NSLayoutAnchorと同じようなものを作ってみるも、NSLayoutAnchorでいいや、となって使わなかったもの

LayoutConstraint.swift

//
// LayoutConstraint.swift
//
// Copyright (c) 2020 Hironori Ichimiya <hiron@hironytic.com>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//

import UIKit

struct LayoutItem {
    let item: Any
    
    init(_ item: Any) {
        self.item = item
    }
    
    var left: AttributedLayoutItem { attributedLayoutItem(attribute: .left) }
    var right: AttributedLayoutItem { attributedLayoutItem(attribute: .right) }
    var top: AttributedLayoutItem { attributedLayoutItem(attribute: .top) }
    var bottom: AttributedLayoutItem { attributedLayoutItem(attribute: .bottom) }
    var leading: AttributedLayoutItem { attributedLayoutItem(attribute: .leading) }
    var trailing: AttributedLayoutItem { attributedLayoutItem(attribute: .trailing) }
    var width: AttributedLayoutItem { attributedLayoutItem(attribute: .width) }
    var height: AttributedLayoutItem { attributedLayoutItem(attribute: .height) }
    var centerX: AttributedLayoutItem { attributedLayoutItem(attribute: .centerX) }
    var centerY: AttributedLayoutItem { attributedLayoutItem(attribute: .centerY) }
    var lastBaseline: AttributedLayoutItem { attributedLayoutItem(attribute: .lastBaseline) }
    @available(iOS 8.0, *) var firstBaseline: AttributedLayoutItem { attributedLayoutItem(attribute: .firstBaseline) }
    @available(iOS 8.0, *) var leftMargin: AttributedLayoutItem { attributedLayoutItem(attribute: .leftMargin) }
    @available(iOS 8.0, *) var rightMargin: AttributedLayoutItem { attributedLayoutItem(attribute: .rightMargin) }
    @available(iOS 8.0, *) var topMargin: AttributedLayoutItem { attributedLayoutItem(attribute: .topMargin) }
    @available(iOS 8.0, *) var bottomMargin: AttributedLayoutItem { attributedLayoutItem(attribute: .bottomMargin) }
    @available(iOS 8.0, *) var leadingMargin: AttributedLayoutItem { attributedLayoutItem(attribute: .leadingMargin) }
    @available(iOS 8.0, *) var trailingMargin: AttributedLayoutItem { attributedLayoutItem(attribute: .trailingMargin) }
    @available(iOS 8.0, *) var centerXWithinMargins: AttributedLayoutItem { attributedLayoutItem(attribute: .centerXWithinMargins) }
    @available(iOS 8.0, *) var centerYWithinMargins: AttributedLayoutItem { attributedLayoutItem(attribute: .centerYWithinMargins) }
    var notAnAttribute: AttributedLayoutItem { attributedLayoutItem(attribute: .notAnAttribute) }
    
    private func attributedLayoutItem(attribute: NSLayoutConstraint.Attribute) -> AttributedLayoutItem {
        AttributedLayoutItem(item: item, attribute: attribute)
    }
}

struct AttributedLayoutItem {
    let item: Any
    let attribute: NSLayoutConstraint.Attribute
    
    func lessThanOrEqualTo(_ item2: Any) -> LayoutRelationLackingInAttribute {
        layoutRelationLackingInAttribute(relation: .lessThanOrEqual, item2: item2)
    }
    
    func equalTo(_ item2: Any) -> LayoutRelationLackingInAttribute {
        layoutRelationLackingInAttribute(relation: .equal, item2: item2)
    }

    func greaterThanOrEqualTo(_ item2: Any) -> LayoutRelationLackingInAttribute {
        layoutRelationLackingInAttribute(relation: .greaterThanOrEqual, item2: item2)
    }

    private func layoutRelationLackingInAttribute(relation: NSLayoutConstraint.Relation, item2: Any) -> LayoutRelationLackingInAttribute {
        LayoutRelationLackingInAttribute(item1: item, attribute1: attribute, relation: relation, item2: item2)
    }

    func lessThanOrEqualTo(_ constant: CGFloat) -> LinearLayoutRelation {
        linearLayoutRelation(relation: .lessThanOrEqual, constant: constant)
    }
    
    func equalTo(_ constant: CGFloat) -> LinearLayoutRelation {
        linearLayoutRelation(relation: .equal, constant: constant)
    }
    
    func greaterThanOrEqualTo(_ constant: CGFloat) -> LinearLayoutRelation {
        linearLayoutRelation(relation: .greaterThanOrEqual, constant: constant)
    }

    private func linearLayoutRelation(relation: NSLayoutConstraint.Relation, constant: CGFloat) -> LinearLayoutRelation {
        LinearLayoutRelation(item1: item, attribute1: attribute, relation: relation, item2: nil, attribute2: .notAnAttribute, multiplier: 1.0, constant: constant)
    }
}

struct LayoutRelationLackingInAttribute {
    let item1: Any
    let attribute1: NSLayoutConstraint.Attribute
    let relation: NSLayoutConstraint.Relation
    let item2: Any?
    
