Account:: namespace simplifications and cleanup (#2110)

* Flatten Holding model

* Flatten balance model

* Entries domain renames

* Fix valuations reference

* Fix trades stream

* Fix brakeman warnings

* Fix tests

* Replace existing entryable type references in DB

test/models/balance/reverse_calculator_test.rb

@@ -0,0 +1,59 @@
+require "test_helper"
+
+class Balance::ReverseCalculatorTest < ActiveSupport::TestCase
+  include EntriesTestHelper
+
+  setup do
+    @account = families(:empty).accounts.create!(
+      name: "Test",
+      balance: 20000,
+      cash_balance: 20000,
+      currency: "USD",
+      accountable: Investment.new
+    )
+  end
+
+  # When syncing backwards, we start with the account balance and generate everything from there.
+  test "no entries sync" do
+    assert_equal 0, @account.balances.count
+
+    expected = [ @account.balance, @account.balance ]
+    calculated = Balance::ReverseCalculator.new(@account).calculate
+
+    assert_equal expected, calculated.map(&:balance)
+  end
+
+  test "valuations sync" do
+    create_valuation(account: @account, date: 4.days.ago.to_date, amount: 17000)
+    create_valuation(account: @account, date: 2.days.ago.to_date, amount: 19000)
+
+    expected = [ 17000, 17000, 19000, 19000, 20000, 20000 ]
+    calculated = Balance::ReverseCalculator.new(@account).calculate.sort_by(&:date).map(&:balance)
+
+    assert_equal expected, calculated
+  end
+
+  test "transactions sync" do
+    create_transaction(account: @account, date: 4.days.ago.to_date, amount: -500) # income
+    create_transaction(account: @account, date: 2.days.ago.to_date, amount: 100) # expense
+
+    expected = [ 19600, 20100, 20100, 20000, 20000, 20000 ]
+    calculated = Balance::ReverseCalculator.new(@account).calculate.sort_by(&:date).map(&:balance)
+
+    assert_equal expected, calculated
+  end
+
+  test "multi-entry sync" do
+    create_transaction(account: @account, date: 8.days.ago.to_date, amount: -5000)
+    create_valuation(account: @account, date: 6.days.ago.to_date, amount: 17000)
+    create_transaction(account: @account, date: 6.days.ago.to_date, amount: -500)
+    create_transaction(account: @account, date: 4.days.ago.to_date, amount: -500)
+    create_valuation(account: @account, date: 3.days.ago.to_date, amount: 17000)
+    create_transaction(account: @account, date: 1.day.ago.to_date, amount: 100)
+
+    expected = [ 12000, 17000, 17000, 17000, 16500, 17000, 17000, 20100, 20000, 20000 ]
+    calculated = Balance::ReverseCalculator.new(@account).calculate.sort_by(&:date).map(&:balance)
+
+    assert_equal expected, calculated
+  end
+end