/*
 * Copyright (c) 2010-2013 TMate Software Ltd
 *  
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * For information on how to redistribute this software under
 * the terms of a license other than GNU General Public License
 * contact TMate Software at support@hg4j.com
 */
package org.tmatesoft.hg.repo;

import static org.tmatesoft.hg.core.HgIterateDirection.OldToNew;
import static org.tmatesoft.hg.repo.HgInternals.wrongRevisionIndex;
import static org.tmatesoft.hg.repo.HgRepository.*;
import static org.tmatesoft.hg.util.LogFacility.Severity.Info;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.Arrays;

import org.tmatesoft.hg.core.HgCallbackTargetException;
import org.tmatesoft.hg.core.HgChangesetFileSneaker;
import org.tmatesoft.hg.core.HgIterateDirection;
import org.tmatesoft.hg.core.Nodeid;
import org.tmatesoft.hg.internal.BlameHelper;
import org.tmatesoft.hg.internal.DataAccess;
import org.tmatesoft.hg.internal.FileHistory;
import org.tmatesoft.hg.internal.FileRevisionHistoryChunk;
import org.tmatesoft.hg.internal.FileUtils;
import org.tmatesoft.hg.internal.FilterByteChannel;
import org.tmatesoft.hg.internal.FilterDataAccess;
import org.tmatesoft.hg.internal.Internals;
import org.tmatesoft.hg.internal.Metadata;
import org.tmatesoft.hg.internal.RevlogStream;
import org.tmatesoft.hg.util.ByteChannel;
import org.tmatesoft.hg.util.CancelSupport;
import org.tmatesoft.hg.util.CancelledException;
import org.tmatesoft.hg.util.LogFacility;
import org.tmatesoft.hg.util.Pair;
import org.tmatesoft.hg.util.Path;
import org.tmatesoft.hg.util.ProgressSupport;


/**
 * Regular user data file stored in the repository.
 * 
 * <p> Note, most methods accept index in the file's revision history, not that of changelog. Easy way to obtain 
 * changeset revision index from file's is to use {@link #getChangesetRevisionIndex(int)}. To obtain file's revision 
 * index for a given changeset, {@link HgManifest#getFileRevision(int, Path)} or {@link HgChangesetFileSneaker} may 
 * come handy. 
 *
 * @author Artem Tikhomirov
 * @author TMate Software Ltd.
 */
public final class HgDataFile extends Revlog {

	// absolute from repo root?
	// slashes, unix-style?
	// repo location agnostic, just to give info to user, not to access real storage
	private final Path path;
	private Metadata metadata; // get initialized on first access to file content.
	
	/*package-local*/HgDataFile(HgRepository hgRepo, Path filePath, RevlogStream content) {
		super(hgRepo, content, false);
		path = filePath;
	}

	/*package-local*/HgDataFile(HgRepository hgRepo, Path filePath) {
		super(hgRepo);
		path = filePath;
	}

	// exists is not the best name possible. now it means no file with such name was ever known to the repo.
	// it might be confused with files existed before but lately removed. TODO HgFileNode.exists makes more sense.
	// or HgDataFile.known()
	public boolean exists() {
		return content != null; // XXX need better impl
	}

	/**
	 * Human-readable file name, i.e. "COPYING", not "store/data/_c_o_p_y_i_n_g.i"
	 */
	public Path getPath() {
		return path; // hgRepo.backresolve(this) -> name? In this case, what about hashed long names?
	}

	/**
	 * Handy shorthand for {@link #getLength(int) length(getRevisionIndex(nodeid))}
	 *
	 * @param nodeid revision of the file
	 * 
	 * @return size of the file content at the given revision
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public int getLength(Nodeid nodeid) throws HgRuntimeException {
		try {
			return getLength(getRevisionIndex(nodeid));
		} catch (HgInvalidControlFileException ex) {
			throw ex.isRevisionSet() ? ex : ex.setRevision(nodeid);
		} catch (HgInvalidRevisionException ex) {
			throw ex.isRevisionSet() ? ex : ex.setRevision(nodeid);
		}
	}
	
