This module replaces Odoo core's overtime calculation with one that satisfies the expectation:

overtime = (time recorded in hr.attendance records) - (expected working hours as per working calendar)

for every given day.

Note this is a draft and as of yet rather an invitation for discussion. The rough idea is:

• for every attendance, calculate the amount of working hours for the date with Odoo's resource calendar api (this way we get support for whatever module messes with work calendars for free), compute overtime as the difference between that and the worked hours from the attendances
• have a cronjob that creates overtime records for days without attendances as -(hours from the work calendar)

Currently this is super slow, but _compute_missing_overtime can be sped up considerably with some sql and a bit more convoluted grouping. It might also be worthwhile to have a start date for recalculations that admins can move forward periodically.

Further plan is to add hr_attendance_overtime_from_work_calendar_demo that depends on hr_holidays + hr_holidays_public and adds a bunch of (corner) test cases for this, and fix whatever comes out there.