Functions Practice

// PROJECT 1: Calculator
func calculate(_ a: Double, _ b: Double,
               operation: String) -> Double? {
    switch operation {
    case "+": return a + b
    case "-": return a - b
    case "*": return a * b
    case "/":
        guard b != 0 else { return nil }
        return a / b
    default: return nil
    }
}

print(calculate(10, 5, operation: "+")!)  // 15.0
print(calculate(10, 5, operation: "/")!)  // 2.0

// PROJECT 2: String Formatter
func formatName(first: String, last: String,
                style: String = "full") -> String {
    switch style {
    case "full": return "\(first) \(last)"
    case "initials":
        return "\(first.prefix(1)). \(last.prefix(1))."
    case "last-first": return "\(last), \(first)"
    default: return "\(first) \(last)"
    }
}

print(formatName(first: "John", last: "Doe"))
print(formatName(first: "John", last: "Doe", style: "initials"))

// PROJECT 3: Array Processor
func processNumbers(_ numbers: Int...,
                   using transform: (Int) -> Int) -> [Int] {
    return numbers.map(transform)
}

let doubled = processNumbers(1, 2, 3, 4, 5) { $0 * 2 }
print(doubled)  // [2, 4, 6, 8, 10]

// PROJECT 4: Password Validator
func validatePassword(_ password: String) -> (valid: Bool, errors: [String]) {
    var errors: [String] = []

    if password.count < 8 {
        errors.append("Must be at least 8 characters")
    }
    if !password.contains(where: { $0.isNumber }) {
        errors.append("Must contain a number")
    }
    if !password.contains(where: { $0.isUppercase }) {
        errors.append("Must contain uppercase letter")
    }

    return (errors.isEmpty, errors)
}

let result = validatePassword("hello")
if !result.valid {
    print("Errors: \(result.errors)")
}

// PROJECT 5: Function Factory
func makeGreeting(language: String) -> (String) -> String {
    func english(_ name: String) -> String {
        return "Hello, \(name)!"
    }
    func spanish(_ name: String) -> String {
        return "¡Hola, \(name)!"
    }
    func french(_ name: String) -> String {
        return "Bonjour, \(name)!"
    }

    switch language {
    case "es": return spanish
    case "fr": return french
    default: return english
    }
}

let greetInSpanish = makeGreeting(language: "es")
print(greetInSpanish("Carlos"))  // ¡Hola, Carlos!