gistfile1.txt

struct PurchaseEvent: Hashable {
    let customerId: String
    let date: String
    let amount: Double
}

final class RevenueTracker {
    private var totalsByDate: [String: [String: Double]] = [:]

    func addPurchase(_ event: PurchaseEvent) {
        var totals = totalsByDate[event.date, default: [:]]
        totals[event.customerId, default: 0] += event.amount
        totalsByDate[event.date] = totals
    }

    func averageRevenuePerCustomer(on date: String) -> Double {
        guard let totals = totalsByDate[date], !totals.isEmpty else {
            return 0
        }
        let totalRevenue = totals.values.reduce(0, +)
        return totalRevenue / Double(totals.count)
    }
}