SelectionView.swift

//
//  SelectionView.swift
//  Proton
//
//  Created by Rajdeep Kwatra on 4/1/20.
//  Copyright © 2020 Rajdeep Kwatra. All rights reserved.
//
//  Licensed under the Apache License, Version 2.0 (the "License");
//  you may not use this file except in compliance with the License.
//  You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.
//

import Foundation
import UIKit

class SelectionView: UIView {
    var onRemoveFromSuperview: (() -> Void)?
    init(frame: CGRect = .zero, onRemoveFromSuperview: (() -> Void)? = nil) {
        super.init(frame: frame)
        self.onRemoveFromSuperview = onRemoveFromSuperview
        self.alpha = 0.5
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        guard let originalResult = super.hitTest(point, with: event),
              event?.type == .touches
        else { return nil }
        
        guard originalResult == self else {
            return originalResult
        }
        removeFromSuperview()
        onRemoveFromSuperview?()

        for other in (superview?.subviews ?? []) where other != self {
            let convertedPoint = convert(point, to: other)
            if let hit = other.hitTest(convertedPoint, with: event) {
                return hit
            }
        }
        return nil
    }
    
    func addTo(parent: UIView, selectionColor: UIColor? = nil) {
        applyTintColor(selectionColor)
        self.translatesAutoresizingMaskIntoConstraints = false
        parent.addSubview(self)
        NSLayoutConstraint.activate([
            self.topAnchor.constraint(equalTo: parent.topAnchor),
            self.bottomAnchor.constraint(equalTo: parent.bottomAnchor),
            self.leadingAnchor.constraint(equalTo: parent.leadingAnchor),
            self.trailingAnchor.constraint(equalTo: parent.trailingAnchor),
        ])
        parent.bringSubviewToFront(self)
    }

    private func applyTintColor(_ selectionColor: UIColor? = nil) {
        // TintColor needs to be picked up from UIButton as it is the only control that
        // provides correct color for macOS accents.
        self.backgroundColor = selectionColor ?? UIButton().tintColor
    }
}