CavalliumDBEngine/src/main/java/it/cavallium/dbengine/database/disk/LLLocalKeyPrefixReactiveRocksIterator.java

package it.cavallium.dbengine.database.disk;

import static it.cavallium.dbengine.database.LLUtils.MARKER_ROCKSDB;
import static it.cavallium.dbengine.database.LLUtils.generateCustomReadOptions;
import static it.cavallium.dbengine.database.LLUtils.isBoundedRange;
import static it.cavallium.dbengine.utils.StreamUtils.streamWhileNonNull;

import com.google.common.collect.Iterators;
import com.google.common.collect.Streams;
import it.cavallium.buffer.Buf;
import it.cavallium.dbengine.database.LLRange;
import it.cavallium.dbengine.database.LLUtils;
import it.cavallium.dbengine.database.disk.rocksdb.LLReadOptions;
import it.cavallium.dbengine.utils.DBException;
import it.cavallium.dbengine.utils.StreamUtils;
import java.io.IOException;
import java.util.Objects;
import java.util.concurrent.CompletionException;
import java.util.function.Supplier;
import java.util.stream.Stream;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.rocksdb.ReadOptions;
import org.rocksdb.RocksDBException;

public class LLLocalKeyPrefixReactiveRocksIterator {

	protected static final Logger logger = LogManager.getLogger(LLLocalKeyPrefixReactiveRocksIterator.class);

	private final RocksDBColumn db;
	private final int prefixLength;
	private final LLRange range;
	private final Supplier<LLReadOptions> readOptions;
	private final boolean canFillCache;
	private final boolean smallRange;

	public LLLocalKeyPrefixReactiveRocksIterator(RocksDBColumn db,
			int prefixLength,
			LLRange range,
			Supplier<LLReadOptions> readOptions,
			boolean canFillCache,
			boolean smallRange) {
		this.db = db;
		this.prefixLength = prefixLength;
		this.range = range;
		this.readOptions = readOptions != null ? readOptions : LLReadOptions::new;
		this.canFillCache = canFillCache;
		this.smallRange = smallRange;
	}


	public Stream<Buf> stream() {
		return streamWhileNonNull(() -> {
			try (var readOptions = generateCustomReadOptions(this.readOptions.get(), canFillCache, isBoundedRange(range), smallRange);
					var rocksIterator = db.newRocksIterator(readOptions, range, false)) {
				if (logger.isTraceEnabled()) {
					logger.trace(MARKER_ROCKSDB, "Range {} started", LLUtils.toStringSafe(range));
				}
				Buf firstGroupKey = null;
				while (rocksIterator.isValid()) {
					// Note that the underlying array is subject to changes!
					Buf key = rocksIterator.keyBuf();
					var keyLen = key.size();
					if (keyLen >= prefixLength) {
						if (firstGroupKey == null) {
							firstGroupKey = key.copy();
							assert firstGroupKey == null || firstGroupKey.size() >= prefixLength;
						} else if (!LLUtils.equals(firstGroupKey,
								0,
								key,
								0,
								prefixLength
						)) {
							break;
						}
					} else {
						logger.error("Skipped a key with length {}, the expected minimum prefix key length is {}!"
								+ " This key will be dropped", key.size(), prefixLength);
					}
					rocksIterator.next();
				}

				if (firstGroupKey != null) {
					var groupKeyPrefix = firstGroupKey.subList(0, prefixLength);

					if (logger.isTraceEnabled()) {
						logger.trace(MARKER_ROCKSDB,
								"Range {} is reading prefix {}",
								LLUtils.toStringSafe(range),
								LLUtils.toStringSafe(groupKeyPrefix)
						);
					}

					return groupKeyPrefix;
				} else {
					if (logger.isTraceEnabled()) {
						logger.trace(MARKER_ROCKSDB, "Range {} ended", LLUtils.toStringSafe(range));
					}
					return null;
				}
			} catch (RocksDBException ex) {
				if (logger.isTraceEnabled()) {
					logger.trace(MARKER_ROCKSDB, "Range {} failed", LLUtils.toStringSafe(range));
				}
				throw new CompletionException(new DBException("Range failed", ex));
			}
		});
	}

}