DaxDialogViewController.swift

//
//  DaxDialogViewController.swift
//  DuckDuckGo
//
//  Copyright © 2020 DuckDuckGo. 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 UIKit

class DaxDialogViewController: UIViewController {
    
    @IBOutlet weak var topSpacing: NSLayoutConstraint!

    @IBOutlet weak var icon: UIView!
    @IBOutlet weak var pointer: UIView!
    @IBOutlet weak var textArea: UIView!
    @IBOutlet weak var button: UIButton!
    @IBOutlet weak var label: UILabel!
    
    @IBOutlet weak var tapToCompleteGestureRecognizer: UIGestureRecognizer!
    
    var message: String? {
        didSet {
            initLabel()
        }
    }
    var accessibleMessage: String?
    var cta: String? {
        didSet {
            initCTA()
        }
    }
    
    func calculateHeight() -> CGFloat {
        guard let text = message ?? cta, !text.isEmpty else { return 370.0 }
        
        let attributes = attributedString(from: text, color: .black).attributes(at: 0, effectiveRange: nil)
        
        let size = (text as NSString).boundingRect(with: CGSize(width: label.bounds.width, height: 1000),
                                                   options: [.usesFontLeading, .usesLineFragmentOrigin],
                                                   attributes: attributes,
                                                   context: nil)

        let iconHeight = icon.bounds.height
        let topMargin: CGFloat = 20.0
        let buttonHeight: CGFloat = cta != nil ? 60.0 : 0.0
        let bottomMargin: CGFloat = 24.0
        return iconHeight + topMargin + size.height + buttonHeight + bottomMargin
    }
    
    var onTapCta: (() -> Void)?
    
    private var position: Int = 0
    private var chars = [Character]()
    
    private func atEnd(_ position: Int) -> Bool {
        return position >= chars.count
    }
    
    var isFinished: Bool { atEnd(position) }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        decorate()

        initLabel()
        initCTA()
        
        applyPointerRotation()
        textArea.displayDropShadow()
        button.displayDropShadow()
    }
    
    private func initLabel() {
        label?.text = nil

        // Use the accessible message if present, otherwise remove markdown and use the message
        label?.accessibilityLabel = accessibleMessage ?? message?.attributedStringFromMarkdown(color: .black).string

        chars = Array(message ?? "")
    }
    
    private func applyPointerRotation() {
        let rads = CGFloat(45 * Double.pi / 180)
        pointer.layer.transform = CATransform3DMakeRotation(rads, 0.0, 0.0, 1.0)
    }
    
    private func initCTA() {
        if let title = cta {
            button?.isHidden = false
            button?.setTitle(title, for: .normal)
        } else {
            button?.isHidden = true
        }
    }
    
    func start() {
        position = 0
        showNextChar()
    }
    
    func finish() {
        position = chars.count
        updateMessage()
    }
    
    @IBAction func onTap() {
        finish()
    }
    
    @IBAction func onButtonTap() {
        onTapCta?()
    }
    
    func reset() {
        position = 0
        updateMessage()
    }
    
    private func showNextChar() {
        guard !atEnd(position) else { return }
        
        position += 1
        while !atEnd(position) && (chars[position].isWhitespace || chars[position].isMarkdownIndicator) {
            position += 1
        }
        updateMessage()
        
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.02) {
            self.showNextChar()
        }
    }
    
    private func updateMessage() {
        let theme = ThemeManager.shared.currentTheme
        
        guard let message = message else { return }
        let baseText = attributedString(from: String(Array(message)[0 ..< position]), color: theme.daxDialogTextColor)
        label.attributedText = baseText
        
        let restOfString = String(Array(message)[position...])
        guard let nextWhitespace = restOfString.firstIndex(where: { $0.isWhitespace }) else { return }
        let restOfWord = String(restOfString[restOfString.startIndex ..< nextWhitespace])
        let invisible = attributedString(from: restOfWord, color: theme.daxDialogBackgroundColor)
        
        let combined = NSMutableAttributedString()
        combined.append(baseText)
        combined.append(invisible)
        label.attributedText = combined
        
        if label.bounds.height == 0 {
            label.setNeedsLayout()
            label.layoutIfNeeded()
        }
    }
    
    private func attributedString(from string: String, color: UIColor) -> NSAttributedString {
        return string.attributedStringFromMarkdown(color: color, fontSize: isSmall ? 16 : 18)
    }
}

extension DaxDialogViewController {

    private func decorate() {
        let theme = ThemeManager.shared.currentTheme
        textArea.backgroundColor = theme.daxDialogBackgroundColor
        pointer.backgroundColor = theme.daxDialogBackgroundColor
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)

        if traitCollection.hasDifferentColorAppearance(comparedTo: previousTraitCollection) {
            finish()
        }
    }
}