metamask-extension/ui/app/hooks/useEthFiatAmount.js

import { useMemo } from 'react'
import { useSelector } from 'react-redux'
import { getConversionRate, getCurrentCurrency, getShouldShowFiat } from '../selectors'
import { decEthToConvertedCurrency } from '../helpers/utils/conversions.util'
import { formatCurrency } from '../helpers/utils/confirm-tx.util'

/**
 * Get an Eth amount converted to fiat and formatted for display
 *
 * @param {string} [tokenAmount] - The eth amount to convert
 * @param {object} [overrides] - A configuration object that allows the called to explicitly
 *                              ensure fiat is shown even if the property is not set in state.
 * @param {boolean} [overrides.showFiat] - If truthy, ensures the fiat value is shown even if the showFiat value from state is falsey
 * @param {boolean} hideCurrencySymbol Indicates whether the returned formatted amount should include the trailing currency symbol
 * @return {string} - The formatted token amount in the user's chosen fiat currency
 */
export function useEthFiatAmount (ethAmount, overrides = {}, hideCurrencySymbol) {
  const conversionRate = useSelector(getConversionRate)
  const currentCurrency = useSelector(getCurrentCurrency)
  const userPrefersShownFiat = useSelector(getShouldShowFiat)
  const showFiat = overrides.showFiat ?? userPrefersShownFiat
  const formattedFiat = useMemo(
    () => decEthToConvertedCurrency(ethAmount, currentCurrency, conversionRate),
    [conversionRate, currentCurrency, ethAmount],
  )

  if (!showFiat || currentCurrency.toUpperCase() === 'ETH' || conversionRate <= 0 || ethAmount === undefined) {
    return undefined
  }

  return hideCurrencySymbol
    ? formatCurrency(formattedFiat, currentCurrency)
    : `${formatCurrency(formattedFiat, currentCurrency)} ${currentCurrency.toUpperCase()}`
}