store: add class definitions and stub for repack

Summary:
This introduces the high level classes that will implement the generic repack
logic.

Test Plan: Ran the repack in conjunction with later commits that use these apis.

Reviewers: rmcelroy, ttung, lcharignon, quark, mitrandir

Reviewed By: mitrandir

Differential Revision: https://phabricator.intern.facebook.com/D3249577

Signature: t1:3249577:1462225435:000f9cc29ae2a3d7fdbedf546c8936ef45d1e4cf

remotefilelog/repack.py

@@ -0,0 +1,84 @@
+import os
+from collections import defaultdict
+from mercurial import util
+from mercurial.node import nullid, bin, hex
+from mercurial.i18n import _
+import shallowutil
+
+class repacker(object):
+    """Class for orchestrating the repack of data and history information into a
+    new format.
+    """
+    def __init__(self, repo, data, history):
+        self.repo = repo
+        self.data = data
+        self.history = history
+
+    def run(self, targetdata, targethistory):
+        ledger = repackledger()
+
+        # Populate ledger from source
+        self.data.markledger(ledger)
+        self.history.markledger(ledger)
+
+        # Run repack
+        self.repackdata(ledger, targetdata)
+        self.repackhistory(ledger, targethistory)
+
+        # Call cleanup on each source
+        for source in ledger.sources:
+            source.cleanup(ledger)
+
+    def repackdata(self, ledger, target):
+        pass
+
+    def repackhistory(self, ledger, target):
+        pass
+
+class repackledger(object):
+    """Storage for all the bookkeeping that happens during a repack. It contains
+    the list of revisions being repacked, what happened to each revision, and
+    which source store contained which revision originally (for later cleanup).
+    """
+    def __init__(self):
+        self.entries = {}
+        self.sources = {}
+
+    def markdataentry(self, source, filename, node):
+        """Mark the given filename+node revision as having a data rev in the
+        given source.
+        """
+        entry = self._getorcreateentry(filename, node)
+        entry.datasource = True
+        self.sources.setdefault(source, set()).add(entry)
+
+    def markhistoryentry(self, source, filename, node):
+        """Mark the given filename+node revision as having a history rev in the
+        given source.
+        """
+        entry = self._getorcreateentry(filename, node)
+        entry.historysource = True
+        self.sources.setdefault(source, set()).add(entry)
+
+    def _getorcreateentry(self, filename, node):
+        value = self.entries.get((filename, node))
+        if not value:
+            value = repackentry(filename, node)
+            self.entries[(filename, node)] = value
+
+        return value
+
+class repackentry(object):
+    """Simple class representing a single revision entry in the repackledger.
+    """
+    def __init__(self, filename, node):
+        self.filename = filename
+        self.node = node
+        # If the revision has a data entry in the source
+        self.datasource = False
+        # If the revision has a history entry in the source
+        self.historysource = False
+        # If the revision's data entry was repacked into the repack target
+        self.datarepacked = False
+        # If the revision's history entry was repacked into the repack target
+        self.historyrepacked = False