//
//  NSManagedObject+FetchHelpers.swift
//  CoreDataStack
//
//  Created by Robert Edwards on 9/21/16.
//  Copyright © 2015-2016 Big Nerd Ranch. All rights reserved.
//

import Foundation

import CoreData

/**
 Extends `NSFetchRequestResult` with
 methods that make fetching, inserting, deleting, and change management easier.
 */
@available(iOS, introduced: 10.0)
@available(tvOS, introduced: 10.0)
@available(OSX, introduced: 10.12)
extension NSFetchRequestResult where Self: NSManagedObject {
    /**
     Creates a new fetch request for the `NSManagedObject` entity.

     - parameter context: `NSManagedObjectContext` to create the object within.

     - returns: `NSFetchRequest`: The new fetch request.
     */
    static public func fetchRequestForEntity(inContext context: NSManagedObjectContext) -> NSFetchRequest<Self> {
        let fetchRequest = NSFetchRequest<Self>()
        fetchRequest.entity = entity()
        return fetchRequest
    }

    /**
     Fetches the first Entity that matches the optional predicate within the specified `NSManagedObjectContext`.

     - parameter context: `NSManagedObjectContext` to find the entities within.
     - parameter predicate: An optional `NSPredicate` for filtering

     - throws: Any error produced from `executeFetchRequest`

     - returns: `Self?`: The first entity that matches the optional predicate or `nil`.
     */
    static public func findFirstInContext(_ context: NSManagedObjectContext, predicate: NSPredicate? = nil) throws -> Self? {
        let fetchRequest = fetchRequestForEntity(inContext: context)
        fetchRequest.predicate = predicate
        fetchRequest.fetchLimit = 1
        fetchRequest.returnsObjectsAsFaults = false
        fetchRequest.fetchBatchSize = 1
        return try context.fetch(fetchRequest).first
    }

    /**
     Fetches all Entities within the specified `NSManagedObjectContext`.

     - parameter context: `NSManagedObjectContext` to find the entities within.
     - parameter sortDescriptors: Optional array of `NSSortDescriptors` to apply to the fetch
     - parameter predicate: An optional `NSPredicate` for filtering

     - throws: Any error produced from `executeFetchRequest`

     - returns: `[Self]`: The array of matching entities.
     */
    static public func allInContext(_ context: NSManagedObjectContext, predicate: NSPredicate? = nil, sortDescriptors: [NSSortDescriptor]? = nil) throws -> [Self] {
        let fetchRequest = fetchRequestForEntity(inContext: context)
        fetchRequest.sortDescriptors = sortDescriptors
        fetchRequest.predicate = predicate
        return try context.fetch(fetchRequest)
    }

    // MARK: - Counting Objects

    /**
     Returns count of Entities that matches the optional predicate within the specified `NSManagedObjectContext`.

     - parameter context: `NSManagedObjectContext` to count the entities within.
     - parameter predicate: An optional `NSPredicate` for filtering

     - throws: Any error produced from `countForFetchRequest`

     - returns: `Int`: Count of entities that matches the optional predicate.
     */
    static public func countInContext(_ context: NSManagedObjectContext, predicate: NSPredicate? = nil) throws -> Int {
        let fetchReqeust = fetchRequestForEntity(inContext: context)
        fetchReqeust.includesSubentities = false
        fetchReqeust.predicate = predicate
        return try context.count(for: fetchReqeust)
    }

    // MARK: - Removing Objects

    /**
     Removes all entities from within the specified `NSManagedObjectContext`.

     - parameter context: `NSManagedObjectContext` to remove the entities from.

     - throws: Any error produced from `executeFetchRequest`
     */
    static public func removeAllInContext(_ context: NSManagedObjectContext) throws {
        let fetchRequest = fetchRequestForEntity(inContext: context)
        try removeAllObjectsReturnedByRequest(fetchRequest, inContext: context)
    }

    /**
     Removes all entities from within the specified `NSManagedObjectContext` excluding a supplied array of entities.

     - parameter context: The `NSManagedObjectContext` to remove the Entities from.
     - parameter except: An Array of `NSManagedObjects` belonging to the `NSManagedObjectContext` to exclude from deletion.

     - throws: Any error produced from `executeFetchRequest`
     */
    static public func removeAllInContext(_ context: NSManagedObjectContext, except toKeep: [Self]) throws {
        let fetchRequest = fetchRequestForEntity(inContext: context)
        fetchRequest.predicate = NSPredicate(format: "NOT (self IN %@)", toKeep)
        try removeAllObjectsReturnedByRequest(fetchRequest, inContext: context)
    }

    // MARK: Private Funcs

    static private func removeAllObjectsReturnedByRequest(_ fetchRequest: NSFetchRequest<Self>, inContext context: NSManagedObjectContext) throws {
        // A batch delete would be more efficient here on iOS 9 and up
        //  however it complicates things since the request requires a context with
        //  an NSPersistentStoreCoordinator directly connected. (MOC cannot be a child of another MOC)
        fetchRequest.includesPropertyValues = false
        fetchRequest.includesSubentities = false
        try context.fetch(fetchRequest).lazy.forEach(context.delete(_:))
    }
}