//

//  CoreDataStack.swift

//  CoreDataStackDemo

//

//  Created by wangbiao on 15/10/29.

//  Copyright © 2015年 wangbiao. All rights reserved.

//

import CoreData

class CoreDataStack: NSObject {

    // MARK: - Properties

    let context: NSManagedObjectContext

    let coordinator: NSPersistentStoreCoordinator

    let model: NSManagedObjectModel

    let store: NSPersistentStore?

    // MARK: - Singleton

    static func defaultStack() -> CoreDataStack {

        return instance

    }

    fileprivate static let instance = CoreDataStack()

    fileprivate override init() {

        // 构建托管对象模型

        let bundle = Bundle.main

        let modelURL = bundle.url(forResource: "Test", withExtension: "momd")!

        model = NSManagedObjectModel(contentsOf: modelURL)!

        // 构建持久化存储助理

        coordinator = NSPersistentStoreCoordinator(managedObjectModel: model)

        // 构建托管对象上下文，并且将助理连接到上下文

        context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)

        context.persistentStoreCoordinator = coordinator

        // 构建持久化存储

        let manager = FileManager.default

        let urls = manager.urls(for: .documentDirectory, in: .userDomainMask)

        let documentsURL = urls.first!

        let storeURL = documentsURL.appendingPathComponent("Test")

        store = (try! coordinator.addPersistentStore(ofType: NSSQLiteStoreType,

            configurationName: nil, at: storeURL, options: nil))

    }

    // MARK: - Function

    func saveContext () {

        if context.hasChanges {

            do {

                try context.save()

            } catch {

                print("Save failed...")

            }

        }

    }

}

//新增数据

func insertStudent(sno: String, name: String, score: Int) {

        // 获取上下文（也就是从”coreData基础“里面的那个类里面获取）

        let context = CoreDataStack.defaultStack().context

        // 构建实体对象

        let student = NSEntityDescription.insertNewObject(forEntityName: "Student",

            into: context) as! Student

        // 设置相关属性

        student.sno = sno

        student.name = name

        student.score = score as NSNumber?

    }

// 查询数据

    func fetchStudents() {

        // 获取上下文

        let context = CoreDataStack.defaultStack().context

        // 构建抓取请求

        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Student")

        // 指定按照学号(sno)升序排列

        let sort = NSSortDescriptor(key: "sno", ascending: true,

            selector: #selector(NSString.localizedStandardCompare(_:)))

        request.sortDescriptors = [sort]

        // 构建查询条件

//        request.predicate = NSPredicate(format: "score > 60")

//        request.predicate = NSPredicate(format: "name like 'a*'")

        do {

            let students = (try context.fetch(request)) as! [Student]

            for student in students {

                print("\(student.sno!), \(student.name!), \(student.score!)")

            }

        } catch {

            print("Fetch failed...")

        }

    }

// 统计信息

    func countStudents() {

//        // 1. 统计分数大于90的人数

//

//        // 获取上下文

//        let context = CoreDataStack.defaultStack().context

//

//        // 构建抓取请求

//        let request = NSFetchRequest(entityName: "Student")

//        request.predicate = NSPredicate(format: "score > 90")

//        request.resultType = .CountResultType

//

//        do {

//            let entries = (try context.executeFetchRequest(request))

//            let count = entries.first!.integerValue

//            print("Count: \(count)")

//        } catch {

//            print("Fetch failed...")

//        }

        // 2. 计算平均分数

        // 获取上下文

        let context = CoreDataStack.defaultStack().context

        // 构建抓取请求

        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Student")

        request.resultType = .dictionaryResultType // 指定返回结果为字典

        // 构建表达式

        let description = NSExpressionDescription()

        description.name = "AverageScore"

        let args = [NSExpression(forKeyPath: "score")]

        description.expression = NSExpression(forFunction: "average:", arguments: args)

        description.expressionResultType = .floatAttributeType // 指定返回值类型

        // 将求平均值的表达式设置给request的属性

        request.propertiesToFetch = [description]

        do {

            let entries = (try context.fetch(request))

            let result = entries.first! as! NSDictionary

            let averageScore = result["AverageScore"]!

            print("Average: \(averageScore)")

        } catch {

            print("Fetch failed...")

        }

    }

// 修改数据

    func updateStudents() {

        // 获取上下文

        let context = CoreDataStack.defaultStack().context

        // 构建抓取请求

        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Student")

        request.predicate = NSPredicate(format: "name like 'a*'")

        do {

            let students = (try context.fetch(request)) as! [Student]

            for student in students {

                student.score =

            }

        } catch {

            print("Fetch failed...")

        }

        // 保存

        CoreDataStack.defaultStack().saveContext()

        // 备注: 批量更新 & 异步操作 ???

    }

    // 删除数据

    func deleteStudents() {

        // 获取上下文

        let context = CoreDataStack.defaultStack().context

        // 构建抓取请求

        let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Student")

        request.predicate = NSPredicate(format: "score < 60")

        do {

            let students = (try context.fetch(request)) as! [Student]

            for student in students {

                context.delete(student)

            }

        } catch {

            print("Fetch failed...")

        }

        // 保存

        CoreDataStack.defaultStack().saveContext()

    }