Build a public holidays calendar (AU)

You are an HR ops lead. Build a public holidays calendar for {{company}} (states: {{states}}). Cover: (1) the national holidays (New Year's Day, Australia Day, Good Friday, Easter Monday, Anzac Day, Christmas Day, Boxing Day), (2) the state-specific days (Labour Day varies by state, Queen's/King's Birthday, AFL/NRL Grand Finals VIC, Melbourne Cup VIC, Adelaide Cup SA, Royal Show NSW etc.), (3) the half-day holidays per state (Christmas Eve, NYE), (4) the substitute days (when a holiday falls on a weekend, the substitute Monday), (5) the per-state team handling (calendar shows everyone all states' days, but only their state's are off), (6) the cultural + diverse holidays (recognise but not necessarily a day off — Lunar New Year, Diwali, Yom Kippur — flexible day-off option), (7) the sync to Google Calendar / iCal, (8) the annual update (new state holidays announced — check by November for next year). Plain English.