- Capture previous version of event pre-overwrite for use in notification hooks

- Use previous version of event in email hooks to determine added/deleted/updated email type

radicale/app/__init__.py

@@ -323,7 +323,7 @@ class Application(ApplicationPartDelete, ApplicationPartHead,
                 if "W" in self._rights.authorization(user, principal_path):
                     with self._storage.acquire_lock("w", user):
                         try:
-                            new_coll = self._storage.create_collection(principal_path)
+                            new_coll, _, _ = self._storage.create_collection(principal_path)
                             if new_coll:
                                 jsn_coll = self.configuration.get("storage", "predefined_collections")
                                 for (name_coll, props) in jsn_coll.items():

radicale/app/delete.py

@@ -24,7 +24,7 @@ from typing import Optional
 
 from radicale import httputils, storage, types, xmlutils
 from radicale.app.base import Access, ApplicationBase
-from radicale.hook import DeleteHookNotificationItem
+from radicale.hook import HookNotificationItem, HookNotificationItemTypes
 from radicale.log import logger
 
 
@@ -82,10 +82,12 @@ class ApplicationPartDelete(ApplicationBase):
                         return httputils.NOT_ALLOWED
                 for i in item.get_all():
                     hook_notification_item_list.append(
-                        DeleteHookNotificationItem(
-                            access.path,
-                            i.uid,
-                            old_content=item.serialize()  # type: ignore
+                        HookNotificationItem(
+                            notification_item_type=HookNotificationItemTypes.DELETE,
+                            path=access.path,
+                            uid=i.uid,
+                            old_content=item.serialize(),  # type: ignore
+                            new_content=None
                         )
                     )
                 xml_answer = xml_delete(base_prefix, path, item)
@@ -93,10 +95,12 @@ class ApplicationPartDelete(ApplicationBase):
                 assert item.collection is not None
                 assert item.href is not None
                 hook_notification_item_list.append(
-                    DeleteHookNotificationItem(
-                        access.path,
-                        item.uid,
-                        old_content=item.serialize()  # type: ignore
+                    HookNotificationItem(
+                        notification_item_type=HookNotificationItemTypes.DELETE,
+                        path=access.path,
+                        uid=item.uid,
+                        old_content=item.serialize(),  # type: ignore
+                        new_content=None,
                     )
                 )
                 xml_answer = xml_delete(

radicale/app/proppatch.py

@@ -102,9 +102,9 @@ class ApplicationPartProppatch(ApplicationBase):
                                            item)
                 if xml_content is not None:
                     hook_notification_item = HookNotificationItem(
-                        HookNotificationItemTypes.CPATCH,
-                        access.path,
-                        DefusedET.tostring(
+                        notification_item_type=HookNotificationItemTypes.CPATCH,
+                        path=access.path,
+                        new_content=DefusedET.tostring(
                             xml_content,
                             encoding=self._encoding
                         ).decode(encoding=self._encoding)

radicale/app/put.py

@@ -243,14 +243,27 @@ class ApplicationPartPut(ApplicationBase):
 
             if write_whole_collection:
                 try:
-                    etag = self._storage.create_collection(
-                        path, prepared_items, props).etag
+                    col, replaced_items, new_item_hrefs = self._storage.create_collection(
+                        href=path,
+                        items=prepared_items,
+                        props=props)
                     for item in prepared_items:
-                        hook_notification_item = HookNotificationItem(
-                            HookNotificationItemTypes.UPSERT,
-                            access.path,
-                            item.serialize()
-                        )
+                        # Try to grab the previously-existing item by href
+                        existing_item = replaced_items.get(item.href, None)
+                        if existing_item:
+                            hook_notification_item = HookNotificationItem(
+                                notification_item_type=HookNotificationItemTypes.UPSERT,
+                                path=access.path,
+                                old_content=existing_item.serialize(),
+                                new_content=item.serialize()
+                            )
+                        else:  # We assume the item is new because it was not in the replaced_items
+                            hook_notification_item = HookNotificationItem(
+                                notification_item_type=HookNotificationItemTypes.UPSERT,
+                                path=access.path,
+                                old_content=None,
+                                new_content=item.serialize()
+                            )
                         self._hook.notify(hook_notification_item)
                 except ValueError as e:
                     logger.warning(
@@ -267,12 +280,23 @@ class ApplicationPartPut(ApplicationBase):
 
