Basic Account Balance Sync Algorithm (#501)

* Sketch out sync interface

* Add basic account sync algorithm

* Update logic for final balance in series

* Remove start_date concept

* Clean up tests

* Improve clarity of test

* Update app/models/account.rb

Co-authored-by: Rob Zolkos <rob@zolkos.com>
Signed-off-by: Zach Gollwitzer <zach.gollwitzer@gmail.com>

* Update app/models/transaction.rb

Co-authored-by: Rob Zolkos <rob@zolkos.com>
Signed-off-by: Zach Gollwitzer <zach.gollwitzer@gmail.com>

* Update app/models/valuation.rb

Co-authored-by: Rob Zolkos <rob@zolkos.com>
Signed-off-by: Zach Gollwitzer <zach.gollwitzer@gmail.com>

* Re-organize code, simplify job interface

* Consolidate balance calculations

* More cleanup

---------

Signed-off-by: Zach Gollwitzer <zach.gollwitzer@gmail.com>
Co-authored-by: Rob Zolkos <rob@zolkos.com>

test/models/account/balance_calculator_test.rb

@@ -0,0 +1,50 @@
+require "test_helper"
+
+class Account::BalanceCalculatorTest < ActiveSupport::TestCase
+    test "syncs account with only valuations" do
+        account = accounts(:collectable)
+        account.accountable = account_other_assets(:one)
+
+        daily_balances = Account::BalanceCalculator.new(account).daily_balances
+
+        expected_balances = [
+            400, 400, 400, 400, 400, 400, 400, 400, 400, 400,
+            400, 400, 400, 400, 400, 400, 400, 400, 700, 700,
+            700, 700, 700, 700, 700, 700, 550, 550, 550, 550,
+            550
+        ].map(&:to_d)
+
+        assert_equal expected_balances, daily_balances.map { |b| b[:balance] }
+    end
+
+    test "syncs account with only transactions" do
+        account = accounts(:checking)
+        account.accountable = account_depositories(:checking)
+
+        daily_balances = Account::BalanceCalculator.new(account).daily_balances
+
+        expected_balances = [
+            4000, 3985, 3985, 3985, 3985, 3985, 3985, 3985, 5060, 5060,
+            5060, 5060, 5060, 5060, 5060, 5040, 5040, 5040, 5010, 5010,
+            5010, 5010, 5010, 5010, 5010, 5000, 5000, 5000, 5000, 5000,
+            5000
+        ].map(&:to_d)
+
+        assert_equal expected_balances, daily_balances.map { |b| b[:balance] }
+    end
+
+    test "syncs account with both valuations and transactions" do
+        account = accounts(:savings_with_valuation_overrides)
+        account.accountable = account_depositories(:savings)
+        daily_balances = Account::BalanceCalculator.new(account).daily_balances
+
+        expected_balances = [
+            21250, 21750, 21750, 21750, 21750, 21000, 21000, 21000, 21000, 21000,
+            21000, 21000, 19000, 19000, 19000, 19000, 19000, 19000, 19500, 19500,
+            19500, 19500, 19500, 19500, 19500, 19700, 19700, 20500, 20500, 20500,
+            20000
+        ].map(&:to_d)
+
+        assert_equal expected_balances, daily_balances.map { |b| b[:balance] }
+    end
+end

test/models/account/syncable_test.rb

@@ -0,0 +1,32 @@
+require "test_helper"
+
+class Account::SyncableTest < ActiveSupport::TestCase
+    test "account has no balances until synced" do
+        account = accounts(:savings_with_valuation_overrides)
+        account.accountable = account_depositories(:savings)
+
+        assert_equal 0, account.balances.count
+    end
+
+    test "account has balances after syncing" do
+        account = accounts(:savings_with_valuation_overrides)
+        account.accountable = account_depositories(:savings)
+        account.sync
+
+        assert_equal 31, account.balances.count
+    end
+
+    test "stale balances are purged after syncing" do
+        account = accounts(:savings_with_valuation_overrides)
+        account.accountable = account_depositories(:savings)
+
+        # Create old, stale balances that should be purged (since they are before account start date)
+        account.balances.create!(date: 1.year.ago, balance: 1000)
+        account.balances.create!(date: 2.years.ago, balance: 2000)
+        account.balances.create!(date: 3.years.ago, balance: 3000)
+
+        account.sync
+
+        assert_equal 31, account.balances.count
+    end
+end