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    * Copyright (C) 2017, Google Inc.
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
    *
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  package org.eclipse.jgit.internal.storage.reftable;
  
  import java.io.IOException;
  import java.io.OutputStream;
  import java.util.ArrayDeque;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.eclipse.jgit.internal.storage.reftable.ReftableWriter.Stats;
  import org.eclipse.jgit.lib.PersonIdent;
  import org.eclipse.jgit.lib.ReflogEntry;
  
  /**
   * Merges reftables and compacts them into a single output.
   * <p>
   * For a partial compaction callers should {@link #setIncludeDeletes(boolean)}
   * to {@code true} to ensure the new reftable continues to use a delete marker
   * to shadow any lower reftable that may have the reference present.
   * <p>
   * By default all log entries within the range defined by
   * {@link #setMinUpdateIndex(long)} and {@link #setMaxUpdateIndex(long)} are
   * copied, even if no references in the output file match the log records.
   * Callers may truncate the log to a more recent time horizon with
   * {@link #setOldestReflogTimeMillis(long)}, or disable the log altogether with
   * {@code setOldestReflogTimeMillis(Long.MAX_VALUE)}.
   */
  public class ReftableCompactor {
  	private final ReftableWriter writer;
  	private final ArrayDeque<ReftableReader> tables = new ArrayDeque<>();
  
  	private long compactBytesLimit;
  	private long bytesToCompact;
  	private boolean includeDeletes;
  	private long minUpdateIndex = -1;
  	private long maxUpdateIndex;
  	private long oldestReflogTimeMillis;
  	private Stats stats;
  
  	/**
  	 * Creates a new compactor.
  	 *
  	 * @param out
  	 *            stream to write the compacted tables to. Caller is responsible
  	 *            for closing {@code out}.
  	 */
  	public ReftableCompactor(OutputStream out) {
  		writer = new ReftableWriter(out);
  	}
  
  	/**
  	 * Set configuration for the reftable.
  	 *
  	 * @param cfg
  	 *            configuration for the reftable.
  	 * @return {@code this}
  	 */
 	public ReftableCompactor setConfig(ReftableConfig cfg) {
 		writer.setConfig(cfg);
 		return this;
 	}
 
 	/**
 	 * Set limit on number of bytes from source tables to compact.
 	 *
 	 * @param bytes
 	 *            limit on number of bytes from source tables to compact.
 	 * @return {@code this}
 	 */
 	public ReftableCompactor setCompactBytesLimit(long bytes) {
 		compactBytesLimit = bytes;
 		return this;
 	}
 
 	/**
 	 * Whether to include deletions in the output, which may be necessary for
 	 * partial compaction.
 	 *
 	 * @param deletes
 	 *            {@code true} to include deletions in the output, which may be
 	 *            necessary for partial compaction.
 	 * @return {@code this}
 	 */
 	public ReftableCompactor setIncludeDeletes(boolean deletes) {
 		includeDeletes = deletes;
 		return this;
 	}
 
 	/**
 	 * Set the minimum update index for log entries that appear in the compacted
 	 * reftable.
 	 *
 	 * @param min
 	 *            the minimum update index for log entries that appear in the
 	 *            compacted reftable. This should be 1 higher than the prior
 	 *            reftable's {@code maxUpdateIndex} if this table will be used
 	 *            in a stack.
 	 * @return {@code this}
 	 */
 	public ReftableCompactor setMinUpdateIndex(long min) {
 		minUpdateIndex = min;
 		return this;
 	}
 
 	/**
 	 * Set the maximum update index for log entries that appear in the compacted
 	 * reftable.
 	 *
 	 * @param max
 	 *            the maximum update index for log entries that appear in the
 	 *            compacted reftable. This should be at least 1 higher than the
 	 *            prior reftable's {@code maxUpdateIndex} if this table will be
 	 *            used in a stack.
 	 * @return {@code this}
 	 */
 	public ReftableCompactor setMaxUpdateIndex(long max) {
 		maxUpdateIndex = max;
 		return this;
 	}
 
 	/**
 	 * Set oldest reflog time to preserve.
 	 *
 	 * @param timeMillis
 	 *            oldest log time to preserve. Entries whose timestamps are
 	 *            {@code >= timeMillis} will be copied into the output file. Log
 	 *            entries that predate {@code timeMillis} will be discarded.
 	 *            Specified in Java standard milliseconds since the epoch.
 	 * @return {@code this}
 	 */
 	public ReftableCompactor setOldestReflogTimeMillis(long timeMillis) {
 		oldestReflogTimeMillis = timeMillis;
 		return this;
 	}
 
