Anchor.swift

//
//  Anchor.swift
//  AnchorTest
//
//  Created by Jonathan Wight on 7/10/15.
//  Copyright © 2015 schwa.io. All rights reserved.
//

#if os(OSX)
import AppKit
internal typealias View = NSView
#elseif os(iOS)
import UIKit
internal typealias View = UIView
#endif

public extension View {
    @objc(d12_anchors)
    var anchors: Anchors {
        return Anchors(item:self)
    }
}

/// Generator for the actual anchors in a way that makes sense, semantically.
@objc(D12Anchors)
public class Anchors {
    internal let item: View

    internal init(item: View) {
        self.item = item
    }

    // MARK: X–Axis Anchors
    public var leadingAnchor: LayoutXAxisAnchor {
        return LayoutXAxisAnchor(item: item, attribute: .Leading)
    }
    public var trailingAnchor: LayoutXAxisAnchor {
        return LayoutXAxisAnchor(item: item, attribute: .Trailing)
    }
    public var leftAnchor: LayoutXAxisAnchor {
        return LayoutXAxisAnchor(item: item, attribute: .Left)
    }
    public var rightAnchor: LayoutXAxisAnchor {
        return LayoutXAxisAnchor(item: item, attribute: .Right)
    }
    public var centerXAnchor: LayoutXAxisAnchor {
        return LayoutXAxisAnchor(item: item, attribute: .CenterX)
    }

    // MARK: Y–Axis Anchors
    public var topAnchor: LayoutYAxisAnchor {
        return LayoutYAxisAnchor(item: item, attribute: .Top)
    }
    public var bottomAnchor: LayoutYAxisAnchor {
        return LayoutYAxisAnchor(item: item, attribute: .Bottom)
    }
    public var centerYAnchor: LayoutYAxisAnchor {
        return LayoutYAxisAnchor(item: item, attribute: .CenterY)
    }
    public var firstBaselineAnchor: LayoutYAxisAnchor {
        return LayoutYAxisAnchor(item: item, attribute: .FirstBaseline)
    }
    public var lastBaselineAnchor: LayoutYAxisAnchor {
        return LayoutYAxisAnchor(item: item, attribute: .LastBaseline)
    }

    // MARK: Size Anchors
    public var widthAnchor: LayoutDimension {
        return LayoutDimension(item: item, attribute: .Width)
    }
    public var heightAnchor: LayoutDimension {
        return LayoutDimension(item: item, attribute: .Height)
    }
}


// MARK: -

/**
 A LayoutAnchor represents an edge or dimension of a layout item.
 Its concrete subclasses allow concise creation of constraints.
 The idea is that instead of invoking
 
    +[NSLayoutConstraint constraintWithItem: attribute: relatedBy: toItem: attribute: multiplier: constant:]
    
 directly, you can instead do something like this:
 
    [myView.topAnchor constraintEqualToAnchor:otherView.topAnchor constant:10];
 
 The `-constraint*` methods are available in multiple flavors to support use of different relations and omission of unused options.
 */
@objc(D12LayoutAnchor)
public class LayoutAnchor {

    internal var item: View
    internal var attribute: NSLayoutAttribute

    internal init(item: View, attribute: NSLayoutAttribute) {
        self.item = item
        self.attribute = attribute
    }

    /// Returns a new, inactive constraint of the form thisAnchor = otherAnchor + constant.
    public func constraintEqualToAnchor(anchor: LayoutAnchor, constant c: CGFloat = 0) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: item, attribute: attribute, relatedBy: .Equal, toItem: anchor.item, attribute: anchor.attribute, multiplier: 1.0, constant: c)
    }

    /// Returns a new, inactive constraint of the form thisAnchor ≧ otherAnchor + constant.
    public func constraintGreaterThanOrEqualToAnchor(anchor: LayoutAnchor, constant c: CGFloat = 0) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: item, attribute: attribute, relatedBy: .GreaterThanOrEqual, toItem: anchor.item, attribute: anchor.attribute, multiplier: 1.0, constant: c)
    }

    /// Returns a new, inactive constraint of the form thisAnchor ≦ otherAnchor + constant.
    public func constraintLessThanOrEqualToAnchor(anchor: LayoutAnchor, constant c: CGFloat = 0) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: item, attribute: attribute, relatedBy: .LessThanOrEqual, toItem: anchor.item, attribute: anchor.attribute, multiplier: 1.0, constant: c)
    }
}

// MARK: - Axis-specific subclasses for location anchors
/// Subclass for leading/trailing, left/right, and centerX anchors.
@objc(D12LayoutXAxisAnchor)
public class LayoutXAxisAnchor : LayoutAnchor {
}

/// Subclass for top/bottom, firstBaseline/lastBaseLine, and centerY anchors
@objc(D12LayoutYAxisAnchor)
public class LayoutYAxisAnchor : LayoutAnchor {
}

// MARK: -

/**
 This layout anchor subclass is used for sizes (width & height).
 */
@objc(D12LayoutDimension)
public class LayoutDimension : LayoutAnchor {
    
    /// Returns a new, inactive constraint of the form attribute = constant.
    public func constraintEqualToConstant(c: CGFloat) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: item, attribute: attribute, relatedBy: .Equal, toItem: nil, attribute:.NotAnAttribute, multiplier: 1.0, constant: c)
    }

    /// Returns a new, inactive constraint of the form attribute ≧ constant.
    public func constraintGreaterThanOrEqualToConstant(c: CGFloat) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: item, attribute: attribute, relatedBy: .GreaterThanOrEqual, toItem: nil, attribute:.NotAnAttribute, multiplier: 1.0, constant: c)
    }

    /// Returns a new, inactive constraint of the form attribute ≦ constant.
    public func constraintLessThanOrEqualToConstant(c: CGFloat) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: item, attribute: attribute, relatedBy: .LessThanOrEqual, toItem: nil, attribute:.NotAnAttribute, multiplier: 1.0, constant: c)
    }

    /// Returns a new, inactive constraint of the form attribute = otherAnchor.attribute * multiplier + constant.
    public func constraintEqualToAnchor(anchor: LayoutDimension, multiplier m: CGFloat, constant c: CGFloat = 0) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: item, attribute: attribute, relatedBy: .Equal, toItem: anchor.item, attribute: anchor.attribute, multiplier: m, constant: c)
    }

    /// Returns a new, inactive constraint of the form attribute ≧ otherAnchor.attribute * multiplier + constant.
    public func constraintGreaterThanOrEqualToAnchor(anchor: LayoutDimension, multiplier m: CGFloat, constant c: CGFloat = 0) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: item, attribute: attribute, relatedBy: .GreaterThanOrEqual, toItem: anchor.item, attribute: anchor.attribute, multiplier: m, constant: c)
    }

    /// Returns a new, inactive constraint of the form attribute ≦ otherAnchor.attribute * multiplier + constant.
    public func constraintLessThanOrEqualToAnchor(anchor: LayoutDimension, multiplier m: CGFloat, constant c: CGFloat = 0) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: item, attribute: attribute, relatedBy: .LessThanOrEqual, toItem: anchor.item, attribute: anchor.attribute, multiplier: m, constant: c)
    }
}

I hope it goes without saying that this is completely untested: the changes I made to the original were written in GitHub’s online editor.
While most are of cosmetic nature — documentation comments and whitespace — I am not really sure if replacing the duplicated methods by default parameters was a smart move in terms of ObjC compatibility. So I’m not sure if they make it over to Objective–C as two separate methods. (So far, every piece of Swift I wrote didn’t need to be callable by ObjC code.) And I don’t have Xcode on this machine to test that out.