	/**
 	 * @param fileRevisionIndex - revision local index, non-negative. From predefined constants, only {@link HgRepository#TIP} makes sense. 
	 * @return size of the file content at the revision identified by local revision number.
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public int getLength(int fileRevisionIndex) throws HgRuntimeException {
		if (wrongRevisionIndex(fileRevisionIndex) || fileRevisionIndex == BAD_REVISION) {
			throw new HgInvalidRevisionException(fileRevisionIndex);
		}
		if (fileRevisionIndex == TIP) {
			fileRevisionIndex = getLastRevision();
		} else if (fileRevisionIndex == WORKING_COPY) {
			File f = getRepo().getFile(this);
			if (f.exists()) {
				// single revision can't be greater than 2^32, shall be safe to cast to int
				return Internals.ltoi(f.length());
			}
			Nodeid fileRev = getWorkingCopyRevision();
			if (fileRev == null) {
				throw new HgInvalidRevisionException(String.format("File %s is not part of working copy", getPath()), null, fileRevisionIndex);
			}
			fileRevisionIndex = getRevisionIndex(fileRev);
		}
		if (metadata == null || !metadata.checked(fileRevisionIndex)) {
			checkAndRecordMetadata(fileRevisionIndex);
		}
		final int dataLen = content.dataLength(fileRevisionIndex);
		if (metadata.known(fileRevisionIndex)) {
			return dataLen - metadata.dataOffset(fileRevisionIndex);
		}
		return dataLen;
	}
	
	/**
	 * Reads content of the file from working directory. If file present in the working directory, its actual content without
	 * any filters is supplied through the sink. If file does not exist in the working dir, this method provides content of a file 
	 * as if it would be refreshed in the working copy, i.e. its corresponding revision (according to dirstate) is read from the 
	 * repository, and filters repo -> working copy get applied.
	 * 
	 * NOTE, if file is missing from the working directory and is not part of the dirstate (but otherwise legal repository file,
	 * e.g. from another branch), no content would be supplied.
	 *     
	 * @param sink content consumer
	 * @throws CancelledException if execution of the operation was cancelled
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public void workingCopy(ByteChannel sink) throws CancelledException, HgRuntimeException {
		File f = getRepo().getFile(this);
		if (f.exists()) {
			final CancelSupport cs = CancelSupport.Factory.get(sink);
			final ProgressSupport progress = ProgressSupport.Factory.get(sink);
			final long flength = f.length();
			final int bsize = (int) Math.min(flength, 32*1024);
			progress.start((int) (flength > Integer.MAX_VALUE ? flength >>> 15 /*32 kb buf size*/ : flength));
			ByteBuffer buf = ByteBuffer.allocate(bsize);
			FileInputStream fis = null;
			try {
				fis = new FileInputStream(f);
				FileChannel fc = fis.getChannel();
				while (fc.read(buf) != -1) {
					cs.checkCancelled();
					buf.flip();
					int consumed = sink.write(buf);
					progress.worked(flength > Integer.MAX_VALUE ? 1 : consumed);
					buf.compact();
				}
			} catch (IOException ex) {
				throw new HgInvalidFileException("Working copy read failed", ex, f);
			} finally {
				progress.done();
				if (fis != null) {
					new FileUtils(getRepo().getSessionContext().getLog()).closeQuietly(fis);
				}
			}
		} else {
			Nodeid fileRev = getWorkingCopyRevision();
			if (fileRev == null) {
				// no content for this data file in the working copy - it is not part of the actual working state.
				// XXX perhaps, shall report this to caller somehow, not silently pass no data?
				return;
			}
			final int fileRevIndex = getRevisionIndex(fileRev);
			contentWithFilters(fileRevIndex, sink);
		}
	}
	
