CoreStore/Sources/Transactions/AsynchronousDataTransaction.swift

//
//  AsynchronousDataTransaction.swift
//  CoreStore
//
//  Copyright © 2015 John Rommel Estropia
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

import Foundation
import CoreData


// MARK: - AsynchronousDataTransaction

/**
 The `AsynchronousDataTransaction` provides an interface for `NSManagedObject` creates, updates, and deletes. A transaction object should typically be only used from within a transaction block initiated from `DataStack.beginAsynchronous(_:)`, or from `CoreStore.beginAsynchronous(_:)`.
 */
public final class AsynchronousDataTransaction: BaseDataTransaction {
    
    /**
     Saves the transaction changes. This method should not be used after the `commit()` method was already called once.
     
     - parameter completion: the block executed after the save completes. Success or failure is reported by the `SaveResult` argument of the block.
     */
    public func commit(_ completion: @escaping (_ result: SaveResult) -> Void = { _ in }) {
        
        CoreStore.assert(
            self.transactionQueue.cs_isCurrentExecutionContext(),
            "Attempted to commit a \(cs_typeName(self)) outside its designated queue."
        )
        CoreStore.assert(
            !self.isCommitted,
            "Attempted to commit a \(cs_typeName(self)) more than once."
        )
        
        self.isCommitted = true
        let group = DispatchGroup()
        group.enter()
        self.context.saveAsynchronouslyWithCompletion { (result) -> Void in
            
            self.result = result
            completion(result)
            group.leave()
        }
        group.wait()
    }
    
    /**
     Begins a child transaction synchronously where NSManagedObject creates, updates, and deletes can be made. This method should not be used after the `commit()` method was already called once.
     
     - parameter closure: the block where creates, updates, and deletes can be made to the transaction. Transaction blocks are executed serially in a background queue, and all changes are made from a concurrent `NSManagedObjectContext`.
     - returns: a `SaveResult` value indicating success or failure, or `nil` if the transaction was not comitted synchronously
     */
    @discardableResult
    public func beginSynchronous(_ closure: @escaping (_ transaction: SynchronousDataTransaction) -> Void) -> SaveResult? {
        
        CoreStore.assert(
            self.transactionQueue.cs_isCurrentExecutionContext(),
            "Attempted to begin a child transaction from a \(cs_typeName(self)) outside its designated queue."
        )
        CoreStore.assert(
            !self.isCommitted,
            "Attempted to begin a child transaction from an already committed \(cs_typeName(self))."
        )
        
        return SynchronousDataTransaction(
            mainContext: self.context,
            queue: self.childTransactionQueue,
            closure: closure).performAndWait()
    }
    
    
    // MARK: BaseDataTransaction
    
    /**
     Creates a new `NSManagedObject` with the specified entity type.
     
     - parameter into: the `Into` clause indicating the destination `NSManagedObject` entity type and the destination configuration
     - returns: a new `NSManagedObject` instance of the specified entity type.
     */
    public override func create<T: NSManagedObject>(_ into: Into<T>) -> T {
        
        CoreStore.assert(
            !self.isCommitted,
            "Attempted to create an entity of type \(cs_typeName(into.entityClass)) from an already committed \(cs_typeName(self))."
        )
        
        return super.create(into)
    }
    
    /**
     Returns an editable proxy of a specified `NSManagedObject`. This method should not be used after the `commit()` method was already called once.
     
     - parameter object: the `NSManagedObject` type to be edited
     - returns: an editable proxy for the specified `NSManagedObject`.
     */
    public override func edit<T: NSManagedObject>(_ object: T?) -> T? {
        
        CoreStore.assert(
            !self.isCommitted,
            "Attempted to update an entity of type \(cs_typeName(object)) from an already committed \(cs_typeName(self))."
        )
        
        return super.edit(object)
    }
    
    /**
     Returns an editable proxy of the object with the specified `NSManagedObjectID`. This method should not be used after the `commit()` method was already called once.
     
     - parameter into: an `Into` clause specifying the entity type
     - parameter objectID: the `NSManagedObjectID` for the object to be edited
     - returns: an editable proxy for the specified `NSManagedObject`.
     */
    public override func edit<T: NSManagedObject>(_ into: Into<T>, _ objectID: NSManagedObjectID) -> T? {
        
        CoreStore.assert(
            !self.isCommitted,
            "Attempted to update an entity of type \(cs_typeName(into.entityClass)) from an already committed \(cs_typeName(self))."
        )
        
        return super.edit(into, objectID)
    }
    
    /**
     Deletes a specified `NSManagedObject`. This method should not be used after the `commit()` method was already called once.
     
     - parameter object: the `NSManagedObject` type to be deleted
     */
    public override func delete(_ object: NSManagedObject?) {
        
        CoreStore.assert(
            !self.isCommitted,
            "Attempted to delete an entity of type \(cs_typeName(object)) from an already committed \(cs_typeName(self))."
        )
        
        super.delete(object)
    }
    
    /**
     Deletes the specified `NSManagedObject`s.
     
     - parameter object1: the `NSManagedObject` type to be deleted
     - parameter object2: another `NSManagedObject` type to be deleted
     - parameter objects: other `NSManagedObject`s type to be deleted
     */
    public override func delete(_ object1: NSManagedObject?, _ object2: NSManagedObject?, _ objects: NSManagedObject?...) {
        
        CoreStore.assert(
            !self.isCommitted,
            "Attempted to delete an entities from an already committed \(cs_typeName(self))."
        )
        
        super.delete(([object1, object2] + objects).flatMap { $0 })
    }
    
    /**
     Deletes the specified `NSManagedObject`s.
     
     - parameter objects: the `NSManagedObject`s type to be deleted
     */
    public override func delete<S: Sequence>(_ objects: S) where S.Iterator.Element: NSManagedObject {
        
        CoreStore.assert(
            !self.isCommitted,
            "Attempted to delete an entities from an already committed \(cs_typeName(self))."
        )
        
        super.delete(objects)
    }
    
    
    // MARK: Internal
    
    internal init(mainContext: NSManagedObjectContext, queue: DispatchQueue, closure: @escaping (_ transaction: AsynchronousDataTransaction) -> Void) {
        
        self.closure = closure
        
        super.init(mainContext: mainContext, queue: queue, supportsUndo: false, bypassesQueueing: false)
    }
    
    internal func perform() {
        
        self.transactionQueue.async {
            
            self.closure(self)
            if !self.isCommitted && self.hasChanges {
                
                CoreStore.log(
                    .warning,
                    message: "The closure for the \(cs_typeName(self)) completed without being committed. All changes made within the transaction were discarded."
                )
            }
        }
    }
    
    internal func performAndWait() -> SaveResult? {
        
        self.transactionQueue.sync {
            
            self.closure(self)
            
            if !self.isCommitted && self.hasChanges {
                
                CoreStore.log(
                    .warning,
                    message: "The closure for the \(cs_typeName(self)) completed without being committed. All changes made within the transaction were discarded."
                )
            }
        }
        return self.result
    }
    
    
    // MARK: Private
    
    private let closure: (_ transaction: AsynchronousDataTransaction) -> Void
}