AddressBalance command fetches balance for the given coin-type/address pair

[coveralls]

Pull Request Test Coverage Report for Build 240

• 0 of 30 (0.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.4%) to 53.204%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
bitcoin/wallet.go	0	10	0.0%
litecoin/wallet.go	0	10	0.0%
zcash/wallet.go	0	10	0.0%
<!--	Total:	0	30	0.0%	-->

Totals
Change from base Build 238:	-0.4%
Covered Lines:	2009
Relevant Lines:	3776

---

💛 - Coveralls

[andreygrehov]

@placer14 good call. I'm not sure if extraction will work, wallet.Utxo doesn't know how to convert its ScriptPubkey to btcutil.Address.

https://github.com/OpenBazaar/multiwallet/pull/40/files#diff-d06015dd60330e13eb491a605f0bed80R184

Any ideas?

A callback approach could do the job I believe. Something along these lines:

func (w *BitcoinWallet) AddressBalance(addr btc.Address) (confirmed, unconfirmed int64) {
    utxos, _ := w.db.Utxos().Filter(func(utxo wi.Utxo) bool {
        utxoAddr, _ := w.ScriptToAddress(utxo.ScriptPubkey)
        return addr.String() == utxoAddr.String()
    })
    txns, _ := w.db.Txns().GetAll(false)
    return util.CalcBalance(filteredUtxos, txns)
}

It's not that shorter though.

[placer14]

I like the callback approach. Unfortunately that shifts the Utxo interface in the wallet-interface. You could make that interface local without impacting external dependancies, probably, but I'm not sure it's worth all of that infrastructure just to collapse this behavior. Let's call it a wash and leave it as is. If we can get a blessing from @cpacia then I'd be fine with merging this.

[andreygrehov]

@placer14 cool, thanks. We'll need to get another PR for go-ethwallet before merging this one in.

[andreygrehov]

@cpacia does this PR make any sense? If not, we should close it out. Otherwise, let me know.