HTMLText.swift

import SwiftUI

struct HTMLText: View {
  let html: String
  var customColor: Color = .primary
  var font: Font = .body

  var body: some View {
    if let data = html.data(using: .utf8),
      let nsAttributedString = try? NSMutableAttributedString(
        data: data,
        options: [
          .documentType: NSAttributedString.DocumentType.html,
          .characterEncoding: String.Encoding.utf8.rawValue,
        ],
        documentAttributes: nil
      )
    {
      let modifiedAttributedString = applyCustomStyles(to: nsAttributedString)
      let attributedString = AttributedString(modifiedAttributedString)
      Text(attributedString)
    } else {
      Text(html).foregroundStyle(customColor).font(font)
    }
  }

  private func applyCustomStyles(
    to nsAttributedString: NSMutableAttributedString
  ) -> NSAttributedString {
    nsAttributedString.enumerateAttributes(
      in: NSRange(location: 0, length: nsAttributedString.length)
    ) { attributes, range, _ in
      if attributes.keys.contains(.foregroundColor) {
        nsAttributedString.removeAttribute(.foregroundColor, range: range)
      }

      let fontSize = fontSize(for: font)
      let currentFont =
        attributes[.font] as? UIFont
        ?? UIFont.systemFont(ofSize: UIFont.systemFontSize)
      let newFont = currentFont.withSize(fontSize)
      nsAttributedString.addAttribute(
        .font,
        value: newFont,
        range: range
      )

      nsAttributedString.addAttribute(
        .foregroundColor,
        value: UIColor(customColor),
        range: range
      )
    }

    return nsAttributedString
  }

  private func fontSize(for font: Font) -> CGFloat {
    let textStyleMapping: [Font: UIFont.TextStyle] = [
      .largeTitle: .largeTitle,
      .title: .title1,
      .title2: .title2,
      .title3: .title3,
      .headline: .headline,
      .subheadline: .subheadline,
      .body: .body,
      .callout: .callout,
      .caption: .caption1,
      .caption2: .caption2,
      .footnote: .footnote
    ]
    let textStyle = textStyleMapping[font, default: .body]
    return UIFont.preferredFont(forTextStyle: textStyle).pointSize
  }
}