Convert BcpCoin amount to strings

[webmaster128]

[ethanfrey]

Fixed point format:

{
  "amount": "1234",
  "sigFigs": 2
}

is equivalent to "12.34" (amount * 10^-sigFigs)

We must add conversions between FixedPoint and the native serialized format for the blocchains. Also add clone

Helper functions to convert to/from UI "12.34" <-> FixedPoint and functions to add/subtract/compare two FixedPoints can be implemented in client library (wallet-demo) and use native BigInt.

[webmaster128]

This can be decomposed into the old form using string operations:

const coin = { amount: "1234", fractionalDigits: 2, }
const fractional = BigInt(coin.amount.slice(-coin.fractionalDigits)); // 34n
const whole = BigInt(coin.amount.slice(0, -coin.fractionalDigits)); // 12n

const coin2 = { amount: "1234", fractionalDigits: 8, }
const fractional2 = BigInt(coin2.amount.slice(-coin2.fractionalDigits)); // 1234n
const whole2 = BigInt(coin2.amount.slice(0, -coin2.fractionalDigits)); // 0n

BigInt could be replaced by Long or BN. However, we should give the TypeScript implementation a try that was merged yesterday: microsoft/TypeScript#25886

There is no native BigDecimal interface yet

BigInt could form the basis of an eventual BigDecimal implementation.

https://developers.google.com/web/updates/2018/05/bigint

[webmaster128]

amount -> quantity as amount described the whole object.

interface BcpCoin {
    readonly quantity: string;
    readonly fractionalDigits: number;
}

As discussed, BcpCoin could be renamed to BcpAmount.

[ethanfrey]

I agree with the format. Let's just look at the three affected types.

Currently iov-bcp-types/src/bcp.ts:

export interface BcpTicker {
  readonly tokenTicker: TokenTicker;
  readonly sigFigs: number;
  readonly tokenName: string;
}


export interface BcpCoin extends BcpTicker {
  readonly whole: number;
  readonly fractional: number;
}

And in transactions.ts:

export interface FungibleToken {
  readonly whole: number;
  readonly fractional: number;
  readonly tokenTicker: TokenTicker;
}

---

Changes:

FungibleToken -> BcpAmount as mentioned above:

export interface BcpAmount {
  readonly quantity: string;
  readonly fractionalDigits: number;
  readonly tokenTicker: TokenTicker;
}

type BcpCoin = BcpAmount & BcpTicker ???
So it has the full value information, but also enhanced with tokenName and sigFigs (which is the maximum fractional digits supported by the ticker (maybe change this name).

BcpCoin is supposed to have all this info for display, but we can reconsider what exactly belongs inside

[webmaster128]

Oh, I was not aware what BcpCoin contains. FungibleToken was already renamed to Amount. So

1. Use quantity: string and fractionalDigits: number in Amount
2. type BcpCoin = Amount & BcpTicker if that works. Otherwise extend BcpTicker compatible to 1.
3. Rename Amount -> BcpAmount?

Regarding 3.: how do we decide what a Bcp* type is?

[ethanfrey]

Points 1. and 2. sound good, and I trust you to figure the best way to combine them as a BcpCoin

Re 3. Amount is fine with me. Actually, I don't know if we need the BcpPrefix, if that is also in the package, but maybe it is clearer.

Just do what you think is best with the naming. I just wanted to point out the three different types we use. BcpCoin is used as a return value, Amount as an argument to the blockchain. (Require minimal needed info, provide more context)