Created
January 30, 2020 21:49
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Calculate optimal standing order for prepaid account
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#!/usr/bin/env python | |
import datetime | |
current_balance = 450 | |
desired_buffer_days = 30 | |
planned_charge_period_days = 365.25/6 | |
past_charges = [ | |
(datetime.date(2019, 6, 30), 525), | |
(datetime.date(2019, 7, 22), 1250), | |
(datetime.date(2019, 12, 1), 500), | |
] | |
boundary_days = [d for d, __ in past_charges[:2] + past_charges[-2:]] | |
earliest_period_days = (boundary_days[1] - boundary_days[0]).days | |
latest_period_days = (boundary_days[-1] - boundary_days[-2]).days | |
total_days = (boundary_days[-1] - boundary_days[0]).days + 0.5*( | |
earliest_period_days + latest_period_days) | |
daily_cost = sum(x for __, x in past_charges)/total_days | |
planned_charge = planned_charge_period_days*daily_cost | |
min_balance = desired_buffer_days*daily_cost | |
days_until_first_charge = max( | |
0, int((current_balance - min_balance)/daily_cost)) | |
first_charge_date = datetime.date.today() + datetime.timedelta( | |
days=days_until_first_charge) | |
print( | |
'charge the amount {:d}, start on {}\n' | |
'daily cost: {:g}, min balance: {:d}'.format( | |
int(round(planned_charge)), first_charge_date, daily_cost, | |
int(round(min_balance)))) |
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