/*
    * Copyright (C) 2011, Google Inc. and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.internal.storage.dfs;
  
  import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.COMPACT;
  import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.GC;
  import static org.eclipse.jgit.internal.storage.pack.PackExt.INDEX;
  import static org.eclipse.jgit.internal.storage.pack.PackExt.PACK;
  import static org.eclipse.jgit.internal.storage.pack.PackExt.REFTABLE;
  import static org.eclipse.jgit.internal.storage.pack.StoredObjectRepresentation.PACK_DELTA;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Set;
  
  import org.eclipse.jgit.errors.IncorrectObjectTypeException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.internal.storage.file.PackIndex;
  import org.eclipse.jgit.internal.storage.file.PackReverseIndex;
  import org.eclipse.jgit.internal.storage.pack.PackWriter;
  import org.eclipse.jgit.internal.storage.reftable.ReftableCompactor;
  import org.eclipse.jgit.internal.storage.reftable.ReftableConfig;
  import org.eclipse.jgit.lib.AnyObjectId;
  import org.eclipse.jgit.lib.NullProgressMonitor;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.ObjectIdSet;
  import org.eclipse.jgit.lib.ProgressMonitor;
  import org.eclipse.jgit.revwalk.RevFlag;
  import org.eclipse.jgit.revwalk.RevObject;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.storage.pack.PackConfig;
  import org.eclipse.jgit.storage.pack.PackStatistics;
  import org.eclipse.jgit.util.BlockList;
  import org.eclipse.jgit.util.io.CountingOutputStream;
  
  /**
   * Combine several pack files into one pack.
   * <p>
   * The compactor combines several pack files together by including all objects
   * contained in each pack file into the same output pack. If an object appears
   * multiple times, it is only included once in the result. Because the new pack
   * is constructed by enumerating the indexes of the source packs, it is quicker
   * than doing a full repack of the repository, however the result is not nearly
   * as space efficient as new delta compression is disabled.
   * <p>
   * This method is suitable for quickly combining several packs together after
   * receiving a number of small fetch or push operations into a repository,
   * allowing the system to maintain reasonable read performance without expending
   * a lot of time repacking the entire repository.
   */
  public class DfsPackCompactor {
  	private final DfsRepository repo;
  	private final List<DfsPackFile> srcPacks;
  	private final List<DfsReftable> srcReftables;
  	private final List<ObjectIdSet> exclude;
  
  	private PackStatistics newStats;
  	private DfsPackDescription outDesc;
  
  	private int autoAddSize;
  	private ReftableConfig reftableConfig;
  
  	private RevWalk rw;
  	private RevFlag added;
  	private RevFlag isBase;
  
  	/**
  	 * Initialize a pack compactor.
  	 *
  	 * @param repository
  	 *            repository objects to be packed will be read from.
  	 */
  	public DfsPackCompactor(DfsRepository repository) {
  		repo = repository;
  		autoAddSize = 5 * 1024 * 1024; // 5 MiB
  		srcPacks = new ArrayList<>();
  		srcReftables = new ArrayList<>();
  		exclude = new ArrayList<>(4);
  	}
  
  	/**
  	 * Set configuration to write a reftable.
  	 *
  	 * @param cfg
  	 *            configuration to write a reftable. Reftable compacting is
 	 *            disabled (default) when {@code cfg} is {@code null}.
 	 * @return {@code this}
 	 */
 	public DfsPackCompactor setReftableConfig(ReftableConfig cfg) {
 		reftableConfig = cfg;
 		return this;
 	}
 
 	/**
 	 * Add a pack to be compacted.
 	 * <p>
 	 * All of the objects in this pack will be copied into the resulting pack.
 	 * The resulting pack will order objects according to the source pack's own
 	 * description ordering (which is based on creation date), and then by the
 	 * order the objects appear in the source pack.
 	 *
 	 * @param pack
 	 *            a pack to combine into the resulting pack.
 	 * @return {@code this}
 	 */
 	public DfsPackCompactor add(DfsPackFile pack) {
 		srcPacks.add(pack);
 		return this;
 	}
 
 	/**
 	 * Add a reftable to be compacted.
 	 *
 	 * @param table
 	 *            a reftable to combine.
 	 * @return {@code this}
 	 */
 	public DfsPackCompactor add(DfsReftable table) {
 		srcReftables.add(table);
 		return this;
 	}
 
