From 150e700d024516d77caf4cc62e8878fbfd413014 Mon Sep 17 00:00:00 2001
From: Tobias Brox <tobias@redpill-linpro.com>
Date: Sun, 1 Oct 2023 23:36:09 +0200
Subject: [PATCH] WIP: a check_reverse_relation method

---
 caldav/__init__.py   |  2 +-
 caldav/objects.py    | 46 +++++++++++++++++++++++++++++++++++++++++++-
 tests/test_caldav.py | 18 +++++++++++++++++
 3 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/caldav/__init__.py b/caldav/__init__.py
index b7ea935c..c1bc367b 100644
--- a/caldav/__init__.py
+++ b/caldav/__init__.py
@@ -3,7 +3,7 @@
 
 import vobject.icalendar
 
-__version__ = "1.3.6"
+__version__ = "1.4.0dev"
 
 from .davclient import DAVClient
 from .objects import *
diff --git a/caldav/objects.py b/caldav/objects.py
index 01c19794..2afa602b 100644
--- a/caldav/objects.py
+++ b/caldav/objects.py
@@ -798,7 +798,6 @@ def _handle_relations(self, uid, ical_data):
     ## TODO: think more through this - is `save_foo` better than `add_foo`?
     ## `save_foo` should not be used for updating existing content on the
     ## calendar!
-
     add_event = save_event
     add_todo = save_todo
     add_journal = save_journal
@@ -1709,10 +1708,18 @@ class CalendarObjectResource(DAVObject):
     event, a todo-item, a journal entry, or a free/busy entry
     """
 
+    ## There is also STARTTOFINISH in RFC9253, it does not have any reverse
     RELTYPE_REVERSER: ClassVar = {
         "PARENT": "CHILD",
         "CHILD": "PARENT",
         "SIBLING": "SIBLING",
+        ## this is how Tobias Brox inteprets RFC9253:
+        "DEPENDENT": "FINISHTOSTART",
+        "FINISHTOSTART": "DEPENDENT",
+        ## next/first is a special case, linked list
+        ## it needs special handling when length of list<>2
+        "NEXT": "FIRST",
+        "FIRST": "NEXT",
     }
 
     _ENDPARAM = None
@@ -1827,6 +1834,8 @@ def set_relation(
             if set_reverse:
                 other = self.parent.object_by_uid(uid)
         if set_reverse:
+            ## TODO: special handling of NEXT/FIRST.
+            ## STARTTOFINISH does not have any equivalent "reverse".
             reltype_reverse = self.RELTYPE_REVERSER[reltype]
             other.set_relation(other=self, reltype=reltype_reverse, set_reverse=False)
 
@@ -1870,6 +1879,10 @@ def get_relatives(
 
         TODO: this is partially overlapped by plann.lib._relships_by_type
         in the plann tool.  Should consolidate the code.
+
+        TODO: should probably return some kind of object instead of a weird dict structure.
+        (but due to backward compatibility requirement, such an object should behave like
+        the current dict)
         """
         ret = defaultdict(set)
         relations = self.icalendar_component.get("RELATED-TO", [])
@@ -1895,6 +1908,37 @@ def get_relatives(
                             raise
         return ret
 
+
+    def check_reverse_relations(self, pdb: bool = False) -> list:
+        """
+        Goes through all relations and verifies that the return relation is set
+        Returns a list of objects missing a reverse (or an empty list if everything is OK)
+        """
+        ret = []
+        relations = self.get_relatives()
+        for reltype in relations:
+            for other in relations[reltype]:
+                revreltype = self.RELTYPE_REVERSER[reltype]
+                ## TODO: special case FIRST/NEXT needs special handling
+                other_relations = other.get_relatives(
+                    fetch_objects=False, reltypes={revreltype}
+                )
+                if (
+                    not str(self.icalendar_component["uid"])
+                    in other_relations[revreltype]
+                ):
+                    if pdb:
+                        import pdb
+
+                        pdb.set_trace()
+                    ret.append((other, revreltype))
+        return ret
+
+    ## TODO: fix this (and consolidate with _handle_relations / set_relation?)
+    # def ensure_reverse_relations(self):
+    #     missing_relations = self.check_reverse_relations()
+    #     ...
+
     def _get_icalendar_component(self, assert_one=False):
         """Returns the icalendar subcomponent - which should be an
         Event, Journal, Todo or FreeBusy from the icalendar class
diff --git a/tests/test_caldav.py b/tests/test_caldav.py
index c5068b93..fe51a5b5 100644
--- a/tests/test_caldav.py
+++ b/tests/test_caldav.py
@@ -1498,6 +1498,24 @@ def testCreateChildParent(self):
         assert len(foo["PARENT"]) == 1
         foo = parent_.get_relatives(relfilter=lambda x: x.params.get("GAP"))
 
+        ## verify the check_reverse_relations method (TODO: move to a separate test)
+        assert parent_.check_reverse_relations() == []
+        assert child_.check_reverse_relations() == []
+        assert grandparent_.check_reverse_relations() == []
+
+        ## My grandchild is also my child ... that sounds fishy
+        grandparent_.set_relation(child, reltype='CHILD', set_reverse=False)
+
+        ## The check_reverse should tell that something is amiss
+        missing_parent = grandparent_.check_reverse_relations()
+        assert len(missing_parent) == 1
+        assert missing_parent[0][0].icalendar_component['uid'] == 'ctuid2'
+        assert missing_parent[0][1] == 'PARENT'
+        ## But only when run on the grandparent.  The child is blissfully
+        ## unaware who the second parent is (even if reloading it).
+        child_.load()
+        assert child_.check_reverse_relations() == []
+
     def testSetDue(self):
         self.skip_on_compatibility_flag("read_only")