It depends.
Custom calendars are difficult to handle, some are on monthly reporting, some weekly or some are periodic reporters. Further if you are looking for multiple countries like in Middle East where for some the Friday is off and for others Sunday is off. In the same breadth, for Muslims, the moon sighting which will impact the Ramadan as well as Eid. Even holidays which are different for different countries. So its difficult that a single solution fits for all.
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