reminders: Add API endpoint to schedule reminders.

zerver/views/reminders.py

@@ -0,0 +1,35 @@
+from django.http import HttpRequest, HttpResponse
+from django.utils.timezone import now as timezone_now
+from pydantic import Json
+
+from zerver.actions.reminders import schedule_reminder_for_message
+from zerver.lib.exceptions import DeliveryTimeNotInFutureError
+from zerver.lib.request import RequestNotes
+from zerver.lib.response import json_success
+from zerver.lib.timestamp import timestamp_to_datetime
+from zerver.lib.typed_endpoint import typed_endpoint
+from zerver.models import UserProfile
+
+
+@typed_endpoint
+def create_reminders_message_backend(
+    request: HttpRequest,
+    user_profile: UserProfile,
+    *,
+    message_id: Json[int],
+    scheduled_delivery_timestamp: Json[int],
+) -> HttpResponse:
+    deliver_at = timestamp_to_datetime(scheduled_delivery_timestamp)
+    if deliver_at <= timezone_now():
+        raise DeliveryTimeNotInFutureError
+
+    client = RequestNotes.get_notes(request).client
+    assert client is not None
+
+    reminder_id = schedule_reminder_for_message(
+        user_profile,
+        client,
+        message_id,
+        deliver_at,
+    )
+    return json_success(request, data={"reminder_id": reminder_id})