const axios = require('axios');

const API_URL = 'https://api.openweathermap.org/data/2.5';
const CACHE_MINUTES = 10; // OpenWeatherMap only updates about every 10 minutes anyway
const FORECAST_DAYS = 5;

// only pass through icon codes like "10d" so the page can build the image URL safely
function iconCode(icon) {
    return /^\d\d[dn]$/.test(icon || '') ? icon : null;
}

// the 5 day forecast comes in 3 hour slots; roll them up into one entry per local day
function dailyForecast(forecast) {
    const offset = (forecast.city?.timezone || 0) * 1000;
    const days = new Map();

    for (const slot of forecast.list || []) {
        const local = new Date(slot.dt * 1000 + offset);
        const key = local.toISOString().slice(0, 10);
        if (!days.has(key)) days.set(key, { date: key, low: Infinity, high: -Infinity, pop: 0, noon: null });

        const day = days.get(key);
        day.low = Math.min(day.low, slot.main.temp_min);
        day.high = Math.max(day.high, slot.main.temp_max);
        day.pop = Math.max(day.pop, slot.pop || 0);

        // the slot nearest midday best represents the day's conditions
        const distance = Math.abs(local.getUTCHours() - 12);
        if (!day.noon || distance < day.noon.distance) day.noon = { distance, weather: slot.weather?.[0] };
    }

    return [...days.values()].slice(0, FORECAST_DAYS).map(day => ({
        date: day.date,
        low: Math.round(day.low),
        high: Math.round(day.high),
        pop: Math.round(day.pop * 100),
        condition: day.noon?.weather?.main || null,
        icon: iconCode(day.noon?.weather?.icon)
    }));
}

function createWeatherService({ apiKey, zipCode }) {
    const enabled = !!(apiKey && zipCode);
    // US zip by default; "12345,ca" style values pass through untouched
    const zip = zipCode && zipCode.includes(',') ? zipCode : `${zipCode},us`;

    let cache = null;
    let fetchedAt = 0;
    let pending = null;
    let lastError = null;

    async function fetchWeather() {
        const params = { zip, units: 'imperial', appid: apiKey };
        const [current, forecast] = await Promise.all([
            axios.get(`${API_URL}/weather`, { params }),
            axios.get(`${API_URL}/forecast`, { params })
        ]);

        const c = current.data;
        return {
            place: c.name,
            updatedAt: c.dt * 1000,
            temp: Math.round(c.main.temp),
            feelsLike: Math.round(c.main.feels_like),
            high: Math.round(c.main.temp_max),
            low: Math.round(c.main.temp_min),
            humidity: c.main.humidity,
            wind: Math.round(c.wind?.speed || 0),
            condition: c.weather?.[0]?.main || null,
            description: c.weather?.[0]?.description || null,
            icon: iconCode(c.weather?.[0]?.icon),
            sunrise: c.sys?.sunrise ? c.sys.sunrise * 1000 : null,
            sunset: c.sys?.sunset ? c.sys.sunset * 1000 : null,
            forecast: dailyForecast(forecast.data)
        };
    }

    async function getWeather() {
        if (!enabled) return { enabled: false };

        if (Date.now() - fetchedAt > CACHE_MINUTES * 60 * 1000) {
            // share one request between callers that arrive while it's in flight
            pending = pending || fetchWeather()
                .then(data => {
                    cache = data;
                    lastError = null;
                })
                .catch(err => {
                    lastError = err.response?.data?.message || err.message;
                    console.error('Weather error: ', lastError);
                })
                .finally(() => {
                    fetchedAt = Date.now();
                    pending = null;
                });
            await pending;
        }

        return { enabled: true, error: lastError, ...cache };
    }

    return { getWeather };
}

module.exports = {
    createWeatherService
};