Auto-fill debt data from on-premise mainframe

Gemfile

@@ -22,6 +22,8 @@ gem 'puma', '~> 4.1'
 # Reduces boot times through caching; required in config/boot.rb
 gem 'bootsnap', '>= 1.4.2', require: false
 
+gem 'faker', '~> 2.10.1'
+
 # Use Rack CORS for handling Cross-Origin Resource Sharing (CORS), making cross-origin AJAX possible
 # gem 'rack-cors'
 

Gemfile.lock

@@ -63,6 +63,8 @@ GEM
     concurrent-ruby (1.1.8)
     crass (1.0.6)
     erubi (1.10.0)
+    faker (2.10.2)
+      i18n (>= 1.6, < 2)
     ffi (1.15.0)
     globalid (0.4.2)
       activesupport (>= 4.2.0)
@@ -149,6 +151,7 @@ PLATFORMS
 DEPENDENCIES
   bootsnap (>= 1.4.2)
   byebug
+  faker (~> 2.10.1)
   listen (~> 3.2)
   pg (~> 1.2.2)
   puma (~> 4.1)

app/controllers/debt_controller.rb

@@ -1,5 +1,6 @@
 class DebtController < ApplicationController
   before_action :load_borrower
+  before_action :load_debt, except: [:index, :create]
 
   def index
     render json: { debts: @borrower.debts }, status: :ok
@@ -24,12 +25,25 @@ def create
   end
 
   def show
-    @debt = @borrower.debts.find_by(id: params[:id])
+    render json: { debt: @debt }, status: :ok
+  end
 
-    if @debt
+  def autofill
+    begin
+      @debt.autofill!
       render json: { debt: @debt }, status: :ok
-    else
-      render json: { error: "Debt not found" }, status: :not_found
+    rescue Debt::DebtServiceError => e
+      render json: { errors: e }, status: :service_unavailable
+    end
+  end
+
+  def payoff_amount
+    num_days_before_payoff = params[:num_days_before_payoff] || Debt::DEFAULT_NUM_DAYS_BEFORE_PAYOFF
+
+    begin
+      render json: { payoff_amount: @debt.payoff_amount(num_days_before_payoff) }, status: :ok
+    rescue ArgumentError => e
+      render json: { errors: e }, status: :internal_server_error
     end
   end
 
@@ -42,4 +56,12 @@ def load_borrower
       render json: {error: "Borrower not found" }, status: :not_found
     end
   end
+
+  def load_debt
+    @debt = @borrower.debts.find_by(id: params[:debt_id] || params[:id])
+
+    if @debt.nil?
+      render json: {error: "Debt not found" }, status: :not_found
+    end
+  end
 end

app/models/debt.rb

@@ -1,5 +1,43 @@
 class Debt < ApplicationRecord
+
+  class DebtServiceError < StandardError; end
+
+  DEFAULT_NUM_DAYS_BEFORE_PAYOFF = 30.freeze
+
   belongs_to :borrower
 
-  validates :borrower, :account_number, :description, :status, presence: true 
+  validates :borrower, :account_number, :description, :status, presence: true
+
+  def autofill!
+    raise DebtServiceError, "Service credentials unspecified" if ENV["SERVICE_CREDENTIALS"].nil?
+
+    # BEGIN HAND-WAVING
+    # For the purpose of this examination, assume that the following is making a call to retrieve these values from on-premise mainframe.
+
+    self.current_balance = Faker::Number.decimal(l_digits: 5, r_digits: 2)
+    self.interest_rate =  Faker::Number.decimal(l_digits: 1, r_digits: 3)
+    self.current_balance =  Faker::Number.decimal(l_digits: 5, r_digits: 2)
+    self.outstanding_interest_amount =  Faker::Number.decimal(l_digits: 4, r_digits: 2)
+    self.servicer_address =  Faker::Address.full_address
+    self.last_payment_date =  Faker::Date.backward
+    self.last_payment_amount =  Faker::Number.decimal(l_digits: 3, r_digits: 2)
+    self.last_statement_balance =  Faker::Number.decimal(l_digits: 3, r_digits: 2)
+    self.last_statement_issue_date =  Faker::Date.backward
+    self.next_payment_due_date =  Faker::Date.forward
+
+    # END HAND-WAVING
+
+    nil
+  end
+
+  def payoff_amount(num_days_before_payoff = DEFAULT_NUM_DAYS_BEFORE_PAYOFF)
+    raise ArgumentError, "num_days_before_payoff must be an integer" unless num_days_before_payoff.is_a? Integer
+    raise ArgumentError, "num_days_before_payoff must be positive" if num_days_before_payoff < 0
+
+    daily_interest_rate = (self.outstanding_interest_amount / 100) / 365
+    daily_interest_amount = self.current_balance * daily_interest_rate
+    accumulated_interest_before_payoff = daily_interest_amount * num_days_before_payoff
+
+    self.current_balance + accumulated_interest_before_payoff
+  end
 end