                 href = posixpath.basename(pathutils.strip_path(path))
                 try:
-                    etag = parent_item.upload(href, prepared_item).etag
-                    hook_notification_item = HookNotificationItem(
-                        HookNotificationItemTypes.UPSERT,
-                        access.path,
-                        prepared_item.serialize()
-                    )
+                    uploaded_item, replaced_item = parent_item.upload(href, prepared_item)
+                    etag = uploaded_item.etag
+                    if replaced_item:
+                        # If the item was replaced, we notify with the old content
+                        hook_notification_item = HookNotificationItem(
+                            notification_item_type=HookNotificationItemTypes.UPSERT,
+                            path=access.path,
+                            old_content=replaced_item.serialize(),
+                            new_content=prepared_item.serialize()
+                        )
+                    else:  # If it was a new item, we notify with no old content
+                        hook_notification_item = HookNotificationItem(
+                            notification_item_type=HookNotificationItemTypes.UPSERT,
+                            path=access.path,
+                            old_content=None,
+                            new_content=prepared_item.serialize()
+                        )
                     self._hook.notify(hook_notification_item)
                 except ValueError as e:
                     # return better matching HTTP result in case errno is provided and catched

radicale/config.py

@@ -477,7 +477,7 @@ DEFAULT_CONFIG_SCHEMA: types.CONFIG_SCHEMA = OrderedDict([
             "value": "False",
             "help": "Send one email to all attendees, versus one email per attendee",
             "type": bool}),
-        ("added_template", {
+        ("new_or_added_to_event_template", {
             "value": """Hello $attendee_name,
 
 You have been added as an attendee to the following calendar event.
@@ -487,20 +487,31 @@ You have been added as an attendee to the following calendar event.
     $event_location
 
 This is an automated message. Please do not reply.""",
-            "help": "Template for the email sent when an event is added or updated. Select placeholder words prefixed with $ will be replaced",
+            "help": "Template for the email sent when an event is created or attendee is added. Select placeholder words prefixed with $ will be replaced",
             "type": str}),
-        ("removed_template", {
+        ("deleted_or_removed_from_event_template", {
             "value": """Hello $attendee_name,
 
-You have been removed as an attendee from the following calendar event.
+The following event has been deleted.
 
     $event_title
     $event_start_time - $event_end_time
     $event_location
 
 This is an automated message. Please do not reply.""",
-            "help": "Template for the email sent when an event is deleted. Select placeholder words prefixed with $ will be replaced",
+            "help": "Template for the email sent when an event is deleted or attendee is removed. Select placeholder words prefixed with $ will be replaced",
             "type": str}),
+        ("updated_event_template", {
+            "value": """Hello $attendee_name,
+The following event has been updated.
+    $event_title
+    $event_start_time - $event_end_time
+    $event_location
+    
+This is an automated message. Please do not reply.""",
+            "help": "Template for the email sent when an event is updated. Select placeholder words prefixed with $ will be replaced",
+            "type": str
+        })
     ])),
     ("web", OrderedDict([
         ("type", {

radicale/hook/__init__.py

@@ -55,10 +55,21 @@ def _cleanup(path):
 
 class HookNotificationItem:
 
-    def __init__(self, notification_item_type, path, content):
+    def __init__(self, notification_item_type, path, uid=None, new_content=None, old_content=None):
         self.type = notification_item_type.value
         self.point = _cleanup(path)
-        self.content = content
+        self.uid = uid
+        self.new_content = new_content
+        self.old_content = old_content
+
+    @property
+    def content(self):  # For backward compatibility
+        return self.uid or self.new_content or self.old_content
+
+    @property
+    def replaces_existing_item(self) -> bool:
+        """Check if this notification item replaces/deletes an existing item."""
+        return self.old_content is not None
 
     def to_json(self):
         return json.dumps(
@@ -67,9 +78,3 @@ class HookNotificationItem:
             sort_keys=True,
             indent=4
         )
-
-
-class DeleteHookNotificationItem(HookNotificationItem):
-    def __init__(self, path, uid, old_content=None):
-        super().__init__(notification_item_type=HookNotificationItemTypes.DELETE, path=path, content=uid)
-        self.old_content = old_content

radicale/hook/email/__init__.py

@@ -29,8 +29,7 @@ from typing import Any, Dict, List, Optional, Sequence, Tuple
 
 import vobject
 
-from radicale.hook import (BaseHook, DeleteHookNotificationItem,
-                           HookNotificationItem, HookNotificationItemTypes)
+from radicale.hook import (BaseHook, HookNotificationItem, HookNotificationItemTypes)
 from radicale.log import logger
 
