Money Conventions

This page describes how KahunaCart stores and calculates monetary amounts. It applies to every price, adjustment and transaction in the store.

KahunaCart uses vendored brick/money for calculation and BIGINT minor units for storage. Nothing monetary is ever a float.

Storage

• Every monetary column is named *_minor and holds the amount in the currency's minor unit. 1999 is $19.99, and 500 is ¥500, because JPY has no minor unit and brick/money knows that.
• Currency is stored once per order, in kahunacart_orders.currency as an ISO 4217 code. That order's items, adjustments and transactions are all in that currency.
• Catalog prices are in the store currency from config.
• Adjustment amount_minor is negative for discounts and positive for charges.
• Transaction amounts are always positive. Direction comes from type, either purchase or refund.

Calculation

• All arithmetic happens on Brick\Money\Money values obtained through Grav\Plugin\KahunaCart\Money\Money::minor() and stored back with ::toMinor().
• Raw integer math on minor units is allowed only for straight sums. Anything involving rates, division or allocation goes through brick/money.
• Default rounding is HALF_UP, applied explicitly at defined points, such as after a percentage or tax computation. It is never applied implicitly mid-chain. The Money helper's methods encode these points, so do not call brick with other rounding modes.
• Order-level amounts distributed across line items use Money::allocate(), which wraps brick's split() and guarantees no cent is created or lost. Order discounts and order-level tax back-allocation both use it.
• Tax-inclusive prices back-calculate the included tax with Money::includedTax(). The result is stored as an adjustment with included = 1, so it appears on receipts without changing the total.

Related

• Tax
• Shipping
• Coupons