BKLabel.swift

private let kEllipsesCharacter = "\u{2026}"

/// This componet is designed to resolve those problems:
/// 1. Calculate frame.
/// 2. TouchableLinks.
/// 3. Line/Height limits and followed by "..."/"...全文"/... .
class BKLabel: UIView {

    /// 文本内容
    var attributedText: NSAttributedString? {
        didSet {
            if attributedText != oldValue {
                reset()
            }
        }
    }

    /// 限制行数
    var limitNumberOfLines = 0 {
        didSet {
            if limitNumberOfLines != oldValue {
                reset()
            }
        }
    }

    /// 限制宽高
    var limitWidth = CGFloat.greatestFiniteMagnitude {
        didSet {
            if limitWidth != oldValue {
                reset()
            }
        }
    }
    var limitHeight = CGFloat.greatestFiniteMagnitude {
        didSet {
            if limitHeight != oldValue {
                reset()
            }
        }
    }

    /// 尾部截断文案, 默认"..."
    var truncatedAttributedString: NSAttributedString? {
        didSet {
            if truncatedAttributedString != oldValue {
                reset()
            }
        }
    }

    /// 点击链接以及点击内容的回调
    /// 倘若不设置回调, 则控件不响应点击事件, 往上透传
    var clickLinkCallBack: ((URL) -> ())?
    var clickContentCallBack: (() -> ())?

    private(set) var numberOfLines = 0
    private(set) var maxNumberOfLines = 0

    private var lines: [CTLine]?
    private var lineOrigins: [CGPoint]?
    private var calculateSize: CGSize?

    fileprivate lazy var tapGestureRecognizer: UITapGestureRecognizer = {
        let gestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(didTapLabel(_:)))
        gestureRecognizer.cancelsTouchesInView = false
        gestureRecognizer.delaysTouchesBegan = false
        gestureRecognizer.delaysTouchesEnded = false

        return gestureRecognizer
    }()

    override init(frame: CGRect) {
        super.init(frame: frame)

        backgroundColor = .white
        addGestureRecognizer(tapGestureRecognizer)
    }

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

    override func draw(_ rect: CGRect) {
        if lines == nil {
            calculateLines()
        }

        if let lines = lines, let lineOrigins = lineOrigins, let context = UIGraphicsGetCurrentContext() {
            context.textMatrix = CGAffineTransform.identity
            context.translateBy(x: 0, y: size.height)
            context.scaleBy(x: 1.0, y: -1.0)

            lines.enumerated().forEach({ (index, line) in
                guard let position = lineOrigins[safe: index] else { return }

                context.textPosition = position
                CTLineDraw(line, context)
            })
        }
    }

    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        if let attributes = attributesFromPoint(point) {
            if let _ = attributes[NSAttributedStringKey.link] {
                return self
            }
        }

        if let _ = clickContentCallBack {
            return self
        } else {
            return nil
        }
    }

}

extension BKLabel {

    override var intrinsicContentSize: CGSize {
        if let calculateSize = calculateSize {
            return CGSize(width: nearbyint(calculateSize.width * 2) / 2, height: nearbyint(calculateSize.height * 2) / 2)
        } else {
            calculateLines()

            if let calculateSize =  calculateSize {
                return CGSize(width: nearbyint(calculateSize.width * 2) / 2, height: nearbyint(calculateSize.height * 2) / 2)
            } else {
                return .zero
            }
        }
    }

    @objc func didTapLabel(_ gestureRecognizer: UITapGestureRecognizer) {
        if let attributes = attributesFromPoint(gestureRecognizer.location(in: self)) {
            if let url = attributes[NSAttributedStringKey.link] as? URL {
                clickLinkCallBack?(url)
                return
            } else if let urlString = attributes[NSAttributedStringKey.link] as? String, let url = URL(string: urlString) {
                clickLinkCallBack?(url)
                return
            }
        }

        clickContentCallBack?()
    }

    private func attributesFromPoint(_ point: CGPoint) -> [NSAttributedStringKey: Any]? {
        guard let lines = lines, let calculateSize = calculateSize, let attributedText = attributedText else {
            return nil
        }

        for (index, line) in lines.enumerated() {
            guard let origin = lineOrigins?[safe: index] else {
                break
            }

