import { comparatorDistanceUnits } from '@adalo/constants'

export interface Coordinate {
  latitude: number
  longitude: number
}

type DistanceUnit =
  typeof comparatorDistanceUnits[keyof typeof comparatorDistanceUnits]

const KMS_PER_MILE = 1.609344 // 1 mi = 5280 ft ~= 5280 ft * (~1852 m/6076.11549 ft) ~= 1609.34400 m (ref: https://web.archive.org/web/20111210164956/http://ts.nist.gov/weightsandmeasures/publications/appxc.cfm)
const EARTH_RADIUS_IN_KMS: number = 6378.8 // Source: https://www.geeksforgeeks.org/program-distance-two-points-earth/

function asRadians(degrees: number) {
  return degrees * (Math.PI / 180)
}

export function kilometersBetweenLocations(
  a: Coordinate,
  b: Coordinate
): number {
  const { latitude: latA, longitude: lonA } = a
  const { latitude: latB, longitude: lonB } = b

  // Haversine Formula
  // from https://www.movable-type.co.uk/scripts/latlong.html
  const latARad = asRadians(latA)
  const latBRad = asRadians(latB)
  const deltaLatRad = asRadians(latB - latA)
  const deltaLonRad = asRadians(lonB - lonA)

  const intermediate =
    Math.sin(deltaLatRad / 2) * Math.sin(deltaLatRad / 2) +
    Math.cos(latARad) *
      Math.cos(latBRad) *
      Math.sin(deltaLonRad / 2) *
      Math.sin(deltaLonRad / 2)
  return (
    EARTH_RADIUS_IN_KMS *
    2 *
    Math.atan2(Math.sqrt(intermediate), Math.sqrt(1 - intermediate))
  )
}

export function asKilometers(value: number, unit: DistanceUnit): number {
  switch (unit) {
    case comparatorDistanceUnits.KILOMETERS:
      // no-op
      return value
    case comparatorDistanceUnits.MILES:
      return value * KMS_PER_MILE
    default:
      throw new Error(`Unknown unit: ${unit}`)
  }
}

export const convertToMiles = (value: number): number => value / KMS_PER_MILE