FontFitUtil

FontFitUtil.swift

import Foundation

class FontFitUtil {
  
  class func bestFontForText(_ text: String, font: UIFont, container: UIView) -> UIFont {
    return bestFontForText(text, font: font, container: container.bounds.size)
  }
  
  class func bestFontForText(_ text: String, font: UIFont, container: CGSize) -> UIFont {
    //make rect to calculate text a little bit smaller
    
    guard container != CGSize.zero else { return font }
    
    let paragraph = NSMutableParagraphStyle()
    paragraph.lineBreakMode = .byWordWrapping
    let boundingBox = text.boundingRect(with: CGSize(width: container.width, height: CGFloat.greatestFiniteMagnitude),
                                        options: [.usesLineFragmentOrigin, .usesFontLeading],
                                        attributes: [NSAttributedStringKey.font: font, NSAttributedStringKey.paragraphStyle: paragraph],
                                        context: nil)
    
    if boundingBox.height > container.height {
      return bestFontForText(text, font: font.adding(points: -1), container: container)
    } else {
      return font
    }
  }
  
  ///manually calculate best to fit font size for textfields
  class func updateTextFieldFont(_ textField: UITextField) {
    guard let text = textField.text else { return }
    
    textField.layoutIfNeeded()
    
    let maxFont = UIFont(descriptor: Font.title.uiFont().fontDescriptor, size: maxFontSizeToStartScaling())
    let resultFont = bestFontForText(text, font: maxFont, container: textField.bounds.size)
    textField.font = resultFont
  }
  
  ///manually calculate best to fit font size for textfields
  class func updateSystemFontLabel(_ label: UILabel) {
    guard let text = label.text else { return }
    
    label.layoutIfNeeded()
    
    let maxFont = UIFont(descriptor: UIFont.systemFont(ofSize: maxFontSizeToStartScaling(fontWeight: .ultraLight), weight: .ultraLight).fontDescriptor,
                         size: maxFontSizeToStartScaling(fontWeight: .ultraLight))
    let resultFont = bestFontForText(text, font: maxFont, container: label.bounds.size)
    label.font = resultFont
  }
  
  class func maxFontSizeToStartScaling(fontWeight: UIFont.Weight? = nil) -> CGFloat {
    if let weight = fontWeight {
      if weight == .ultraLight {
        return 60
      }
    }
    if LayoutBuilder.isExtraExtraLargeCategory || LayoutBuilder.isExtraLargeCategory {
      return 40
    }
    if LayoutBuilder.isLargeCategory {
      return 32
    }
    if LayoutBuilder.isMediumCategory {
      return 24
    }
    return 20
  }
  
}