Improve handling of cost_basis during holding materialization and display (#619)

- Refactored `persist_holdings` to separate and conditionally upsert holdings with and without cost_basis.
- Updated `avg_cost` logic to treat 0 cost_basis as unknown and return nil when cost_basis cannot be determined.
- Modified trend and investment calculation to exclude holdings with unknown cost_basis.
- Adjusted `average_cost` formatting to handle nil values in API responses and views.
- Added comprehensive tests to ensure cost_basis preservation and fallback behavior.
- Localized `unknown` label for display when cost_basis is unavailable.

Co-authored-by: Josh Waldrep <joshua.waldrep5+github@gmail.com>

app/models/assistant/function/get_holdings.rb

@@ -105,8 +105,8 @@ class Assistant::Function::GetHoldings < Assistant::Function
         amount: holding.amount.to_f,
         formatted_amount: holding.amount_money.format,
         weight: holding.weight&.round(2),
-        average_cost: holding.avg_cost.to_f,
-        formatted_average_cost: holding.avg_cost.format,
+        average_cost: holding.avg_cost&.to_f,
+        formatted_average_cost: holding.avg_cost&.format,
         account: holding.account.name,
         date: holding.date
       }

app/models/holding.rb

@@ -27,12 +27,16 @@ class Holding < ApplicationRecord
     account.balance.zero? ? 1 : amount / account.balance * 100
   end
 
-  # Basic approximation of cost-basis
+  # Returns average cost per share, or nil if unknown.
+  #
   # Uses pre-computed cost_basis if available (set during materialization),
-  # otherwise falls back to calculating from trades
+  # otherwise falls back to calculating from trades. Returns nil when cost
+  # basis cannot be determined (no trades and no provider cost_basis).
   def avg_cost
-    # Use stored cost_basis if available (eliminates N+1 queries)
-    return Money.new(cost_basis, currency) if cost_basis.present?
+    # Use stored cost_basis if available and positive (eliminates N+1 queries)
+    # Note: cost_basis of 0 is treated as "unknown" since providers sometimes
+    # return 0 when they don't have the data
+    return Money.new(cost_basis, currency) if cost_basis.present? && cost_basis.positive?
 
     # Fallback to calculation for holdings without pre-computed cost_basis
     calculate_avg_cost
@@ -75,6 +79,7 @@ class Holding < ApplicationRecord
   private
     def calculate_trend
       return nil unless amount_money
+      return nil unless avg_cost # Can't calculate trend without cost basis
 
       start_amount = qty * avg_cost
 
@@ -83,6 +88,8 @@ class Holding < ApplicationRecord
         previous: start_amount
     end
 
+    # Calculates weighted average cost from buy trades.
+    # Returns nil if no trades exist (cost basis is unknown).
     def calculate_avg_cost
       trades = account.trades
         .with_entry
@@ -101,13 +108,10 @@ class Holding < ApplicationRecord
         Arel.sql("SUM(trades.qty)")
       )
 
-      weighted_avg =
-        if total_qty && total_qty > 0
-          total_cost / total_qty
-        else
-          price
-        end
+      # Return nil when no trades exist - cost basis is genuinely unknown
+      # Previously this fell back to current market price, which was misleading
+      return nil unless total_qty && total_qty > 0
 
-      Money.new(weighted_avg || price, currency)
+      Money.new(total_cost / total_qty, currency)
     end
 end

app/models/holding/materializer.rb

@@ -27,14 +27,38 @@ class Holding::Materializer
     end
 
     def persist_holdings
+      return if @holdings.empty?
+
       current_time = Time.now
 
-      account.holdings.upsert_all(
-        @holdings.map { |h| h.attributes
-               .slice("date", "currency", "qty", "price", "amount", "security_id", "cost_basis")
-               .merge("account_id" => account.id, "updated_at" => current_time) },
-        unique_by: %i[account_id security_id date currency]
-      )
+      # Separate holdings into those with and without computed cost_basis
+      holdings_with_cost_basis, holdings_without_cost_basis = @holdings.partition { |h| h.cost_basis.present? }
+
+      # Upsert holdings that have computed cost_basis (from trades)
+      # These will overwrite any existing provider cost_basis with the trade-derived value
+      if holdings_with_cost_basis.any?
+        account.holdings.upsert_all(
+          holdings_with_cost_basis.map { |h|
+            h.attributes
+              .slice("date", "currency", "qty", "price", "amount", "security_id", "cost_basis")
+              .merge("account_id" => account.id, "updated_at" => current_time)
+          },
+          unique_by: %i[account_id security_id date currency]
+        )
+      end
+
+      # Upsert holdings WITHOUT cost_basis column - preserves existing provider cost_basis
+      # This handles securities that have no trades (e.g., SimpleFIN-only holdings)
+      if holdings_without_cost_basis.any?
+        account.holdings.upsert_all(
+          holdings_without_cost_basis.map { |h|
+            h.attributes
+              .slice("date", "currency", "qty", "price", "amount", "security_id")
+              .merge("account_id" => account.id, "updated_at" => current_time)
+          },
+          unique_by: %i[account_id security_id date currency]
+        )
+      end
     end
 
     def purge_stale_holdings

app/models/investment_statement.rb

@@ -133,8 +133,12 @@ class InvestmentStatement
     holdings = current_holdings.to_a
     return nil if holdings.empty?
 
-    current = holdings.sum(&:amount)
-    previous = holdings.sum { |h| h.qty * h.avg_cost.amount }
+    # Only include holdings with known cost basis in the calculation
+    holdings_with_cost_basis = holdings.select(&:avg_cost)
+    return nil if holdings_with_cost_basis.empty?
+
+    current = holdings_with_cost_basis.sum(&:amount)
+    previous = holdings_with_cost_basis.sum { |h| h.qty * h.avg_cost.amount }
 
     Trend.new(current: current, previous: previous)
   end