	/**
	 * @return file revision as recorded in repository manifest for dirstate parent, or <code>null</code> if no file revision can be found 
	 */
	private Nodeid getWorkingCopyRevision() throws HgInvalidControlFileException {
		final Pair<Nodeid, Nodeid> wcParents = getRepo().getWorkingCopyParents();
		Nodeid p = wcParents.first().isNull() ? wcParents.second() : wcParents.first();
		final HgChangelog clog = getRepo().getChangelog();
		final int csetRevIndex;
		if (p.isNull()) {
			// no dirstate parents 
			getRepo().getSessionContext().getLog().dump(getClass(), Info, "No dirstate parents, resort to TIP", getPath());
			// if it's a repository with no dirstate, use TIP then
			csetRevIndex = clog.getLastRevision();
			if (csetRevIndex == -1) {
				// shall not happen provided there's .i for this data file (hence at least one cset)
				// and perhaps exception is better here. However, null as "can't find" indication seems reasonable.
				return null;
			}
		} else {
			// common case to avoid searching complete changelog for nodeid match
			final Nodeid tipRev = clog.getRevision(TIP);
			if (tipRev.equals(p)) {
				csetRevIndex = clog.getLastRevision();
			} else {
				// bad luck, need to search honestly
				csetRevIndex = getRepo().getChangelog().getRevisionIndex(p);
			}
		}
		Nodeid fileRev = getRepo().getManifest().getFileRevision(csetRevIndex, getPath());
		// it's possible for a file to be in working dir and have store/.i but to belong e.g. to a different
		// branch than the one from dirstate. Thus it's possible to get null fileRev
		// which would serve as an indication this data file is not part of working copy
		return fileRev;
	}
	
	/**
	 * Access content of a file revision
	 * XXX not sure distinct method contentWithFilters() is the best way to do, perhaps, callers shall add filters themselves?
	 * 
 	 * @param fileRevisionIndex - revision local index, non-negative. From predefined constants, {@link HgRepository#TIP} and {@link HgRepository#WORKING_COPY} make sense. 
	 * @param sink content consumer
	 * 
	 * @throws CancelledException if execution of the operation was cancelled
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public void contentWithFilters(int fileRevisionIndex, ByteChannel sink) throws CancelledException, HgRuntimeException {
		if (fileRevisionIndex == WORKING_COPY) {
			workingCopy(sink); // pass un-mangled sink
		} else {
			content(fileRevisionIndex, new FilterByteChannel(sink, getRepo().getFiltersFromRepoToWorkingDir(getPath())));
		}
	}

	/**
	 * Retrieve content of specific revision. Content is provided as is, without any filters (e.g. keywords, eol, etc.) applied.
	 * For filtered content, use {@link #contentWithFilters(int, ByteChannel)}. 
	 * 
 	 * @param fileRevisionIndex - revision local index, non-negative. From predefined constants, {@link HgRepository#TIP} and {@link HgRepository#WORKING_COPY} make sense. 
	 * @param sink content consumer
	 * 
	 * @throws CancelledException if execution of the operation was cancelled
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public void content(int fileRevisionIndex, ByteChannel sink) throws CancelledException, HgRuntimeException {
		// for data files need to check heading of the file content for possible metadata
		// @see http://mercurial.selenic.com/wiki/FileFormats#data.2BAC8-
		if (fileRevisionIndex == TIP) {
			fileRevisionIndex = getLastRevision();
		}
		if (fileRevisionIndex == WORKING_COPY) {
			// sink is supposed to come into workingCopy without filters
			// thus we shall not get here (into #content) from #contentWithFilters(WC)
			workingCopy(sink);
			return;
		}
		if (wrongRevisionIndex(fileRevisionIndex) || fileRevisionIndex == BAD_REVISION) {
			throw new HgInvalidRevisionException(fileRevisionIndex);
		}
		if (sink == null) {
			throw new IllegalArgumentException();
		}
		if (metadata == null) {
			metadata = new Metadata(getRepo());
		}
		ErrorHandlingInspector insp;
		final LogFacility lf = getRepo().getSessionContext().getLog();
		if (metadata.none(fileRevisionIndex)) {
			insp = new ContentPipe(sink, 0, lf);
		} else if (metadata.known(fileRevisionIndex)) {
			insp = new ContentPipe(sink, metadata.dataOffset(fileRevisionIndex), lf);
		} else {
			// do not know if there's metadata
			insp = new MetadataInspector(metadata, new ContentPipe(sink, 0, lf));
		}
		insp.checkCancelled();
		super.content.iterate(fileRevisionIndex, fileRevisionIndex, true, insp);
		try {
			insp.checkFailed();
		} catch (HgInvalidControlFileException ex) {
			ex = ex.setFileName(getPath());
			throw ex.isRevisionIndexSet() ? ex : ex.setRevisionIndex(fileRevisionIndex);
		} catch (IOException ex) {
			HgInvalidControlFileException e = new HgInvalidControlFileException("Revision content access failed", ex, null);
			throw content.initWithIndexFile(e).setFileName(getPath()).setRevisionIndex(fileRevisionIndex);
		}
	}

