Gemini/Gemini-iOS/UIViewController+Children.swift

//
//  UIViewController+Children.swift
//  Gemini-iOS
//
//  Created by Shadowfacts on 12/17/20.
//

import UIKit

// Based on MVCTodo by Dave DeLong: https://github.com/davedelong/MVCTodo/blob/841649dd6aa31bacda3ad7ef9a9a836f66281e50/MVCTodo/Extensions/UIViewController.swift
extension UIViewController {
    func embedChild(_ newChild: UIViewController, in container: UIView? = nil) {
        // if the view controller is already a child of something else, remove it
        if let oldParent = newChild.parent, oldParent != self {
            newChild.beginAppearanceTransition(false, animated: false)
            newChild.willMove(toParent: nil)
            newChild.removeFromParent()
            
            if newChild.viewIfLoaded?.superview != nil {
                newChild.viewIfLoaded?.removeFromSuperview()
            }
            
            newChild.endAppearanceTransition()
        }
        
        // since .view returns an IUO, by default the type of this is "UIView?"
        // explicitly type the variable because We Know Better™
        var targetContainer: UIView = container ?? self.view
        if !targetContainer.isContainedWithin(view) {
            targetContainer = view
        }
        
        // add the view controller as a child
        if newChild.parent != self {
            newChild.beginAppearanceTransition(true, animated: false)
            addChild(newChild)
            newChild.didMove(toParent: self)
            targetContainer.embedSubview(newChild.view)
            newChild.endAppearanceTransition()
        } else {
            // the view controller is already a child
            // make sure it's in the right view
            
            // we don't do the appearance transition stuff here,
            // because the vc is already a child, so *presumably*
            // that transition stuff has already appened
            targetContainer.embedSubview(newChild.view)
        }
    }
    
    func removeViewAndController() {
        view.removeFromSuperview()
        removeFromParent()
    }
}

// Based on MVCTodo by Dave DeLong: https://github.com/davedelong/MVCTodo/blob/841649dd6aa31bacda3ad7ef9a9a836f66281e50/MVCTodo/Extensions/UIView.swift
extension UIView {
    func embedSubview(_ subview: UIView) {
        if subview.superview == self { return }
        
        if subview.superview != nil {
            subview.removeFromSuperview()
        }
        
        subview.frame = bounds
        addSubview(subview)
        
        NSLayoutConstraint.activate([
            subview.leadingAnchor.constraint(equalTo: leadingAnchor),
            subview.trailingAnchor.constraint(equalTo: trailingAnchor),
            subview.topAnchor.constraint(equalTo: topAnchor),
            subview.bottomAnchor.constraint(equalTo: bottomAnchor)
        ])
    }
    
    func isContainedWithin(_ other: UIView) -> Bool {
        var current: UIView? = self
        while let proposedView = current {
            if proposedView == other { return true }
            current = proposedView.superview
        }
        return false
    }
}