from landscape.diff import diff


class UserChanges(object):
"""Detect changes made since the last snapshot was taken.

If no snapshot is available all users and groups are reported.
When a snapshot is available, only the changes between the current
state and the snapshotted state are transmitted to the server.
"""

def __init__(self, persist, provider):
super(UserChanges, self).__init__()
self._persist = persist
self._provider = provider
# FIXME This shouldn't really be necessary. Not having it
# here with the current factoring is also problematic. Figure
# out a clean way to factor this. Gustavo suggested splitting
# it into _build_old_data and _build_new_data and just calling
# that from the necessary places.
self._refresh()

def _refresh(self):
"""Load the previous snapshot and update current data."""
self._old_users = self._persist.get("users", {})
self._old_groups = self._persist.get("groups", {})
self._new_users = self._create_index(
"username", self._provider.get_users())
self._new_groups = self._create_index(
"name", self._provider.get_groups())

def snapshot(self):
"""Save the current state and use it as a comparison snapshot."""
self._persist.set("users", self._new_users)
self._persist.set("groups", self._new_groups)

def clear(self):
"""
Reset the snapshot state and forget all knowledge of users and
groups.
"""
self._persist.remove("users")
self._persist.remove("groups")

def _create_index(self, key, sequence):
"""
Given a key and a sequence of dicts, return a dict of the form
C{{dict[key]: dict, ...}}.
"""
index = {}
for data in sequence:
index[data[key]] = data
return index

def create_diff(self):
"""Returns the changes since the last snapshot.

See landscape.message_schemas.USERS schema for a description of the
dictionary returned by this method.
"""
self._refresh()
changes = {}
changes.update(self._detect_user_changes())
changes.update(self._detect_group_changes())
return changes

def _detect_user_changes(self):
"""
Compare the current user snapshot to the old one and return a
C{dict} with C{create-users}, C{update-users} and
C{delete-users} fields. Fields without data aren't included
in the result.
"""
changes = {}
creates, updates, deletes = diff(self._old_users, self._new_users)
if creates:
changes["create-users"] = list(creates.itervalues())
if updates:
changes["update-users"] = list(updates.itervalues())
if deletes:
changes["delete-users"] = list(deletes.iterkeys())
return changes

def _detect_group_changes(self):
"""
Compare the current group snapshot to the old one and create a
C{dict} with C{create-groups}, C{delete-groups},
C{create-group-members} and {delete-group-members} fields.
Fields without data aren't included in the result.
"""
changes = {}
creates, updates, deletes = diff(self._old_groups, self._new_groups)

if creates:
groups = []
create_members = {}
for value in creates.itervalues():
# Use a copy to avoid removing the 'members' element
# from stored data.
value = value.copy()
members = value.pop("members")
if members:
create_members[value["name"]] = members
groups.append(value)
changes["create-groups"] = groups
if create_members:
changes["create-group-members"] = create_members

if updates:
remove_members = {}
create_members = {}
update_groups = []
for groupname, new_data in updates.iteritems():
old_data = self._old_groups[groupname]
old_members = set(old_data["members"])
new_members = set(new_data["members"])
created = new_members - old_members
if created:
create_members[groupname] = sorted(created)
removed = old_members - new_members
if removed:
remove_members[groupname] = sorted(removed)
if old_data["gid"] != new_data["gid"]:
update_groups.append({"name": groupname,
"gid": new_data["gid"]})
if create_members:
members = changes.setdefault("create-group-members", {})
members.update(create_members)
if remove_members:
members = changes.setdefault("delete-group-members", {})
members.update(remove_members)
if update_groups:
members = changes.setdefault("update-groups", [])
members.extend(update_groups)

if deletes:
changes["delete-groups"] = deletes.keys()

return changes