ServerSentEvents.swift

import AsyncHTTPClient
import Foundation

struct ServerSentEvent {
    let name: String
    let data: String

    init(_ substring: Substring) {
        let lines = substring.split(whereSeparator: \.isNewline)
        self.name = String(lines
            .filter({ $0.starts(with: "event: ") })
            .map({ $0.dropFirst("event: ".count) })
            .joined())
        self.data = String(lines
            .filter({ $0.starts(with: "data: ") })
            .map({ $0.dropFirst("data: ".count) })
            .joined())
    }
}

private let validNewlineCharacters = ["\r\n", "\n", "\r"]
private let delimiters = validNewlineCharacters.map { "\($0)\($0)" }

func findEvents(in substring: inout Substring) -> [ServerSentEvent] {
    var foundEvents: [ServerSentEvent] = []
    while true {
        let firstMatch = delimiters.compactMap({ substring.range(of: $0) }).first
        guard let firstMatch else { break }

        let eventContent = substring[..<firstMatch.lowerBound]
        substring = substring[firstMatch.lowerBound...]
        substring.removeFirst(2)
        foundEvents.append(ServerSentEvent(eventContent))
    }
    return foundEvents
}


extension HTTPClientResponse {
    var serverSentEvents: AsyncStream<ServerSentEvent> {
        AsyncStream(ServerSentEvent.self, { continuation in
            Task {
                var string = Substring()
                for try await buffer in self.body {

                    string += String(buffer: buffer)
                    let events = findEvents(in: &string)

                    for event in events {
                        if event.data == "[DONE]" {
                            continuation.finish()
                        } else {
                            continuation.yield(event)
                        }
                    }
                }
                // throw error if there is one -- test this
                if !(200..<300).contains(status.code)  {
                    throw StatusCodeError(code: Int(status.code), jsonData: Data(string.utf8))
                }
            }
        })
    }
}