session-ios/SessionUIKit/Components/TappableLabel.swift

import UIKit

// Requirements:
// • Links should show up properly and be tappable.
// • Text should * not * be selectable.
// • The long press interaction that shows the context menu should still work.

// See https://stackoverflow.com/questions/47983838/how-can-you-change-the-color-of-links-in-a-uilabel

public protocol TappableLabelDelegate: AnyObject {
    func tapableLabel(_ label: TappableLabel, didTapUrl url: String, atRange range: NSRange)
}

public class TappableLabel: UILabel {
    public private(set) var links: [String: NSRange] = [:]
    private lazy var highlightedMentionBackgroundView: HighlightMentionBackgroundView = HighlightMentionBackgroundView(targetLabel: self)
    private(set) var layoutManager = NSLayoutManager()
    private(set) var textContainer = NSTextContainer(size: CGSize.zero)
    private(set) var textStorage = NSTextStorage() {
        didSet {
            textStorage.addLayoutManager(layoutManager)
        }
    }

    public weak var delegate: TappableLabelDelegate?

    public override var attributedText: NSAttributedString? {
        didSet {
            guard let attributedText: NSAttributedString = attributedText else {
                textStorage = NSTextStorage()
                links = [:]
                return
            }

            textStorage = NSTextStorage(attributedString: attributedText)
            findLinksAndRange(attributeString: attributedText)
            highlightedMentionBackgroundView.maxPadding = highlightedMentionBackgroundView
                .calculateMaxPadding(for: attributedText)
            highlightedMentionBackgroundView.frame = self.bounds.insetBy(
                dx: -highlightedMentionBackgroundView.maxPadding,
                dy: -highlightedMentionBackgroundView.maxPadding
            )
        }
    }

    public override var lineBreakMode: NSLineBreakMode {
        didSet {
            textContainer.lineBreakMode = lineBreakMode
        }
    }

    public override var numberOfLines: Int {
        didSet {
            textContainer.maximumNumberOfLines = numberOfLines
        }
    }
    
    public var containsLinks: Bool {
        return !links.isEmpty
    }
    
    // MARK: - Initialization

    public override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }

    public required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setup()
    }

    private func setup() {
        isUserInteractionEnabled = true
        layoutManager.addTextContainer(textContainer)
        textContainer.lineFragmentPadding = 0
        textContainer.lineBreakMode = lineBreakMode
        textContainer.maximumNumberOfLines  = numberOfLines
        numberOfLines = 0
    }
    
    // MARK: - Layout
    
    public override func didMoveToSuperview() {
        super.didMoveToSuperview()

        // Note: Because we want the 'highlight' content to appear behind the label we need
        // to add the 'highlightedMentionBackgroundView' below it in the view hierarchy
        //
        // In order to try and avoid adding even more complexity to UI components which use
        // this 'TappableLabel' we are going some view hierarchy manipulation and forcing
        // these elements to maintain the same superview
        highlightedMentionBackgroundView.removeFromSuperview()
        superview?.insertSubview(highlightedMentionBackgroundView, belowSubview: self)
    }
    
    public override func layoutSubviews() {
        super.layoutSubviews()
        
        textContainer.size = bounds.size
        highlightedMentionBackgroundView.frame = self.frame.insetBy(
            dx: -highlightedMentionBackgroundView.maxPadding,
            dy: -highlightedMentionBackgroundView.maxPadding
        )
    }
    
    // MARK: - Functions

    private func findLinksAndRange(attributeString: NSAttributedString) {
        links = [:]
        let enumerationBlock: (Any?, NSRange, UnsafeMutablePointer<ObjCBool>) -> Void = { [weak self] value, range, isStop in
            guard let strongSelf = self else { return }
            if let value = value {
                let stringValue = "\(value)"
                strongSelf.links[stringValue] = range
            }
        }
        attributeString.enumerateAttribute(.link, in: NSRange(0..<attributeString.length), options: [.longestEffectiveRangeNotRequired], using: enumerationBlock)
        attributeString.enumerateAttribute(.attachment, in: NSRange(0..<attributeString.length), options: [.longestEffectiveRangeNotRequired], using: enumerationBlock)
    }

    public override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let locationOfTouch = touches.first?.location(in: self) else {
            return
        }
        
        handleTouch(at: locationOfTouch)
    }
    
    public func handleTouch(at point: CGPoint) {
        textContainer.size = bounds.size
        
        let indexOfCharacter = layoutManager.glyphIndex(for: point, in: textContainer)
        for (urlString, range) in links where NSLocationInRange(indexOfCharacter, range) {
            delegate?.tapableLabel(self, didTapUrl: urlString, atRange: range)
            return
        }
    }
}