Module calculator 

Core shift calculation functions.

All functions are pure: given the same inputs, always produce the same outputs. No platform dependencies, no I/O, no state.

The algorithm

date → calculate_day_offset(date, reference_date)
     → normalize_cycle_index(offset, cycle_length)
     → cycle[index]  →  ShiftType

Team phase offset is added to the day offset before normalization:

offset = (date - reference_date) + team_phase_offset

Functions

calculate_day_offset

Number of days between date and reference_date.

get_shift_info

Get full shift info (date, day of cycle, cycle index, shift type) in one call.

get_shift_type_for_date

Get the shift type for a given date.

normalize_cycle_index

Normalize any offset into the range 0..cycle_length.

team_phase_offset_for

Team phase offset in days.