// UIViewController subclass
override func viewDidLoad() {
   super.viewDidLoad()
   
   // Create a label
   let label = UILabel()
   label.text = "SwiftAutoLayout is neato!"
   
   // Constrain its leading and centerY anchors to be equal to our view's respective anchors
   // Because label doesn't yet have a parent, it will become a child of our view
   label.constrain(to: view).leading().centerY()
}

// Wrap a label in a container view that has a grey background and some internal padding.
let container = UIView()
container.backgroundColor = .gray
container.directionalLayoutMargins = NSDirectionalEdgeInsets(top: 8, leading: 8, bottom: 8, trailing: 8)
container.constrain(to: view).centerXY()

// Constrain a label to the layout margins guide of the container. This means we
// get padding for free! No need to define constants in these constraints.
// Label will become a child of the layout guide's owning view.
let label = UILabel()
label.constrain(to: container.layoutMarginsGuide).leadingTrailingTopBottom()

// Ensure the label doesn't get wider than our view within a constant. 
// Since label is a child of container by this point, SwiftAutoLayout doesn't set its parent.
label.constrain(to: view).width(.lessThanOrEqual, constant: -60, priority: .defaultHigh)

// The view hierarchy is now:
// view
//  └ container
//     └ label

// Simple leading padding of 16 points
label.constrain(to: view).leading(constant: 16)

// Simple trailing padding of 16 points. 
// NOTE: Constraints between trailing and bottom anchors have their items reversed
// so your constants can always be positive when insetting!
label.constrain(to: view).trailing(constant: 16)

// Get as customized as you like!
label.constrain(to: view).top(.greaterThanOrEqual, constant: 8, multiplier: 0.5, priority: .defaultLow)

// In common scenarios where multiple constraints are defined together, 
// helper methods create multiple constraints using the supplied arguments
label.constrain(to: view).leadingTrailing(constant: 16).topBottom(constant: 8)

// As a bonus, this makes it super easy to pin a view to a container,
// become its child, and disable its resizing mask in a single line of code
label.constrain(to: view).leadingTrailingTopBottom()

// And as a bonus to that bonus, if you want the label to be constrained to
// the view's margins inset from the safe area, use its margins layout guide!
label.constrain(to: view.layoutMarginsGuide).leadingTrailingTopBottom()

// You can grab a reference to the builder itself...
let builder = label.constrain(to: view).leading().centerY()
print(builder.constraints.last!) // NSLayoutConstraint between centerY anchors

// ...or just access the array of constraints directly!
let constraint = label.constrain(to: view).centerY(constant: 0).constraints.last!

// Then use the constraint later as needed.
constraint.constant = 100

// Keep in mind some helper methods create multiple constraints in the order they're named.
// This should be clear based on method name, and their documentation will specify constraint count.
let constraints = label.constrain(to: view).leadingTrailingTopBottom().constraints
print(constraints.count) // 4

// You can put constraints on their own lines thanks to functional chanining. Here we 
// dynamically activate a constraint later, as such its priority must be lower than `.required`
let constraint = label.constrainSelf()
   .height(constant: 0, priority: .required - 1, activate: false)
   .constraints.last!
   
constraint.isActive = true // smoosh!

label.constrain(to: view).leadingTrailing(constant: .systemSpacing)

// NSLayoutXAxisAnchor: Constrain label's centerXAnchor to view's leadingAnchor
label.constrain(to: view).xAxis(.centerX, to: .leading)

// NSLayoutYAxisAnchor: Constrain label's centerYAnchor to view's topAnchor
label.constrain(to: view).yAxis(.centerY, to: .top)

// NSLayoutDimension: Constrain label's widthAnchor to view's heightAnchor
label.constrain(to: view).dimension(.width, to: .height)

// Create a layout guide that will determine a height in which some buttons
// will be spread out along the x axis, and centered on the y axis
let buttonsLayoutGuide = UILayoutGuide()
buttonsLayoutGuide.constrain(to: view.layoutMarginsGuide).leadingTrailing().bottom()
buttonsLayoutGuide.constrainSelf().height(constant: 60)

let buttons = [UIButton(), UIButton(), UIButton()]
buttons.forEach { $0.constrainSelf().widthHeight(constant: 40) }
zip(buttons, [0.5, 1.0, 1.5]) { (button, multiplier)
   button.constrain(to: buttonsLayoutGuide).centerX(multiplier: multiplier).centerY()
}