Plaid sync domain improvements (#2267)

Breaks our Plaid sync process out into more manageable classes. Notably, this moves the sync process to a distinct, 2-step flow:

1. Import stage - we first make API calls and import Plaid data to "mirror" tables
2. Processing stage - read the raw data, apply business rules, build internal domain models and sync balances

This provides several benefits:

- Plaid syncs can now be "replayed" without fetching API data again
- Mirror tables provide better audit and debugging capabilities
- Eliminates the "all or nothing" sync behavior that is currently in place, which is brittle

test/models/plaid_account/liabilities/credit_processor_test.rb

@@ -0,0 +1,39 @@
+require "test_helper"
+
+class PlaidAccount::Liabilities::CreditProcessorTest < ActiveSupport::TestCase
+  setup do
+    @plaid_account = plaid_accounts(:one)
+    @plaid_account.update!(
+      plaid_type: "credit",
+      plaid_subtype: "credit_card"
+    )
+
+    @plaid_account.account.update!(
+      accountable: CreditCard.new,
+    )
+  end
+
+  test "updates credit card minimum payment and APR from Plaid data" do
+    @plaid_account.update!(raw_liabilities_payload: {
+      credit: {
+        minimum_payment_amount: 100,
+        aprs: [ { apr_percentage: 15.0 } ]
+      }
+    })
+
+    processor = PlaidAccount::Liabilities::CreditProcessor.new(@plaid_account)
+    processor.process
+
+    assert_equal 100, @plaid_account.account.credit_card.minimum_payment
+    assert_equal 15.0, @plaid_account.account.credit_card.apr
+  end
+
+  test "does nothing when liability data absent" do
+    @plaid_account.update!(raw_liabilities_payload: {})
+    processor = PlaidAccount::Liabilities::CreditProcessor.new(@plaid_account)
+    processor.process
+
+    assert_nil @plaid_account.account.credit_card.minimum_payment
+    assert_nil @plaid_account.account.credit_card.apr
+  end
+end

test/models/plaid_account/liabilities/mortgage_processor_test.rb

@@ -0,0 +1,44 @@
+require "test_helper"
+
+class PlaidAccount::Liabilities::MortgageProcessorTest < ActiveSupport::TestCase
+  setup do
+    @plaid_account = plaid_accounts(:one)
+    @plaid_account.update!(
+      plaid_type: "loan",
+      plaid_subtype: "mortgage"
+    )
+
+    @plaid_account.account.update!(accountable: Loan.new)
+  end
+
+  test "updates loan interest rate and type from Plaid data" do
+    @plaid_account.update!(raw_liabilities_payload: {
+      mortgage: {
+        interest_rate: {
+          type: "fixed",
+          percentage: 4.25
+        }
+      }
+    })
+
+    processor = PlaidAccount::Liabilities::MortgageProcessor.new(@plaid_account)
+    processor.process
+
+    loan = @plaid_account.account.loan
+
+    assert_equal "fixed", loan.rate_type
+    assert_equal 4.25, loan.interest_rate
+  end
+
+  test "does nothing when mortgage data absent" do
+    @plaid_account.update!(raw_liabilities_payload: {})
+
+    processor = PlaidAccount::Liabilities::MortgageProcessor.new(@plaid_account)
+    processor.process
+
+    loan = @plaid_account.account.loan
+
+    assert_nil loan.rate_type
+    assert_nil loan.interest_rate
+  end
+end

test/models/plaid_account/liabilities/student_loan_processor_test.rb

@@ -0,0 +1,68 @@
+require "test_helper"
+
+class PlaidAccount::Liabilities::StudentLoanProcessorTest < ActiveSupport::TestCase
+  setup do
+    @plaid_account = plaid_accounts(:one)
+    @plaid_account.update!(
+      plaid_type: "loan",
+      plaid_subtype: "student"
+    )
+
+    # Change the underlying accountable to a Loan so the helper method `loan` is available
+    @plaid_account.account.update!(accountable: Loan.new)
+  end
+
+  test "updates loan details including term months from Plaid data" do
+    @plaid_account.update!(raw_liabilities_payload: {
+      student: {
+        interest_rate_percentage: 5.5,
+        origination_principal_amount: 20000,
+        origination_date: Date.new(2020, 1, 1),
+        expected_payoff_date: Date.new(2022, 1, 1)
+      }
+    })
+
+    processor = PlaidAccount::Liabilities::StudentLoanProcessor.new(@plaid_account)
+    processor.process
+
+    loan = @plaid_account.account.loan
+
+    assert_equal "fixed", loan.rate_type
+    assert_equal 5.5, loan.interest_rate
+    assert_equal 20000, loan.initial_balance
+    assert_equal 24, loan.term_months
+  end
+
+  test "handles missing payoff dates gracefully" do
+    @plaid_account.update!(raw_liabilities_payload: {
+      student: {
+        interest_rate_percentage: 4.8,
+        origination_principal_amount: 15000,
+        origination_date: Date.new(2021, 6, 1)
+        # expected_payoff_date omitted
+      }
+    })
+
+    processor = PlaidAccount::Liabilities::StudentLoanProcessor.new(@plaid_account)
+    processor.process
+
+    loan = @plaid_account.account.loan
+
+    assert_nil loan.term_months
+    assert_equal 4.8, loan.interest_rate
+    assert_equal 15000, loan.initial_balance
+  end
+
+  test "does nothing when loan data absent" do
+    @plaid_account.update!(raw_liabilities_payload: {})
+
+    processor = PlaidAccount::Liabilities::StudentLoanProcessor.new(@plaid_account)
+    processor.process
+
+    loan = @plaid_account.account.loan
+
+    assert_nil loan.interest_rate
+    assert_nil loan.initial_balance
+    assert_nil loan.term_months
+  end
+end