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

import { useMemo } from 'react'
import { useSelector } from 'react-redux'
import { formatCurrency, getValueFromWeiHex } from '../helpers/utils/confirm-tx.util'

/**
 * Defines the shape of the options parameter for useCurrencyDisplay
 * @typedef {Object} UseCurrencyOptions
 * @property {string} [displayValue]     - When present is used in lieu of formatting the inputValue
 * @property {string} [prefix]           - String to prepend to the final result
 * @property {number} [numberOfDecimals] - Number of significant decimals to display
 * @property {string} [denomination]     - Denomination (wei, gwei) to convert to for display
 * @property {string} [currency]         - Currency type to convert to. Will override nativeCurrency
 */

/**
 * Defines the return shape of the second value in the tuple
 * @typedef {Object} CurrencyDisplayParts
 * @property {string} [prefix]  - string to prepend to the value for display
 * @property {string} value     - string representing the value, formatted for display
 * @property {string} [suffix]  - string to append to the value for display
 */

/**
 * useCurrencyDisplay hook
 *
 * Given a hexadecimal encoded value string and an object of parameters used for formatting the
 * display, produce both a fully formed string and the pieces of that string used for displaying
 * the currency to the user
 * @param {string} inputValue          - The value to format for display
 * @param {UseCurrencyOptions} opts    - An object for options to format the inputValue
 * @return {[string, CurrencyDisplayParts]}
 */
export function useCurrencyDisplay (inputValue, { displayValue, prefix, numberOfDecimals, denomination, currency, ...opts }) {
  const { currentCurrency, nativeCurrency, conversionRate } = useSelector(
    ({ metamask: { currentCurrency, nativeCurrency, conversionRate } }) => ({
      currentCurrency,
      nativeCurrency,
      conversionRate,
    })
  )

  const toCurrency = currency || currentCurrency

  const value = useMemo(() => {
    if (displayValue) {
      return displayValue
    }
    return formatCurrency(
      getValueFromWeiHex({
        value: inputValue,
        fromCurrency: nativeCurrency,
        toCurrency,
        conversionRate,
        numberOfDecimals: numberOfDecimals || 2,
        toDenomination: denomination,
      }),
      toCurrency
    )
  }, [inputValue, nativeCurrency, conversionRate, displayValue, numberOfDecimals, denomination, toCurrency])

  let suffix

  if (!opts.hideLabel) {
    suffix = opts.suffix || toCurrency.toUpperCase()
  }


  return [`${prefix || ''}${value}${suffix ? ' ' + suffix : ''}`, { prefix, value, suffix }]
}