	/**
	 * Walk complete change history of the file.
	 * @param inspector callback to visit changesets
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public void history(HgChangelog.Inspector inspector) throws HgRuntimeException {
		history(0, getLastRevision(), inspector);
	}

	/**
	 * Walk subset of the file's change history.
	 * @param start revision local index, inclusive; non-negative or {@link HgRepository#TIP}
	 * @param end revision local index, inclusive; non-negative or {@link HgRepository#TIP}
	 * @param inspector callback to visit changesets
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public void history(int start, int end, HgChangelog.Inspector inspector) throws HgRuntimeException {
		if (!exists()) {
			throw new IllegalStateException("Can't get history of invalid repository file node"); 
		}
		final int last = getLastRevision();
		if (end == TIP) {
			end = last;
		}
		if (start == TIP) {
			start = last;
		}
		HgInternals.checkRevlogRange(start, end, last);

		final int[] commitRevisions = new int[end - start + 1];
		final boolean[] needsSorting = { false };
		RevlogStream.Inspector insp = new RevlogStream.Inspector() {
			int count = 0;
			public void next(int revisionNumber, int actualLen, int baseRevision, int linkRevision, int parent1Revision, int parent2Revision, byte[] nodeid, DataAccess data) {
				if (count > 0) {
					if (commitRevisions[count -1] > linkRevision) {
						needsSorting[0] = true;
					}
				}
				commitRevisions[count++] = linkRevision;
			}
		};
		content.iterate(start, end, false, insp);
		final HgChangelog changelog = getRepo().getChangelog();
		if (needsSorting[0]) {
			// automatic tools (svnmerge?) produce unnatural file history
			// (e.g. cpython/Lib/doctest.py, revision 164 points to cset 63509, 165 - to 38453) 
			Arrays.sort(commitRevisions);
		}
		changelog.rangeInternal(inspector, commitRevisions);
	}
	
	/**
	 * For a given revision of the file (identified with revision index), find out index of the corresponding changeset.
	 *
	 * @return changeset revision index
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public int getChangesetRevisionIndex(int fileRevisionIndex) throws HgRuntimeException {
		return content.linkRevision(fileRevisionIndex);
	}

	/**
	 * Complements {@link #getChangesetRevisionIndex(int)} to get changeset revision that corresponds to supplied file revision
	 * 
	 * @param nid revision of the file
	 * @return changeset revision
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public Nodeid getChangesetRevision(Nodeid nid) throws HgRuntimeException {
		int changelogRevision = getChangesetRevisionIndex(getRevisionIndex(nid));
		return getRepo().getChangelog().getRevision(changelogRevision);
	}

	/**
	 * Tells whether this file originates from another repository file
	 * @return <code>true</code> if this file is a copy of another from the repository
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public boolean isCopy() throws HgRuntimeException {
		if (metadata == null || !metadata.checked(0)) {
			checkAndRecordMetadata(0);
		}
		if (!metadata.known(0)) {
			return false;
		}
		return metadata.find(0, "copy") != null;
	}

	/**
	 * Get name of the file this one was copied from.
	 * 
	 * @return name of the file origin
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public Path getCopySourceName() throws HgRuntimeException {
		if (isCopy()) {
			Path.Source ps = getRepo().getSessionContext().getPathFactory();
			return ps.path(metadata.find(0, "copy"));
		}
		throw new UnsupportedOperationException(); // XXX REVISIT, think over if Exception is good (clients would check isCopy() anyway, perhaps null is sufficient?)
	}
	
