notes/Notes/Storage/FileStorage.swift

//
//  CloudFileStorage.swift
//  Notes
//
//  Created by Laurent Morvillier on 16/09/2022.
//

import Foundation
import UIKit

struct StorageRequest {
    var filename: String
    var content: String
}

let idleTimeBeforeSaving = 2.0

fileprivate extension NSMetadataItem {
    
    var url: URL? {
        return self.value(forAttribute: NSMetadataItemURLKey) as? URL
    }
    
}

/// Should we have a way to go from local to iCloud?
/// https://stackoverflow.com/questions/33886846/best-way-to-use-icloud-documents-storage
/// Should we store the files locally whatever the iCloud choice is?
class FileStorage : FileOperator {
    
    static var main: FileStorage = FileStorage()
    
    fileprivate var _cloudContainerURL: URL?
    
    fileprivate var _cloudStorageDetermined: Bool = false
    
    fileprivate let containerTeamId = "notes"
    fileprivate let containerIdentifier = "notes"
    
    fileprivate var _timer: Timer? = nil
    fileprivate var _downloadTimer: Timer? = nil

    fileprivate var _downloads: [NSMetadataItem] = []
    
    fileprivate var _storageRequests: [String : String] = [:]
    
    init() {
        
        let uit = FileManager.default.ubiquityIdentityToken
        print("ubiquityIdentityToken = \(String(describing: uit))")
        
        DispatchQueue.global(qos: .userInteractive).async {
            self._cloudContainerURL = FileManager.default.url(forUbiquityContainerIdentifier: nil)
            self._cloudStorageDetermined = true
            print("Cloud container URL is : \(String(describing: self._cloudContainerURL?.absoluteString))")
            
//            self._makeLocalCopyIfNecessary()
            
        }
    }
    
    fileprivate func _directoryURL() throws -> URL {
        let documentDirectory = try FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
        return documentDirectory
    }
    
    fileprivate func _makeLocalCopyIfNecessary() {
        
        // if the local dir is not empty, do nothing
        if let docDir = try? self._directoryURL(), let files = try? FileManager.default.contentsOfDirectory(atPath: docDir.absoluteString), files.count > 0 {
            return
        }
        
        guard let _ = self._cloudContainerURL else {
            return
        }
        
        NotificationCenter.default.addObserver(self, selector: #selector(metaDataQueryNotified(notification:)), name: NSNotification.Name.NSMetadataQueryDidFinishGathering, object: nil)
        
        let query = NSMetadataQuery()
        query.searchScopes = [NSMetadataQueryUbiquitousDocumentsScope]
        query.start()
        
    }
    
    @objc func metaDataQueryNotified(notification: Notification) {
        
        guard let query = notification.object as? NSMetadataQuery else {
            print("object = \(notification.object ?? "")")
            return
        }
        
        for case let item as NSMetadataItem in query.results {
            
            if let url = item.value(forAttribute: NSMetadataItemURLKey) as? URL {
                self._downloadItem(item, url: url)
            } else {
                print("item has no URL")
            }
        }
    }
    
    
    fileprivate func _downloadItem(_ item: NSMetadataItem, url: URL) {
        do {
            try FileManager.default.startDownloadingUbiquitousItem(at: url)
            self._startStatusTimer(item: item)
        } catch {
            print("error = \(error)")
        }
    }
    
    fileprivate func _startStatusTimer(item: NSMetadataItem) {
        self._downloads.append(item)
        if self._downloadTimer == nil {
            self._downloadTimer = Timer.scheduledTimer(timeInterval: 0.5, target: self, selector: #selector(self._verifyDownloadStatus), userInfo: nil, repeats: false)
        }
    }
    
    @objc fileprivate func _verifyDownloadStatus() {
        
        let downloads = Array(self._downloads)
        
        for item in downloads {
            if item.value(forAttribute: NSMetadataUbiquitousItemDownloadingStatusKey) as? String == NSMetadataUbiquitousItemDownloadingStatusCurrent {
                
                self._makeLocalCopy(item: item)
                self._downloads.removeAll(where: { $0.url == item.url })
            }
        }
        
    }
    
    fileprivate func _makeLocalCopy(item: NSMetadataItem) {
        
        guard let fileURL = item.url, let docURL = try? self._directoryURL() else {
            return
        }
        
        do {
            try FileManager.default.copyItem(at: fileURL, to: docURL)
        } catch {
            print("error: \(error)") // TODO
        }
        
    }
    
    // MARK: - FileOperator
    
    func requestStorage(filename: String, content: String) {
        
        self._storageRequests[filename] = content
        
        self._timer?.invalidate()
        self._timer = Timer.scheduledTimer(timeInterval: idleTimeBeforeSaving, target: self, selector: #selector(self._storageRequested), userInfo: nil, repeats: false)

    }
    
    @objc fileprivate func _storageRequested() {
        
        for (filename, content) in self._storageRequests {
            do {
                try self._store(filename: filename, content: content)
            } catch {
                // TODO show errors to users, possibly by notifications
                print("error: \(error.localizedDescription)")
            }
        }
        self._storageRequests.removeAll()
    }
    
    fileprivate func _store(filename: String, content: String) throws {
        let fileURL = try self._directoryURL().appending(path: filename)
        print("Store file to: \(fileURL.absoluteString)")
        
        try content.write(to: fileURL, atomically: true, encoding: .utf8)
        
        try self._copyToCloudContainerIfNecessary(fileURL: fileURL, filename: filename)
    }
    
    func getContent(filename: String) throws -> String? {
        let fileURL = try self._directoryURL().appending(path: filename)
        return try String(contentsOf: fileURL)
    }
    
    func lastEditDate(filename: String) throws -> Date? {
        let fileURL = try self._directoryURL().appending(path: filename)
        let attributes = try FileManager.default.attributesOfItem(atPath: fileURL.absoluteString)
        return attributes[FileAttributeKey.modificationDate] as? Date
    }
    
    fileprivate func _copyToCloudContainerIfNecessary(fileURL: URL, filename: String) throws {
        guard let containerURL = self._cloudContainerURL else {
            print("cloud container is nil, stays local")
            return
        }
        let cloudURL = containerURL.appending(path: filename)
        print("cloud copy to: \(cloudURL)...")
        
//        if FileManager.default.fileExists(atPath: cloudURL.absoluteString) {
//            try FileManager.default.removeItem(at: cloudURL)
//        }
        
        try FileManager.default.copyItem(at: fileURL, to: cloudURL)
    }
    
    deinit {
        self._timer?.invalidate()
    }

}