[wallet] Doesn't calculate fee on empty balance (#1652)

packages/mobile/src/fees/saga.test.ts

@@ -1,12 +1,13 @@
 import BigNumber from 'bignumber.js'
 import { expectSaga } from 'redux-saga-test-plan'
 import * as matchers from 'redux-saga-test-plan/matchers'
-import { call } from 'redux-saga/effects'
+import { call, select } from 'redux-saga/effects'
 import { getReclaimEscrowGas } from 'src/escrow/saga'
 import { feeEstimated, FeeType } from 'src/fees/actions'
 import { estimateFeeSaga } from 'src/fees/saga'
 import { getInvitationVerificationFeeInWei, getInviteTxGas } from 'src/invite/saga'
 import { getSendTxGas } from 'src/send/saga'
+import { stableTokenBalanceSelector } from 'src/stableToken/reducer'
 import { getConnectedAccount } from 'src/web3/saga'
 import { mockAccount } from 'test/values'
 
@@ -32,6 +33,8 @@ describe(estimateFeeSaga, () => {
       .provide([
         [call(getConnectedAccount), mockAccount],
         [matchers.call.fn(getInviteTxGas), new BigNumber(GAS_AMOUNT)],
+        [matchers.call.fn(getInviteTxGas), new BigNumber(GAS_AMOUNT)],
+        [select(stableTokenBalanceSelector), '1'],
       ])
       .put(
         feeEstimated(
@@ -50,6 +53,7 @@ describe(estimateFeeSaga, () => {
       .provide([
         [call(getConnectedAccount), mockAccount],
         [matchers.call.fn(getSendTxGas), new BigNumber(GAS_AMOUNT)],
+        [select(stableTokenBalanceSelector), '1'],
       ])
       .put(feeEstimated(FeeType.SEND, new BigNumber(10000).times(GAS_AMOUNT).toString()))
       .run()
@@ -60,8 +64,19 @@ describe(estimateFeeSaga, () => {
       .provide([
         [call(getConnectedAccount), mockAccount],
         [matchers.call.fn(getReclaimEscrowGas), new BigNumber(GAS_AMOUNT)],
+        [select(stableTokenBalanceSelector), '1'],
       ])
       .put(feeEstimated(FeeType.SEND, new BigNumber(10000).times(GAS_AMOUNT).toString()))
       .run()
   })
+
+  it("doesn't calculates fee if the balance is zero", async () => {
+    await expectSaga(estimateFeeSaga, { feeType: FeeType.SEND })
+      .provide([
+        [select(stableTokenBalanceSelector), '0'],
+        [matchers.call.fn(getSendTxGas), new BigNumber(GAS_AMOUNT)],
+      ])
+      .put(feeEstimated(FeeType.SEND, '0'))
+      .run()
+  })
 })

packages/mobile/src/fees/saga.ts

@@ -1,13 +1,14 @@
 import { getStableTokenContract } from '@celo/walletkit'
 import BigNumber from 'bignumber.js'
-import { call, CallEffect, put, takeLatest } from 'redux-saga/effects'
+import { call, CallEffect, put, select, takeLatest } from 'redux-saga/effects'
 import { showError } from 'src/alert/actions'
 import { ErrorMessages } from 'src/app/ErrorMessages'
 import { getReclaimEscrowGas } from 'src/escrow/saga'
 import { Actions, EstimateFeeAction, feeEstimated, FeeType } from 'src/fees/actions'
 import { getInvitationVerificationFeeInWei, getInviteTxGas } from 'src/invite/saga'
 import { getSendTxGas } from 'src/send/saga'
 import { CeloDefaultRecipient } from 'src/send/Send'
+import { stableTokenBalanceSelector } from 'src/stableToken/reducer'
 import { BasicTokenTransfer } from 'src/tokens/saga'
 import Logger from 'src/utils/Logger'
 import { web3 } from 'src/web3/contracts'
@@ -27,6 +28,23 @@ const placeholderSendTx: BasicTokenTransfer = {
 
 export function* estimateFeeSaga({ feeType }: EstimateFeeAction) {
   Logger.debug(`${TAG}/estimateFeeSaga`, `updating for ${feeType}`)
+
+  const balance = yield select(stableTokenBalanceSelector)
+
+  if (!balance) {
+    Logger.warn(`${TAG}/estimateFeeSaga`, 'Balance is null or empty string')
+    yield put(feeEstimated(feeType, '0'))
+    return
+  }
+
+  if (balance === '0') {
+    Logger.warn(`${TAG}/estimateFeeSaga`, "Can't estimate fee with zero balance")
+    yield put(feeEstimated(feeType, '0'))
+    return
+  }
+
+  Logger.debug(`${TAG}/estimateFeeSaga`, `balance is ${balance}`)
+
   try {
     const account = yield call(getConnectedAccount)
 

packages/mobile/src/stableToken/reducer.ts

@@ -1,3 +1,4 @@
+import { RootState } from 'src/redux/reducers'
 import { Actions, ActionTypes } from 'src/stableToken/actions'
 
 export interface State {
@@ -29,3 +30,5 @@ export const reducer = (state: State | undefined = initialState, action: ActionT
       return state
   }
 }
+
+export const stableTokenBalanceSelector = (state: RootState) => state.stableToken.balance