Calculates trend based on previous transaction's balance on the same date

[nicogaldamez]

Why?

• Balance was calculated using the previous date's balance instead of the previous transaction's balance.
• Fixes Bug: When balance and transaction exist on same day, balances not correctly calculated #1418

What?

Add a new method to the Entry model to calculate the balance based on the last entry's balance from the same day

What should we test?

Create two entries: an account valuation and an expense (or income) on the same day. The account valuation entry's trend and amount should use the balance of the other entry instead of the previous day's balance.

Paired with @bruno-costanzo

[zachgoll]

@nicogaldamez I agree with this logic; definitely more intuitive!

I'll go ahead and merge this because I think it gets the logic in place that we'll need. Longer term (and this is something I'll be returning to shortly), I think all of this logic probably needs to be consolidated to the Account::Balance::Syncer, and we should store a end_balance directly on the Account::Entry model, which will be calculated in the background.

That way, in these views, we can just read that value rather than performing all these queries.

[bruno-costanzo]

@zachgoll Note that persisting the value may lead to having to recalculate the after_balance for each subsequent transaction when entering a new entry on an old date.

[zachgoll]

@bruno-costanzo yep, definitely a denormalization trade-off, but in this case, I think it's worth it given the cost of running all these queries for every single transaction on every page load. Our account sync process should handle it nicely though!