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

app/models/holding/base_calculator.rb

@@ -0,0 +1,63 @@
+class Holding::BaseCalculator
+  attr_reader :account
+
+  def initialize(account)
+    @account = account
+  end
+
+  def calculate
+    Rails.logger.tagged(self.class.name) do
+      holdings = calculate_holdings
+      Holding.gapfill(holdings)
+    end
+  end
+
+  private
+    def portfolio_cache
+      @portfolio_cache ||= Holding::PortfolioCache.new(account)
+    end
+
+    def empty_portfolio
+      securities = portfolio_cache.get_securities
+      securities.each_with_object({}) { |security, hash| hash[security.id] = 0 }
+    end
+
+    def generate_starting_portfolio
+      empty_portfolio
+    end
+
+    def transform_portfolio(previous_portfolio, trade_entries, direction: :forward)
+      new_quantities = previous_portfolio.dup
+
+      trade_entries.each do |trade_entry|
+        trade = trade_entry.entryable
+        security_id = trade.security_id
+        qty_change = trade.qty
+        qty_change = qty_change * -1 if direction == :reverse
+        new_quantities[security_id] = (new_quantities[security_id] || 0) + qty_change
+      end
+
+      new_quantities
+    end
+
+    def build_holdings(portfolio, date)
+      portfolio.map do |security_id, qty|
+        price = portfolio_cache.get_price(security_id, date)
+
+        if price.nil?
+          Rails.logger.warn "No price found for security #{security_id} on #{date}"
+          next
+        end
+
+        Holding.new(
+          account_id: account.id,
+          security_id: security_id,
+          date: date,
+          qty: qty,
+          price: price.price,
+          currency: price.currency,
+          amount: qty * price.price
+        )
+      end.compact
+    end
+end