package hydrogen

import "math"

// PressureMassKg converts pressure (MPa), temperature (C) and total water volume (L)
// using the existing real-gas compressibility equation.
func PressureMassKg(pressureMPa, temperatureC, capacityLiter float64) (float64, bool) {
	temperatureK := temperatureC + 273.15
	if pressureMPa < 0 || pressureMPa > 70 || temperatureK < 220 || temperatureK > 1000 || capacityLiter <= 0 || capacityLiter > 10000 {
		return 0, false
	}
	a := [...]float64{0.05888460, -0.06136111, -0.002650473, 0.002731125, 0.001802374, -0.001150707, 0.00009588528, -0.0000001109040, 0.0000000001264403}
	b := [...]float64{1.325, 1.87, 2.5, 2.8, 2.938, 3.14, 3.37, 3.75, 4.0}
	c := [...]float64{1, 1, 2, 2, 2.42, 2.63, 3, 4, 5}

	z := 1.0
	for index := range a {
		z += a[index] * math.Pow(100/temperatureK, b[index]) * math.Pow(pressureMPa, c[index])
	}
	if z <= 0 {
		return 0, false
	}
	density := pressureMPa * 1000 / (8.314472 * temperatureK * z) * 0.00201588 * 1000
	mass := density * capacityLiter / 1000
	return mass, !math.IsNaN(mass) && !math.IsInf(mass, 0) && mass >= 0 && mass <= 500
}