package weather

import "math"

// Attempts to complete missing fields that may not
// be set by a specific provider, such as DewPoint and WindChill
//
// If enrich is called repeated with the same station ID, measurements
// will be recorded to produce averages. This will be more stable
// and support scaling if Redis is available
// TODO: Implement average tracker
func (u *WeatherUpdate) Enrich() {
	if u.WindChillF == 0 {
		u.WindChillF = CalculateWindChill(u.TempF, u.WindSpeedMPH)
	}

	if u.DewPointF == 0 {
		u.DewPointF = CalculateDewPoint(u.TempF, float32(u.Humidity))
	}

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

func CalculateDewPoint(tempF, humidity float32) float32 {
	// Convert temperature from Fahrenheit to Celsius
	tempC := (tempF - 32) * 5 / 9

	// Calculate the dew point using the Magnus-Tetens approximation
	a := float32(17.27)
	b := float32(237.7)

	alpha := (a*tempC)/(b+tempC) + float32(math.Log(float64(humidity)/100))
	dewPointC := (b * alpha) / (a - alpha)

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

func CalculateWindChill(tempF float32, windSpeedMPH float32) float32 {
	if windSpeedMPH <= 3 {
		// Wind chill calculation doesn't apply for very low wind speeds
		return tempF
	}

	// Formula for calculating wind chill
	return float32(
		35.74 + 0.6215*float64(tempF) -
			35.75*math.Pow(float64(windSpeedMPH), 0.16) +
			0.4275*float64(tempF)*
				math.Pow(float64(windSpeedMPH), 0.16))
}