Tusker/Tusker/HTMLConverter.swift

//
//  HTMLConverter.swift
//  Tusker
//
//  Created by Shadowfacts on 12/3/22.
//  Copyright © 2022 Shadowfacts. All rights reserved.
//

import UIKit
import HTMLStreamer
import WebURL
import WebURLFoundationExtras

class HTMLConverter {
    
    static let defaultFont = UIFont.systemFont(ofSize: 17)
    static let defaultMonospaceFont = UIFont.monospacedSystemFont(ofSize: 17, weight: .regular)
    static let defaultColor = UIColor.label
    static let defaultParagraphStyle: NSParagraphStyle = {
        let style = NSMutableParagraphStyle()
        // 2 points is enough that it doesn't make things look weirdly spaced out, but leaves a slight gap when there are multiple lines of emojis
        style.lineSpacing = 2
        return style
    }()
    
    private let converter: AttributedStringConverter<Callbacks>
    
    init(font: UIFont, monospaceFont: UIFont, fontMetrics: UIFontMetrics, color: UIColor, paragraphStyle: NSParagraphStyle) {
        let config = AttributedStringConverterConfiguration(
            font: font,
            monospaceFont: monospaceFont,
            fontMetrics: fontMetrics,
            color: color,
            paragraphStyle: paragraphStyle
        )
        self.converter = AttributedStringConverter(configuration: config)
    }
   
    func convert(_ html: String) -> NSAttributedString {
        converter.convert(html: html)
    }
}

extension HTMLConverter {
    // note: this is duplicated in NotificationExtension
    struct Callbacks: HTMLConversionCallbacks {
        static func makeURL(string: String) -> URL? {
            // Converting WebURL to URL is a small but non-trivial expense (since it works by
            // serializing the WebURL as a string and then having Foundation parse it again),
            // so, if available, use the system parser which doesn't require another round trip.
            if #available(iOS 16.0, macOS 13.0, *),
               let url = try? URL.ParseStrategy().parse(string) {
                url
            } else if let web = WebURL(string),
                      let url = URL(web) {
                url
            } else {
                URL(string: string)
            }
        }
        
        static func elementAction(name: String, attributes: [Attribute]) -> ElementAction {
            guard name == "span" else {
                return .default
            }
            let clazz = attributes.attributeValue(for: "class")
            if clazz == "invisible" {
                return .skip
            } else if clazz == "ellipsis" {
                return .append("…")
            } else {
                return .default
            }
        }
    }
}