Expose state stake and account balance breakdown

[kcole16]

Overview

We currently do not expose an account's complete balance breakdown, specifically the "state stake". This is necessary to compute the account's spendable balance.

Both the Wallet and Explorer need to retrieve and display the state stake amount, and it's likely app devs will want the same data (so they can determine if users have a sufficient NEAR balance for a TX).

account/<account_id> RPC example

{
  "result": {
    "amount": "10000000999999952626000000",
    "locked": "0",
    "storage_usage": 387
  }
}

The spendable balance = amount - state_stake

The state stake can be calculated from storage_usage * storage_amount_per_byte.

cost_per_byte can be retrieved from RPC method = EXPERIMENTAL_genesis_config which exposes runtime_config.storage_amount_per_byte

cc @Patrick1904 @vgrichina

[kcole16]

One way to do this is to add this getAccountBalance function to the Account object: https://github.com/near/near-api-js/blob/master/src/account.ts

I'd also change it to just return object with all different "types" of balance instead of taking type argument.

Originally posted by @vgrichina in near/near-wallet#534 (comment)

Should return a balance object with the following:

{
	total: '1000',
	state-staked: '1',
	staked: '100',
	available: ‘899'
}

Or add the above balance param to the AccountState interface

[vgrichina]

Note that there is generally no changes needed in near-api-js to get info from experimental endpoints.

sendJsonRpc can be used directly for such situations:

near-api-js/src/providers/json-rpc-provider.ts

Line 114 in db51150

async sendJsonRpc(method: string, params: any[]): Promise<any> {

[bowenwang1996]

@kcole16 for regular users state stake is usually quite small (something like 0.01), do you think it is still good to display that?

[kcole16]

@bowenwang1996 We're planning to display as "minimum balance". The total balance will be displayed in most places by default, and spendable will be highlighted on TX and "Send Money" pages.

near/near-wallet#481