import Foundation
import CoreData

protocol StorageServiceProtocol {
    
    var context: NSManagedObjectContext { get }
    func store(vehicle: Vehicle) throws -> CDVehicle
}

public class StorageService: StorageServiceProtocol {
    
    private static var instance: StorageService?
    
    private let container: NSPersistentCloudKitContainer
    
    public static var shared: StorageService {
        get async throws {
            if let instance = StorageService.instance {
                return instance
            } else {
                let service = StorageService()
                try await service.loadPersistentStores()
                StorageService.instance = service
                return service
            }
        }
    }
    
    init(inMemory: Bool = false) {
        
        let bundle = Bundle(for: Self.self)
        let url = bundle.url(forResource: "AutoCat2", withExtension: "momd")
        let mom = NSManagedObjectModel(contentsOf: url!)
        
        container = NSPersistentCloudKitContainer(name: "AutoCat2", managedObjectModel: mom!)
        if inMemory {
            container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
        }
    }
    
    private func loadPersistentStores() async throws {
        try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<Void, Error>) in
            container.loadPersistentStores(completionHandler: { (storeDescription, error) in
                if let error = error as NSError? {
                    continuation.resume(throwing: error)
                } else {
                    continuation.resume(returning: ())
                }
            })
        }
    }
    
    private func save() throws {
        guard context.hasChanges else {
            return
        }
        
        do {
            try context.save()
        } catch {
            context.rollback()
            throw error
        }
    }
    
    // MARK: - StorageServiceProtocol
    
    public var context: NSManagedObjectContext {
        container.viewContext
    }
    
    public func store(vehicle: Vehicle) throws -> CDVehicle {
        
        let cdVehicle = CDVehicle(vehicle: vehicle, context: context)
        try save()
        return cdVehicle
    }
}