[Feature] Rule action for basic calculation instead of only being able to set it

[dj-bauer]

Verified feature request does not already exist?

• I have searched and found no existing issue

💻

• Would you like to implement this feature?

Pitch: what problem are you trying to solve?

When creating a rule there is already the possibility to set the amount transferred, but now i would like basic arithmetic functionality or at least multiplying by a factor.

My usecase is this:
I have an account for cash, and one for my Food court balance.
When I load up my food card with more than 20€ at a time, i get a 5% bonus.
So far we can add the following rule for this:

if
    account is Cash
    payee is Mensa
    amount is greater  equal 20€
then
    set amount to 21€

I believe this functionality could be useful to a number of applications, where you get bonuses or similar.

Describe your ideal solution to this problem

My imagined way of implementing this functionality in the user interface would be by adding a fourth action.
So far we have the action set, prepend to notes and append to notes.

We could add another field, that says calculate which lets you select an operation like for the start +, -, *, /.
Each of these operations obviously has two operands associated with it, so two fields show up, which can either be filled with variables associated with the transaction, or constant values.
This would allow an action like the following:
calculate amount as "amount * 1.05"
So the action would be calculate of the type Multiplication and it has the transaction field amount and the constant 1.05 associated with it.

Teaching and learning

We could expand the tab of actions in the Rule documentation entry.

[github-actions]

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