 	/**
 	 * Add all of the tables, in the specified order.
 	 * <p>
 	 * Unconditionally adds all tables, ignoring the
 	 * {@link #setCompactBytesLimit(long)}.
 	 *
 	 * @param readers
 	 *            tables to compact. Tables should be ordered oldest first/most
 	 *            recent last so that the more recent tables can shadow the
 	 *            older results. Caller is responsible for closing the readers.
 	 * @throws java.io.IOException
 	 *             update indexes of a reader cannot be accessed.
 	 */
 	public void addAll(List<ReftableReader> readers) throws IOException {
 		for (ReftableReader r : readers) {
 			tables.add(r);
 			adjustUpdateIndexes(r);
 		}
 	}
 
 	/**
 	 * Try to add this reader at the bottom of the stack.
 	 * <p>
 	 * A reader may be rejected by returning {@code false} if the compactor is
 	 * already rewriting its {@link #setCompactBytesLimit(long)}. When this
 	 * happens the caller should stop trying to add tables, and execute the
 	 * compaction.
 	 *
 	 * @param reader
 	 *            the reader to insert at the bottom of the stack. Caller is
 	 *            responsible for closing the reader.
 	 * @return {@code true} if the compactor accepted this table; {@code false}
 	 *         if the compactor has reached its limit.
 	 * @throws java.io.IOException
 	 *             if size of {@code reader}, or its update indexes cannot be read.
 	 */
 	public boolean tryAddFirst(ReftableReader reader) throws IOException {
 		long sz = reader.size();
 		if (compactBytesLimit > 0 && bytesToCompact + sz > compactBytesLimit) {
 			return false;
 		}
 		bytesToCompact += sz;
 		adjustUpdateIndexes(reader);
 		tables.addFirst(reader);
 		return true;
 	}
 
 	private void adjustUpdateIndexes(ReftableReader reader) throws IOException {
 		if (minUpdateIndex == -1) {
 			minUpdateIndex = reader.minUpdateIndex();
 		} else {
 			minUpdateIndex = Math.min(minUpdateIndex, reader.minUpdateIndex());
 		}
 		maxUpdateIndex = Math.max(maxUpdateIndex, reader.maxUpdateIndex());
 	}
 
 	/**
 	 * Write a compaction to {@code out}.
 	 *
 	 * @throws java.io.IOException
 	 *             if tables cannot be read, or cannot be written.
 	 */
 	public void compact() throws IOException {
 		MergedReftable mr = new MergedReftable(new ArrayList<>(tables));
 		mr.setIncludeDeletes(includeDeletes);
 
 		writer.setMinUpdateIndex(Math.max(minUpdateIndex, 0));
 		writer.setMaxUpdateIndex(maxUpdateIndex);
 		writer.begin();
 		mergeRefs(mr);
 		mergeLogs(mr);
 		writer.finish();
 		stats = writer.getStats();
 	}
 
 	/**
 	 * Get statistics of the last written reftable.
 	 *
 	 * @return statistics of the last written reftable.
 	 */
 	public Stats getStats() {
 		return stats;
 	}
 
 	private void mergeRefs(MergedReftable mr) throws IOException {
 		try (RefCursor rc = mr.allRefs()) {
 			while (rc.next()) {
 				writer.writeRef(rc.getRef(), rc.getRef().getUpdateIndex());
 			}
 		}
 	}
 
 	private void mergeLogs(MergedReftable mr) throws IOException {
 		if (oldestReflogTimeMillis == Long.MAX_VALUE) {
 			return;
 		}
 
 		try (LogCursor lc = mr.allLogs()) {
 			while (lc.next()) {
 				long updateIndex = lc.getUpdateIndex();
 				if (updateIndex < minUpdateIndex
 						|| updateIndex > maxUpdateIndex) {
 					// Cannot merge log records outside the header's range.
 					continue;
 				}
 
 				String refName = lc.getRefName();
 				ReflogEntry log = lc.getReflogEntry();
 				if (log == null) {
 					if (includeDeletes) {
 						writer.deleteLog(refName, updateIndex);
 					}
 					continue;
 				}
 
 				PersonIdent who = log.getWho();
 				if (who.getWhen().getTime() >= oldestReflogTimeMillis) {
 					writer.writeLog(
 							refName,
 							updateIndex,
 							who,
 							log.getOldId(),
 							log.getNewId(),
 							log.getComment());
 				}
 			}
 		}
 	}
 }