func legacyPrice(kind: String, amount: Int) -> Int {
    if kind == "B" && amount > 0 { return amount - 30 }
    return amount
}

func refactoredPrice(kind: String, amount: Int) -> Int {
    let discount = kind == "B" && amount > 0 ? 30 : 0
    return amount - discount
}

let cases: [(String, Int, Int)] = [
    ("B", -1, -1), ("B", 0, 0), ("B", 1, -29),
    ("B", 29, -1), ("B", 30, 0), ("B", 31, 1),
    ("B", 100, 70), ("A", 100, 100), ("A", 0, 0)
]
var clampDifferences = 0
for (kind, amount, expected) in cases {
    precondition(legacyPrice(kind: kind, amount: amount) == expected)
    precondition(refactoredPrice(kind: kind, amount: amount) == expected)
    let changed = kind == "B" && amount > 0 ? max(0, amount - 30) : amount
    if changed != expected { clampDifferences += 1 }
}
precondition(clampDifferences == 2)
print("cases=9 preserved=9 clamp-differences=2")