FIX: remove duplicated holidays because of timezone change (#489)

When a user updates timezone, it creates duplicated holidays.

Beside the fix, migration was added to remove duplicated records. Timezone change can only update date for 24 hours, so we are searching for records with start date around that range.

db/migrate/20231124021939_delete_similar_holidays.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class DeleteSimilarHolidays < ActiveRecord::Migration[7.0]
+  def up
+    execute <<~SQL
+      DELETE
+        FROM calendar_events ce
+      WHERE
+        ce.id IN (SELECT DISTINCT(ce3.id) FROM calendar_events ce2
+                  LEFT JOIN calendar_events ce3 ON ce3.user_id = ce2.user_id AND ce3.description = ce2.description
+                  WHERE ce2.start_date >= (ce3.start_date - INTERVAL '1 days')
+                    AND ce2.start_date <= (ce3.start_date + INTERVAL '1 days')
+                    AND ce2.timezone IS NOT NULL
+                    AND ce3.timezone IS NULL
+                    AND ce3.id != ce2.id
+                    AND ce2.post_id IS NULL
+                    AND ce3.post_id IS NULL
+        )
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

jobs/scheduled/create_holiday_events.rb

@@ -76,17 +76,24 @@ module Jobs
                 end
 
               event =
-                CalendarEvent.find_or_initialize_by(
-                  topic_id: topic_id,
-                  user_id: user_id,
-                  description: holiday[:name],
-                  start_date: date,
-                  region: region,
-                )
+                CalendarEvent
+                  .where(topic_id: topic_id, user_id: user_id, description: holiday[:name])
+                  .where(
+                    "start_date >= :from AND start_date <= :to",
+                    from: date - 1.day,
+                    to: date + 1.day,
+                  )
+                  .first_or_initialize
 
-              event.username = usernames[user_id]
-              event.timezone = tz.name if tz
-              event.save!
+              event.update!(
+                topic_id: topic_id,
+                user_id: user_id,
+                description: holiday[:name],
+                start_date: date,
+                region: region,
+                username: usernames[user_id],
+                timezone: tz&.name,
+              )
             end
           end
       end

spec/jobs/scheduled/create_holiday_events_spec.rb

@@ -124,6 +124,19 @@ describe DiscourseCalendar::CreateHolidayEvents do
     expect(created_event.reload.username).to eq("new_username")
   end
 
+  it "does not create duplicates when timezone is changed" do
+    frenchy
+    DiscourseCalendar::CreateHolidayEvents.new.execute(nil)
+    created_event = CalendarEvent.last
+    expect(created_event.timezone).to eq(frenchy.user_option.timezone)
+    frenchy.user_option.update!(timezone: "Asia/Taipei")
+
+    expect { DiscourseCalendar::CreateHolidayEvents.new.execute(nil) }.not_to change {
+      CalendarEvent.count
+    }
+    expect(created_event.reload.timezone).to eq("Asia/Taipei")
+  end
+
   it "cleans up holidays from deactivated/silenced/suspended users" do
     frenchy
     freeze_time Time.zone.local(2019, 8, 1)