sure/app/components/UI/account/chart.rb

class UI::Account::Chart < ApplicationComponent
  attr_reader :account

  def initialize(account:, period: nil, view: nil)
    @account = account
    @period = period
    @view = view
  end

  def period
    @period ||= Period.last_30_days
  end

  def holdings_value_money
    account.balance_money - account.cash_balance_money
  end

  # Money value shown as the main indicator for the selected chart view.
  def view_balance_money
    case view
    when "balance"
      account.balance_money
    when "holdings_balance"
      holdings_value_money
    when "cash_balance"
      account.cash_balance_money
    when "gains"
      gains_money
    end
  end

  # Formatted main indicator. Gains are signed explicitly (e.g. "+€79.53") since
  # a gain of zero-or-more is otherwise indistinguishable from a balance.
  def view_balance_display
    signed_format(view_balance_money)
  end

  # Formatted family-currency amount for foreign-currency accounts, signed the
  # same way as the main indicator. Nil when no conversion applies.
  def converted_balance_display
    converted_balance_money&.then { |money| signed_format(money) }
  end

  # Label displayed above the main indicator, based on account type and chart view.
  def title
    case account.accountable_type
    when "Investment", "Crypto"
      case view
      when "balance"
        I18n.t("UI.account.chart.title.total_account_value")
      when "holdings_balance"
        I18n.t("UI.account.chart.title.holdings_value")
      when "cash_balance"
        I18n.t("UI.account.chart.title.cash_value")
      when "gains"
        I18n.t("UI.account.chart.title.total_gains")
      end
    when "Property"
      I18n.t("UI.account.chart.title.estimated_property_value")
    when "Vehicle"
      I18n.t("UI.account.chart.title.estimated_vehicle_value")
    when "CreditCard", "OtherLiability"
      I18n.t("UI.account.chart.title.debt_balance")
    when "Loan"
      I18n.t("UI.account.chart.title.remaining_principal_balance")
    else
      I18n.t("UI.account.chart.title.balance")
    end
  end

  def foreign_currency?
    account.currency != account.family.currency
  end

  # Main indicator converted to the family currency for foreign-currency accounts,
  # or nil when no conversion applies (same currency or missing exchange rate).
  def converted_balance_money
    return nil unless foreign_currency?

    begin
      base_money = view == "gains" ? gains_money : account.balance_money
      base_money.exchange_to(account.family.currency)
    rescue Money::ConversionError
      nil
    end
  end

  def view
    @view ||= "balance"
  end

  def series
    account.balance_series(period: period, view: view)
  end

  # Current total unrealized gains, taken from the series so the main indicator
  # always matches the last point of the chart (there is no stored gains column).
  def gains_money
    series.values.last&.value || Money.new(0, account.currency)
  end

  def trend
    series.trend
  end

  def comparison_label
    start_date = series.start_date
    return period.comparison_label if start_date.blank?

    if start_date > period.start_date
      I18n.t("UI.account.chart.vs_available_history")
    else
      period.comparison_label
    end
  end

  private
    # Prefixes positive gains with "+"; other views keep plain Money formatting.
    def signed_format(money)
      return money.format unless view == "gains" && money.amount.positive?

      "+#{money.format}"
    end
end