Refactor income tax calculator. (#43)

* Add callable gem.

* Break up income tax calculator into multiple, smaller services.

* Refactor incomes methods in concern.

* Uninstall callable gem, add callable module, configure to be used in application.

* Refactor downstream.

* Lint.

* Add test for federal tax calculator.

* Add test for fica and state tax calculators.

* Lint.

* Specs for net income calculator

* Refactor with use of new services.

* Remove commented out code.

* Fix service.

* Fix net income service.

* Add standard deduction to federal tax calculator.

app/controllers/concerns/dashboard_builder.rb

@@ -12,8 +12,8 @@ def build_dashboard_variables!
     @fixed_expenses = FixedExpense.get_ordered
     @savings_rate = SavingsRate.savings
     @investing_rate = SavingsRate.investing
-    build_taxed_income_vars!
-    build_savings_vars!
+    build_income_tax_variables!
+    build_savings_vars!(salary_income: @salary_taxed.net_income, hourly_income: @hourly_taxed.net_income)
     build_guilt_free_vars!
     build_total_cost_vars!
   end

app/controllers/concerns/guilt_free.rb

@@ -2,8 +2,8 @@
 
 module GuiltFree
   def build_guilt_free_vars!
-    @guilt_free_salary = GuiltFreeCalculator.new(@salary_taxed.total_net_income, salary_savings_totalizer)
-    @guilt_free_hourly = GuiltFreeCalculator.new(@hourly_taxed.total_net_income, hourly_savings_totalizer)
+    @guilt_free_salary = GuiltFreeCalculator.new(@salary_taxed.net_income, salary_savings_totalizer)
+    @guilt_free_hourly = GuiltFreeCalculator.new(@hourly_taxed.net_income, hourly_savings_totalizer)
   end
 
   def salary_savings_totalizer

app/controllers/concerns/save_income.rb

@@ -2,38 +2,29 @@
 
 module SaveIncome
   extend ActiveSupport::Concern
-  include TaxedIncome
 
-  def build_savings_vars!
-    @hourly_saving = hourly_saving
-    @hourly_invest = hourly_investing
-    @salary_saving = salary_saving
-    @salary_invest = salary_investing
+  def build_savings_vars!(salary_income:, hourly_income:)
+    @salary_saving = savings(income: salary_income)
+    @salary_invest = investing(income: salary_income)
+    @hourly_saving = savings(income: hourly_income)
+    @hourly_invest = investing(income: hourly_income)
   end
 
-  def salary_investing
-    SavingsCalculator.new(tax_on_salary, set_invest_rate)
-  end
-
-  def salary_saving
-    SavingsCalculator.new(tax_on_salary, set_save_rate)
-  end
+  private
 
-  def hourly_investing
-    SavingsCalculator.new(tax_on_hourly, set_invest_rate)
+  def savings(income:)
+    SavingsCalculator.new(income, savings_rate)
   end
 
-  def hourly_saving
-    SavingsCalculator.new(tax_on_hourly, set_save_rate)
+  def investing(income:)
+    SavingsCalculator.new(income, investing_rate)
   end
 
-  private
-
-  def set_save_rate
-    SavingsRate.savings.rate
+  def savings_rate
+    @savings_rate ||= SavingsRate.savings_rate
   end
 
-  def set_invest_rate
-    SavingsRate.investing.rate
+  def investing_rate
+    @investing_rate ||= SavingsRate.investing_rate
   end
 end

app/controllers/concerns/taxed_income.rb

@@ -1,18 +1,28 @@
 # frozen_string_literal: true
 
 module TaxedIncome
-  def tax_on_salary
-    income = Income.find_by(income_type: "Salary")
-    IncomeTaxCalculatorService.new(income: income)
+  extend ActiveSupport::Concern
+
+  def build_income_tax_variables!
+    @salary_taxed = build_income_tax_object(income: salary_income)
+    @hourly_taxed = build_income_tax_object(income: hourly_income)
+  end
+
+  private
+
+  def salary_income
+    @salary_income = Income.find_by(income_type: "Salary").weekly_income * 52
   end
 
-  def tax_on_hourly
-    income = Income.find_by(income_type: "Hourly")
-    IncomeTaxCalculatorService.new(income: income)
+  def hourly_income
+    @hourly_income = Income.find_by(income_type: "Hourly").weekly_income * 52
   end
 
