Swift Functions

// Use functions when you plan to reuse the code again and again. 
// 1. Benefit: One change changes the code everywhere the code is used.
// 2. Benefit: Break up code to follow more easily
// 3. Benefit: Function composition. 

func showWelcome() {
    print("Welcome to my app!")
    print("By default This prints out a conversion")
    print("chart from centimeters to inches, but you")
    print("can also set a custom range if you want.")
}

showWelcome() // Callsite

// Use parameters number: Int
a
func printTimesTables(number: Int) {
    for i in 1...12 {
        print("\(i) x \(number) is \(i * number)")
    }
}

printTimesTables(number: 5)

// Return data

 func rollDice() -> Int {
    return Int.random(in: 1...6)
}

let result = rollDice()
print(result)


// return is not necessary when it is oneline

 func rollDice() -> Int {
    Int.random(in: 1...6)
}


func pythagoras(a: Double, b: Double) -> Double {
    let input = a * a + b * b
    let root = sqrt(input)
    return root
}

let c = pythagoras(a: 3, b: 4)
print(c)

func pythagoras(a: Double, b: Double) -> Double {
    sqrt(a * a + b * b)
}

// return multiple values

// Use Array
func getUser() -> [String] {
    ["Taylor", "Swift"]
}

let user = getUser()
print("Name: \(user[0]) \(user[1])") 

// Use Dictionary
func getUser() -> [String: String] {
    [
        "firstName": "Taylor",
        "lastName": "Swift"
    ]
}

let user = getUser()
print("Name: \(user["firstName", default: "Anonymous"]) \(user["lastName", default: "Anonymous"])") 

// Use Tuple, know exact type and value while dictionary doesn't know
func getUser() -> (firstName: String, lastName: String) {
    (firstName: "Taylor", lastName: "Swift")
}

let user = getUser()
print("Name: \(user.firstName) \(user.lastName)")

let (firstName, lastName) = getUser()
print("Name: \(firstName) \(lastName)")

let (firstName, _) = getUser()
print("Name: \(firstName)")

// Simplfy
func getUser() -> (firstName: String, lastName: String) {
    ("Taylor", "Swift")
}

func getUser() -> (String, String) {
    ("Taylor", "Swift")
}

let user = getUser()
print("Name: \(user.0) \(user.1)")

// Naming Parameters

func rollDice(sides: Int, count: Int) -> [Int] {
    // Start with an empty array
    var rolls = [Int]()

    // Roll as many dice as needed
    for _ in 1...count {
        // Add each result to our array
        let roll = Int.random(in: 1...sides)
        rolls.append(roll)
    }

    // Send back all the rolls
    return rolls
}

let rolls = rollDice(sides: 6, count: 4)

// The parameter determine the name
func hireEmployee(name: String) { }
func hireEmployee(title: String) { }
func hireEmployee(location: String) { }

// Use _ to ignore the parameter name 
// BEFORE
func isUppercase(string: String) -> Bool {
    string == string.uppercased()
}

let string = "HELLO, WORLD"
let result = isUppercase(string: string)
// AFTER
func isUppercase(_ string: String) -> Bool {
    string == string.uppercased()
}

let string = "HELLO, WORLD"
let result = isUppercase(string)

// Custom external parameter naming
// BEFORE
func printTimesTables(number: Int) {
    for i in 1...12 {
        print("\(i) x \(number) is \(i * number)")
    }
}

printTimesTables(number: 5)
// AFTER
func printTimesTables(for number: Int) {
    for i in 1...12 {
        print("\(i) x \(number) is \(i * number)")
    }
}

printTimesTables(for: 5)

// Provide default values for parameters
// Shorter, simpler code most of the time, but flexibility when we need it – perfect.
// simplify complex function, and make your code easier to write.

func printTimesTables(for number: Int, end: Int = 12) {
    for i in 1...end {
        print("\(i) x \(number) is \(i * number)")
    }
}

printTimesTables(for: 5, end: 20)
printTimesTables(for: 8)

var characters = ["Lana", "Pam", "Ray", "Sterling"]
print(characters.count)
characters.removeAll()
print(characters.count)

characters.removeAll(keepingCapacity: true)

// Handle Errors in functions
// 
enum PasswordError: Error {
    case short, obvious
}

func checkPassword(_ password: String) throws -> String {
    if password.count < 5 {
        throw PasswordError.short
    }

    if password == "12345" {
        throw PasswordError.obvious
    }

    if password.count < 8 {
        return "OK"
    } else if password.count < 10 {
        return "Good"
    } else {
        return "Excellent"
    }
}

let string = "12345"


do {
    let result = try checkPassword(string)
    print("Password rating: \(result)")
} catch PasswordError.short {
    print("Please use a longer password.")
} catch PasswordError.obvious {
    print("I have the same combination on my luggage!")
} catch {
    print("There was an error.")
}

// do try catch, by forcing us to use try before every throwing function, we’re explicitly acknowledging which parts of our code can cause errors.
do {
    try throwingFunction1()
    nonThrowingFunction1()
    try throwingFunction2()
    nonThrowingFunction2()
    try throwingFunction3()
} catch {
    // handle errors
}