align.swift

public extension UIView {
    func alignCenterX(_ constant: CGFloat = 0, multiplier: CGFloat = 1, to view: UIView,
                     attribute: NSLayoutAttribute = .centerX,
                     relation: NSLayoutRelation = .equal,
                     priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        return alignAttribute(attribute: .centerX, relation: relation,
                              to: view, otherAttribute: attribute,
                              multiplier: multiplier,
                              constant: constant, priority: priority)
    }

    func alignCenterY(_ constant: CGFloat = 0, multiplier: CGFloat = 1, to view: UIView,
                      attribute: NSLayoutAttribute = .centerY,
                      relation: NSLayoutRelation = .equal,
                      priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        return alignAttribute(attribute: .centerY, relation: relation,
                              to: view, otherAttribute: attribute,
                              multiplier: multiplier,
                              constant: constant, priority: priority)
    }

    func alignCenter(to view: UIView) -> [NSLayoutConstraint] {
        return [alignCenterX(to: view), alignCenterY(to: view)]
    }
}

public extension UIView {
    func alignHeight(_ constant: CGFloat = 0, multiplier: CGFloat = 1, to view: UIView,
                     attribute: NSLayoutAttribute = .height,
                     relation: NSLayoutRelation = .equal,
                     priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        return alignAttribute(attribute: .height, relation: relation,
                              to: view, otherAttribute: attribute,
                              multiplier: multiplier,
                              constant: constant, priority: priority)
    }

    func constraintHeight(constant: CGFloat) -> NSLayoutConstraint {
        return alignAttribute(attribute: .height, relation: .equal, to: nil,
                              otherAttribute: .height, constant: constant)
    }
}

public extension UIView {
    func alignWidth(_ constant: CGFloat = 0, multiplier: CGFloat = 1, to view: UIView,
                    attribute: NSLayoutAttribute = .width,
                    relation: NSLayoutRelation = .equal,
                    priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        return alignAttribute(attribute: .width, relation: relation,
                              to: view, otherAttribute: attribute,
                              multiplier: multiplier,
                              constant: constant, priority: priority)
    }

    func constraintWidth(constant: CGFloat) -> NSLayoutConstraint {
        return alignAttribute(attribute: .width, relation: .equal, to: nil,
                              otherAttribute: .width, constant: constant)
    }
}

public extension UIView {
    func alignLeading(_ constant: CGFloat = 0, multiplier: CGFloat = 1, to view: UIView,
                      attribute: NSLayoutAttribute = .leading,
                      relation: NSLayoutRelation = .equal,
                      priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        return alignAttribute(attribute: .leading, relation: relation,
                              to: view, otherAttribute: attribute,
                              multiplier: multiplier,
                              constant: constant, priority: priority)
    }

    func alignTrailing(_ constant: CGFloat = 0, multiplier: CGFloat = 1, to view: UIView,
                       attribute: NSLayoutAttribute = .trailing,
                       relation: NSLayoutRelation = .equal,
                       priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        return alignAttribute(attribute: .trailing, relation: relation,
                              to: view, otherAttribute: attribute,
                              multiplier: multiplier,
                              constant: constant, priority: priority)
    }

    func alignTop(_ constant: CGFloat = 0, multiplier: CGFloat = 1, to view: UIView,
                  attribute: NSLayoutAttribute = .top,
                  relation: NSLayoutRelation = .equal,
                  priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        return alignAttribute(attribute: .top, relation: relation,
                              to: view, otherAttribute: attribute,
                              multiplier: multiplier,
                              constant: constant, priority: priority)
    }

    func alignBottom(_ constant: CGFloat = 0, multiplier: CGFloat = 1, to view: UIView,
                     attribute: NSLayoutAttribute = .bottom,
                     relation: NSLayoutRelation = .equal,
                     priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        return alignAttribute(attribute: .bottom, relation: relation,
                              to: view, otherAttribute: attribute,
                              multiplier: multiplier,
                              constant: constant, priority: priority)
    }
}

public extension UIView {
    func alignAttribute(attribute: NSLayoutAttribute, relation: NSLayoutRelation,
                        to otherView: UIView? = nil,
                        otherAttribute: NSLayoutAttribute = .notAnAttribute,
                        multiplier: CGFloat = 1, constant: CGFloat = 0,
                        priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        return alignUsing(item: self, attribute, relation, otherView, otherAttribute,
                          multipler: multiplier, constant: constant, priority: priority)
    }
}

private extension UIView {
    func alignUsing(item: UIView, _ attribute: NSLayoutAttribute, _ relation: NSLayoutRelation,
                    _ otherItem: UIView? = nil,
                    _ otherAttribute: NSLayoutAttribute = .notAnAttribute,
                    multipler: CGFloat = 1, constant: CGFloat = 0,
                    priority: UILayoutPriority = UILayoutPriorityRequired) -> NSLayoutConstraint {
        let constraint = NSLayoutConstraint(item: item, attribute, relation, otherItem,
                                            otherAttribute, multipler: multipler,
                                            constant: constant, priority: priority)
        addConstraint(constraint)

        return constraint
    }
}

private extension NSLayoutConstraint {
    convenience init(item: UIView, _ attribute: NSLayoutAttribute, _ relation: NSLayoutRelation,
                     _ otherItem: UIView? = nil, _ otherAttribute: NSLayoutAttribute = .notAnAttribute,
                     multipler: CGFloat = 1, constant: CGFloat = 0,
                     priority: UILayoutPriority = UILayoutPriorityRequired) {
        self.init(item: item, attribute: attribute, relatedBy: relation, toItem: otherItem,
                  attribute: otherAttribute, multiplier: multiplier, constant: constant)
        self.priority = priority
    }
}