//
//  PersistentContainer.swift
//  Reader
//
//  Created by Shadowfacts on 12/24/21.
//

import CoreData
import Fervor

class PersistentContainer: NSPersistentContainer {
    
    private static let managedObjectModel: NSManagedObjectModel = {
        let url = Bundle.main.url(forResource: "Reader", withExtension: "momd")!
        return NSManagedObjectModel(contentsOf: url)!
    }()
    
    private(set) lazy var backgroundContext: NSManagedObjectContext = {
        let context = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
        // todo: should the background context really be parented to the view context, or should they both be direct children of the PSC?
        context.parent = self.viewContext
        return context
    }()
    
    init(account: LocalData.Account) {
        super.init(name: "\(account.id)", managedObjectModel: PersistentContainer.managedObjectModel)
        
        loadPersistentStores { description, error in
            if let error = error {
                fatalError("Unable to load persistent store: \(error)")
            }
        }
    }
    
    func sync(serverGroups: [Fervor.Group], serverFeeds: [Fervor.Feed]) async throws {
        try await backgroundContext.perform {
            let existingGroups = try self.backgroundContext.fetch(Group.fetchRequest())
            for group in serverGroups {
                if let existing = existingGroups.first(where: { $0.id == group.id }) {
                    existing.updateFromServer(group)
                } else {
                    let mo = Group(context: self.backgroundContext)
                    mo.updateFromServer(group)
                }
            }
            for removed in existingGroups where !serverGroups.contains(where: { $0.id == removed.id }) {
                self.backgroundContext.delete(removed)
            }
            
            let existingFeeds = try self.backgroundContext.fetch(Feed.fetchRequest())
            for feed in serverFeeds {
                if let existing = existingFeeds.first(where: { $0.id == feed.id }) {
                    existing.updateFromServer(feed)
                } else {
                    let mo = Feed(context: self.backgroundContext)
                    mo.updateFromServer(feed)
                }
            }
            
            if self.backgroundContext.hasChanges {
                try self.backgroundContext.save()
                try self.viewContext.save()
            }
        }
    }
    
}