JustOneThing/Model/PersistenceController.swift

//
//  PersistenceController.swift
//  JustOneThing
//
//  Created by Alan Francis on 07/07/2023.
//

import CoreData

//MARK: - URL Extension
// https://developer.apple.com/forums/thread/78120
// There's an issue with tvOS and the path to the local DB.
// This little extension encapsulates that
public extension URL {
    /// Returns a URL for the given app group and database pointing to the sqlite database.
    static func storeURL(for appGroup: String, databaseName: String) -> URL {
        var containerUrl:URL
        
        guard let initialContainer = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: appGroup) else {
            fatalError("Shared file container could not be created.")
        }

        #if os(tvOS)
           containerUrl = initialContainer.appendingPathComponent("Library/Caches")
        #else
            containerUrl = initialContainer
        #endif
    
        return containerUrl.appendingPathComponent("\(databaseName).sqlite")
    }
}

//MARK: - PeristenceController
struct PersistenceController {
    let container: NSPersistentCloudKitContainer

    init(inMemory: Bool = false) {
        container = NSPersistentCloudKitContainer(name: "JustOneThingCloudModel")

        if inMemory {
            container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
        } else {
            let url = URL.storeURL(for: "group.com.alancfrancis.apps.JustOneThing", databaseName: "JustOneThingCloudModel")
            container.persistentStoreDescriptions.first!.url = url
        }
        
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                Self.processError(error:error)
            }
        })

        container.viewContext.automaticallyMergesChangesFromParent = true
    }
}

//MARK: - static convenience
extension PersistenceController {
    static let shared = PersistenceController()
    
    var viewContext:NSManagedObjectContext {
        get {
            container.viewContext
        }
    }
}

//MARK: - error handling
extension PersistenceController {
    static func processError(error:NSError) {
        // Replace this implementation with code to handle the error appropriately.
        // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.

        /*
         Typical reasons for an error here include:
         * The parent directory does not exist, cannot be created, or disallows writing.
         * The persistent store is not accessible, due to permissions or data protection when the device is locked.
         * The device is out of space.
         * The store could not be migrated to the current model version.
         Check the error message to determine what the actual problem was.
         */
        fatalError("Unresolved error \(error), \(error.userInfo)")
    }
}


extension PersistenceController {
    static var preview: PersistenceController = {
        let result = PersistenceController(inMemory: true)
        let viewContext = result.container.viewContext
        var i = 1
        for _ in 0..<10 {
            let newItem = PersistentThing(context: viewContext)
            newItem.text = "action \(i)"
            newItem.createdAt = Date()
            newItem.uuid = UUID()
            i = i+1
        }
        do {
            try viewContext.save()
        } catch {
            // Replace this implementation with code to handle the error appropriately.
            // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
        return result
    }()
}