {
      return stateNamespace;
    }

    public String getTimerId() {
      return timerId;
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) {
        return true;
      }
      if (o == null || getClass() != o.getClass()) {
        return false;
      }

      TimerKey<?> timerKey = (TimerKey<?>) o;

      if (key != null ? !key.equals(timerKey.key) : timerKey.key != null) {
        return false;
      }
      if (!stateNamespace.equals(timerKey.stateNamespace)) {
        return false;
      }

      return timerId.equals(timerKey.timerId);
    }

    @Override
    public int hashCode() {
      int result = key != null ? key.hashCode() : 0;
      result = 31 * result + stateNamespace.hashCode();
      result = 31 * result + timerId.hashCode();
      return result;
    }

    @Override
    public String toString() {
      return "TimerKey{"
          + "key="
          + key
          + ", stateNamespace="
          + stateNamespace
          + ", timerId='"
          + timerId
          + '\''
          + '}';
    }
  }

  /** Coder for {@link TimerKey}. */
  public static class TimerKeyCoder<K> extends StructuredCoder<TimerKey<K>> {
    private static final StringUtf8Coder STRING_CODER = StringUtf8Coder.of();

    private final Coder<K> keyCoder;
    private final Coder<? extends BoundedWindow> windowCoder;

    TimerKeyCoder(Coder<K> keyCoder, Coder<? extends BoundedWindow> windowCoder) {
      this.keyCoder = keyCoder;
      this.windowCoder = windowCoder;
    }

    @Override
    public void encode(TimerKey<K> value, OutputStream outStream)
        throws CoderException, IOException {

      // encode the timestamp first
      STRING_CODER.encode(value.timerId, outStream);
      STRING_CODER.encode(value.stateNamespace.stringKey(), outStream);

      if (keyCoder != null) {
        keyCoder.encode(value.key, outStream);
      }
    }

    @Override
    public TimerKey<K> decode(InputStream inStream) throws CoderException, IOException {
      // decode the timestamp first
      final String timerId = STRING_CODER.decode(inStream);
      // The namespace needs two-phase deserialization:
      // first from bytes into a string, then from string to namespace object using windowCoder.
      final StateNamespace namespace =
          StateNamespaces.fromString(STRING_CODER.decode(inStream), windowCoder);
      K key = null;
      if (keyCoder != null) {
        key = keyCoder.decode(inStream);
      }

      return new TimerKey<>(key, namespace, timerId);
    }

    @Override
    public List<? extends Coder<?>> getCoderArguments() {
      return Arrays.asList(keyCoder, windowCoder);
    }

    @Override
    public void verifyDeterministic() throws NonDeterministicException {}
  }
}