 	/**
 	 * Automatically select pack and reftables to be included, and add them.
 	 * <p>
 	 * Packs are selected based on size, smaller packs get included while bigger
 	 * ones are omitted.
 	 *
 	 * @return {@code this}
 	 * @throws java.io.IOException
 	 *             existing packs cannot be read.
 	 */
 	public DfsPackCompactor autoAdd() throws IOException {
 		DfsObjDatabase objdb = repo.getObjectDatabase();
 		for (DfsPackFile pack : objdb.getPacks()) {
 			DfsPackDescription d = pack.getPackDescription();
 			if (d.getFileSize(PACK) < autoAddSize)
 				add(pack);
 			else
 				exclude(pack);
 		}
 
 		if (reftableConfig != null) {
 			for (DfsReftable table : objdb.getReftables()) {
 				DfsPackDescription d = table.getPackDescription();
 				if (d.getPackSource() != GC
 						&& d.getFileSize(REFTABLE) < autoAddSize) {
 					add(table);
 				}
 			}
 		}
 		return this;
 	}
 
 	/**
 	 * Exclude objects from the compacted pack.
 	 *
 	 * @param set
 	 *            objects to not include.
 	 * @return {@code this}.
 	 */
 	public DfsPackCompactor exclude(ObjectIdSet set) {
 		exclude.add(set);
 		return this;
 	}
 
 	/**
 	 * Exclude objects from the compacted pack.
 	 *
 	 * @param pack
 	 *            objects to not include.
 	 * @return {@code this}.
 	 * @throws java.io.IOException
 	 *             pack index cannot be loaded.
 	 */
 	public DfsPackCompactor exclude(DfsPackFile pack) throws IOException {
 		final PackIndex idx;
 		try (DfsReader ctx = (DfsReader) repo.newObjectReader()) {
 			idx = pack.getPackIndex(ctx);
 		}
 		return exclude(idx);
 	}
 
 	/**
 	 * Compact the pack files together.
 	 *
 	 * @param pm
 	 *            progress monitor to receive updates on as packing may take a
 	 *            while, depending on the size of the repository.
 	 * @throws java.io.IOException
 	 *             the packs cannot be compacted.
 	 */
 	public void compact(ProgressMonitor pm) throws IOException {
 		if (pm == null) {
 			pm = NullProgressMonitor.INSTANCE;
 		}
 
 		DfsObjDatabase objdb = repo.getObjectDatabase();
 		try (DfsReader ctx = objdb.newReader()) {
 			if (reftableConfig != null && !srcReftables.isEmpty()) {
 				compactReftables(ctx);
 			}
 			compactPacks(ctx, pm);
 
 			List<DfsPackDescription> commit = getNewPacks();
 			Collection<DfsPackDescription> remove = toPrune();
 			if (!commit.isEmpty() || !remove.isEmpty()) {
 				objdb.commitPack(commit, remove);
 			}
 		} finally {
 			rw = null;
 		}
 	}
 
 	private void compactPacks(DfsReader ctx, ProgressMonitor pm)
 			throws IOException, IncorrectObjectTypeException {
 		DfsObjDatabase objdb = repo.getObjectDatabase();
 		PackConfig pc = new PackConfig(repo);
 		pc.setIndexVersion(2);
 		pc.setDeltaCompress(false);
 		pc.setReuseDeltas(true);
 		pc.setReuseObjects(true);
 
 		try (PackWriter pw = new PackWriter(pc, ctx)) {
 			pw.setDeltaBaseAsOffset(true);
 			pw.setReuseDeltaCommits(false);
 
 			addObjectsToPack(pw, ctx, pm);
 			if (pw.getObjectCount() == 0) {
 				return;
 			}
 
 			boolean rollback = true;
 			initOutDesc(objdb);
 			try {
 				writePack(objdb, outDesc, pw, pm);
 				writeIndex(objdb, outDesc, pw);
 
