Account Invoice - Change Currency

This module adds a currency-change tool to draft customer and vendor invoices in Odoo Accounting.

On the invoice form, next to the journal/currency area, users with multi-currency rights see a Custom Rate field and a refresh button labelled Update Currency. The button is only available to accounting managers and only while the invoice is still in draft.

When the user changes the invoice currency and clicks the button, Odoo converts every invoice line's unit price from the currency the invoice was originally created in to the newly selected currency, then recalculates taxes and totals. The original unit price of each line is remembered so conversions can be repeated without losing the starting value.

A custom exchange rate can be entered before converting. By default Odoo proposes the rate between the invoice's original currency and the new currency; after a first conversion, the rate is proposed between the last used currency and the current one. The custom rate field is hidden when the invoice is already in its original currency and is read-only once the invoice is no longer draft.

The module touches account.move, account.move.line and res.currency. It also stores the original currency on the invoice when it is created, so the conversion always starts from the right base.