 PLUGIN_CONFIG_SCHEMA = {
@@ -63,7 +62,7 @@ PLUGIN_CONFIG_SCHEMA = {
             "value": "",
             "type": str
         },
-        "added_template": {
+        "new_or_added_to_event_template": {
             "value": """Hello $attendee_name,
 
 You have been added as an attendee to the following calendar event.
@@ -75,15 +74,25 @@ You have been added as an attendee to the following calendar event.
 This is an automated message. Please do not reply.""",
             "type": str
         },
-        "removed_template": {
+        "deleted_or_removed_from_event_template": {
             "value": """Hello $attendee_name,
 
-You have been removed as an attendee from the following calendar event.
+The following event has been deleted.
 
     $event_title
     $event_start_time - $event_end_time
     $event_location
 
+This is an automated message. Please do not reply.""",
+            "type": str
+        },
+        "updated_event_template": {
+            "value": """Hello $attendee_name,
+The following event has been updated.
+    $event_title
+    $event_start_time - $event_end_time
+    $event_location
+    
 This is an automated message. Please do not reply.""",
             "type": str
         },
@@ -143,14 +152,22 @@ SMTP_SSL_VERIFY_MODES: Sequence[str] = (SMTP_SSL_VERIFY_MODE_ENUM.NONE.value,
                                         SMTP_SSL_VERIFY_MODE_ENUM.REQUIRED.value)
 
 
-def ics_contents_contains_invited_event(contents: str):
+def read_ics_event(contents: str) -> Optional['Event']:
+    """
+    Read the vobject item from the provided string and create an Event.
+    """
+    v_cal: vobject.base.Component = vobject.readOne(contents)
+    cal: Calendar = Calendar(vobject_item=v_cal)
+    return cal.event if cal.event else None
+
+
+def ics_contents_contains_event(contents: str):
     """
-    Check if the ICS contents contain an event (versus a VTODO or VJOURNAL).
+    Check if the ICS contents contain an event (versus a VADDRESSBOOK, VTODO or VJOURNAL).
     :param contents: The contents of the ICS file.
     :return: True if the ICS file contains an event, False otherwise.
     """
-    cal = vobject.readOne(contents)
-    return cal.vevent is not None
+    return read_ics_event(contents) is not None
 
 
 def extract_email(value: str) -> Optional[str]:
@@ -165,6 +182,27 @@ def extract_email(value: str) -> Optional[str]:
     return value if "@" in value else None
 
 
+def determine_added_removed_and_unaltered_attendees(original_event: 'Event',
+                                                    new_event: 'Event') -> (
+        Tuple)[List['Attendee'], List['Attendee'], List['Attendee']]:
+    """
+    Determine the added, removed and unaltered attendees between two events.
+    """
+    original_event_attendees = {attendee.email: attendee for attendee in original_event.attendees}
+    new_event_attendees = {attendee.email: attendee for attendee in new_event.attendees}
+    # Added attendees are those who are in the new event but not in the original event
+    added_attendees = [new_event_attendees[email] for email in new_event_attendees if
+                       email not in original_event_attendees]
+    # Removed attendees are those who are in the original event but not in the new event
+    removed_attendees = [original_event_attendees[email] for email in original_event_attendees if
+                         email not in new_event_attendees]
+    # Unaltered attendees are those who are in both events
+    unaltered_attendees = [original_event_attendees[email] for email in original_event_attendees if
+                           email in new_event_attendees]
+
+    return added_attendees, removed_attendees, unaltered_attendees
+
+
 class ContentLine:
     _key: str
     value: Any
@@ -611,8 +649,9 @@ class EmailConfig:
                  from_email: str,
                  send_mass_emails: bool,
                  dryrun: bool,
-                 added_template: MessageTemplate,
-                 removed_template: MessageTemplate):
+                 new_or_added_to_event_template: MessageTemplate,
+                 deleted_or_removed_from_event_template: MessageTemplate,
+                 updated_event_template: MessageTemplate):
         self.host = host
         self.port = port
         self.security = SMTP_SECURITY_TYPE_ENUM.from_string(value=security)
@@ -622,10 +661,9 @@ class EmailConfig:
         self.from_email = from_email
         self.send_mass_emails = send_mass_emails
         self.dryrun = dryrun
-        self.added_template = added_template
-        self.removed_template = removed_template
-        self.updated_template = added_template  # Reuse added template for updated events
-        self.deleted_template = removed_template  # Reuse removed template for deleted events
+        self.new_or_added_to_event_template = new_or_added_to_event_template
+        self.deleted_or_removed_from_event_template = deleted_or_removed_from_event_template
+        self.updated_event_template = updated_event_template
 
