//
//  Persistence.swift
//  Shared
//
//  Created by Trey Tartt on 1/5/22.
//

import CoreData

struct PersistenceController {
    static let shared = PersistenceController.persistenceController
    
    private static var persistenceController: PersistenceController {
#if targetEnvironment(simulator)
        return PersistenceController(inMemory: false)
#else
        return PersistenceController(inMemory: false)
#endif

    }
    
    public var viewContext: NSManagedObjectContext {
        return PersistenceController.shared.container.viewContext
    }
    
    public func add(mood: Mood, forDate date: Date) {
        let newItem = MoodEntry(context: viewContext)
        newItem.timestamp = Date()
        newItem.moodValue = Int16(mood.rawValue)
        newItem.date = date
        
        do {
            try viewContext.save()
        } catch {
            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
    }
    
    public func moodEntries(forStartDate date: Date, count: Int) -> [MoodEntry] {
        let fetchRequest = NSFetchRequest<MoodEntry>(entityName: "MoodEntry")

        fetchRequest.fetchLimit = count
        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "date", ascending: false)]

        var calendar = Calendar.current
        calendar.timeZone = NSTimeZone.local

        let dateFrom = calendar.startOfDay(for: Date())

        // Set predicate as date being today's date
        let fromPredicate = NSPredicate(format: "date <= %@", dateFrom as NSDate)
        let datePredicate = NSCompoundPredicate(andPredicateWithSubpredicates: [fromPredicate])
        fetchRequest.predicate = datePredicate
        let entries = try! viewContext.fetch(fetchRequest)
        
        if entries.count >= count {
            return Array(entries)
        } else {
            return entries
        }
    }
    
    func populateTestData() {
        for idx in 1..<25 {
            let newItem = MoodEntry(context: viewContext)
            newItem.timestamp = Date()
            newItem.moodValue = Int16(Mood.allValues.randomElement()!.rawValue)
            newItem.date = Calendar.current.date(byAdding: .day, value: -idx, to: Date())
        }
        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)")
        }
    }
    
    func populateMemory() {
        for idx in 1..<25 {
            let newItem = MoodEntry(context: viewContext)
            newItem.timestamp = Calendar.current.date(byAdding: .day, value: -idx, to: Date())
            newItem.moodValue = Int16(Mood.allValues.randomElement()!.rawValue)
            newItem.date = Calendar.current.date(byAdding: .day, value: -idx, to: Date())
        }
        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)")
        }
    }
    
    func fillInMissingDates() {
        let fetchRequest = NSFetchRequest<MoodEntry>(entityName: "MoodEntry")
        fetchRequest.sortDescriptors = [NSSortDescriptor(key: "date", ascending: false)]
        let entries = try! viewContext.fetch(fetchRequest)
        
        if let earliestDate = entries.last?.date {
            let diffInDays = Calendar.current.dateComponents([.day], from: earliestDate, to: Date()).day
            
            for idx in 1..<diffInDays! {
                let searchDay = Calendar.current.date(byAdding: .day, value: -idx, to: Date())
                if entries.filter({ Calendar.current.isDate($0.date!, inSameDayAs:searchDay!) }).isEmpty {
                    self.add(mood: .missing, forDate: searchDay!)
                }
            }
        }
    }
    
    func clearDB() {
        let fetchRequest: NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: "MoodEntry")
        let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
        
        do {
            try viewContext.executeAndMergeChanges(using: deleteRequest)
            try viewContext.save()
        } catch let error as NSError {
            fatalError("Unresolved error \(error), \(error.userInfo)")
        }
    }
    
    public func randomEntries(count: Int) -> [MoodEntry] {
        var entries = [MoodEntry]()
        
        for idx in 0..<count {
            let newItem = MoodEntry(context: viewContext)
            newItem.timestamp = Calendar.current.date(byAdding: .day, value: -idx, to: Date())
            newItem.moodValue = Int16(Mood.allValues.randomElement()!.rawValue)
            newItem.date = Calendar.current.date(byAdding: .day, value: -idx, to: Date())
            entries.append(newItem)
        }
        return entries
    }
    
    let container: NSPersistentCloudKitContainer
    
    init(inMemory: Bool = false) {
        container = NSPersistentCloudKitContainer(name: "Feels")
        if inMemory {
            container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
        }
        container.viewContext.automaticallyMergesChangesFromParent = true
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as 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 NSManagedObjectContext {
    
    /// Executes the given `NSBatchDeleteRequest` and directly merges the changes to bring the given managed object context up to date.
    ///
    /// - Parameter batchDeleteRequest: The `NSBatchDeleteRequest` to execute.
    /// - Throws: An error if anything went wrong executing the batch deletion.
    public func executeAndMergeChanges(using batchDeleteRequest: NSBatchDeleteRequest) throws {
        batchDeleteRequest.resultType = .resultTypeObjectIDs
        let result = try execute(batchDeleteRequest) as? NSBatchDeleteResult
        let changes: [AnyHashable: Any] = [NSDeletedObjectsKey: result?.result as? [NSManagedObjectID] ?? []]
        NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [self])
    }
}