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/trend_calculator.rb

@@ -0,0 +1,94 @@
+# The current system calculates a single, end-of-day balance every day for each account for simplicity.
+# In most cases, this is sufficient.  However, for the "Activity View", we need to show intraday balances
+# to show users how each entry affects their balances.  This class calculates intraday balances by
+# interpolating between end-of-day balances.
+class Balance::TrendCalculator
+  BalanceTrend = Struct.new(:trend, :cash, keyword_init: true)
+
+  class << self
+    def for(entries)
+      return nil if entries.blank?
+
+      account = entries.first.account
+
+      date_range = entries.minmax_by(&:date)
+      min_entry_date, max_entry_date = date_range.map(&:date)
+
+      # In case view is filtered and there are entry gaps, refetch all entries in range
+      all_entries = account.entries.where(date: min_entry_date..max_entry_date).chronological.to_a
+      balances = account.balances.where(date: (min_entry_date - 1.day)..max_entry_date).chronological.to_a
+      holdings = account.holdings.where(date: (min_entry_date - 1.day)..max_entry_date).to_a
+
+      new(all_entries, balances, holdings)
+    end
+  end
+
+  def initialize(entries, balances, holdings)
+    @entries = entries
+    @balances = balances
+    @holdings = holdings
+  end
+
+  def trend_for(entry)
+    intraday_balance = nil
+    intraday_cash_balance = nil
+
+    start_of_day_balance = balances.find { |b| b.date == entry.date - 1.day && b.currency == entry.currency }
+    end_of_day_balance = balances.find { |b| b.date == entry.date && b.currency == entry.currency }
+
+    return BalanceTrend.new(trend: nil) if start_of_day_balance.blank? || end_of_day_balance.blank?
+
+    todays_holdings_value = holdings.select { |h| h.date == entry.date }.sum(&:amount)
+
+    prior_balance = start_of_day_balance.balance
+    prior_cash_balance = start_of_day_balance.cash_balance
+    current_balance = nil
+    current_cash_balance = nil
+
+    todays_entries = entries.select { |e| e.date == entry.date }
+
+    todays_entries.each_with_index do |e, idx|
+      if e.valuation?
+        current_balance = e.amount
+        current_cash_balance = e.amount
+      else
+        multiplier = e.account.liability? ? 1 : -1
+        balance_change = e.trade? ? 0 : multiplier * e.amount
+        cash_change = multiplier * e.amount
+
+        current_balance = prior_balance + balance_change
+        current_cash_balance = prior_cash_balance + cash_change
+      end
+
+      if e.id == entry.id
+        # Final entry should always match the end-of-day balances
+        if idx == todays_entries.size - 1
+          intraday_balance = end_of_day_balance.balance
+          intraday_cash_balance = end_of_day_balance.cash_balance
+        else
+          intraday_balance = current_balance
+          intraday_cash_balance = current_cash_balance
+        end
+
+        break
+      else
+        prior_balance = current_balance
+        prior_cash_balance = current_cash_balance
+      end
+    end
+
+    return BalanceTrend.new(trend: nil) unless intraday_balance.present?
+
+    BalanceTrend.new(
+      trend: Trend.new(
+        current: Money.new(intraday_balance, entry.currency),
+        previous: Money.new(prior_balance, entry.currency),
+        favorable_direction: entry.account.favorable_direction
+      ),
+      cash: Money.new(intraday_cash_balance, entry.currency),
+    )
+  end
+
+  private
+    attr_reader :entries, :balances, :holdings
+end