/**
 * @desc This is the average energy spent in transfer and process 1gb of data
 * based on the calculation made in "Energy Intensity of Web Data" on
 * https://www.websitecarbon.com/how-does-it-work/
 * @type {number}
 */
const AVERAGE_KILO_WATT_HOUR_PER_GB = 1.805;

/**
 * @desc This is the average amount of co2 grams created for every kWh of energy in the US energy grid
 * @type {number}
 */
const AVERAGE_CARBON_FACTOR_GRID = 475;
/**
 * @desc 1gigabyte in bytes
 * @type {number}
 */
const GIGABYTE_TO_BYTES = 1073741824;
/**
 * @desc formula to adjust the value of data transferred
 * Assuming that 25% of the users have already visited the page and have cached data, where
 * they have to download a 2% of the assets.
 * Ported from: https://gitlab.com/wholegrain/carbon-api-2-0/blob/master/helpers/statistics.php#L25
 * @param {number} val
 * @returns {number}
 */
const adjustDataTransfer = (val: number) => {
  return val * 0.75 + 0.02 * val * 0.25;
};
/**
 * @desc formula to calculate the energy consumption of a website given his byte size
 * Ported from: https://gitlab.com/wholegrain/carbon-api-2-0/blob/master/helpers/statistics.php#L33
 * @param {number} bytes
 * @returns {number}
 */
const energyConsumption = (bytes: number) => {
  return bytes * (AVERAGE_KILO_WATT_HOUR_PER_GB / GIGABYTE_TO_BYTES);
};
/**
 * @desc formula to calculate the co2 emitted to create this amount of energy
 * @param {number} energy
 * @param carbonFactor provided carbon factor
 * @returns {number} as grams of co2
 */
const getCo2Grid = (energy: number, carbonFactor: number = AVERAGE_CARBON_FACTOR_GRID) => {
  return energy * carbonFactor;
};

export interface CO2Props {
  byteSize: number;
  co2Factor?: number;
  isDataAdjusted: boolean;
}

/**
 * @desc calculate the carbon footprint based on the size, factor and applies an adjustment based on possible
 * cached files
 * @param byteSize
 * @param co2Factor
 * @param isDataAdjusted
 */
export const calculateCo2 = ({ byteSize, co2Factor, isDataAdjusted = false }: CO2Props): number => {
  const adjustedDataTransfer = isDataAdjusted ? adjustDataTransfer(byteSize) : byteSize;
  const consumedEnergy = energyConsumption(adjustedDataTransfer);
  return getCo2Grid(consumedEnergy, co2Factor);
};