-  def build_taxed_income_vars!
-    @salary_taxed = tax_on_salary
-    @hourly_taxed = tax_on_hourly
+  def build_income_tax_object(income:)
+    federal_tax = FederalTaxCalculator.call(income: income)
+    fica_tax = FicaTaxCalculator.call(income: income)
+    state_tax = StateTaxCalculator.call(income: income)
+    net_income = income - (fica_tax + federal_tax + state_tax)
+    OpenStruct.new(federal_tax: federal_tax, fica_tax: fica_tax, state_tax: state_tax, net_income: net_income)
   end
 end

app/services/federal_tax_calculator.rb

@@ -0,0 +1,27 @@
+class FederalTaxCalculator
+  include Callable
+
+  def initialize(income:)
+    self.income = income
+  end
+
+  def call
+    calculate
+  end
+
+  private
+
+  attr_accessor :income
+
+  def calculate
+    bracket = FederalTaxBracket.where("bottom_range_cents <= ?", taxable_income.fractional).order(:bottom_range_cents).last
+    taxable_at_bracket_rate = Money.new(taxable_income - bracket.bottom_range)
+    rated = bracket.rate * taxable_at_bracket_rate
+    rated + bracket.cumulative
+  end
+
+  def taxable_income
+    # 2024 standard deduction = 13,850
+    @taxable_income ||= income - Money.new(13_850_00)
+  end
+end

app/services/fica_tax_calculator.rb

@@ -0,0 +1,15 @@
+class FicaTaxCalculator
+  include Callable
+
+  def initialize(income:)
+    self.income = income
+  end
+
+  def call
+    income * 0.0765
+  end
+
+  private
+
+  attr_accessor :income
+end

app/services/net_income_calculator.rb

@@ -0,0 +1,32 @@
+class NetIncomeCalculator
+  attr_reader :annual_income, :daily_income, :weekly_income, :monthly_income, :quarterly_income, :biannual_income
+
+  def initialize(annual_income:)
+    @annual_income = annual_income
+    @biannual_income = calculate_biannual_income
+    @quarterly_income = calculate_quarterly_income
+    @monthly_income = calculate_monthly_income
+    @weekly_income = calculate_weekly_income
+    @daily_income = calculate_daily_income
+  end
+
+  def calculate_biannual_income
+    @annual_income / 2
+  end
+
+  def calculate_quarterly_income
+    @annual_income / 4
+  end
+
+  def calculate_monthly_income
+    @annual_income / 12
+  end
+
+  def calculate_weekly_income
+    @annual_income / 52
+  end
+
+  def calculate_daily_income
+    @annual_income / 365
+  end
+end

app/services/savings_calculator.rb

@@ -11,8 +11,8 @@ class SavingsCalculator
     :daily_saving
 
   def initialize(income_type, saving_rate)
-    @annual_income = income_type.annual_income
-    @saving_rate = saving_rate
+    @annual_income = income_type
+    @saving_rate = saving_rate.rate
     @annual_saving = calculate_savings
     @bi_weekly_saving = calculate_bi_weekly_saving
     @daily_saving = calculate_daily_saving

app/services/state_tax_calculator.rb

@@ -0,0 +1,16 @@
+class StateTaxCalculator
+  include Callable
+
+  def initialize(income:)
+    self.income = income
+  end
+
+  #  Colorado state tax rate is 4.4%
+  def call
+    income * 0.044
+  end
+
+  private
+
+  attr_accessor :income
+end

app/views/shared/_taxed_income.html.erb

@@ -1,9 +1,9 @@
-<% paid_taxes = [ taxed_income.federal_income_tax, taxed_income.fica_tax, taxed_income.state_tax, taxed_income.total_net_income ] %>
+<% paid_taxes = [ taxed_income.federal_tax, taxed_income.fica_tax, taxed_income.state_tax, taxed_income.net_income ] %>
 
 <% paid_taxes.each do |tax| %>
   <% if annual %>
     <div class="px-5"><%= humanized_money_with_symbol(tax) %></div>
   <% else %>
     <div class="px-5"><%= humanized_money_with_symbol(tax / 26) %></div>
   <% end %>
-<% end %>
+<% end %>

config/application.rb

@@ -23,6 +23,10 @@ class Application < Rails::Application
     # Initialize configuration defaults for originally generated Rails version.
     config.load_defaults 7.0
 