     def __str__(self) -> str:
         """
@@ -639,26 +677,16 @@ class EmailConfig:
 
     def send_added_email(self, attendees: List[Attendee], event: EmailEvent) -> bool:
         """
-        Send a notification for added attendees.
+        Send a notification for created events (and/or adding attendees).
         :param attendees: The attendees to inform.
-        :param event: The event the attendee is being added to.
+        :param event: The event being created (or the event the attendee is being added to).
         :return: True if the email was sent successfully, False otherwise.
         """
         ics_attachment = ICSEmailAttachment(file_content=event.ics_content, file_name=f"{event.file_name}")
 
-        return self._prepare_and_send_email(template=self.added_template, attendees=attendees, event=event,
+        return self._prepare_and_send_email(template=self.new_or_added_to_event_template, attendees=attendees, event=event,
                                             ics_attachment=ics_attachment)
 
-    def send_removed_email(self, attendees: List[Attendee], event: EmailEvent) -> bool:
-        """
-        Send a notification for removed attendees.
-        :param attendees: The attendees to inform.
-        :param event: The event the attendee is being removed from.
-        :return: True if the email was sent successfully, False otherwise.
-        """
-        return self._prepare_and_send_email(template=self.removed_template, attendees=attendees, event=event,
-                                            ics_attachment=None)
-
     def send_updated_email(self, attendees: List[Attendee], event: EmailEvent) -> bool:
         """
         Send a notification for updated events.
@@ -668,17 +696,17 @@ class EmailConfig:
         """
         ics_attachment = ICSEmailAttachment(file_content=event.ics_content, file_name=f"{event.file_name}")
 
-        return self._prepare_and_send_email(template=self.updated_template, attendees=attendees, event=event,
+        return self._prepare_and_send_email(template=self.updated_event_template, attendees=attendees, event=event,
                                             ics_attachment=ics_attachment)
 
     def send_deleted_email(self, attendees: List[Attendee], event: EmailEvent) -> bool:
         """
-        Send a notification for deleted events.
+        Send a notification for deleted events (and/or removing attendees).
         :param attendees: The attendees to inform.
-        :param event: The event being deleted.
+        :param event: The event being deleted (or the event the attendee is being removed from).
         :return: True if the email was sent successfully, False otherwise.
         """
-        return self._prepare_and_send_email(template=self.deleted_template, attendees=attendees, event=event,
+        return self._prepare_and_send_email(template=self.deleted_or_removed_from_event_template, attendees=attendees, event=event,
                                             ics_attachment=None)
 
