--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hgext3rd/fastimport/vendor/python_fastimport/reftracker.py	Tue Jan 19 22:56:34 2021 +0000
@@ -0,0 +1,68 @@
+# Copyright (C) 2009 Canonical 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; either version 2 of the License, or
+# (at your option) any later version.
+#
+# 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.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+"""Tracker of refs."""
+
+from __future__ import absolute_import
+
+
+class RefTracker(object):
+
+    def __init__(self):
+        # Head tracking: last ref, last id per ref & map of commit ids to ref*s*
+        self.last_ref = None
+        self.last_ids = {}
+        self.heads = {}
+
+    def dump_stats(self, note):
+        self._show_stats_for(self.last_ids, "last-ids", note=note)
+        self._show_stats_for(self.heads, "heads", note=note)
+
+    def clear(self):
+        self.last_ids.clear()
+        self.heads.clear()
+
+    def track_heads(self, cmd):
+        """Track the repository heads given a CommitCommand.
+
+        :param cmd: the CommitCommand
+        :return: the list of parents in terms of commit-ids
+        """
+        # Get the true set of parents
+        if cmd.from_ is not None:
+            parents = [cmd.from_]
+        else:
+            last_id = self.last_ids.get(cmd.ref)
+            if last_id is not None:
+                parents = [last_id]
+            else:
+                parents = []
+        parents.extend(cmd.merges)
+
+        # Track the heads
+        self.track_heads_for_ref(cmd.ref, cmd.id, parents)
+        return parents
+
+    def track_heads_for_ref(self, cmd_ref, cmd_id, parents=None):
+        if parents is not None:
+            for parent in parents:
+                if parent in self.heads:
+                    del self.heads[parent]
+        self.heads.setdefault(cmd_id, set()).add(cmd_ref)
+        self.last_ids[cmd_ref] = cmd_id
+        self.last_ref = cmd_ref
+
+