#!/usr/bin/python3

# SPDX-License-Identifier: Apache-2.0
# Copyright 2020 IBM Corp.

# https://en.wikipedia.org/wiki/Barometric_formula

from math import exp, log
import sys
import argparse

Pb = 101325.00
Tb = 288.15
Lb = -0.0065
hb = 0
Rstar = 8.3144598
g0 = 9.80665
M = 0.0289644
C0 = 273.15

def P(h):
    return Pb * exp((-g0 * M * (h - hb)) / (Rstar * Tb))

def T(h):
    return (h - hb) * Lb + Tb

def Hp(p):
    return (log(p / Pb) * (Rstar * Tb)) / (-g0 * M) + hb

def Ht(t):
    return ((t - Tb) / Lb) + hb

def K(c):
    return C0 + c

def C(k):
    return k - C0

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--height", type=float, default=None, help="Height above sea level in metres")
    parser.add_argument("--temperature", type=float, default=None, help="Temperature in Celcius")
    parser.add_argument("--pressure", type=float, default=None, help="Atmospheric pressure in Pascals")
    args = parser.parse_args()
    out = []
    if args.height is not None:
        local = []
        local.append("Height")
        p = P(args.height)
        local.append("Pressure at {:.2f}m: {:.2f}Pa".format(args.height, p))
        c = C(T(args.height))
        local.append("Temperature at {:.2f}m: {:.2f}C".format(args.height, c))
        out.append("\n\t".join(local))
    if args.temperature is not None:
        local = []
        local.append("Temperature")
        ht = Ht(K(args.temperature))
        local.append("Height at {:.2f}C: {:.2f}m".format(args.temperature, ht))
        p = P(ht)
        local.append("Pressure at {:.2f}m: {:.2f}Pa".format(ht, p))
        out.append("\n\t".join(local))
    if args.pressure is not None:
        local = []
        local.append("Pressure")
        hp = Hp(args.pressure)
        local.append("Height at {:.2f}Pa: {:.2f}m".format(args.pressure, hp))
        t = C(T(hp))
        local.append("Temperature at {:.2f}m: {:.2f}C".format(hp, t))
        out.append("\n\t".join(local))
    print("\n\n".join(out))

if __name__ == "__main__":
    main()