     def _prepare_and_send_email(self, template: MessageTemplate, attendees: List[Attendee],
@@ -825,7 +853,6 @@ def _read_event(vobject_data: str) -> EmailEvent:
 class Hook(BaseHook):
     def __init__(self, configuration):
         super().__init__(configuration)
-        self.dryrun = self.configuration.get("hook", "dryrun")
         self.email_config = EmailConfig(
             host=self.configuration.get("hook", "smtp_server"),
             port=self.configuration.get("hook", "smtp_port"),
@@ -836,14 +863,18 @@ class Hook(BaseHook):
             from_email=self.configuration.get("hook", "from_email"),
             send_mass_emails=self.configuration.get("hook", "mass_email"),
             dryrun=self.configuration.get("hook", "dryrun"),
-            added_template=MessageTemplate(
+            new_or_added_to_event_template=MessageTemplate(
                 subject="You have been added to an event",
-                body=self.configuration.get("hook", "added_template")
+                body=self.configuration.get("hook", "new_or_added_to_event_template")
             ),
-            removed_template=MessageTemplate(
-                subject="You have been removed from an event",
-                body=self.configuration.get("hook", "removed_template")
+            deleted_or_removed_from_event_template=MessageTemplate(
+                subject="An event you were invited to has been deleted",
+                body=self.configuration.get("hook", "deleted_or_removed_from_event_template")
             ),
+            updated_event_template=MessageTemplate(
+                subject="An event you are invited to has been updated",
+                body=self.configuration.get("hook", "updated_event_template")
+            )
         )
         logger.info(
             "Email hook initialized with configuration: %s",
@@ -881,50 +912,97 @@ class Hook(BaseHook):
             return
 
         elif notification_type == HookNotificationItemTypes.UPSERT:
-            # Handle upsert notifications (POST request for new item and PUT for updating existing item)
-
-            # We don't have access to the original content for a PUT request, just the incoming data
+            # Handle upsert notifications
 
-            item_str: str = notification_item.content  # type: ignore # A serialized vobject.base.Component
+            new_item_str: str = notification_item.new_content  # type: ignore # A serialized vobject.base.Component
+            previous_item_str: Optional[str] = notification_item.old_content
 
-            if not ics_contents_contains_invited_event(contents=item_str):
-                # If the ICS file does not contain an event, we do not send any notifications.
+            if not ics_contents_contains_event(contents=new_item_str):
+                # If ICS file does not contain an event, do not send any notifications (regardless of previous content).
                 logger.debug("No event found in the ICS file, skipping notification.")
                 return
 
-            email_event: EmailEvent = _read_event(vobject_data=item_str)  # type: ignore
+            email_event: EmailEvent = _read_event(vobject_data=new_item_str)  # type: ignore
+
+            if not previous_item_str:
+                # Dealing with a completely new event, no previous content to compare against.
+                # Email every attendee about the new event.
+                logger.debug("New event detected, sending notifications to all attendees.")
+                email_success: bool = self.email_config.send_added_email(  # type: ignore
+                    attendees=email_event.event.attendees,
+                    event=email_event
+                )
+                if not email_success:
+                    logger.error("Failed to send some or all added email notifications for event: %s", email_event.event.uid)
+                return
 
-            email_success: bool = self.email_config.send_updated_email(  # type: ignore
-                attendees=email_event.event.attendees,
-                event=email_event
-            )
-            if not email_success:
-                logger.error("Failed to send some or all email notifications for event: %s", email_event.event.uid)
+            # Dealing with an update to an existing event, compare new and previous content.
+            new_event: Event = read_ics_event(contents=new_item_str)
+            previous_event: Optional[Event] = read_ics_event(contents=previous_item_str)
+            if not previous_event:
+                # If we cannot parse the previous event for some reason, simply treat it as a new event.
+                logger.warning("Previous event content could not be parsed, treating as a new event.")
+                email_success: bool = self.email_config.send_added_email(  # type: ignore
+                    attendees=email_event.event.attendees,
+                    event=email_event
+                )
+                if not email_success:
+                    logger.error("Failed to send some or all added email notifications for event: %s", email_event.event.uid)
+                return
+
+            # Determine added, removed, and unaltered attendees
+            added_attendees, removed_attendees, unaltered_attendees = determine_added_removed_and_unaltered_attendees(
+                original_event=previous_event, new_event=new_event)
+
+            # Notify added attendees as "event created"
+            if added_attendees:
+                email_success: bool = self.email_config.send_added_email(  # type: ignore
+                    attendees=added_attendees,
+                    event=email_event
+                )
+                if not email_success:
+                    logger.error("Failed to send some or all added email notifications for event: %s", email_event.event.uid)
+
+            # Notify removed attendees as "event deleted"
+            if removed_attendees:
+                email_success: bool = self.email_config.send_deleted_email(  # type: ignore
+                    attendees=removed_attendees,
+                    event=email_event
+                )
+                if not email_success:
+                    logger.error("Failed to send some or all removed email notifications for event: %s", email_event.event.uid)
+
+            # Notify unaltered attendees as "event updated"
+            if unaltered_attendees:
+                # TODO: Determine WHAT was updated in the event and send a more specific message if needed
+                # TODO: Don't send an email to unaltered attendees if only change was adding/removing other attendees
+                email_success: bool = self.email_config.send_updated_email(  # type: ignore
+                    attendees=unaltered_attendees,
+                    event=email_event
+                )
+                if not email_success:
+                    logger.error("Failed to send some or all updated email notifications for event: %s", email_event.event.uid)
 
