//
//  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

/// 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 _containerURL: URL?
    
    fileprivate var _cloudStorageDetermined: Bool = false
    
    fileprivate let containerIdentifier = "notes"
    
    fileprivate var _timer: Timer? = nil
    
    fileprivate var _storageRequests: [String : String] = [:]
    
    init() {
        DispatchQueue.global(qos: .userInteractive).async {
            self._containerURL = FileManager.default.url(forUbiquityContainerIdentifier: self.containerIdentifier)
            self._cloudStorageDetermined = true
            print("Cloud container URL is : \(String(describing: self._containerURL?.absoluteString))")
        }
    }
    
    fileprivate func _directoryURL() throws -> URL {
        let documentDirectory = try FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
        return documentDirectory
    }
    
    // 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._containerURL else {
            return
        }
        let cloudURL = containerURL.appending(path: filename)
        try FileManager.default.copyItem(at: fileURL, to: cloudURL)
        print("cloud copy to: \(cloudURL)")
    }
    
    deinit {
        self._timer?.invalidate()
    }

}