CascadingLabel.swift

import UIKit

/*
 EXAMPLE:
 let hangulCharacterSet = CharacterSet(charactersIn: "가"..."힣").union(CharacterSet(charactersIn: "ㄱ"..."ㆎ"))
 let nanumGothicDescriptor = UIFontDescriptor(name: "NanumGothic", size: 17).addingCharacterSet(hangulCharacterSet)
 let font = UIFont.systemFont(ofSize: 17).addingFrontCascadeDescriptors([nanumGothicDescriptor])
 
 let label = UILabel()
 label.font = font
 label.text = "Swift 프로그래밍 언어"
 label.respectFontDescriptorSize()
 */

extension String {
    // TODO: 연속되는 Range는 합쳐서 반환하기
    // TODO: NSRange 대신 Range 사용하기
    func rangesOfCharacter(from aSet: CharacterSet) -> [NSRange] {
        var ranges: [NSRange] = []
        
        for (index, character) in self.enumerated() {
            guard let scalar = character.unicodeScalars.first else {
                continue
            }
            
            if aSet.contains(scalar) {
                let range = NSRange(location: index, length: 1)
                ranges.append(range)
            }
        }
        return ranges
    }
}

extension UIFontDescriptor {
    func addingCharacterSet(_ characterSet: CharacterSet) -> UIFontDescriptor {
        return self.addingAttributes([.characterSet: characterSet])
    }
    
    var cascadeList: [UIFontDescriptor]? {
        return self.fontAttributes[.cascadeList] as? [UIFontDescriptor]
    }
    
    var characterSet: CharacterSet? {
        return self.fontAttributes[.characterSet] as? CharacterSet
    }
    
    var size: CGFloat? {
        return self.fontAttributes[.size] as? CGFloat
    }
}

extension UIFont {
    convenience init(cascadeDescriptors: [UIFontDescriptor], finalDescriptor: UIFontDescriptor, size: CGFloat) {
        var descriptors = cascadeDescriptors
        
        /*
         원래는 descriptors.removeFirst()로 base로서 사용할 descriptor를 제거해야 하나,
         cascadeList 속성을 갖고 있는 descriptor로 UIFont를 초기화할 때 base descriptor의 characterSet 속성이 접근 불가능해지는 버그가 있어
         base descriptor를 cascadeList에도 추가하여 나중에도 base descriptor에 접근 가능하게 한다.
         참고 1: 이 때 base descriptor와 cascadeList[0]은 완전히 동일하므로 cascading 사용에 문제가 없다.
         참고 2: base descriptor의 characterSet 속성은 접근만 불가능해지는 것일 뿐, 폰트에서는 여전히 base descriptor의 characterSet이 적용되어진 것으로 보여진다.
         */
        guard let firstDescriptor = descriptors.first else {  // descriptors.removeFirst()
            self.init(descriptor: finalDescriptor, size: size)
            return
        }
        
        descriptors.append(finalDescriptor)
        
        let descriptor = firstDescriptor.addingAttributes([.cascadeList: descriptors])
        
        self.init(descriptor: descriptor, size: size)
    }
    
    func addingFrontCascadeDescriptors(_ cascadeDescriptors: [UIFontDescriptor]) -> UIFont {
        return UIFont(cascadeDescriptors: cascadeDescriptors, finalDescriptor: self.fontDescriptor, size: self.pointSize)
    }
}

extension UILabel {
    var mutatingAttributedText: NSMutableAttributedString? {
        if let attributedText = self.attributedText {
            if let mutableAttributedText = attributedText as? NSMutableAttributedString {
                return mutableAttributedText
            } else {
                return NSMutableAttributedString(attributedString: attributedText)
            }
        } else {
            return nil
        }
    }
}

class CascadingLabel: UILabel {
    var respectsFontDescriptorSize: Bool = false
    var lineHeight: CGFloat? {
        didSet {
            self.updateLineHeight()
        }
    }
    var lineHeightMultipleForFontPointSize: CGFloat? {
        didSet {
            guard let lineHeightMultiple = self.lineHeightMultipleForFontPointSize else {
                return
            }
            self.lineHeight = self.font.pointSize * lineHeightMultiple
            self.updateLineHeight()
        }
    }
    private var descriptorsToAlignMiddle: [(shiftingFontDescriptor: UIFontDescriptor, basisFontDescriptor: UIFontDescriptor)] = []
    
    override var text: String? {
        didSet {
            if respectsFontDescriptorSize {
                self.respectFontDescriptorSize()
            }
            
            if lineHeight != nil {
                self.updateLineHeight()
            }
            
            for (shiftingFontDescriptor, basisFontDescriptor) in descriptorsToAlignMiddle {
                self.alignMiddle(lineHeightOf: shiftingFontDescriptor, toCapHeightOf: basisFontDescriptor)
            }
        }
    }
    
