LineReader

LineReader

public struct LineReader {
    enum Error: Swift.Error {
        case cannotOpenFile(URL)
    }

    private let subject = PassthroughSubject<String, LineReader.Error>()

    var linePublisher: AnyPublisher<String, LineReader.Error> {
        subject.eraseToAnyPublisher()
    }

    public func read(file: URL, lines linesToRead: Int? = nil) {
        guard let filePointer: UnsafeMutablePointer<FILE> = fopen(file.path, "r") else {
            subject.send(completion: .failure(.cannotOpenFile(file)))
            return
        }

        var buffer: UnsafeMutablePointer<CChar>? = nil
        var cap: Int = 0
        var bytesRead = getline(&buffer, &cap, filePointer)

        var readLines = 0
        while bytesRead > 0 {
            if linesToRead == readLines {
                break
            }
            let str = String(cString: buffer!).trimmingCharacters(in: .newlines)
            subject.send(str)
            bytesRead = getline(&buffer, &cap, filePointer)
            readLines += 1
        }

        subject.send(completion: .finished)
    }
}