	/**
	 * 
	 * @return revision this file was copied from
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public Nodeid getCopySourceRevision() throws HgRuntimeException {
		if (isCopy()) {
			return Nodeid.fromAscii(metadata.find(0, "copyrev")); // XXX reuse/cache Nodeid
		}
		throw new UnsupportedOperationException();
	}

	/**
	 * Get file flags recorded in the manifest
 	 * @param fileRevisionIndex - revision local index, non-negative, or {@link HgRepository#TIP}. 
	 * @see HgManifest#getFileFlags(int, Path) 
	 * @throws HgRuntimeException subclass thereof to indicate issues with the library. <em>Runtime exception</em>
	 */
	public HgManifest.Flags getFlags(int fileRevisionIndex) throws HgRuntimeException {
		int changesetRevIndex = getChangesetRevisionIndex(fileRevisionIndex);
		return getRepo().getManifest().getFileFlags(changesetRevIndex, getPath());
	}
	
	/**
	 * mimic 'hg diff -r clogRevIndex1 -r clogRevIndex2'
	 */
	public void diff(int clogRevIndex1, int clogRevIndex2, HgBlameInspector insp) throws HgCallbackTargetException {
		// FIXME clogRevIndex1 and clogRevIndex2 may point to different files, need to decide whether to throw an exception
		// or to attempt to look up correct file node (tricky)
		int fileRevIndex1 = fileRevIndex(this, clogRevIndex1);
		int fileRevIndex2 = fileRevIndex(this, clogRevIndex2);
		BlameHelper bh = new BlameHelper(insp, 5);
		bh.useFileUpTo(this, clogRevIndex2);
		bh.diff(fileRevIndex1, clogRevIndex1, fileRevIndex2, clogRevIndex2);
	}
	
	/**
	 * Walk file history up/down to revision at given changeset and report changes for each revision
	 */
	public void annotate(int changelogRevisionIndex, HgBlameInspector insp, HgIterateDirection iterateOrder) throws HgCallbackTargetException {
		annotate(0, changelogRevisionIndex, insp, iterateOrder);
	}

	/**
	 * Walk file history range and report changes for each revision
	 */
	public void annotate(int changelogRevIndexStart, int changelogRevIndexEnd, HgBlameInspector insp, HgIterateDirection iterateOrder) throws HgCallbackTargetException {
		if (wrongRevisionIndex(changelogRevIndexStart) || wrongRevisionIndex(changelogRevIndexEnd)) {
			throw new IllegalArgumentException();
		}
		// Note, changelogRevIndexEnd may be TIP, while the code below doesn't tolerate constants
		//
		int lastRevision = getRepo().getChangelog().getLastRevision();
		if (changelogRevIndexEnd == TIP) {
			changelogRevIndexEnd = lastRevision;
		}
		HgInternals.checkRevlogRange(changelogRevIndexStart, changelogRevIndexEnd, lastRevision);
		if (!exists()) {
			return;
		}
		FileHistory fileHistory = new FileHistory(this, changelogRevIndexStart, changelogRevIndexEnd);
		fileHistory.build();
		BlameHelper bh = new BlameHelper(insp, 10);
		for (FileRevisionHistoryChunk fhc : fileHistory.iterate(OldToNew)) {
			// iteration order is not important here
			bh.useFileUpTo(fhc.getFile(), fhc.getEndChangeset());
		}
		int[] fileClogParentRevs = new int[2];
		int[] fileParentRevs = new int[2];
		for (FileRevisionHistoryChunk fhc : fileHistory.iterate(iterateOrder)) {
			for (int fri : fhc.fileRevisions(iterateOrder)) {
				int clogRevIndex = fhc.changeset(fri);
				// the way we built fileHistory ensures we won't walk past [changelogRevIndexStart..changelogRevIndexEnd]
				assert clogRevIndex >= changelogRevIndexStart;
				assert clogRevIndex <= changelogRevIndexEnd;
				fhc.fillFileParents(fri, fileParentRevs);
				fhc.fillCsetParents(fri, fileClogParentRevs);
				bh.annotateChange(fri, clogRevIndex, fileParentRevs, fileClogParentRevs);
			}
		}
	}