    var left: LayoutRelation { layoutRelation(attribute2: .left) }
    var right: LayoutRelation { layoutRelation(attribute2: .right) }
    var top: LayoutRelation { layoutRelation(attribute2: .top) }
    var bottom: LayoutRelation { layoutRelation(attribute2: .bottom) }
    var leading: LayoutRelation { layoutRelation(attribute2: .leading) }
    var trailing: LayoutRelation { layoutRelation(attribute2: .trailing) }
    var width: LayoutRelation { layoutRelation(attribute2: .width) }
    var height: LayoutRelation { layoutRelation(attribute2: .height) }
    var centerX: LayoutRelation { layoutRelation(attribute2: .centerX) }
    var centerY: LayoutRelation { layoutRelation(attribute2: .centerY) }
    var lastBaseline: LayoutRelation { layoutRelation(attribute2: .lastBaseline) }
    @available(iOS 8.0, *) var firstBaseline: LayoutRelation { layoutRelation(attribute2: .firstBaseline) }
    @available(iOS 8.0, *) var leftMargin: LayoutRelation { layoutRelation(attribute2: .leftMargin) }
    @available(iOS 8.0, *) var rightMargin: LayoutRelation { layoutRelation(attribute2: .rightMargin) }
    @available(iOS 8.0, *) var topMargin: LayoutRelation { layoutRelation(attribute2: .topMargin) }
    @available(iOS 8.0, *) var bottomMargin: LayoutRelation { layoutRelation(attribute2: .bottomMargin) }
    @available(iOS 8.0, *) var leadingMargin: LayoutRelation { layoutRelation(attribute2: .leadingMargin) }
    @available(iOS 8.0, *) var trailingMargin: LayoutRelation { layoutRelation(attribute2: .trailingMargin) }
    @available(iOS 8.0, *) var centerXWithinMargins: LayoutRelation { layoutRelation(attribute2: .centerXWithinMargins) }
    @available(iOS 8.0, *) var centerYWithinMargins: LayoutRelation { layoutRelation(attribute2: .centerYWithinMargins) }
    var notAnAttribute: LayoutRelation { layoutRelation(attribute2: .notAnAttribute) }

    private func layoutRelation(attribute2: NSLayoutConstraint.Attribute) -> LayoutRelation {
        LayoutRelation(item1: item1, attribute1: attribute1, relation: relation, item2: item2, attribute2: attribute2)
    }
}

struct LayoutRelation {
    let item1: Any
    let attribute1: NSLayoutConstraint.Attribute
    let relation: NSLayoutConstraint.Relation
    let item2: Any?
    let attribute2: NSLayoutConstraint.Attribute
    
    func times(_ multiplier: CGFloat) -> MultipliedLayoutRelation {
        MultipliedLayoutRelation(item1: item1, attribute1: attribute1, relation: relation, item2: item2, attribute2: attribute2, multiplier: multiplier)
    }
    
    func plus(_ constant: CGFloat) -> LinearLayoutRelation {
        LinearLayoutRelation(item1: item1, attribute1: attribute1, relation: relation, item2: item2, attribute2: attribute2, multiplier: 1.0, constant: constant)
    }
    
    func minus(_ constant: CGFloat) -> LinearLayoutRelation {
        LinearLayoutRelation(item1: item1, attribute1: attribute1, relation: relation, item2: item2, attribute2: attribute2, multiplier: 1.0, constant: -constant)
    }
}

struct MultipliedLayoutRelation {
    let item1: Any
    let attribute1: NSLayoutConstraint.Attribute
    let relation: NSLayoutConstraint.Relation
    let item2: Any?
    let attribute2: NSLayoutConstraint.Attribute
    let multiplier: CGFloat
    
    func plus(_ constant: CGFloat) -> LinearLayoutRelation {
        LinearLayoutRelation(item1: item1, attribute1: attribute1, relation: relation, item2: item2, attribute2: attribute2, multiplier: multiplier, constant: constant)
    }
    
    func minus(_ constant: CGFloat) -> LinearLayoutRelation {
        LinearLayoutRelation(item1: item1, attribute1: attribute1, relation: relation, item2: item2, attribute2: attribute2, multiplier: multiplier, constant: -constant)
    }
}

struct LinearLayoutRelation {
    let item1: Any
    let attribute1: NSLayoutConstraint.Attribute
    let relation: NSLayoutConstraint.Relation
    let item2: Any?
    let attribute2: NSLayoutConstraint.Attribute
    let multiplier: CGFloat
    let constant: CGFloat
}

extension NSLayoutConstraint {
    convenience init(_ r: LinearLayoutRelation) {
        self.init(item: r.item1, attribute: r.attribute1, relatedBy: r.relation, toItem: r.item2, attribute: r.attribute2, multiplier: r.multiplier, constant: r.constant)
    }
    
    convenience init(_ r: MultipliedLayoutRelation) {
        self.init(item: r.item1, attribute: r.attribute1, relatedBy: r.relation, toItem: r.item2, attribute: r.attribute2, multiplier: r.multiplier, constant: 0.0)
    }

    convenience init(_ r: LayoutRelation) {
        self.init(item: r.item1, attribute: r.attribute1, relatedBy: r.relation, toItem: r.item2, attribute: r.attribute2, multiplier: 1.0, constant: 0.0)
    }
}