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/balance/sync_cache.rb

@@ -0,0 +1,46 @@
+class Balance::SyncCache
+  def initialize(account)
+    @account = account
+  end
+
+  def get_valuation(date)
+    converted_entries.find { |e| e.date == date && e.valuation? }
+  end
+
+  def get_holdings(date)
+    converted_holdings.select { |h| h.date == date }
+  end
+
+  def get_entries(date)
+    converted_entries.select { |e| e.date == date && (e.transaction? || e.trade?) }
+  end
+
+  private
+    attr_reader :account
+
+    def converted_entries
+      @converted_entries ||= account.entries.order(:date).to_a.map do |e|
+        converted_entry = e.dup
+        converted_entry.amount = converted_entry.amount_money.exchange_to(
+          account.currency,
+          date: e.date,
+          fallback_rate: 1
+        ).amount
+        converted_entry.currency = account.currency
+        converted_entry
+      end
+    end
+
+    def converted_holdings
+      @converted_holdings ||= account.holdings.map do |h|
+        converted_holding = h.dup
+        converted_holding.amount = converted_holding.amount_money.exchange_to(
+          account.currency,
+          date: h.date,
+          fallback_rate: 1
+        ).amount
+        converted_holding.currency = account.currency
+        converted_holding
+      end
+    end
+end