sure/app/models/trade/create_form.rb

class Trade::CreateForm
  include ActiveModel::Model

  attr_accessor :account, :date, :amount, :currency, :qty,
                :price, :ticker, :manual_ticker, :type, :transfer_account_id

  # Either creates a trade, transaction, or transfer based on type
  # Returns the model, regardless of success or failure
  def create
    case type
    when "buy", "sell"
      create_trade
    when "interest"
      create_interest_income
    when "deposit", "withdrawal"
      create_transfer
    end
  end

  private
    # Users can either look up a ticker from a provider or enter a manual, "offline" ticker (that we won't fetch prices for)
    def security
      ticker_symbol, exchange_operating_mic = ticker.present? ? ticker.split("|") : [ manual_ticker, nil ]

      Security::Resolver.new(
        ticker_symbol,
        exchange_operating_mic: exchange_operating_mic
      ).resolve
    end

    def create_trade
      signed_qty = type == "sell" ? -qty.to_d : qty.to_d
      signed_amount = signed_qty * price.to_d

      trade_entry = account.entries.new(
        name: Trade.build_name(type, qty, security.ticker),
        date: date,
        amount: signed_amount,
        currency: currency,
        entryable: Trade.new(
          qty: signed_qty,
          price: price,
          currency: currency,
          security: security,
          category: investment_category_for(type)
        )
      )

      if trade_entry.save
        trade_entry.lock_saved_attributes!
        account.sync_later
      end

      trade_entry
    end

    def investment_category_for(trade_type)
      # Buy trades are categorized as "Savings & Investments" (expense)
      # Sell trades are left uncategorized for now
      return nil unless trade_type == "buy"

      account.family.categories.find_by(name: "Savings & Investments")
    end

    def create_interest_income
      signed_amount = amount.to_d * -1

      entry = account.entries.build(
        name: "Interest payment",
        date: date,
        amount: signed_amount,
        currency: currency,
        entryable: Transaction.new
      )

      if entry.save
        entry.lock_saved_attributes!
        account.sync_later
      end

      entry
    end

    def create_transfer
      if transfer_account_id.present?
        from_account_id = type == "withdrawal" ? account.id : transfer_account_id
        to_account_id = type == "withdrawal" ? transfer_account_id : account.id

        Transfer::Creator.new(
          family: account.family,
          source_account_id: from_account_id,
          destination_account_id: to_account_id,
          date: date,
          amount: amount
        ).create
      else
        create_unlinked_transfer
      end
    end

    # If user doesn't provide the reciprocal account, it's a regular transaction
    def create_unlinked_transfer
      signed_amount = type == "deposit" ? amount.to_d * -1 : amount.to_d

      entry = account.entries.build(
        name: signed_amount < 0 ? "Deposit to #{account.name}" : "Withdrawal from #{account.name}",
        date: date,
        amount: signed_amount,
        currency: currency,
        entryable: Transaction.new
      )

      if entry.save
        entry.lock_saved_attributes!
        account.sync_later
      end

      entry
    end
end