import { fetchJson, fromUnix, maybe, maybeMsToKph, MAX_DAYS, msToKph, ProviderError, round1 } from "../../http";
import type { CurrentWeather, DailyForecast, HourlyForecast, ProviderForecast } from "../../types";
import { OWM_LABEL, popToPercent, precipitation, toCondition, type OwmWeatherTag } from "./shared";

/**
 * OpenWeather ONE CALL 4.0 (needs a separate "One Call" subscription;
 * 1,000 calls/day free, card on file). Docs: https://openweathermap.org/api/one-call-4
 *
 *   /data/4.0/onecall/current         → now
 *   /data/4.0/onecall/timeline/1h     → hourly, 48 h of forecast, 20 records per page
 *   /data/4.0/onecall/timeline/1day   → daily, 10 records per page
 *
 * Timelines are paginated with a `next` URL, and each page costs one call.
 * A full load here is about 5 calls; the 10-minute cache keeps that sane.
 */

const BASE_URL = "https://api.openweathermap.org/data/4.0/onecall";
const HOURS_AVAILABLE = 48;

interface OcRecord {
  dt: number;
  temp: number | { min: number; max: number; day: number };
  feels_like: number | { day: number };
  humidity: number;
  pressure: number;
  dew_point: number;
  uvi: number;
  clouds: number;
  visibility?: number; // metres
  wind_speed: number;
  wind_gust?: number;
  wind_deg: number;
  pop?: number;
  rain?: number | { "1h": number };
  snow?: number | { "1h": number };
  weather: OwmWeatherTag[];
  sunrise?: number;
  sunset?: number;
  summary?: string;
}

interface OcPage {
  data: OcRecord[];
  next?: string;
  timezone?: string;
}

/** Rain/snow is a number on daily records and `{ "1h": n }` on current/hourly ones. */
const volume = (v: OcRecord["rain"]) => (typeof v === "number" ? v : v?.["1h"]);

/** Follows `next` links until we have `wanted` records or the timeline ends. */
async function fetchTimeline(firstUrl: string, key: string, wanted: number): Promise<OcRecord[]> {
  const records: OcRecord[] = [];
  let url: string | undefined = firstUrl;

  while (url && records.length < wanted) {
    const page: OcPage = await fetchJson<OcPage>(url, OWM_LABEL);
    records.push(...page.data);
    // Make sure follow-up pages carry the key even if `next` omits it.
    url = page.next ? (page.next.includes("appid=") ? page.next : `${page.next}&appid=${key}`) : undefined;
  }
  return records.slice(0, wanted);
}

function toHourly(r: OcRecord): HourlyForecast {
  return {
    time: fromUnix(r.dt),
    tempC: round1(r.temp as number),
    feelsLikeC: round1(r.feels_like as number),
    condition: toCondition(r.weather[0].id),
    isDay: r.weather[0].icon.endsWith("d"),
    precipChance: popToPercent(r.pop),
    precipMm: precipitation(volume(r.rain), volume(r.snow)),
    windKph: msToKph(r.wind_speed),
    gustKph: maybeMsToKph(r.wind_gust),
    windDeg: r.wind_deg,
    humidity: r.humidity,
    uvIndex: maybe(r.uvi),
  };
}

function toDaily(r: OcRecord): DailyForecast {
  const temp = r.temp as { min: number; max: number };
  return {
    time: fromUnix(r.dt), // OpenWeather stamps daily records at local midday
    highC: round1(temp.max),
    lowC: round1(temp.min),
    condition: toCondition(r.weather[0].id),
    summary: r.summary ?? r.weather[0].description,
    precipChance: popToPercent(r.pop),
    precipMm: precipitation(volume(r.rain), volume(r.snow)),
    windKph: msToKph(r.wind_speed),
    gustKph: maybeMsToKph(r.wind_gust),
    windDeg: r.wind_deg,
    uvIndexMax: maybe(r.uvi),
    humidity: r.humidity,
    sunrise: r.sunrise ? fromUnix(r.sunrise) : null,
    sunset: r.sunset ? fromUnix(r.sunset) : null,
  };
}

function toCurrent(r: OcRecord): CurrentWeather {
  const hour = toHourly(r);
  return {
    time: hour.time,
    tempC: hour.tempC,
    feelsLikeC: hour.feelsLikeC ?? hour.tempC,
    condition: hour.condition,
    description: r.weather[0].description,
    isDay: hour.isDay,
    humidity: r.humidity,
    windKph: hour.windKph,
    gustKph: hour.gustKph,
    windDeg: hour.windDeg,
    pressureHpa: r.pressure,
    dewPointC: round1(r.dew_point),
    visibilityKm: r.visibility === undefined ? null : round1(r.visibility / 1000),
    uvIndex: maybe(r.uvi),
    cloudCover: r.clouds,
    precipMm: hour.precipMm,
  };
}

export async function getOneCallForecast(lat: number, lon: number, key: string): Promise<ProviderForecast> {
  const query = `lat=${lat}&lon=${lon}&units=metric&appid=${key}`;
  const nowSeconds = Math.floor(Date.now() / 1000);
  const startOfHour = nowSeconds - (nowSeconds % 3600);

  const [currentPage, hourly, daily] = await Promise.all([
    fetchJson<OcPage>(`${BASE_URL}/current?${query}`, OWM_LABEL),
    fetchTimeline(`${BASE_URL}/timeline/1h?${query}&start=${startOfHour}`, key, HOURS_AVAILABLE),
    fetchTimeline(`${BASE_URL}/timeline/1day?${query}&start=${nowSeconds}`, key, MAX_DAYS),
  ]);

  const currentRecord = currentPage.data[0];
  if (!currentRecord) throw new ProviderError("OpenWeather returned no current reading", 502);

  return {
    timeZone: currentPage.timezone ?? null,
    hourlyStepHours: 1,
    alerts: [], // 4.0 only returns alert IDs; the API route adds NWS alerts for US locations
    current: toCurrent(currentRecord),
    hourly: hourly.map(toHourly),
    daily: daily.map(toDaily),
  };
}