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.rb

@@ -0,0 +1,65 @@
+class Holding < ApplicationRecord
+  include Monetizable, Gapfillable
+
+  monetize :amount
+
+  belongs_to :account
+  belongs_to :security
+
+  validates :qty, :currency, :date, :price, :amount, presence: true
+  validates :qty, :price, :amount, numericality: { greater_than_or_equal_to: 0 }
+
+  scope :chronological, -> { order(:date) }
+  scope :for, ->(security) { where(security_id: security).order(:date) }
+
+  delegate :ticker, to: :security
+
+  def name
+    security.name || ticker
+  end
+
+  def weight
+    return nil unless amount
+    return 0 if amount.zero?
+
+    account.balance.zero? ? 1 : amount / account.balance * 100
+  end
+
+  # Basic approximation of cost-basis
+  def avg_cost
+    avg_cost = account.entries.trades
+                  .joins("INNER JOIN trades ON trades.id = entries.entryable_id")
+                  .where("trades.security_id = ? AND trades.qty > 0 AND entries.date <= ?", security.id, date)
+                  .average(:price)
+
+    Money.new(avg_cost || price, currency)
+  end
+
+  def trend
+    @trend ||= calculate_trend
+  end
+
+  def trades
+    account.entries.where(entryable: account.trades.where(security: security)).reverse_chronological
+  end
+
+  def destroy_holding_and_entries!
+    transaction do
+      account.entries.where(entryable: account.trades.where(security: security)).destroy_all
+      destroy
+    end
+
+    account.sync_later
+  end
+
+  private
+    def calculate_trend
+      return nil unless amount_money
+
+      start_amount = qty * avg_cost
+
+      Trend.new \
+        current: amount_money,
+        previous: start_amount
+    end
+end