natural_rules.py

"""
Covers 'natural' update rules, rules that are set by law, economics and/or mathematics, as opposed to rules that articulate the assumptions of the forecasting model.
"""

import model
import tax

def apply_tax(deltas: model.deltas_state, previous_funds: model.funds_state, previous_deltas: model.deltas_state):
    """Set income tax owed, *ignoring* RRSP contributions (since savings can only be calculated after the tax has been determined)."""
    income_tax = tax.get_income_tax(deltas.gross_salary)
    return deltas.update_tax(income_tax)

def apply_tax_refund(deltas: model.deltas_state, previous_funds: model.funds_state, previous_deltas: model.deltas_state):
    """
    Calculates and sets the tax refund/extra-owed for the current year, based on the overpayment (because of RRSP contributions) or underpayment (because 
    of RRSP deductions) in the previous year.
    """
    post_rrsp_tax = tax.get_income_tax(previous_deltas.taxable_income)
    diff = previous_deltas.tax - post_rrsp_tax
    if previous_deltas.rrsp > 0 and previous_deltas.tax > 0 and previous_deltas.rrsp_interest < previous_deltas.rrsp:
        assert diff > 0
        
    return deltas.update_tax_refund(diff)

def get_calculate_investment_interest(rrsp_interest_rate: float, tfsa_interest_rate: float):
    """
    Gets a rule which applies compound interest to accumulate savings, according to the supplied interest rates (fractions).
    """

    def calculate_investment_interest(deltas: model.deltas_state, previous_funds: model.funds_state, previous_deltas: model.deltas_state):
        output = deltas.update_rrsp_interest(previous_funds.rrsp_savings * rrsp_interest_rate)
        output = output.update_tfsa_interest(previous_funds.tfsa_savings * tfsa_interest_rate)

        return output
    
    return calculate_investment_interest