print("------ Chapter 21: Extensions")

print("\n-------- Section: Extension Syntax\n")

class SomeType {
}

protocol SomeProtocol {
}

protocol AnotherProtocol {
}

extension SomeType {
    // new functionality to add to SomeType goes here
}

extension SomeType: SomeProtocol, AnotherProtocol {
    // implementation of protocol requirements goes here
}


print("\n-------- Section: Computed Properties\n")

extension Double {
    var km: Double { return self * 1_000.0 }
    var m: Double { return self }
    var cm: Double { return self / 100.0 }
    var mm: Double { return self / 1_000.0 }
    var ft: Double { return self / 3.28084 }
}

let oneInch = 25.4.mm
print("One inch is \(oneInch) meters")
// Prints "One inch is 0.0254 meters"
let threeFeet = 3.ft
print("Three feet is \(threeFeet) meters")
// Prints "Three feet is 0.914399970739201 meters"

let aMarathon = 42.km + 195.m
print("A marathon is \(aMarathon) meters long")
// Prints "A marathon is 42195.0 meters long"


print("\n-------- Section: Initializers\n")

struct Size {
    var width = 0.0, height = 0.0
}

struct Point {
    var x = 0.0, y = 0.0
}

struct Rect {
    var origin = Point()
    var size = Size()
}

let defaultRect = Rect()
let memberwiseRect = Rect(origin: Point(x: 2.0, y: 2.0),
                          size: Size(width: 5.0, height: 5.0))
print("defaultRect = \(defaultRect)")
print("memberwiseRect = \(memberwiseRect)")

extension Rect {
    init(center: Point, size: Size) {
        let originX = center.x - (size.width / 2)
        let originY = center.y - (size.height / 2)
        self.init(origin: Point(x: originX, y: originY), size: size)
    }
}

let centerRect = Rect(center: Point(x: 4.0, y: 4.0),
                      size: Size(width: 3.0, height: 3.0))
// centerRect's origin is (2.5, 2.5) and its size is (3.0, 3.0)
print("centerRect = \(centerRect)")


print("\n-------- Section: Methods\n")

extension Int {
    func repetitions(task: () -> Void) {
        for _ in 0..<self {
            task()
        }
    }
}

3.repetitions {
    print("Hello!")
}
// Hello!
// Hello!
// Hello!


print("\n---------- Mutating Instance Methods\n")

extension Int {
    mutating func square() {
        self = self * self
    }
}
var someInt = 3
someInt.square()
// someInt is now 9
print("someInt = \(someInt)")


print("\n-------- Section: Subscripts\n")

extension Int {
    subscript(digitIndex: Int) -> Int {
        var decimalBase = 1
        for _ in 0..<digitIndex {
            decimalBase *= 10
        }
        return (self / decimalBase) % 10
    }
}

print("746381295[0] = \(746381295[0])")
// returns 5
print("746381295[1] = \(746381295[1])")
// returns 9
print("746381295[2] = \(746381295[2])")
// returns 2
print("746381295[8] = \(746381295[8])")
// returns 7

print("746381295[9] = \(746381295[9])")
// returns 0, as if you had requested:
print("0746381295[9] = \(0746381295[9])")


print("\n-------- Section: Nested Types\n")

extension Int {
    enum Kind {
        case negative, zero, positive
    }
    var kind: Kind {
        switch self {
        case 0:
            return .zero
        case let x where x > 0:
            return .positive
        default:
            return .negative
        }
    }
}

func printIntegerKinds(_ numbers: [Int]) {
    for number in numbers {
        switch number.kind {
        case .negative:
            print("- ", terminator: "")
        case .zero:
            print("0 ", terminator: "")
        case .positive:
            print("+ ", terminator: "")
        }
    }
    print("")
}

printIntegerKinds([3, 19, -27, 0, -6, 0, 7])
// Prints "+ + - 0 - 0 + "