	/**
	 * Annotates changes of the file against its parent(s). 
	 * Unlike {@link #annotate(HgDataFile, int, Inspector, HgIterateDirection)}, doesn't
	 * walk file history, looks at the specified revision only. Handles both parents (if merge revision).
	 */
	public void annotateSingleRevision(int changelogRevisionIndex, HgBlameInspector insp) throws HgCallbackTargetException {
		// TODO detect if file is text/binary (e.g. looking for chars < ' ' and not \t\r\n\f
		int fileRevIndex = fileRevIndex(this, changelogRevisionIndex);
		int[] fileRevParents = new int[2];
		parents(fileRevIndex, fileRevParents, null, null);
		if (changelogRevisionIndex == TIP) {
			changelogRevisionIndex = getChangesetRevisionIndex(fileRevIndex);
		}
		BlameHelper bh = new BlameHelper(insp, 5);
		bh.useFileUpTo(this, changelogRevisionIndex);
		int[] fileClogParentRevs = new int[2];
		fileClogParentRevs[0] = fileRevParents[0] == NO_REVISION ? NO_REVISION : getChangesetRevisionIndex(fileRevParents[0]);
		fileClogParentRevs[1] = fileRevParents[1] == NO_REVISION ? NO_REVISION : getChangesetRevisionIndex(fileRevParents[1]);
		bh.annotateChange(fileRevIndex, changelogRevisionIndex, fileRevParents, fileClogParentRevs);
	}

	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder(getClass().getSimpleName());
		sb.append('(');
		sb.append(getPath());
		sb.append(')');
		return sb.toString();
	}
	
	private void checkAndRecordMetadata(int localRev) throws HgInvalidControlFileException {
		if (metadata == null) {
			metadata = new Metadata(getRepo());
		}
		// use MetadataInspector without delegate to process metadata only
		RevlogStream.Inspector insp = new MetadataInspector(metadata, null);
		super.content.iterate(localRev, localRev, true, insp);
	}
	

	private static int fileRevIndex(HgDataFile df, int csetRevIndex) {
		Nodeid fileRev = df.getRepo().getManifest().getFileRevision(csetRevIndex, df.getPath());
		return df.getRevisionIndex(fileRev);
	}


	private static class MetadataInspector extends ErrorHandlingInspector implements RevlogStream.Inspector {
		private final Metadata metadata;
		private final RevlogStream.Inspector delegate;

		/**
		 * @param _metadata never <code>null</code>
		 * @param chain <code>null</code> if no further data processing other than metadata is desired
		 */
		public MetadataInspector(Metadata _metadata, RevlogStream.Inspector chain) {
			metadata = _metadata;
			delegate = chain;
			setCancelSupport(CancelSupport.Factory.get(chain));
		}

		public void next(int revisionNumber, int actualLen, int baseRevision, int linkRevision, int parent1Revision, int parent2Revision, byte[] nodeid, DataAccess data) {
			try {
				if (metadata.tryRead(revisionNumber, data)) {
					// da is in prepared state (i.e. we consumed all bytes up to metadata end).
					// However, it's not safe to assume delegate won't call da.reset() for some reason,
					// and we need to ensure predictable result.
					data.reset();
					int offset = metadata.dataOffset(revisionNumber);
					data = new FilterDataAccess(data, offset, data.length() - offset);
				} else {
					data.reset();
				}
				if (delegate != null) {
					delegate.next(revisionNumber, actualLen, baseRevision, linkRevision, parent1Revision, parent2Revision, nodeid, data);
				}
			} catch (IOException ex) {
				recordFailure(ex);
			} catch (HgInvalidControlFileException ex) {
				recordFailure(ex.isRevisionIndexSet() ? ex : ex.setRevisionIndex(revisionNumber));
			}
		}

		@Override
		public void checkFailed() throws HgRuntimeException, IOException, CancelledException {
			super.checkFailed();
			if (delegate instanceof ErrorHandlingInspector) {
				// TODO need to add ErrorDestination (ErrorTarget/Acceptor?) and pass it around (much like CancelSupport get passed)
				// so that delegate would be able report its failures directly to caller without this hack
				((ErrorHandlingInspector) delegate).checkFailed();
			}
		}
	}
}