 				PackStatistics stats = pw.getStatistics();
 
 				outDesc.setPackStats(stats);
 				newStats = stats;
 				rollback = false;
 			} finally {
 				if (rollback) {
 					objdb.rollbackPack(Collections.singletonList(outDesc));
 				}
 			}
 		}
 	}
 
 	private long estimatePackSize() {
 		// Every pack file contains 12 bytes of header and 20 bytes of trailer.
 		// Include the final pack file header and trailer size here and ignore
 		// the same from individual pack files.
 		long size = 32;
 		for (DfsPackFile pack : srcPacks) {
 			size += pack.getPackDescription().getFileSize(PACK) - 32;
 		}
 		return size;
 	}
 
 	private void compactReftables(DfsReader ctx) throws IOException {
 		DfsObjDatabase objdb = repo.getObjectDatabase();
 		Collections.sort(srcReftables, objdb.reftableComparator());
 
 		initOutDesc(objdb);
 		try (DfsReftableStack stack = DfsReftableStack.open(ctx, srcReftables);
 		     DfsOutputStream out = objdb.writeFile(outDesc, REFTABLE)) {
 			ReftableCompactor compact = new ReftableCompactor(out);
 			compact.addAll(stack.readers());
 			compact.setIncludeDeletes(true);
 			compact.setConfig(configureReftable(reftableConfig, out));
 			compact.compact();
 			outDesc.addFileExt(REFTABLE);
 			outDesc.setReftableStats(compact.getStats());
 		}
 	}
 
 	private void initOutDesc(DfsObjDatabase objdb) throws IOException {
 		if (outDesc == null) {
 			outDesc = objdb.newPack(COMPACT, estimatePackSize());
 		}
 	}
 
 	/**
 	 * Get all of the source packs that fed into this compaction.
 	 *
 	 * @return all of the source packs that fed into this compaction.
 	 */
 	public Collection<DfsPackDescription> getSourcePacks() {
 		Set<DfsPackDescription> src = new HashSet<>();
 		for (DfsPackFile pack : srcPacks) {
 			src.add(pack.getPackDescription());
 		}
 		for (DfsReftable table : srcReftables) {
 			src.add(table.getPackDescription());
 		}
 		return src;
 	}
 
 	/**
 	 * Get new packs created by this compaction.
 	 *
 	 * @return new packs created by this compaction.
 	 */
 	public List<DfsPackDescription> getNewPacks() {
 		return outDesc != null
 				? Collections.singletonList(outDesc)
 				: Collections.emptyList();
 	}
 
 	/**
 	 * Get statistics corresponding to the {@link #getNewPacks()}.
 	 * May be null if statistics are not available.
 	 *
 	 * @return statistics corresponding to the {@link #getNewPacks()}.
 	 *
 	 */
 	public List<PackStatistics> getNewPackStatistics() {
 		return outDesc != null
 				? Collections.singletonList(newStats)
 				: Collections.emptyList();
 	}
 
 	private Collection<DfsPackDescription> toPrune() {
 		Set<DfsPackDescription> packs = new HashSet<>();
 		for (DfsPackFile pack : srcPacks) {
 			packs.add(pack.getPackDescription());
 		}
 
 		Set<DfsPackDescription> reftables = new HashSet<>();
 		for (DfsReftable table : srcReftables) {
 			reftables.add(table.getPackDescription());
 		}
 
 		for (Iterator<DfsPackDescription> i = packs.iterator(); i.hasNext();) {
 			DfsPackDescription d = i.next();
 			if (d.hasFileExt(REFTABLE) && !reftables.contains(d)) {
 				i.remove();
 			}
 		}
 
 		for (Iterator<DfsPackDescription> i = reftables.iterator();
 				i.hasNext();) {
 			DfsPackDescription d = i.next();
 			if (d.hasFileExt(PACK) && !packs.contains(d)) {
 				i.remove();
 			}
 		}
 
