Amount Preferences Fixes

[lollerfirst]

Fixes: #129

Changes

• getPreferences checks input amouts against the amounts of the keys
• keepPreferences and sendPreferences as different optional parameters in createSplitPayload.
• modify splitAmount behaviour -in case of no specified preference- to create amounts not from powers of 2
  but from the amounts of the keyset instead.
• splitAmount reorders its outputs by descending/ascending order.

PR Tasks

• Open PR
• run npm run test --> no failing unit tests
• run npm run format

[Egge21M]

This looks good to me, great job! However we should wait for development to be cleaned up (staging and dev got out of sync a bit), so that its a bit clearer which parts of the library this PR touched. Once that is done I can do a final review.

[lollerfirst]

Now the changes are isolated.

[callebtc]

This is an awesome PR!

If we do introduce breaking changed is on how the preference is passed, what do you guys think of getting rid of the (rather cumbersome?) format for the preference as sendPreference: [{ amount: 1, count: 3 }] and instead use a pure array of numbers a la sendPreference: [1, 1, 1]? I think I would prefer that.

[lollerfirst]

Probably a good idea. I think the original motive behind it was noble (not having an array with a billion useless 1s in it) but this is more practical.

[callebtc]

Really like this PR. We have to decide wether this should be a breaking change in the API or not. We could also deprecate the old method for setting the amount preference (see my comment).

[callebtc]

How about we deprecate preference, do the new thing in a new option called outputAmounts, and write a thin translation method that maps preference to outputAmounts, and issue a deprecation warning?

[lollerfirst]

I second this

[callebtc]

Maybe this is out of scope for this PR but we should also get rid of this behavior of the lib where it overwrites amount if preference is set. We should throw an error instead of overwriting things and force the implementor to use the library properly.

Example:

if (options?.preference) {
    amount = options?.preference?.reduce((acc, curr) => acc + curr.amount * curr.count, 0);
}