--- a/src/org/tmatesoft/hg/internal/RevlogStreamWriter.java	Wed Jan 30 15:48:36 2013 +0100
+++ b/src/org/tmatesoft/hg/internal/RevlogStreamWriter.java	Mon Feb 04 18:00:55 2013 +0100
@@ -17,16 +17,19 @@
 package org.tmatesoft.hg.internal;
 
 import static org.tmatesoft.hg.internal.Internals.REVLOGV1_RECORD_SIZE;
+import static org.tmatesoft.hg.repo.HgRepository.NO_REVISION;
 
 import java.io.IOException;
-import java.io.OutputStream;
 import java.nio.ByteBuffer;
 
 import org.tmatesoft.hg.core.Nodeid;
+import org.tmatesoft.hg.core.SessionContext;
+import org.tmatesoft.hg.repo.HgInvalidControlFileException;
+import org.tmatesoft.hg.repo.HgInvalidStateException;
 
 /**
  * 
- * TODO check if index is too big and split into index+data
+ * TODO separate operation to check if index is too big and split into index+data
  * 
  * @author Artem Tikhomirov
  * @author TMate Software Ltd.
@@ -34,13 +37,14 @@
 public class RevlogStreamWriter {
 
 	
-	public static class HeaderWriter {
+	/*XXX public because HgCloneCommand uses it*/
+	public static class HeaderWriter implements DataSerializer.DataSource {
 		private final ByteBuffer header;
 		private final boolean isInline;
 		private long offset;
 		private int length, compressedLength;
 		private int baseRev, linkRev, p1, p2;
-		private Nodeid nodeid;
+		private byte[] nodeid;
 		
 		public HeaderWriter(boolean inline) {
 			isInline = inline;
@@ -74,16 +78,21 @@
 		}
 		
 		public HeaderWriter linkRevision(int linkRevision) {
-			this.linkRev = linkRevision;
+			linkRev = linkRevision;
 			return this;
 		}
 		
 		public HeaderWriter nodeid(Nodeid n) {
-			this.nodeid = n;
+			nodeid = n.toByteArray();
 			return this;
 		}
-
-		public void write(OutputStream out) throws IOException {
+		
+		public HeaderWriter nodeid(byte[] nodeidBytes) {
+			nodeid = nodeidBytes;
+			return this;
+		}
+		
+		public void serialize(DataSerializer out) throws IOException {
 			header.clear();
 			if (offset == 0) {
 				int version = 1 /* RevlogNG */;
@@ -102,34 +111,161 @@
 			header.putInt(linkRev);
 			header.putInt(p1);
 			header.putInt(p2);
-			header.put(nodeid.toByteArray());
+			header.put(nodeid);
 			// assume 12 bytes left are zeros
-			out.write(header.array());
+			out.write(header.array(), 0, header.capacity());
 
 			// regardless whether it's inline or separate data,
 			// offset field always represent cumulative compressedLength 
 			// (while offset in the index file with inline==true differs by n*sizeof(header), where n is entry's position in the file) 
 			offset += compressedLength;
 		}
+		
+		public int serializeLength() {
+			return header.capacity();
+		}
+	}
+
+	private final DigestHelper dh = new DigestHelper();
+	private final RevlogCompressor revlogDataZip;
+	
+	
+	public RevlogStreamWriter(SessionContext ctx, RevlogStream stream) {
+		revlogDataZip = new RevlogCompressor(ctx);
 	}
 	
-	
-	private final DigestHelper dh = new DigestHelper();
+	private int lastEntryBase, lastEntryIndex;
+	private byte[] lastEntryContent;
+	private Nodeid lastEntryRevision;
+	private IntMap<Nodeid> revisionCache = new IntMap<Nodeid>(32);
 	
 	public void addRevision(byte[] content, int linkRevision, int p1, int p2) {
-		Nodeid p1Rev = parent(p1);
-		Nodeid p2Rev = parent(p2);
-		byte[] revisionBytes = dh.sha1(p1Rev, p2Rev, content).asBinary();
-		//final Nodeid revision = Nodeid.fromBinary(revisionBytes, 0);
-		// cache last revision (its delta and baseRev)
+		int revCount = revlogStream.revisionCount();
+		lastEntryIndex = revCount == 0 ? NO_REVISION : revCount - 1;
+		populateLastEntry();
+		//
 		PatchGenerator pg = new PatchGenerator();
-		byte[] prev = null;
-		Patch patch = pg.delta(prev, content);
-		byte[] patchContent;
-		// rest as in HgCloneCommand
+		Patch patch = pg.delta(lastEntryContent, content);
+		int patchSerializedLength = patch.serializedLength();
+		
+		final boolean writeComplete = preferCompleteOverPatch(patchSerializedLength, content.length);
+		DataSerializer.DataSource dataSource = writeComplete ? new DataSerializer.ByteArrayDataSource(content) : patch.new PatchDataSource();
+		revlogDataZip.reset(dataSource);
+		final int compressedLen;
+		final boolean useUncompressedData = preferCompressedOverComplete(revlogDataZip.getCompressedLength(), dataSource.serializeLength());
+		if (useUncompressedData) {
+			// compression wasn't too effective,
+			compressedLen = dataSource.serializeLength() + 1 /*1 byte for 'u' - uncompressed prefix byte*/;
+		} else {
+			compressedLen= revlogDataZip.getCompressedLength();
+		}
+		//
+		Nodeid p1Rev = revision(p1);
+		Nodeid p2Rev = revision(p2);
+		byte[] revisionNodeidBytes = dh.sha1(p1Rev, p2Rev, content).asBinary();
+		//
+
+		DataSerializer indexFile, dataFile, activeFile;
+		indexFile = dataFile = activeFile = null;
+		try {
+			//
+			activeFile = indexFile = revlogStream.getIndexStreamWriter();
+			final boolean isInlineData = revlogStream.isInlineData();
+			HeaderWriter revlogHeader = new HeaderWriter(isInlineData);
+			revlogHeader.length(content.length, compressedLen);
+			revlogHeader.nodeid(revisionNodeidBytes);
+			revlogHeader.linkRevision(linkRevision);
+			revlogHeader.parents(p1, p2);
+			revlogHeader.baseRevision(writeComplete ? lastEntryIndex+1 : lastEntryBase);
+			//
+			revlogHeader.serialize(indexFile);
+			
+			if (isInlineData) {
+				dataFile = indexFile;
+			} else {
+				dataFile = revlogStream.getDataStreamWriter();
+			}
+			activeFile = dataFile;
+			if (useUncompressedData) {
+				dataFile.writeByte((byte) 'u');
+				dataSource.serialize(dataFile);
+			} else {
+				int actualCompressedLenWritten = revlogDataZip.writeCompressedData(dataFile);
+				if (actualCompressedLenWritten != compressedLen) {
+					throw new HgInvalidStateException(String.format("Expected %d bytes of compressed data, but actually wrote %d in %s", compressedLen, actualCompressedLenWritten, revlogStream.getDataFileName()));
+				}
+			}
+			
+			lastEntryContent = content;
+			lastEntryBase = revlogHeader.baseRevision();
+			lastEntryIndex++;
+			lastEntryRevision = Nodeid.fromBinary(revisionNodeidBytes, 0);
+			revisionCache.put(lastEntryIndex, lastEntryRevision);
+		} catch (IOException ex) {
+			String m = String.format("Failed to write revision %d", lastEntryIndex+1, null);
+			HgInvalidControlFileException t = new HgInvalidControlFileException(m, ex, null);
+			if (activeFile == dataFile) {
+				throw revlogStream.initWithDataFile(t);
+			} else {
+				throw revlogStream.initWithIndexFile(t);
+			}
+		} finally {
+			indexFile.done();
+			if (dataFile != null && dataFile != indexFile) {
+				dataFile.done();
+			}
+		}
 	}
 	
-	private Nodeid parent(int parentIndex) {
-		return null;
+	private RevlogStream revlogStream;
+	private Nodeid revision(int revisionIndex) {
+		if (revisionIndex == NO_REVISION) {
+			return Nodeid.NULL;
+		}
+		Nodeid n = revisionCache.get(revisionIndex);
+		if (n == null) {
+			n = Nodeid.fromBinary(revlogStream.nodeid(revisionIndex), 0);
+			revisionCache.put(revisionIndex, n);
+		}
+		return n;
+	}
+	
+	private void populateLastEntry() throws HgInvalidControlFileException {
+		if (lastEntryIndex != NO_REVISION && lastEntryContent == null) {
+			assert lastEntryIndex >= 0;
+			final IOException[] failure = new IOException[1];
+			revlogStream.iterate(lastEntryIndex, lastEntryIndex, true, new RevlogStream.Inspector() {
+				
+				public void next(int revisionIndex, int actualLen, int baseRevision, int linkRevision, int parent1Revision, int parent2Revision, byte[] nodeid, DataAccess data) {
+					try {
+						lastEntryBase = baseRevision;
+						lastEntryRevision = Nodeid.fromBinary(nodeid, 0);
+						lastEntryContent = data.byteArray();
+					} catch (IOException ex) {
+						failure[0] = ex;
+					}
+				}
+			});
+			if (failure[0] != null) {
+				String m = String.format("Failed to get content of most recent revision %d", lastEntryIndex);
+				throw revlogStream.initWithDataFile(new HgInvalidControlFileException(m, failure[0], null));
+			}
+		}
+	}
+	
+	public static boolean preferCompleteOverPatch(int patchLength, int fullContentLength) {
+		return !decideWorthEffort(patchLength, fullContentLength);
+	}
+	
+	public static boolean preferCompressedOverComplete(int compressedLen, int fullContentLength) {
+		if (compressedLen <= 0) { // just in case, meaningless otherwise
+			return false;
+		}
+		return decideWorthEffort(compressedLen, fullContentLength);
+	}
+
+	// true if length obtained with effort is worth it 
+	private static boolean decideWorthEffort(int lengthWithExtraEffort, int lengthWithoutEffort) {
+		return lengthWithExtraEffort < (/* 3/4 of original */lengthWithoutEffort - (lengthWithoutEffort >>> 2));
 	}
 }