sure/app/models/balance/sync_cache.rb

class Balance::SyncCache
  def initialize(account)
    @account = account
  end

  def get_valuation(date)
    entries_by_date[date]&.find { |e| e.valuation? }
  end

  def get_holdings(date)
    holdings_by_date[date] || []
  end

  def get_entries(date)
    entries_by_date[date]&.select { |e| e.transaction? || e.trade? } || []
  end

  private
    attr_reader :account

    def entries_by_date
      @entries_by_date ||= converted_entries.group_by(&:date)
    end

    def holdings_by_date
      @holdings_by_date ||= converted_holdings.group_by(&:date)
    end

    def converted_entries
      @converted_entries ||= account.entries.excluding_split_parents.includes(:entryable).order(:date).to_a.map do |e|
        converted_entry = e.dup

        # Extract custom exchange rate if present on Transaction
        custom_rate = if e.entryable.is_a?(Transaction)
          e.entryable.extra&.dig("exchange_rate")
        end

        # Use Money#exchange_to with custom rate if available, standard lookup otherwise
        converted_entry.amount = converted_entry.amount_money.exchange_to(
          account.currency,
          date: e.date,
          custom_rate: custom_rate
        ).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
        ).amount
        converted_holding.currency = account.currency
        converted_holding
      end
    end
end