config/routes.rb

@@ -1,5 +1,8 @@
 Rails.application.routes.draw do
   resources :borrower, only: [:create, :show] do
-    resources :debt, only: [:create, :show, :index]
+    resources :debt, only: [:create, :show, :index] do
+      put :autofill
+      get :payoff_amount
+    end
   end
 end

test/controllers/debt_controller_test.rb

@@ -55,4 +55,23 @@ class DebtControllerTest < ActionDispatch::IntegrationTest
     assert_equal debt.as_json, JSON.parse(@response.body)["debt"]
   end
 
+  test "autofill" do
+    if ENV["SERVICE_CREDENTIALS"].nil?
+      skip("Service credentials not set. Skipping")
+    end
+
+    debt = debts.last
+
+    put borrower_debt_autofill_url(borrower_id: debt.borrower.id, debt_id: debt.id), as: :json
+    assert_response :ok
+  end
+
+  test "payoff_amount" do
+    debt = debts.last
+
+    get borrower_debt_payoff_amount_url(borrower_id: debt.borrower.id, debt_id: debt.id), as: :json
+
+    assert_response :ok
+    assert_equal debt.payoff_amount.as_json, JSON.parse(@response.body)["payoff_amount"]
+  end
 end

test/models/debt_test.rb

@@ -20,4 +20,54 @@ class DebtTest < ActiveSupport::TestCase
       assert_includes debt.errors.messages.keys, attribute
     end
   end
+
+  test "autofill!" do
+    if ENV["SERVICE_CREDENTIALS"].nil?
+      skip("Service credentials not set. Skipping")
+    end
+
+    debt = Debt.new(
+      account_number: Faker::Number.number(digits: 10),
+      description: Faker::Lorem.sentence,
+      status: "Open"
+    )
+    debt.borrower = Borrower.find(borrowers.first.id)
+    debt.autofill!
+
+    assert debt.valid?
+    assert debt.save
+  end
+
+  test "payoff_amount" do
+    debt = debts.first
+
+    (0..90).each do |num_days_before_payoff|
+      daily_interest_rate = (debt.outstanding_interest_amount / 100) / 365
+      daily_interest_amount = debt.current_balance * daily_interest_rate
+      accumulated_interest_before_payoff = daily_interest_amount * num_days_before_payoff
+
+      assert_equal(
+        (debt.current_balance + accumulated_interest_before_payoff),
+        debt.payoff_amount(num_days_before_payoff)
+      )
+    end
+  end
+
+  test "payoff_amount defaults to #{Debt::DEFAULT_NUM_DAYS_BEFORE_PAYOFF} days" do
+    debt = debts.first
+
+    daily_interest_rate = (debt.outstanding_interest_amount / 100) / 365
+    daily_interest_amount = debt.current_balance * daily_interest_rate
+    accumulated_interest_before_payoff = daily_interest_amount * Debt::DEFAULT_NUM_DAYS_BEFORE_PAYOFF
+
+    assert_equal (debt.current_balance + accumulated_interest_before_payoff), debt.payoff_amount
+  end
+
+  test "payoff_amount throws error with negative parameter" do
+    assert_raises(ArgumentError) { debts.first.payoff_amount(-1) }
+  end
+
+  test "payoff_amount throws error with nil" do
+    assert_raises(ArgumentError) { debts.first.payoff_amount(nil) }
+  end
 end