add statechange for owned-fraction in rgb21 invoice data

[cymqqqq]

Background:

Now there are Amount, and Ownedfraction in the RGB invoice module, that is
pub struct Amount( u64); and pub struct OwnedFraction(u64);. We can perform a state change operation for the amount type when we want to build a transfer transition, and there is also the check_add method for the amount type.
Both the StateChange and check_add for the amount type can perform algorithm operation(+, -).

Then for the rgb21 invoice, there is Ownedfraction which is u64 similar to Amount, and now if we want to build a transfer operation for the rgb21 contract, we just push all of them(owned fraction, token index) into the data state. So I think maybe there is also a state change and a check_add method requirement for the Ownedfraction type, and then the user can add an owned fraction when they want to transfer. Finally, they can push (changed owned fraction, token index) into a data state.

Description:

impl StateChange for Ownedfraction

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 22 lines in your changes missing coverage. Please review.

Project coverage is 17.5%. Comparing base (7f637c6) to head (e480eaf).
Report is 1 commits behind head on master.

Files	Patch %	Lines
src/interface/contract.rs	0.0%	22 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #227     +/-   ##
========================================
- Coverage    17.6%   17.5%   -0.1%     
========================================
  Files          37      37             
  Lines        7535    7557     +22     
========================================
  Hits         1323    1323             
- Misses       6212    6234     +22     

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[dr-orlovsky]

I think it is always nice to have compiler guarantees instead of unreachable - pls see my comments

[dr-orlovsky]

with Ord you can get rid of unreachable and instead enjoy compiler-provided exhaustive security for matches:

Suggested change

	*self = match self {
	OwnedFractionChange::Dec(neg) => OwnedFractionChange::Dec(*neg + sub),
	OwnedFractionChange::Zero => OwnedFractionChange::Dec(sub),
	OwnedFractionChange::Inc(pos) if *pos > sub => OwnedFractionChange::Inc(*pos - sub),
	OwnedFractionChange::Inc(pos) if *pos == sub => OwnedFractionChange::Zero,
	OwnedFractionChange::Inc(pos) if *pos < sub => OwnedFractionChange::Dec(sub - *pos),
	OwnedFractionChange::Inc(_) => unreachable!(),
	};
	*self = match self {
	OwnedFractionChange::Dec(neg) => OwnedFractionChange::Dec(*neg + sub),
	OwnedFractionChange::Zero => OwnedFractionChange::Dec(sub),
	OwnedFractionChange::Inc(pos) => match sub.cmp(pos) {
	Ordering::Less => OwnedFractionChange::Inc(*pos - sub),
	Ordering::Equal => OwnedFractionChange::Zero,
	Ordering::Greater => OwnedFractionChange::Dec(sub - *pos),
	},
	};

[dr-orlovsky]

This must be less, not greater - the order of comparison is reversed in the match

[dr-orlovsky]

ACK. Will wait for review of those actually working with NFTs - @zoedberg and @crisdut

[dr-orlovsky]

The PR makes sense for me. @zoedberg @crisdut can you confirm the same so we can merge it before the next release?