# `Price`

An amount and whether it includes tax, so a gross price is never taken for a net one: shown as its amount, `£10.50`. The amount is never below 0.

[Money and banking](types.md#money-and-banking); not ordered; since Jadpo 0.1.0.

## Make one

Build one from its fields, `Price { amount: ...  includes_tax: ... }`.

This operation gives one: `money.apply_discount`.

## Fields

| Field | Type |
|---|---|
| `amount` | [`Money`](type-money.md) |
| `includes_tax` | `Bool` |

## Text, JSON and storage

It has no single text form, so `text.from` and `text.parse` don't take it. JSON sends an object of its parts.

| JSON |
|---|
| `{"amount":{"amount":1050,"currency":"GBP"},"includes_tax":true}` |
| `{"amount":{"amount":875,"currency":"GBP"},"includes_tax":false}` |
| `{"amount":{"amount":1200,"currency":"EUR"},"includes_tax":true}` |

It is stored in 3 columns, each named for the field, `_` and its suffix. This is `{"amount":{"amount":875,"currency":"GBP"},"includes_tax":false}`:

| Column | Type | Holds |
|---|---|---|
| `<field>_amount` | `bigint` | `875` |
| `<field>_currency` | `char(3)` | `'GBP'` |
| `<field>_includes_tax` | `boolean` | `FALSE` |

## Shown to people

`text.format(value, locale:)` shows it to people in their locale.

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `{"amount":{"amount":1050,"currency":"GBP"},"includes_tax":true}` | `£10.50` |
| `{"amount":{"amount":875,"currency":"GBP"},"includes_tax":false}` | `£8.75` |
| `{"amount":{"amount":1200,"currency":"EUR"},"includes_tax":true}` | `€12.00` |

## Operations

- `money.apply_discount(price: Price, discount: Discount) -> Price`: `price` with `discount` taken off its amount, keeping whether it includes tax: an amount off in the price's currency, or that percentage of the amount, rounded half to even to a minor unit, so 15% off £10.05 is £1.51 off. More off than the price leaves nothing. It fails with `currency_mismatch` for an amount off in another currency.

Like every standard type, it also has the contract's own operations: `text.format`, `json.read`, `json.write` and `==`. It isn't ordered, so `<` and sorting don't take it. [Every standard type meets one contract](../topics/every-standard-type-meets-one-contract.md) says how they work.