import {ConvertCurrencyParams} from "../interfaces.js"

/**
 * Convert currency
 *  + exchange monetary value from one currency into another
 *  + provide a 'rates' object of relativistic currency values
 *  + returns a number
 */
export function convertCurrency({
	value,
	inputCurrency,
	outputCurrency,
	exchangeRates
}: ConvertCurrencyParams): number {

	// get currency rates
	const inputRate = exchangeRates[inputCurrency]
	const outputRate = exchangeRates[outputCurrency]

	// scrutinize currencies and rates for validity
	const currenciesAndRates: [string, number][] = [
		[inputCurrency, inputRate],
		[outputCurrency, outputRate]
	]

	for (const [currency, rate] of currenciesAndRates) {
		if (rate === undefined || rate === null || isNaN(rate))
			throw new Error(`invalid rate "${currency}"`)
	}

	// calculate exchanged currency value
	return value * (outputRate / inputRate)
}