// forecast.mjs
import { queryHourly, getCoords } from './influx.mjs';
import { getCelestialForecast } from './celestial.mjs';

// ── Physics Helpers ───────────────────────────────────────────────────────────

function linearTrend(values) {
	const n = values.length;
	if (n < 2) return 0;
	const xMean = (n - 1) / 2;
	const yMean = values.reduce((a, b) => a + b, 0) / n;
	const num = values.reduce((s, v, i) => s + (i - xMean) * (v - yMean), 0);
	const den = values.reduce((s, _, i) => s + (i - xMean) ** 2, 0);
	return den === 0 ? 0 : num / den;
}

function dewPoint(tempC, humidity) {
	const a = 17.27, b = 237.7;
	const gamma = (a * tempC) / (b + tempC) + Math.log(humidity / 100);
	return (b * gamma) / (a - gamma);
}

function heatIndex(tempC, humidity) {
	const T = tempC * 9 / 5 + 32;
	if (T < 80) return tempC;
	const HI =
		-42.379 + 2.04901523 * T + 10.14333127 * humidity
		- 0.22475541 * T * humidity - 0.00683783 * T * T
		- 0.05481717 * humidity * humidity + 0.00122874 * T * T * humidity
		+ 0.00085282 * T * humidity * humidity - 0.00000199 * T * T * humidity * humidity;
	return (HI - 32) * 5 / 9;
}

function vaporPressureDeficit(tempC, humidity) {
	const svp = 0.6108 * Math.exp((17.27 * tempC) / (tempC + 237.3));
	return Math.round(svp * (1 - humidity / 100) * 1000) / 1000;
}

function absoluteHumidity(tempC, humidity) {
	const svp = 0.6108 * Math.exp((17.27 * tempC) / (tempC + 237.3));
	return Math.round((humidity / 100 * svp * 2165) / (tempC + 273.15) * 1000) / 1000;
}

// ── Pressure Tendency → WMO Weather Rule ─────────────────────────────────────

function pressureRule(trend3h, currentHpa) {
	if (trend3h < -2.0) return { label: 'Storm likely',   code: 211, precipChance: 0.85 };
	if (trend3h < -0.8) return { label: 'Rain likely',    code: 501, precipChance: 0.65 };
	if (trend3h < -0.3) return { label: 'Cloudy',         code: 803, precipChance: 0.35 };
	if (trend3h >  1.5) return { label: 'Clearing',       code: 801, precipChance: 0.05 };
	if (trend3h >  0.3) return { label: 'Improving',      code: 800, precipChance: 0.10 };
	if (currentHpa < 1000) return { label: 'Unsettled',   code: 802, precipChance: 0.30 };
	if (currentHpa < 1013) return { label: 'Partly cloudy', code: 802, precipChance: 0.15 };
	return { label: 'Fair', code: 800, precipChance: 0.05 };
}

// ── Solar Heating Curve ───────────────────────────────────────────────────────
// Uses sun_elevation from celestial.mjs — max ~6°C gain at solar noon, clear sky

function solarTempDelta(sunElevation, cloudFraction) {
	if (sunElevation <= 0) return 0;
	return Math.sin((sunElevation * Math.PI) / 180) * (1 - cloudFraction) * 6;
}

// ── Nocturnal Cooling (Stefan–Boltzmann approximation) ────────────────────────
// Clear nights lose more heat via longwave radiation

function nocturnalCooling(cloudFraction) {
	return (1 - cloudFraction) * 1.5; // °C/hr max clear-sky cooling
}

// ── Humidity Forecast ─────────────────────────────────────────────────────────
// As temp rises, relative humidity drops (conserving absolute humidity)

function forecastHumidity(absHumidity, forecastTempC) {
	const svp = 0.6108 * Math.exp((17.27 * forecastTempC) / (forecastTempC + 237.3));
	const rh = (absHumidity * (forecastTempC + 273.15)) / (svp * 2165) * 100;
	return Math.min(100, Math.max(0, Math.round(rh * 10) / 10));
}

// ── Cloud Cover Estimate ──────────────────────────────────────────────────────
// Derived from humidity + pressure tendency (Oktas-style heuristic)

function estimateClouds(humidity, pressureTrend) {
	let base = humidity / 100 * 0.8;
	if (pressureTrend < -0.3) base = Math.min(1, base + 0.2);
	if (pressureTrend >  0.3) base = Math.max(0, base - 0.15);
	return Math.round(base * 100) / 100;
}