    /* 최종 text와 font를 설정한 뒤에 호출해야 함. */
    private func respectFontDescriptorSize() {
        guard let text = self.text, let cascadeList = self.font.fontDescriptor.cascadeList else {
            return
        }
        
        for descriptor in cascadeList.reversed() {
            let size = descriptor.size ?? 0
            
            let characterSet = descriptor.characterSet ?? CTFontCopyCharacterSet(UIFont(descriptor: descriptor, size: 0)) as CharacterSet
            let rangeList = text.rangesOfCharacter(from: characterSet)
            
            let mutableAttributedString = self.mutatingAttributedText
            
            for range in rangeList {
                let font = UIFont(descriptor: descriptor, size: size)
                mutableAttributedString?.addAttribute(.font, value: font, range: range)
            }
            
            self.attributedText = mutableAttributedString
        }
    }
    
    func alignMiddle(lineHeightOf shiftingFontDescriptor: UIFontDescriptor, toCapHeightOf basisFontDescriptor: UIFontDescriptor) {
        self.descriptorsToAlignMiddle.append((shiftingFontDescriptor, basisFontDescriptor))
        
        guard let text = self.text else {
            return
        }
        
        let shiftingFont = UIFont(descriptor: shiftingFontDescriptor, size: shiftingFontDescriptor.pointSize)
        let basisFont = UIFont(descriptor: basisFontDescriptor, size: basisFontDescriptor.pointSize)
        
        let offset = (basisFont.capHeight / 2) - ((shiftingFont.ascender + shiftingFont.descender) / 2)
        
        let shiftingCharacterSet = shiftingFontDescriptor.characterSet ?? CTFontCopyCharacterSet(shiftingFont) as CharacterSet
        let rangeList = text.rangesOfCharacter(from: shiftingCharacterSet)
        
        let mutableAttributedString = self.mutatingAttributedText
        
        for range in rangeList {
            // TODO: 폰트 크기 문제 때문에 .font를 재할당해야할지 결정해야 함.
            mutableAttributedString?.addAttribute(.baselineOffset, value: offset, range: range)
        }
        
        self.attributedText = mutableAttributedString
    }
    
    // 러프한 코드
    private func updateLineHeight() {
        guard let lineHeight = self.lineHeight, let mutableAttributedString = self.mutatingAttributedText else {
            return
        }
        
        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.maximumLineHeight = lineHeight
        paragraphStyle.minimumLineHeight = lineHeight
        
        mutableAttributedString.addAttribute(.paragraphStyle, value: paragraphStyle, range: NSRange(location: 0, length: mutableAttributedString.length))
        
        self.attributedText = mutableAttributedString
    }
}

extension CascadingLabel {
    func addKoreanFrontCascadeFont(name: String, pointSizeRatio: CGFloat = 1, lineHeightMultiple: CGFloat? = nil) {
        
        // alignMiddle 메소드에 사용할 font descriptor가 addingFrontCascadeDescriptors 호출 시 대체되므로 이전에 미리 할당해 놓는다.
        let basisFontDescriptor = self.font.fontDescriptor
        
        let koreanFontDescriptor = UIFontDescriptor(fontAttributes: [
            .name : name,
            .size: self.font.pointSize * pointSizeRatio,
            .characterSet: CharacterSet.hangulLetters
        ])
        
        self.font = self.font.addingFrontCascadeDescriptors([koreanFontDescriptor])
        
        self.respectsFontDescriptorSize = true
        self.alignMiddle(lineHeightOf: koreanFontDescriptor, toCapHeightOf: basisFontDescriptor)
        
        if lineHeightMultiple != nil {
            self.lineHeightMultipleForFontPointSize = lineHeightMultiple
        }
    }
}