             return
 
         elif notification_type == HookNotificationItemTypes.DELETE:
-            # Handle delete notifications (DELETE requests)
-
-            # Ensure it's a delete notification, as we need the old content
-            if not isinstance(notification_item, DeleteHookNotificationItem):
-                return
+            # Handle delete notifications
 
-            item_str: str = notification_item.old_content  # type: ignore # A serialized vobject.base.Component
+            deleted_item_str: str = notification_item.old_content  # type: ignore # A serialized vobject.base.Component
 
-            if not ics_contents_contains_invited_event(contents=item_str):
+            if not ics_contents_contains_event(contents=deleted_item_str):
                 # If the ICS file does not contain an event, we do not send any notifications.
                 logger.debug("No event found in the ICS file, skipping notification.")
                 return
 
-            email_event: EmailEvent = _read_event(vobject_data=item_str)  # type: ignore
+            email_event: EmailEvent = _read_event(vobject_data=deleted_item_str)  # type: ignore
 
             email_success: bool = self.email_config.send_deleted_email(  # type: ignore
                 attendees=email_event.event.attendees,
                 event=email_event
             )
             if not email_success:
-                logger.error("Failed to send some or all email notifications for event: %s", email_event.event.uid)
+                logger.error("Failed to send some or all deleted email notifications for event: %s", email_event.event.uid)
 
             return
 

radicale/storage/__init__.py

@@ -28,7 +28,7 @@ import json
 import xml.etree.ElementTree as ET
 from hashlib import sha256
 from typing import (Callable, ContextManager, Iterable, Iterator, Mapping,
-                    Optional, Sequence, Set, Tuple, Union, overload)
+                    Optional, Sequence, Set, Tuple, Union, overload, Dict, List)
 
 import vobject
 
@@ -175,8 +175,11 @@ class BaseCollection:
         return False
 
     def upload(self, href: str, item: "radicale_item.Item") -> (
-            "radicale_item.Item"):
-        """Upload a new or replace an existing item."""
+            "radicale_item.Item", Optional["radicale_item.Item"]):
+        """Upload a new or replace an existing item.
+
+        Return the uploaded item and the old item if it was replaced.
+        """
         raise NotImplementedError
 
     def delete(self, href: Optional[str] = None) -> None:
@@ -328,7 +331,8 @@ class BaseStorage:
     def create_collection(
             self, href: str,
             items: Optional[Iterable["radicale_item.Item"]] = None,
-            props: Optional[Mapping[str, str]] = None) -> BaseCollection:
+            props: Optional[Mapping[str, str]] = None) -> (
+            Tuple)[BaseCollection, Dict[str, "radicale_item.Item"], List[str]]:
         """Create a collection.
 
         ``href`` is the sanitized path.

radicale/storage/multifilesystem/create_collection.py

@@ -19,7 +19,7 @@
 
 import os
 from tempfile import TemporaryDirectory
-from typing import Iterable, Optional, cast
+from typing import Iterable, Optional, cast, List, Tuple, Dict
 
 import radicale.item as radicale_item
 from radicale import pathutils
@@ -30,9 +30,37 @@ from radicale.storage.multifilesystem.base import StorageBase
 
 class StoragePartCreateCollection(StorageBase):
 
