UIAlertControllerView.swift

//
//  UIAlertControllerView.swift
//  UIKit
//
//  Created by Geordie Jay on 25.04.18.
//  Copyright © 2018 flowkey. All rights reserved.
//

private let verticalPadding: CGFloat = 18
private let horizontalPadding: CGFloat = 24
private let horizontalGap: CGFloat = 16

class UIAlertControllerView: UIView {
    let header = UILabel(frame: .zero)
    let text: UILabel?
    let style: UIAlertControllerStyle

    var buttons: [UIAlertControllerButton] = []
    var subviewWidth: CGFloat = 0

    init(
        title: String?,
        message: String?,
        actions: [UIAlertAction],
        style: UIAlertControllerStyle)
    {
        self.style = style
        header.text = title
        header.font = UIFont.boldSystemFont(ofSize: 20)
        header.numberOfLines = 0
        header.layer.contentsGravity = .top

        if let message = message {
            text = UILabel(frame: .zero)
            text?.numberOfLines = 0
            text?.text = message
            text?.font = UIFont.systemFont(ofSize: 16)
        } else {
            text = nil
        }

        super.init(frame: .zero)

        buttons = actions.map { action in
            let button = UIAlertControllerButton(frame: .zero)
            button.setTitle(action.title, for: .normal)
            button.setTitleColor(UIColor(hex: 0x757575), for: .normal) // color from react-native settings menu
            button.setTitleColor(.black, for: .highlighted)

            button.onPress = { [weak self] in
                // Always dismiss the AlertController first so we're not trying to
                // present something on it that immediately gets dismissed again.
                (self?.next as? UIAlertController)?.dismiss(animated: true)
                action.handler?(action)
            }

            return button
        }

        clipsToBounds = true
        backgroundColor = .white
        layer.cornerRadius = 3

        addSubview(header)
        text.map { addSubview($0) }
        buttons.forEach { addSubview($0) }

        subviewWidth = {
            // arbitrary mininum width of the alert view
            let minWidth: CGFloat = 300
            
            // assuming a text font size of 16 we want to limit the width
            // of the alert view so that the text stays well readable
            let maxReadableWidth: CGFloat = 540
            
            let maxWidth: CGFloat
            if UIScreen.main.isPortrait {
                maxWidth = min(UIScreen.main.bounds.width - 4 * horizontalPadding, maxReadableWidth)
            } else {
                maxWidth = min(max(minWidth, UIScreen.main.bounds.width / 1.5), maxReadableWidth)
            }

            subviews.forEach { $0.sizeToFit() }
            guard let largestSubviewWidth = subviews.map({ $0.frame.width }).max() else {
                assertionFailure("no subviews exist to determine largestSubviewWidth")
                return minWidth
            }
            return min(maxWidth, max(largestSubviewWidth, minWidth))
        }()
        
        subviews.forEach { $0.clipsToBounds = true }
    }

    override func layoutSubviews() {
        header.frame.origin = CGPoint(x: horizontalPadding, y: verticalPadding)
        header.bounds.width = subviewWidth
        header.textAlignment = .left
        header.sizeToFit()

        text?.frame.origin.x = horizontalPadding
        text?.frame.width = subviewWidth
        text?.sizeToFit()
        text?.frame.minY = header.frame.maxY + verticalPadding

        if style == .alert {
            let totalButtonsWidth = buttons.reduce(0, { $0 + $1.frame.width }) + horizontalGap * CGFloat(buttons.count - 1)
            if totalButtonsWidth < subviewWidth {
                return layoutButtonsHorizontally()
            }
        }
        return layoutButtonsVertically()

    }

    private func layoutButtonsVertically() {
        let fullButtonWidth = subviewWidth + horizontalPadding * 2
        buttons.enumerated().forEach({ index, button in
            button.sizeToFit()
            switch style {
            case .actionSheet:
                button.titleLabelOriginX = horizontalPadding
            case .alert:
                button.titleLabelOriginX = fullButtonWidth - horizontalPadding - button.bounds.width
            }

            button.frame.size.width = fullButtonWidth
            button.frame.size.height += verticalPadding

            if index == 0 {
                button.frame.minY = CGFloat(text?.frame.maxY ?? header.frame.maxY) + verticalPadding
            } else {
                let previousElement = buttons[index - 1]
                button.frame.origin.y = previousElement.frame.maxY
            }

        })
    }

    private func layoutButtonsHorizontally() {
        buttons.enumerated().forEach({ index, button in
            button.sizeToFit()
            button.frame.width += 25
            button.contentHorizontalAlignment = .center
            button.frame.minY = CGFloat(text?.frame.maxY ?? header.frame.maxY) + verticalPadding
            if button == buttons.first {
                button.frame.origin.x = bounds.maxX - button.frame.width - horizontalGap
            } else {
                let previousElement = buttons[index - 1]
                button.frame.origin.x = previousElement.frame.minX - button.frame.width - horizontalGap
            }
        })
    }

    override func sizeThatFits(_ size: CGSize) -> CGSize {
        layoutIfNeeded()
        return CGSize(
            width: subviewWidth + horizontalPadding * 2,
            height: CGFloat(buttons.last?.frame.maxY ?? 0) + verticalPadding
        )
    }
}


class UIAlertControllerButton: Button {
    override var isHighlighted: Bool {
        didSet {
            backgroundColor = isHighlighted ? UIColor.lightGray.withAlphaComponent(0.2) : .clear
        }
    }

    /// Set this to force the x position of the buttons label and ignore the buttons contentHorizontalAlignment.
    /// This is needed to give the vertically layed out buttons the full width of its container while being able to indent its title.
    var titleLabelOriginX: CGFloat?
    
    override func layoutSubviews() {
        super.layoutSubviews()
        if let titleLabelOriginX = titleLabelOriginX {
            titleLabel?.frame.origin.x = titleLabelOriginX
        }
    }
}

private extension UIScreen {
    var isPortrait: Bool {
        return self.bounds.width < self.bounds.height
    }
}