sure/app/models/trade.rb

class Trade < ApplicationRecord
  include Entryable, Monetizable

  monetize :price
  monetize :fee

  belongs_to :security
  belongs_to :category, optional: true

  # Use the same activity labels as Transaction
  ACTIVITY_LABELS = Transaction::ACTIVITY_LABELS.dup.freeze

  validates :qty, presence: true
  validates :price, :currency, presence: true
  validates :investment_activity_label, inclusion: { in: ACTIVITY_LABELS }, allow_nil: true

  # Trade types for categorization
  def buy?
    qty.positive?
  end

  def sell?
    qty.negative?
  end

  class << self
    def build_name(type, qty, ticker)
      prefix = type == "buy" ? "Buy" : "Sell"
      "#{prefix} #{qty.to_d.abs} shares of #{ticker}"
    end
  end

  def unrealized_gain_loss
    return nil unless qty.positive?
    current_price = security.current_price
    return nil if current_price.nil?

    current_value = current_price * qty.abs
    cost_basis = price_money * qty.abs

    Trend.new(current: current_value, previous: cost_basis)
  end

  # Calculates realized gain/loss for sell trades based on avg_cost at time of sale
  # Returns nil for buy trades or when cost basis cannot be determined
  def realized_gain_loss
    return @realized_gain_loss if defined?(@realized_gain_loss)

    @realized_gain_loss = calculate_realized_gain_loss
  end

  # Trades are always excluded from expense budgets
  # They represent portfolio management, not living expenses
  def excluded_from_budget?
    true
  end

  private

    def calculate_realized_gain_loss
      return nil unless sell?

      # Use preloaded holdings if available (set by reports controller to avoid N+1)
      # Treat defined-but-empty preload as authoritative to prevent DB fallback
      holding = if defined?(@preloaded_holdings)
        # Use select + max_by for deterministic selection regardless of array order
        (@preloaded_holdings || [])
          .select { |h| h.security_id == security_id && h.date <= entry.date }
          .max_by(&:date)
      else
        # Fall back to database query only when not preloaded
        entry.account.holdings
          .where(security_id: security_id)
          .where("date <= ?", entry.date)
          .order(date: :desc)
          .first
      end

      return nil unless holding&.avg_cost

      cost_basis = holding.avg_cost * qty.abs
      sale_proceeds = price_money * qty.abs

      Trend.new(current: sale_proceeds, previous: cost_basis)
    end
end