+    def _discover_existing_items_pre_overwrite(self,
+                                               tmp_collection: "multifilesystem.Collection",
+                                               dst_path: str) -> Tuple[Dict[str, radicale_item.Item], List[str]]:
+        """Discover existing items in the collection before overwriting them."""
+        existing_items = {}
+        new_item_hrefs = []
+
+        existing_collection = self._collection_class(
+            cast(multifilesystem.Storage, self),
+            pathutils.unstrip_path(dst_path, True))
+        existing_item_hrefs = set(existing_collection._list())
+        tmp_collection_hrefs = set(tmp_collection._list())
+        for item_href in tmp_collection_hrefs:
+            if item_href not in existing_item_hrefs:
+                # Item in temporary collection does not exist in the existing collection (is new)
+                new_item_hrefs.append(item_href)
+                continue
+            # Item exists in both collections, grab the existing item for reference
+            try:
+                item = existing_collection._get(item_href, verify_href=False)
+                if item is not None:
+                    existing_items[item_href] = item
+            except Exception:
+                # TODO: Log exception?
+                continue
+
+        return existing_items, new_item_hrefs
+
     def create_collection(self, href: str,
                           items: Optional[Iterable[radicale_item.Item]] = None,
-                          props=None) -> "multifilesystem.Collection":
+                          props=None) -> Tuple["multifilesystem.Collection", Dict[str, radicale_item.Item], List[str]]:
         folder = self._get_collection_root_folder()
 
         # Path should already be sanitized
@@ -44,11 +72,14 @@ class StoragePartCreateCollection(StorageBase):
             self._makedirs_synced(filesystem_path)
             return self._collection_class(
                 cast(multifilesystem.Storage, self),
-                pathutils.unstrip_path(sane_path, True))
+                pathutils.unstrip_path(sane_path, True)), {}, []
 
         parent_dir = os.path.dirname(filesystem_path)
         self._makedirs_synced(parent_dir)
 
+        replaced_items: Dict[str, radicale_item.Item] = {}
+        new_item_hrefs: List[str] = []
+
         # Create a temporary directory with an unsafe name
         try:
             with TemporaryDirectory(prefix=".Radicale.tmp-", dir=parent_dir
@@ -68,14 +99,20 @@ class StoragePartCreateCollection(StorageBase):
                         col._upload_all_nonatomic(items, suffix=".vcf")
 
                 if os.path.lexists(filesystem_path):
+                    replaced_items, new_item_hrefs = self._discover_existing_items_pre_overwrite(
+                        tmp_collection=col,
+                        dst_path=sane_path)
                     pathutils.rename_exchange(tmp_filesystem_path, filesystem_path)
                 else:
+                    # If the destination path does not exist, obviously all items are new
+                    new_item_hrefs = list(col._list())
                     os.rename(tmp_filesystem_path, filesystem_path)
                 self._sync_directory(parent_dir)
         except Exception as e:
             raise ValueError("Failed to create collection %r as %r %s" %
                              (href, filesystem_path, e)) from e
 
+        # TODO: Return new-old pairs and just-new items (new vs updated)
         return self._collection_class(
             cast(multifilesystem.Storage, self),
-            pathutils.unstrip_path(sane_path, True))
+            pathutils.unstrip_path(sane_path, True)), replaced_items, new_item_hrefs

radicale/storage/multifilesystem/upload.py

@@ -21,7 +21,7 @@ import errno
 import os
 import pickle
 import sys
-from typing import Iterable, Iterator, TextIO, cast
+from typing import Iterable, Iterator, TextIO, cast, Optional, Tuple
 
 import radicale.item as radicale_item
 from radicale import pathutils
@@ -36,10 +36,11 @@ class CollectionPartUpload(CollectionPartGet, CollectionPartCache,
                            CollectionPartHistory, CollectionBase):
 
     def upload(self, href: str, item: radicale_item.Item
-               ) -> radicale_item.Item:
+               ) -> Tuple[radicale_item.Item, Optional[radicale_item.Item]]:
         if not pathutils.is_safe_filesystem_path_component(href):
             raise pathutils.UnsafePathError(href)
         path = pathutils.path_to_filesystem(self._filesystem_path, href)
+        old_item = self._get(href, verify_href=False)
         try:
             with self._atomic_write(path, newline="") as fo:  # type: ignore
                 f = cast(TextIO, fo)
@@ -67,7 +68,7 @@ class CollectionPartUpload(CollectionPartGet, CollectionPartCache,
         uploaded_item = self._get(href, verify_href=False)
         if uploaded_item is None:
             raise RuntimeError("Storage modified externally")
-        return uploaded_item
+        return uploaded_item, old_item
 
     def _upload_all_nonatomic(self, items: Iterable[radicale_item.Item],
                               suffix: str = "") -> None: