--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/prevayler/implementation/SnapshotterImpl.java	Sat Mar 21 11:00:06 2009 +0000
@@ -0,0 +1,59 @@
+package org.prevayler.implementation;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.ObjectOutputStream;
+import java.io.IOException;
+
+import org.prevayler.PrevalentSystem;
+
+/**
+   Represents a snapshot waiting to be persisted to disk.  Invoke save() to
+   place the snapshot on disk - should only be called once all dirty state
+   (if any) has been flushed to disk.
+
+   @see org.dancres.blitz.txn.TxnManager
+ */
+class SnapshotterImpl implements Snapshotter {
+    private File theTemp;
+    private File theReal;
+    private byte[] theCachedCopy;
+
+    private NumberFileCreator theFileCreator;
+
+    private boolean shouldClean;
+
+    SnapshotterImpl(NumberFileCreator aCreator, boolean doClean)
+        throws IOException {
+
+        theTemp = aCreator.newTempSnapshot();
+        theReal = aCreator.newSnapshot();
+
+        theFileCreator = aCreator;
+        shouldClean = doClean;
+    }
+
+    void cacheSnapshot(PrevalentSystem aSystem) throws IOException {
+        ByteArrayOutputStream myCache = new ByteArrayOutputStream();
+        ObjectOutputStream mySnapper = new ObjectOutputStream(myCache);
+
+        mySnapper.writeObject(aSystem);
+        mySnapper.close();
+
+        theCachedCopy = myCache.toByteArray();
+    }
+
+    public void save() throws IOException {
+        FileOutputStream myOutput = new FileOutputStream(theTemp);
+        myOutput.write(theCachedCopy);
+        myOutput.close();
+
+        if (!theTemp.renameTo(theReal))
+            throw new IOException("Unable to rename " + theTemp +
+                                  " to " + theReal);
+
+        if (shouldClean)
+            theFileCreator.newCleaner().clean();
+    }
+}