#!/usr/bin/python3
''' Calculate SARS tax on payments '''

import locale
import math
import pprint
import re
import sys

'''
    Rates from https://www.sars.gov.za/Tax-Rates/Income-Tax/Pages/Rates%20of%20Tax%20for%20Individuals.aspx
    low is the lowest value for that bracket; rate is the tax percentage applied to that bracket
'''
tax_rates = [
    dict(
        rate = 18,
        high = 205_900,
    ), dict(
        rate = 26,
        high = 321_600,
    ), dict(
        rate = 31,
        high = 445_100,
    ), dict(
        rate = 36,
        high = 584_200,
    ), dict(
        rate = 39,
        high = 744_800,
    ), dict(
        rate = 41,
        high = 1_577_300,
    ), dict(
        rate = 45,
    ),
]
for r in tax_rates:
    idx = tax_rates.index(r)
    if not r.get('high'):
        if idx < len(tax_rates) - 1:
            high = tax_rates[idx+1].get('low')
            r['high'] = high - 1
    if not r.get('low'):
        if idx > 0:
            low = tax_rates[idx-1].get('high')
            r['low'] = low + 1
        else:
            r['low'] = 1
#pprint.pprint(tax_rates)

locale.setlocale( locale.LC_MONETARY, 'en_ZA.UTF-8' )
locale._override_localeconv = {'mon_thousands_sep': ' ', 'mon_decimal_point': '.'}
currency = locale.localeconv()

if len(sys.argv) < 2:
    error()
elif isinstance(sys.argv[1], str):
    try:
        amount = "".join(sys.argv[1:]).strip(currency.get('currency_symbol'))
        amount = re.sub('[,.](\d{2})$','.\g<1>', amount) # convert decimal separator to .
        amount = re.sub('[ ,](\d{3})','\g<1>', amount)   # convert thousands separator to ''
        amount = locale.atof(amount)
        amount = int(amount)
    except Exception as e:
        error(e)
else: 
    error()

''' Are we dealing with a monthly amount or annual amount? 
    Assume anything over R100k is annual.
    If earning more than 100k per month, convert to --month/--year commandline option
'''
if amount > 100_000:
    is_annual = True
else:
    is_annual = False
    print("Notice: value {} determined to be per month, dividing tax rates by 12".format(locale.currency(amount, grouping=True)))

total_tax = 0
for r in tax_rates:
    low = (r.get('low') - 1)
    high = r.get('high')
    rate = r.get('rate')
    if not is_annual:
        low = math.ceil(low/12)
        high = math.ceil(high/12)
    if amount >= low:
        bracket = amount
        if high and amount > high:
            bracket = high
        current = math.ceil(bracket - low)
        total_tax += math.ceil(current * rate / 100)
        print("  {:>6} - {:>6} = {:>6} / {} = {:>6}".format(bracket, low, current, rate, total_tax))
        if amount < high:
            break

print("\nTotal tax on {} is {}".format(locale.currency(amount, grouping=True), locale.currency(total_tax, grouping=True)))

def error(e):
    if e:
        print(e);
    print("{0}: Please enter the annual or monthly amount before tax".format(sys.argv[0]))
    sys.exit()