module Train::Tax::Calculator
  module WithholdingTax

    LOOKUP_TABLE = [
      { lowest:       0.00, highest:  20_833.00, base:       0.00, excess: 0.00 },
      { lowest:  20_833.00, highest:  33_333.00, base:       0.00, excess: 0.20 },
      { lowest:  33_333.00, highest:  66_667.00, base:   2_500.00, excess: 0.25 },
      { lowest: 66_667.00, highest: 166_667.00, base:  10_833.33, excess: 0.30 },
      { lowest: 166_667.00, highest: 666_667.00, base:  40_833.33, excess: 0.32 },
      { lowest: 666_667.00, highest: Float::INFINITY, base: 200_833.33, excess: 0.35 },
    ]

    def self.call(basic_salary)
      taxable_income = taxable_income_for(basic_salary)
      tax_bracket    = tax_bracket_for(taxable_income)

      withholding_tax = ((taxable_income - tax_bracket[:lowest]) * tax_bracket[:excess]) + tax_bracket[:base]

      withholding_tax.round(2)
    end

    private

    def self.taxable_income_for(basic_salary)
      initial_net = basic_salary - Deductions.(basic_salary)

      if basic_salary > 90_000
        additional_tax = ((basic_salary - 90_000) / 12.00)
        return initial_net + additional_tax
      end

      initial_net
    end

    def self.tax_bracket_for(taxable_income)
      LOOKUP_TABLE.select do |bracket|
        taxable_income >= bracket[:lowest] &&
        taxable_income < bracket[:highest]
      end.first
    end

  end
end