Monitor a folder for new files

FolderMonitor.swift

import Foundation

class FolderMonitor {
    private var monitoredFolderURL: URL
    private var folderMonitorQueue: DispatchQueue
    private var folderMonitorSource: DispatchSourceFileSystemObject?
    private var lastFileList: [String] = []

    init(folderURL: URL) {
        self.monitoredFolderURL = folderURL
        self.folderMonitorQueue = DispatchQueue(label: "FolderMonitorQueue", attributes: .concurrent)
        updateLastFileList()
    }

    private func updateLastFileList() {
        do {
            let fileList = try FileManager.default.contentsOfDirectory(atPath: monitoredFolderURL.path)
            self.lastFileList = fileList
        } catch {
            print("Failed to fetch file list: \(error)")
        }
    }

    func startMonitoring(completion: @escaping (String) -> Void) {
        let fileDescriptor = open(monitoredFolderURL.path, O_EVTONLY)
        guard fileDescriptor != -1 else {
            print("Unable to open file descriptor.")
            return
        }

        folderMonitorSource = DispatchSource.makeFileSystemObjectSource(fileDescriptor: fileDescriptor, eventMask: .write, queue: folderMonitorQueue)

        folderMonitorSource?.setEventHandler { [weak self] in
            guard let self = self else { return }
            do {
                let currentFileList = try FileManager.default.contentsOfDirectory(atPath: self.monitoredFolderURL.path)
                let newFiles = currentFileList.filter { !self.lastFileList.contains($0) }
                self.lastFileList = currentFileList // Update the last known file list

                // Notify for each new file found
                newFiles.forEach { newFile in
                    let fullPath = self.monitoredFolderURL.appendingPathComponent(newFile).path
                    completion(fullPath)
                }
            } catch {
                print("Error listing directory contents: \(error)")
            }
        }

        folderMonitorSource?.setCancelHandler {
            close(fileDescriptor)
        }

        folderMonitorSource?.resume()
    }

    func stopMonitoring() {
        folderMonitorSource?.cancel()
        folderMonitorSource = nil
    }
}

// Example usage
let folderURL = URL(fileURLWithPath: "/path/to/your/folder")
let folderMonitor = FolderMonitor(folderURL: folderURL)

folderMonitor.startMonitoring { filePath in
    print("A new file has been created at: \(filePath)")
}

// To stop monitoring, you can call:
// folderMonitor.stopMonitoring()