class GCDDataManager {
    var data: [[String : String]]
    var queue: DispatchQueue
    init(_ dataForFile: [[String : String]], _ queueForFiles: DispatchQueue) {
        data = dataForFile
        queue = queueForFiles
    }

    let file = "data.json"

    func writeData() -> Bool{
        var success: Bool
        success = false
        queue.sync(flags: .barrier) {
            guard let documentDirectoryUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return }
            let fileUrl = documentDirectoryUrl.appendingPathComponent(file)
            do {
                let data = try JSONSerialization.data(withJSONObject: self.data, options: [])
                try data.write(to: fileUrl, options: [])
                success = true
            } catch {
                print(error)
            }
        }
        return success
    }

    func readData() -> [[String : String]]? {
        var success: Bool
        success = false
        var data: [[String : String]]
        data = [["" : ""]]
        queue.sync(flags: .barrier) {
            let fileUrl = Bundle.main.path(forResource: "data", ofType: "json”)

            // Read data from .json file and transform data into an array
            do {
                let data = try Data(contentsOf: fileUrl, options: [])
                guard (try JSONSerialization.jsonObject(with: data, options: []) as? [[String: [String: String]]]) != nil else { return }
                success = true
            } catch {
                print(error)
            }
        }
        if success {
            return data
        }
        else {
            return nil
        }
    }
}