            let lineSize = CTLineGetBoundsWithOptions(line, CTLineBoundsOptions(rawValue: 0)).size
            let lineRect = CGRect(origin: CGPoint(x: origin.x, y: calculateSize.height - origin.y - lineSize.height), size: lineSize)

            if lineRect.contains(point) {
                let convertPoint = CGPoint(x: point.x - lineRect.minX, y: point.y - lineRect.minY)
                let index = CTLineGetStringIndexForPosition(line, convertPoint)

                return attributedText.attributes(at: max(0, min(index, attributedText.length - 1)), effectiveRange: nil)
            }
        }

        return nil
    }

}

extension BKLabel {

    private func reset() {
        numberOfLines = 0
        maxNumberOfLines = 0

        lines = nil
        lineOrigins = nil
        calculateSize = nil
    }

    private func calculateLines() {
        guard let attributedText = attributedText else {
            return
        }

        let frameSetter = CTFramesetterCreateWithAttributedString(attributedText)
        let limitSize = CGSize(width: limitWidth, height: limitHeight)
        let drawSize = CTFramesetterSuggestFrameSizeWithConstraints(frameSetter, CFRangeMake(0,0), nil, limitSize, nil)

        let frame = calculateFrame(drawSize, frameSetter: frameSetter)
        let lines = CTFrameGetLines(frame) as! [CTLine]
        maxNumberOfLines = lines.count

        var lineOrigins = Array.init(repeating: CGPoint.zero, count: maxNumberOfLines)
        CTFrameGetLineOrigins(frame, CFRangeMake(0, 0), &lineOrigins)

        var intrinsicContentHeight: CGFloat = 0
        self.lines = lines.prefix(limitNumberOfLines > 0 ? limitNumberOfLines : lines.count).enumerated().filter({ (index, line) -> Bool in
            guard let origin = lineOrigins[safe: index] else { return false }

            let lineRect = CTLineGetBoundsWithOptions(line, CTLineBoundsOptions(rawValue: 0))
            if drawSize.height - origin.y + lineRect.height < limitHeight {
                intrinsicContentHeight = drawSize.height - origin.y + lineRect.height
                return true
            }
            return false
        }).map { $0.1 }
        numberOfLines = self.lines?.count ?? 0

        if let lastLine = self.lines?.last {
            var lineAscent: CGFloat = 0
            CTLineGetTypographicBounds(lastLine, &lineAscent, nil, nil);

            intrinsicContentHeight -= lineAscent
        }
        calculateSize = CGSize(width: drawSize.width, height: intrinsicContentHeight)

        self.lineOrigins = lineOrigins.map({ (point) -> CGPoint in
            return CGPoint(x: point.x, y: intrinsicContentHeight - (drawSize.height - point.y))
        })

        if let lastLine = self.lines?.last {
            let stringRange = CTLineGetStringRange(lastLine)

            if stringRange.location + stringRange.length < attributedText.length {
                let truncatedString: NSAttributedString
                if let truncatedAttributedString = truncatedAttributedString {
                    truncatedString = truncatedAttributedString
                } else {
                    let attributs = attributedText.attributes(at: stringRange.location + stringRange.length, effectiveRange: nil)
                    truncatedString = NSAttributedString(string: kEllipsesCharacter, attributes: attributs)
                }

                let truncatedSize = truncatedString.size()
                let index = CTLineGetStringIndexForPosition(lastLine, CGPoint(x: limitWidth - truncatedSize.width, y: drawSize.height / 2))

                let displayAttributedString = attributedText.attributedSubstring(from: NSMakeRange(stringRange.location, index - stringRange.location)).appending(truncatedString)
                let truncatedLine = CTLineCreateWithAttributedString(displayAttributedString)

                self.lines?.removeLast()
                self.lines?.append(truncatedLine)
            }
        }

        setNeedsDisplay()
    }

    private func calculateFrame(_ drawSize: CGSize, frameSetter: CTFramesetter) -> CTFrame {
        let path = CGMutablePath()
        path.addRect(CGRect(origin: .zero, size: drawSize))

        return CTFramesetterCreateFrame(frameSetter, CFRangeMake(0, 0), path, nil)
    }

}