AndroidJetpack/Compose-Expense/doc/adr/001_balance_calculation_formula.md

How to calculate edited transaction if balance amount has edited?

Background

An Expense App have Account (cash/bank/ewallet/stock/etc), each Account have balance and record transactions (income, expense)

Use case:

• Initial balance 0
• Create income X 10.000 -> balance become 10.000
• Edit income X to 20.000 -> balance become 20.000
• Edit balance to 0 -> balance become 0
• Edit income X to 30.000 -> balance become 10.000

PS: why it become 10.000 not 30.000?, because the income is already accumulated in the account balance, so that any increased/reduced transaction amount only calculate the diff not whole amount

balance edited time before
transaction_amount record

prev_transaction_amount = get_transaction_amount_before_balance_edited
current_balance = current_balance + (new_transaction_amount - prev_transaction_amount)

Approaches

The following sections would evaluate possible approaches:

Approach #1

Record every edited balance and transaction amount

Cons:

Our storage will be huge if user do edited data often

Approach #2

Create base amount in transaction, whenever balance edited, base amount also updated. Base amount will be used as prev_transaction_amount

Cons:

Updating base amount will takes time if user have many transaction

Decision Log

Proceed with Approach 1

Don't select approach 2 because it require more write operation than approach 1