Start and end balance anchors for historical account balances (#2455)

* Add kind field to valuation

* Fix schema conflict

* Add kind to valuation

* Scaffold opening balance manager

* Opening balance manager implementation

* Update account import to use opening balance manager + tests

* Update account to use opening balance manager

* Fix test assertions, usage of current balance manager

* Lint fixes

* Add Opening Balance manager, add tests to forward calculator

* Add credit card to "all cash" designation

* Simplify valuation model

* Add current balance manager with tests

* Add current balance logic to reverse calculator and plaid sync

* Tweaks to initial calc logic

* Ledger testing helper, tweak assertions for reverse calculator

* Update test assertions

* Extract balance transformer, simplify calculators

* Algo simplifications

* Final tweaks to calculators

* Cleanup

* Fix error, propagate sync errors up to parent

* Update migration script, valuation naming

app/models/account/current_balance_manager.rb

@@ -0,0 +1,86 @@
+class Account::CurrentBalanceManager
+  InvalidOperation = Class.new(StandardError)
+
+  Result = Struct.new(:success?, :changes_made?, :error, keyword_init: true)
+
+  def initialize(account)
+    @account = account
+  end
+
+  def has_current_anchor?
+    current_anchor_valuation.present?
+  end
+
+  # Our system should always make sure there is a current anchor, and that it is up to date.
+  # The fallback is provided for backwards compatibility, but should not be relied on since account.balance is a "cached/derived" value.
+  def current_balance
+    if current_anchor_valuation
+      current_anchor_valuation.entry.amount
+    else
+      Rails.logger.warn "No current balance anchor found for account #{account.id}. Using cached balance instead, which may be out of date."
+      account.balance
+    end
+  end
+
+  def current_date
+    if current_anchor_valuation
+      current_anchor_valuation.entry.date
+    else
+      Date.current
+    end
+  end
+
+  def set_current_balance(balance)
+    # A current balance anchor implies there is an external data source that will keep it updated. Since manual accounts
+    # are tracked by the user, a current balance anchor is not appropriate.
+    raise InvalidOperation, "Manual accounts cannot set current balance anchor. Set opening balance or use a reconciliation instead." if account.manual?
+
+    if current_anchor_valuation
+      changes_made = update_current_anchor(balance)
+      Result.new(success?: true, changes_made?: changes_made, error: nil)
+    else
+      create_current_anchor(balance)
+      Result.new(success?: true, changes_made?: true, error: nil)
+    end
+  end
+
+  private
+    attr_reader :account
+
+    def current_anchor_valuation
+      @current_anchor_valuation ||= account.valuations.current_anchor.includes(:entry).first
+    end
+
+    def create_current_anchor(balance)
+      account.entries.create!(
+        date: Date.current,
+        name: Valuation.build_current_anchor_name(account.accountable_type),
+        amount: balance,
+        currency: account.currency,
+        entryable: Valuation.new(kind: "current_anchor")
+      )
+    end
+
+    def update_current_anchor(balance)
+      changes_made = false
+
+      ActiveRecord::Base.transaction do
+        # Update associated entry attributes
+        entry = current_anchor_valuation.entry
+
+        if entry.amount != balance
+          entry.amount = balance
+          changes_made = true
+        end
+
+        if entry.date != Date.current
+          entry.date = Date.current
+          changes_made = true
+        end
+
+        entry.save! if entry.changed?
+      end
+
+      changes_made
+    end
+end