ahbeng/NUSMods

import axios, { AxiosResponse } from 'axios';
import { isSameDay, addDays } from 'date-fns';

/** An empty object, i.e. `{}` */
type EmptyItem = Record<string, undefined>;

export type WeatherResponse<T> = {
  api_info: {
    status: string;
  };
  // API sometimes returns `[{}]` instead of an array of Ts, no idea why
  items: (T | EmptyItem)[];
};

type ValidPeriod = {
  start: string;
  end: string;
};

type HighLow = {
  low: number;
  high: number;
};

type Wind = {
  speed: HighLow;
  direction: string;
};

type Weather = {
  forecast: string;
  relative_humidity: HighLow;
  temperature: HighLow;
  wind: Wind;
};

type NowCastItem = {
  update_timestamp: string;
  timestamp: string;
  valid_period: ValidPeriod;
  forecasts: {
    area: string;
    forecast: string;
  }[];
};

type DayCastItem = {
  update_timestamp: string;
  timestamp: string;
  valid_period: ValidPeriod;
  general: Weather;
  periods: {
    time: ValidPeriod;
    regions: {
      west: string;
      east: string;
      central: string;
      south: string;
      north: string;
    };
  }[];
};

type FourDayCastItem = {
  update_timestamp: string;
  timestamp: string;
  forecasts: Forecast[];
};

export type Forecast = Weather & {
  date: string;
  timestamp: string;
};

const API_PREFIX = 'https://api.data.gov.sg/v1/environment';
const NOWCAST_AREA = 'Queenstown';

function getResponseData<T>(response: AxiosResponse<WeatherResponse<T>>): T | EmptyItem {
  const { data } = response;
  if (data.api_info.status !== 'healthy') {
    throw new Error(`Weather API returned non-healthy status ${data.api_info.status}`);
  }
  return data.items[0];
}

export function twoHour(): Promise<string | null> {
  return axios
    .get<WeatherResponse<NowCastItem>>(`${API_PREFIX}/2-hour-weather-forecast`)
    .then((response) => {
      const areaForecast = getResponseData(response).forecasts?.find(
        (forecast) => forecast.area === NOWCAST_AREA,
      );
      return areaForecast?.forecast ?? null;
    });
}

export function tomorrow(): Promise<string | null> {
  return axios
    .get<WeatherResponse<DayCastItem>>(`${API_PREFIX}/24-hour-weather-forecast`)
    .then((response) => {
      const tomorrowForecast = getResponseData(response).periods?.find((period) =>
        isSameDay(new Date(period.time.start), addDays(new Date(), 1)),
      );
      // The forecast for tomorrow may not be available, so this can return null
      return tomorrowForecast?.regions?.west ?? null;
    });
}

export function fourDay(): Promise<Forecast[]> {
  return axios
    .get<WeatherResponse<FourDayCastItem>>(`${API_PREFIX}/4-day-weather-forecast`)
    .then((response) => getResponseData(response).forecasts ?? []);
}