adhan-extended/lib/esm/PolarCircleResolution.js

High precision Islamic prayer time library (extended)

import Coordinates from './Coordinates';
import SolarTime from './SolarTime';
import { dateByAddingDays } from './DateUtils';
export const PolarCircleResolution = {
  AqrabBalad: 'AqrabBalad',
  AqrabYaum: 'AqrabYaum',
  Unresolved: 'Unresolved'
};
const LATITUDE_VARIATION_STEP = 0.5; // Degrees to add/remove at each resolution step

const UNSAFE_LATITUDE = 65; // Based on https://en.wikipedia.org/wiki/Midnight_sun

const isValidSolarTime = solarTime => !isNaN(solarTime.sunrise) && !isNaN(solarTime.sunset);

const aqrabYaumResolver = (coordinates, date, daysAdded = 1, direction = 1) => {
  if (daysAdded > Math.ceil(365 / 2)) {
    return null;
  }

  const testDate = new Date(date.getTime());
  testDate.setDate(testDate.getDate() + direction * daysAdded);
  const tomorrow = dateByAddingDays(testDate, 1);
  const solarTime = new SolarTime(testDate, coordinates);
  const tomorrowSolarTime = new SolarTime(tomorrow, coordinates);

  if (!isValidSolarTime(solarTime) || !isValidSolarTime(tomorrowSolarTime)) {
    return aqrabYaumResolver(coordinates, date, daysAdded + (direction > 0 ? 0 : 1), -direction);
  }

  return {
    date,
    tomorrow,
    coordinates,
    solarTime,
    tomorrowSolarTime
  };
};

const aqrabBaladResolver = (coordinates, date, latitude) => {
  const solarTime = new SolarTime(date, { ...coordinates,
    latitude
  });
  const tomorrow = dateByAddingDays(date, 1);
  const tomorrowSolarTime = new SolarTime(tomorrow, { ...coordinates,
    latitude
  });

  if (!isValidSolarTime(solarTime) || !isValidSolarTime(tomorrowSolarTime)) {
    return Math.abs(latitude) >= UNSAFE_LATITUDE ? aqrabBaladResolver(coordinates, date, latitude - Math.sign(latitude) * LATITUDE_VARIATION_STEP) : null;
  }

  return {
    date,
    tomorrow,
    coordinates: new Coordinates(latitude, coordinates.longitude),
    solarTime,
    tomorrowSolarTime
  };
};

export const polarCircleResolvedValues = (resolver, date, coordinates) => {
  const defaultReturn = {
    date,
    tomorrow: dateByAddingDays(date, 1),
    coordinates,
    solarTime: new SolarTime(date, coordinates),
    tomorrowSolarTime: new SolarTime(dateByAddingDays(date, 1), coordinates)
  };

  switch (resolver) {
    case PolarCircleResolution.AqrabYaum:
      {
        return aqrabYaumResolver(coordinates, date) || defaultReturn;
      }

    case PolarCircleResolution.AqrabBalad:
      {
        const {
          latitude
        } = coordinates;
        return aqrabBaladResolver(coordinates, date, latitude - Math.sign(latitude) * LATITUDE_VARIATION_STEP) || defaultReturn;
      }

    default:
      {
        return defaultReturn;
      }
  }
};
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