LL-6959 Add estimateAccountMaxSpendable (#39)

* add estimateAccountMaxSpendable

* add test for estimateMaxSpendable

src/__tests__/wallet.estimateMaxSpendable.test.ts

@@ -0,0 +1,41 @@
+import WalletLedger from '../wallet';
+import * as utils from '../utils';
+import { Account } from '../account';
+import MockBtc from './mocks/Btc';
+
+describe('testing estimateMaxSpendable', () => {
+  const wallet = new WalletLedger();
+  let account: Account;
+  it('should generate an account', async () => {
+    account = await wallet.generateAccount({
+      btc: new MockBtc(),
+      path: "44'/0'",
+      index: 0,
+      network: 'mainnet',
+      derivationMode: 'Legacy',
+      explorer: 'ledgerv3',
+      explorerURI: 'https://explorers.api.vault.ledger.com/blockchain/v3/btc',
+      storage: 'mock',
+      storageParams: [],
+    });
+
+    expect(account.xpub.xpub).toEqual(
+      'xpub6CV2NfQJYxHn7MbSQjQip3JMjTZGUbeoKz5xqkBftSZZPc7ssVPdjKrgh6N8U1zoQDxtSo6jLarYAQahpd35SJoUKokfqf1DZgdJWZhSMqP'
+    );
+  });
+
+  it('should estimate max spendable correctly', async () => {
+    await wallet.syncAccount(account);
+    let maxSpendable = await wallet.estimateAccountMaxSpendable(account, 0);
+    const balance = 109088;
+    expect(maxSpendable.toNumber()).toEqual(balance);
+    let feesPerByte = 100;
+    maxSpendable = await wallet.estimateAccountMaxSpendable(account, feesPerByte);
+    expect(maxSpendable.toNumber()).toEqual(
+      balance - feesPerByte * utils.estimateTxSize(2, 1, account.xpub.crypto, account.xpub.derivationMode)
+    );
+    feesPerByte = 10000;
+    maxSpendable = await wallet.estimateAccountMaxSpendable(account, feesPerByte);
+    expect(maxSpendable.toNumber()).toEqual(0);
+  }, 60000);
+});

src/wallet.ts

@@ -185,6 +185,19 @@ class WalletLedger {
     return flatten(await Promise.all(addresses.map((address) => account.xpub.storage.getAddressUnspentUtxos(address))));
   }
 
+  // eslint-disable-next-line class-methods-use-this
+  async estimateAccountMaxSpendable(account: Account, feePerByte: number) {
+    const addresses = await account.xpub.getXpubAddresses();
+    const utxos = flatten(
+      await Promise.all(addresses.map((address) => account.xpub.storage.getAddressUnspentUtxos(address)))
+    );
+    const balance = await account.xpub.getXpubBalance();
+    // fees if we use all utxo
+    const fees = feePerByte * utils.estimateTxSize(utxos.length, 1, account.xpub.crypto, account.xpub.derivationMode);
+    const maxSpendable = balance.minus(fees);
+    return maxSpendable.lt(0) ? new BigNumber(0) : maxSpendable;
+  }
+
   // eslint-disable-next-line class-methods-use-this
   async getAccountBalance(account: Account) {
     const balance = await account.xpub.getXpubBalance();