SideStore/Sources/SideStoreCore/Protocols/Fetchable.swift

//
//  NSManagedObject+Conveniences.swift
//  AltStore
//
//  Created by Riley Testut on 6/6/19.
//  Copyright © 2019 Riley Testut. All rights reserved.
//

import CoreData

public typealias FetchRequest = NSFetchRequest<NSFetchRequestResult>

public protocol Fetchable: NSManagedObject {}

public extension Fetchable {
    static func first(satisfying predicate: NSPredicate? = nil, sortedBy sortDescriptors: [NSSortDescriptor]? = nil, in context: NSManagedObjectContext,
                      requestProperties: [PartialKeyPath<FetchRequest>: Any?] = [:]) -> Self? {
        let managedObjects = Self.all(satisfying: predicate, sortedBy: sortDescriptors, in: context, requestProperties: requestProperties, returnFirstResult: true)
        return managedObjects.first
    }

    static func all(satisfying predicate: NSPredicate? = nil, sortedBy sortDescriptors: [NSSortDescriptor]? = nil, in context: NSManagedObjectContext,
                    requestProperties: [PartialKeyPath<FetchRequest>: Any?] = [:]) -> [Self] {
        let managedObjects = Self.all(satisfying: predicate, sortedBy: sortDescriptors, in: context, requestProperties: requestProperties, returnFirstResult: false)
        return managedObjects
    }

    static func fetch(_ fetchRequest: NSFetchRequest<Self>, in context: NSManagedObjectContext) -> [Self] {
        do {
            let managedObjects = try context.fetch(fetchRequest)
            return managedObjects
        } catch {
            print("Failed to fetch managed objects. Fetch Request: \(fetchRequest). Error: \(error).")
            return []
        }
    }

    private static func all(satisfying predicate: NSPredicate? = nil, sortedBy sortDescriptors: [NSSortDescriptor]? = nil, in context: NSManagedObjectContext, requestProperties: [PartialKeyPath<FetchRequest>: Any?], returnFirstResult: Bool) -> [Self] {
        let registeredObjects = context.registeredObjects.lazy.compactMap { $0 as? Self }.filter { predicate?.evaluate(with: $0) != false }

        if let managedObject = registeredObjects.first, returnFirstResult {
            return [managedObject]
        }

        let fetchRequest = self.fetchRequest() as! NSFetchRequest<Self>
        fetchRequest.predicate = predicate
        fetchRequest.sortDescriptors = sortDescriptors
        fetchRequest.returnsObjectsAsFaults = false

        for (keyPath, value) in requestProperties {
            // Still no easy way to cast PartialKeyPath back to usable WritableKeyPath :(
            guard let objcKeyString = keyPath._kvcKeyPathString else { continue }
            fetchRequest.setValue(value, forKey: objcKeyString)
        }

        let fetchedObjects = fetch(fetchRequest, in: context)

        if let fetchedObject = fetchedObjects.first, returnFirstResult {
            return [fetchedObject]
        } else {
            return fetchedObjects
        }
    }
}