Equation Editing in SwiftUI with Swift Math

SwiftUIPretendLatexEditor.swift

import SwiftUI
import SwiftMath

enum ContentItem: Identifiable {
  case text(_ text: String, id: Int)
  case equation(_ equation: String, id: Int)
  
//  this is obviously very simplistic/needs improvement if to be used for reals
  static func parse(input: String) -> [ContentItem] {
    let items = input.split(separator: "$$\n")
    
    if items.count == 1 {
      return [.text(input, id: 0)]
    } else {
      var result: [ContentItem] = []
      var i = 0
      
      items.forEach { part in
        let s = String(part).trimmingCharacters(in: .whitespacesAndNewlines)
        
        if i % 2 == 0 {
          result.append(.text(s, id: i))
        } else {
          result.append(.equation(s, id: i))
        }
        
        i += 1
      }
      return result
    }
  }
  
  var id: Int {
    switch self {
    case .equation(_, let id):
      return id
    case .text(_, let id):
      return id
    }
  }
}

struct ContentView: View {
  @State private var text: String = ""
  
  var content: [ContentItem] {
    ContentItem.parse(input: text)
  }
  
  var body: some View {
    VStack {
      TextEditor(text: $text)
        .padding()
        .frame(maxHeight: .infinity)
        .border(.red)
      
      ScrollView {
        LazyVStack {
          ForEach(content) { item in
            switch item {
            case let .equation(eq,_):
              MathView(equation: eq, fontSize: 16).fixedSize(horizontal: false, vertical: true).tag(item.id)
              
            case let .text(text,_):
              Text(text).tag(item.id)
            }
          }
        }.padding()
      }
      .frame(maxHeight: .infinity)
      .border(.yellow)
    }
    
    .padding()
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

struct MathView: UIViewRepresentable {
  var equation: String
  var fontSize: CGFloat
  
  func makeUIView(context: Context) -> MTMathUILabel {
    let view = MTMathUILabel()
    return view
  }
  
  func updateUIView(_ uiView: MTMathUILabel, context: Context) {
    uiView.latex = equation
    uiView.fontSize = fontSize
    uiView.font = MTFontManager().termesFont(withSize: fontSize)
    uiView.textAlignment = .center
    uiView.labelMode = .display
  }
}