 		Set<DfsPackDescription> toPrune = new HashSet<>();
 		toPrune.addAll(packs);
 		toPrune.addAll(reftables);
 		return toPrune;
 	}
 
 	private void addObjectsToPack(PackWriter pw, DfsReader ctx,
 			ProgressMonitor pm) throws IOException,
 			IncorrectObjectTypeException {
 		// Sort packs by description ordering, this places newer packs before
 		// older packs, allowing the PackWriter to be handed newer objects
 		// first and older objects last.
 		Collections.sort(
 				srcPacks,
 				Comparator.comparing(
 						DfsPackFile::getPackDescription,
 						DfsPackDescription.objectLookupComparator()));
 
 		rw = new RevWalk(ctx);
 		added = rw.newFlag("ADDED"); //$NON-NLS-1$
 		isBase = rw.newFlag("IS_BASE"); //$NON-NLS-1$
 		List<RevObject> baseObjects = new BlockList<>();
 
 		pm.beginTask(JGitText.get().countingObjects, ProgressMonitor.UNKNOWN);
 		for (DfsPackFile src : srcPacks) {
 			List<ObjectIdWithOffset> want = toInclude(src, ctx);
 			if (want.isEmpty())
 				continue;
 
 			PackReverseIndex rev = src.getReverseIdx(ctx);
 			DfsObjectRepresentation rep = new DfsObjectRepresentation(src);
 			for (ObjectIdWithOffset id : want) {
 				int type = src.getObjectType(ctx, id.offset);
 				RevObject obj = rw.lookupAny(id, type);
 				if (obj.has(added))
 					continue;
 
 				pm.update(1);
 				pw.addObject(obj);
 				obj.add(added);
 
 				src.representation(rep, id.offset, ctx, rev);
 				if (rep.getFormat() != PACK_DELTA)
 					continue;
 
 				RevObject base = rw.lookupAny(rep.getDeltaBase(), type);
 				if (!base.has(added) && !base.has(isBase)) {
 					baseObjects.add(base);
 					base.add(isBase);
 				}
 			}
 		}
 		for (RevObject obj : baseObjects) {
 			if (!obj.has(added)) {
 				pm.update(1);
 				pw.addObject(obj);
 				obj.add(added);
 			}
 		}
 		pm.endTask();
 	}
 
 	private List<ObjectIdWithOffset> toInclude(DfsPackFile src, DfsReader ctx)
 			throws IOException {
 		PackIndex srcIdx = src.getPackIndex(ctx);
 		List<ObjectIdWithOffset> want = new BlockList<>(
 				(int) srcIdx.getObjectCount());
 		SCAN: for (PackIndex.MutableEntry ent : srcIdx) {
 			ObjectId id = ent.toObjectId();
 			RevObject obj = rw.lookupOrNull(id);
 			if (obj != null && (obj.has(added) || obj.has(isBase)))
 				continue;
 			for (ObjectIdSet e : exclude)
 				if (e.contains(id))
 					continue SCAN;
 			want.add(new ObjectIdWithOffset(id, ent.getOffset()));
 		}
 		Collections.sort(want, (ObjectIdWithOffset a,
 				ObjectIdWithOffset b) -> Long.signum(a.offset - b.offset));
 		return want;
 	}
 
 	private static void writePack(DfsObjDatabase objdb,
 			DfsPackDescription pack,
 			PackWriter pw, ProgressMonitor pm) throws IOException {
 		try (DfsOutputStream out = objdb.writeFile(pack, PACK)) {
 			pw.writePack(pm, pm, out);
 			pack.addFileExt(PACK);
 			pack.setBlockSize(PACK, out.blockSize());
 		}
 	}
 
 	private static void writeIndex(DfsObjDatabase objdb,
 			DfsPackDescription pack,
 			PackWriter pw) throws IOException {
 		try (DfsOutputStream out = objdb.writeFile(pack, INDEX)) {
 			CountingOutputStream cnt = new CountingOutputStream(out);
 			pw.writeIndex(cnt);
 			pack.addFileExt(INDEX);
 			pack.setFileSize(INDEX, cnt.getCount());
 			pack.setBlockSize(INDEX, out.blockSize());
 			pack.setIndexVersion(pw.getIndexVersion());
 		}
 	}
 
 	static ReftableConfig configureReftable(ReftableConfig cfg,
 			DfsOutputStream out) {
 		int bs = out.blockSize();
 		if (bs > 0) {
 			cfg = new ReftableConfig(cfg);
 			cfg.setRefBlockSize(bs);
 			cfg.setAlignBlocks(true);
 		}
 		return cfg;
 	}
 
 	private static class ObjectIdWithOffset extends ObjectId {
 		final long offset;
 
 		ObjectIdWithOffset(AnyObjectId id, long ofs) {
 			super(id);
 			offset = ofs;
 		}
 	}
 }