# 0014. Business rules are configurable

- Status: Accepted
- Date: 2026-10-27

## Context

Shops differ in how they price and charge, even within one country: whether modifiers are charged
per item or once per order line, whether service charge is calculated before or after tax,
whether menu prices include tax. Hard-coding one practice forces every other shop to work around
OpenKedai or fork it.

## Decision

Where a business rule has more than one reasonable practice, OpenKedai makes it a setting
instead of hard-coding one. Each setting has a sensible default: the most common practice, taken
from the country pack where it is country-specific (see [ADR 0006](https://docs.openkedai.com/adr/0006-country-rules-are-data/)),
and can be overridden per outlet, sales channel or item as fits the rule.

Legal requirements are not settings: where the law fixes a rule (for example, service charge is
not subject to SST in Malaysia), the rule is enforced, and the country pack only describes it.

## Consequences

- `packages/core` takes options (for example `serviceChargeBase`, modifier `per`) rather than
  assuming one behaviour; defaults keep simple setups simple.
- Every option needs tests for each of its values, and the back office needs a place to set it.
- More options mean more combinations to test. Add an option when a real practice needs it, and
  keep the default path the well-trodden one.