package weather

import "math"

// Attempts to complete missing fields that may not
// be set by a specific provider, such as DewPoint and WindChill
func (u *WeatherUpdate) Enrich() {
	if u == nil {
		return
	}

	if u.WindChillF == 0 {
		u.WindChillF = CalculateWindChill(u.TempOutdoorF, u.WindSpeedMPH)
	}

	if u.DewPointF == 0 && (u.TempOutdoorF != 0 && u.HumidityOudoor != 0) {
		u.DewPointF = CalculateDewPoint(u.TempOutdoorF, float64(u.HumidityOudoor))
	}

	if u.BaromAbsoluteIn == 0 {
		u.BaromAbsoluteIn = u.BaromRelativeIn
	}
}

func CalculateDewPoint(tempF, humidity float64) float64 {
	// Convert temperature from Fahrenheit to Celsius
	tempC := (tempF - 32) * 5 / 9

	// Calculate the dew point using the Magnus-Tetens approximation
	a := float64(17.27)
	b := float64(237.7)

	alpha := (a*tempC)/(b+tempC) + math.Log(humidity/100)
	dewPointC := (b * alpha) / (a - alpha)

	// Convert dew point back to Fahrenheit
	dewPointF := (dewPointC * 9 / 5) + 32
	return dewPointF
}

func CalculateWindChill(tempF float64, windSpeedMPH float64) float64 {
	if windSpeedMPH <= 3 {
		// Wind chill calculation doesn't apply for very low wind speeds
		return tempF
	}

	// Formula for calculating wind chill
	return 35.74 + 0.6215*tempF -
		35.75*math.Pow(windSpeedMPH, 0.16) +
		0.4275*tempF*math.Pow(windSpeedMPH, 0.16)
}