Hari Baik

The challenge

Choosing the right moment is knowledge held across the archipelago, but it
still lives as something individual people have memorised, and the printed
calendars in circulation say the same thing to every reader, even though the
original reckoning starts from each person's own birth day. There is a second
trap on the technical side: the pawukon calendar runs several cycles at once
and three of them do not divide evenly into 210 days, so an app that computes
them with plain modulo drifts a little at a time, and the error only surfaces
years later, when a holy day quietly disappears from the calendar.

What we built

Hari Baik computes everything from scratch as pure functions, with no
database. Three inheritances sit side by side: wariga for the day category,
primbon for character and leaning, and the 81-number fengshui for weighing a
business name. Caturwara, astawara and sangawara are held at the start of
their cycles as the rules require, and sasih names use nampih sasih, seven
intercalations every nineteen years. From a single birth date the app
assembles a daily reading, a full month calendar, birth traits, partner
compatibility, a life journey map, and a finder for the supporting days
around an event.

What it uses is the reckoning, not the ritual. The only input is a Gregorian
birth date, and what comes back is a reading of the day, not religious
instruction. That is what keeps it sensible across backgrounds, including
from outside Indonesia.

The result

The engine is tested against 41 reference dates and all 210 days of the
pawukon cycle, re-run on every code change. No model is inventing answers:
the same date always gives the same result, and anyone can work it out again.
The app installs to the home screen like any other, ships two themes, and is
available in Indonesian and English. Subscription rules are decided in one
place, so a paid page cannot ship without its guard.