+    # Load in all modules
+    config.autoload_paths << Rails.root.join("lib", "modules")
+    config.eager_load_paths << Rails.root.join("lib", "modules")
+
     # Configuration for the application, engines, and railties goes here.
     #
     # These settings can be overridden in specific environments using the files

lib/modules/callable.rb

@@ -0,0 +1,9 @@
+module Callable
+  extend ActiveSupport::Concern
+
+  class_methods do
+    def call(**args)
+      new(**args).call
+    end
+  end
+end

spec/factories/federal_tax_brackets.rb

@@ -15,27 +15,29 @@
 #  updated_at            :datetime         not null
 #
 FactoryBot.define do
+  # tax_brackets = 10% on first $1,000, 15% from $1,001 to $100,000, 25% from $100,001 to $500,000
+
   factory :federal_tax_bracket do
     tier { "Tier 1" }
     bottom_range_cents { 0 }
-    top_range_cents { 100_000 }
+    top_range_cents { 100_000 } # $1,000.00
     rate { 0.1 }
     cumulative_cents { 0 }
 
     trait :tier_2 do
       tier { "Tier 2" }
-      bottom_range_cents { 1_000_100 }
-      top_range_cents { 10_000_000 }
+      bottom_range_cents { 100_100 } # $1,001.00
+      top_range_cents { 10_000_000 } # $100,000.00
       rate { 0.15 }
-      cumulative_cents { 200_000 }
+      cumulative_cents { 10_000 } # $100.00
     end
 
     trait :tier_3 do
       tier { "Tier 2" }
-      bottom_range_cents { 10_000_100 }
-      top_range_cents { 50_000_000 }
+      bottom_range_cents { 10_000_100 } # $100,001.00
+      top_range_cents { 50_000_000 } # $500,000.00
       rate { 0.25 }
-      cumulative_cents { 500_000 }
+      cumulative_cents { 1_485_000 } # $14,850.00
     end
 
     trait :with_all_tiers do

spec/factories/incomes.rb

@@ -26,11 +26,11 @@
       weekly_income_cents { 300_000 * 40 }
     end
 
-    # trait :with_all_types do
-    #   after :create do |_record|
-    #     create(:income, :hourly)
-    #   end
-    # end
+    trait :with_all_types do
+      after :create do |_record|
+        create(:income, :hourly)
+      end
+    end
 
     # to_create do |instance|
     #   instance.id = Income.find_or_create_by(income_type: instance.income_type).id

spec/services/federal_tax_calculator_spec.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require("rails_helper")
+
+RSpec.describe FederalTaxCalculator, type: :service do
+  subject(:service) do
+    described_class.call(
+      income: salary_income.rate
+    )
+  end
+
+  let!(:salary_income) { create(:income) }
+  let!(:tax_brackets) { create(:federal_tax_bracket, :with_all_tiers) }
+
+  it { expect(service).to be_a Money }
+
+  it "calculates federal tax" do
+    # salary_income = $50,000
+    # standard_deduction = $13,850
+    # tax_brackets = 10% on first $1,000, 15% from $1,001 to $100,000, 25% from $100,001 to $500,000
+
+    expect(service.format).to eq("$5,372.35")
+    expect((salary_income.rate - service).format).to eq("$44,627.65")
+  end
+end

spec/services/fica_tax_calculator_spec.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require("rails_helper")
+
+RSpec.describe FicaTaxCalculator, type: :service do
+  subject(:service) do
+    described_class.call(
+      income: salary_income.rate
+    )
+  end
+
+  let!(:salary_income) { create(:income) }
+  let!(:tax_brackets) { create(:federal_tax_bracket, :with_all_tiers) }
+
+  it { expect(service).to be_a Money }
+
+  it "calculates FICA tax" do
+    # salary_income = $50,000
+
+    expect(service.format).to eq("$3,825.00")
+    expect((salary_income.rate - service).format).to eq("$46,175.00")
+  end
+end

spec/services/net_income_calculator_spec.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require("rails_helper")
+
+RSpec.describe NetIncomeCalculator, type: :service do
+  subject(:service) do
+    described_class.new(
+      annual_income: salary_income.rate
+    )
+  end
+
+  let!(:salary_income) { create(:income) }
+  let!(:tax_brackets) { create(:federal_tax_bracket, :with_all_tiers) }
+
+  it { expect(service).to be_a NetIncomeCalculator }
+
+  it { expect(service.annual_income.format).to eq("$50,000.00") }
+  it { expect(service.biannual_income.format).to eq("$25,000.00") }
+  it { expect(service.quarterly_income.format).to eq("$12,500.00") }
+  it { expect(service.monthly_income.format).to eq("$4,166.67") }
+  it { expect(service.weekly_income.format).to eq("$961.54") }
+  it { expect(service.daily_income.format).to eq("$136.99") }
+end