FetchComment-Custom-Combine-Publisher.swift

struct FetchComment: Publisher {
    typealias Output = CommentItem
    typealias Failure = Error

    //1
    let id: Int
    let nlTagger: NLTagger

    func receive<S>(subscriber: S) where S: Subscriber, Failure == S.Failure, Output == S.Input {
        let request = URLRequest(url: URL(string: "https://hacker-news.firebaseio.com/v0/item/\(id).json")!)
        URLSession.DataTaskPublisher(request: request, session: URLSession.shared)
            .map { $0.data }
            .decode(type: CommentItem.self, decoder: JSONDecoder())
            .map{
                commentItem in
 
                //2
                let data = Data(commentItem.text?.utf8 ?? "".utf8)
                var commentString = commentItem.text
                
                
                if let attributedString = try? NSAttributedString(data: data, options: [.documentType: NSAttributedString.DocumentType.html], documentAttributes: nil) {
                    commentString = attributedString.string
                }
                
                //3
                self.nlTagger.string = commentString

                var sentimentScore = ""
                if let string = self.nlTagger.string{
                    //4
                    let (sentiment,_) = self.nlTagger.tag(at: string.startIndex, unit: .paragraph, scheme: .sentimentScore)
                    sentimentScore = sentiment?.rawValue ?? ""
                }

                //5
                let result = CommentItem(id: commentItem.id, text: commentString, sentimentScore: sentimentScore)
                return result
            }
            .print()
            .receive(subscriber: subscriber)
    }
}