/*
    * Copyright 2021 TiKV Project 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.tikv.common.operation.iterator;
  
  import com.google.protobuf.ByteString;
  import org.tikv.common.TiConfiguration;
  import org.tikv.common.exception.GrpcException;
  import org.tikv.common.exception.TiKVException;
  import org.tikv.common.key.Key;
  import org.tikv.common.region.RegionStoreClient;
  import org.tikv.common.region.RegionStoreClient.RegionStoreClientBuilder;
  import org.tikv.common.region.TiRegion;
  import org.tikv.common.util.BackOffFunction;
  import org.tikv.common.util.BackOffer;
  import org.tikv.kvproto.Kvrpcpb;
  
  public class RawScanIterator extends ScanIterator {
    private final BackOffer scanBackOffer;
  
    public RawScanIterator(
        TiConfiguration conf,
        RegionStoreClientBuilder builder,
        ByteString startKey,
        ByteString endKey,
        int limit,
        boolean keyOnly,
        BackOffer scanBackOffer) {
      super(conf, builder, startKey, endKey, limit, keyOnly);
  
      this.scanBackOffer = scanBackOffer;
    }
  
    @Override
    TiRegion loadCurrentRegionToCache() throws GrpcException {
      BackOffer backOffer = scanBackOffer;
      while (true) {
        try (RegionStoreClient client = builder.build(startKey, backOffer)) {
          client.setTimeout(conf.getRawKVScanTimeoutInMS());
          TiRegion region = client.getRegion();
          if (limit <= 0) {
            currentCache = null;
          } else {
            try {
              currentCache = client.rawScan(backOffer, startKey, limit, keyOnly);
              // Client will get the newest region during scan. So we need to
              // update region after scan.
              region = client.getRegion();
            } catch (final TiKVException e) {
              backOffer.doBackOff(BackOffFunction.BackOffFuncType.BoRegionMiss, e);
              continue;
            }
          }
          return region;
        }
      }
    }
  
    private boolean endOfScan() {
      if (!processingLastBatch) {
        return false;
      }
      ByteString lastKey = currentCache.get(index).getKey();
      return !lastKey.isEmpty() && Key.toRawKey(lastKey).compareTo(endKey) >= 0;
    }
  
    boolean isCacheDrained() {
      return currentCache == null || limit <= 0 || index >= currentCache.size() || index == -1;
    }
  
    @Override
    public boolean hasNext() {
      if (isCacheDrained() && cacheLoadFails()) {
        endOfScan = true;
        return false;
      }
      // continue when cache is empty but not null
      while (currentCache != null && currentCache.isEmpty()) {
        if (cacheLoadFails()) {
          return false;
        }
      }
      return !endOfScan();
    }
  
   private Kvrpcpb.KvPair getCurrent() {
     --limit;
     return currentCache.get(index++);
   }
 
   @Override
   public Kvrpcpb.KvPair next() {
     return getCurrent();
   }
 }