// ── Wind Forecast ─────────────────────────────────────────────────────────────
// Pressure gradient approximation — steeper falls = stronger winds

function forecastWind(currentWind, pressureTrend) {
	const boost = pressureTrend < -1 ? 1.3 : pressureTrend < -0.5 ? 1.1 : 1.0;
	return Math.round(currentWind * boost * 10) / 10;
}

// ── Main 24hr Forecast ────────────────────────────────────────────────────────

export async function get24HourForecast(currentSensors) {
	const now    = new Date();
	const sixAgo = new Date(now - 6 * 3600 * 1000);

	const coords  = await getCoords();
	const history = await queryHourly(sixAgo.toISOString(), now.toISOString());

	// Extract trend series from history
	const pressures  = history.map(r => r.pressure_hpa).filter(Number.isFinite);
	const temps      = history.map(r => r.temperature).filter(Number.isFinite);
	const humidities = history.map(r => r.humidity).filter(Number.isFinite);
	const winds      = history.map(r => r.wind_speed).filter(Number.isFinite);

	const pressureTrend  = linearTrend(pressures);    // hPa/hr
	const tempTrend      = linearTrend(temps);         // °C/hr
	const humidityTrend  = linearTrend(humidities);    // %/hr
	const pressure3h     = pressureTrend * 3;          // 3hr tendency for WMO rules

	// Seed from current sensors
	const seedTemp     = currentSensors.temperature    ?? temps.at(-1)     ?? 20;
	const seedHumidity = currentSensors.humidity       ?? humidities.at(-1) ?? 60;
	const seedPressure = currentSensors.pressure_hpa   ?? pressures.at(-1)  ?? 1013;
	const seedWind     = currentSensors.wind_speed     ?? winds.at(-1)      ?? 0;
	const seedAbsHum   = currentSensors.humidity_abs
		?? absoluteHumidity(seedTemp, seedHumidity);

	const weather = pressureRule(pressure3h, seedPressure);

	// Build 24 hourly slots
	const slots = Array.from({ length: 24 }, (_, i) => {
		const time = new Date(now.getTime() + (i + 1) * 3600 * 1000);
		time.setMinutes(0, 0, 0);

		// Pressure decays toward mean over time (damped trend)
		const pressureDamping = Math.exp(-i * 0.08);
		const pressure = seedPressure + pressureTrend * (i + 1) * pressureDamping;

		// Cloud cover from humidity + pressure tendency
		const clouds = estimateClouds(seedHumidity + humidityTrend * i, pressureTrend);

		// Temperature: solar heating + nocturnal cooling on top of background trend
		// We use a placeholder sun_elevation here — getCelestialForecast will enrich it
		// so we do a two-pass: first build slots, then apply celestial, then fix temp
		const bgTemp = seedTemp + tempTrend * (i + 1);
		const temperature = Math.round(bgTemp * 10) / 10;

		const humidity    = forecastHumidity(seedAbsHum, temperature);
		const wind_speed  = forecastWind(seedWind, pressureTrend);

		return {
			time: time.toISOString().slice(0, 16), // "YYYY-MM-DDTHH:MM"
			temperature,
			humidity,
			humidity_abs:          absoluteHumidity(temperature, humidity),
			dew_point:             Math.round(dewPoint(temperature, humidity) * 100) / 100,
			heat_index:            Math.round(heatIndex(temperature, humidity) * 100) / 100,
			vapor_pressure_deficit: vaporPressureDeficit(temperature, humidity),
			pressure_hpa:          Math.round(pressure * 100) / 100,
			wind_speed,
			clouds,
			precip_chance:         Math.round(weather.precipChance * (1 - i * 0.02) * 100), // confidence decays
			label:                 weather.label,
			code:                  weather.code,
		};
	});

	// Pass through getCelestialForecast to enrich sun/moon data
	const enriched = getCelestialForecast(coords.latitude, coords.longitude, slots);

	// Second pass — apply solar heating now that we have sun_elevation per slot
	for (const slot of enriched) {
		const solar  = solarTempDelta(slot.sun_elevation ?? 0, slot.clouds);
		const cool   = slot.daytime ? 0 : nocturnalCooling(slot.clouds);
		slot.temperature          = Math.round((slot.temperature + solar - cool) * 10) / 10;
		slot.humidity             = forecastHumidity(seedAbsHum, slot.temperature);
		slot.dew_point            = Math.round(dewPoint(slot.temperature, slot.humidity) * 100) / 100;
		slot.heat_index           = Math.round(heatIndex(slot.temperature, slot.humidity) * 100) / 100;
		slot.vapor_pressure_deficit = vaporPressureDeficit(slot.temperature, slot.humidity);
		slot.humidity_abs         = absoluteHumidity(slot.temperature, slot.humidity);
	}

	return enriched;
}