added Publishers for addStorage functions

Sources/DataStack.AddStoragePublisher.swift

@@ -0,0 +1,238 @@
+//
+//  DataStack.AddStoragePublisher.swift
+//  CoreStore
+//
+//  Copyright © 2021 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.
+//
+
+#if canImport(Combine)
+import Combine
+import CoreData
+
+
+// MARK: - DataStack
+
+@available(iOS 13.0, tvOS 13.0, watchOS 6.0, macOS 10.15, *)
+extension DataStack {
+    
+    // MARK: - AddStoragePublisher
+    
+    /**
+     A `Publisher` that emits a `ListSnapshot` whenever changes occur in the `ListPublisher`.
+     
+     - SeeAlso: DataStack.reactive.addStorage(_:)     
+     */
+    public struct AddStoragePublisher<Storage: LocalStorage>: Publisher {
+        
+        // MARK: Internal
+        
+        internal let dataStack: DataStack
+        internal let storage: Storage
+        
+        
+        // MARK: Publisher
+        
+        public typealias Output = Progress
+        public typealias Failure = CoreStoreError
+        
+        public func receive<S: Subscriber>(subscriber: S) where S.Input == Output, S.Failure == Failure {
+            
+            subscriber.receive(
+                subscription: AddStorageSubscription(
+                    dataStack: self.dataStack,
+                    storage: self.storage,
+                    subscriber: subscriber
+                )
+            )
+        }
+        
+        // MARK: - Progress
+        
+        /**
+         A `Progress` contains info on a `LocalStorage`'s setup progress.
+         
+         - SeeAlso: DataStack.reactive.addStorage(_:)
+         */
+        public enum Progress {
+            
+            /**
+             The `LocalStorage` is currently being migrated
+             */
+            case migrating(storage: Storage, progressObject: Foundation.Progress)
+            
+            /**
+             The `LocalStorage` has been added to the `DataStack` and is ready for reading and writing
+             */
+            case finished(storage: Storage, migrationRequired: Bool)
+            
+            /**
+             The fraction of the overall work completed by the migration. Returns a value between 0.0 and 1.0, inclusive.
+             */
+            public var fractionCompleted: Double {
+                
+                switch self {
+                
+                case .migrating(_, let progressObject):
+                    return progressObject.fractionCompleted
+                    
+                case .finished:
+                    return 1
+                }
+            }
+            
+            /**
+             Returns `true` if the storage was successfully added to the stack, `false` otherwise.
+             */
+            public var isCompleted: Bool {
+                
+                switch self {
+                
+                case .migrating:
+                    return false
+                    
+                case .finished:
+                    return true
+                }
+            }
+        }
+        
+        
+        // MARK: - AddStorageSubscriber
+        
+        fileprivate final class AddStorageSubscriber: Subscriber {
+            
+            // MARK: Subscriber
+            
+            typealias Failure = CoreStoreError
+            
+            func receive(subscription: Subscription) {
+                
+                subscription.request(.unlimited)
+            }
+            
+            func receive(_ input: Output) -> Subscribers.Demand {
+                
+                return .unlimited
+            }
+            
+            func receive(completion: Subscribers.Completion<Failure>) {}
+        }
+        
+        
+        // MARK: - AddStorageSubscription
+        
+        fileprivate final class AddStorageSubscription<S: Subscriber>: Subscription where S.Input == Output, S.Failure == CoreStoreError {
+            
+            // MARK: FilePrivate
+            
+            init(
+                dataStack: DataStack,
+                storage: Storage,
+                subscriber: S
+            ) {
+                
+                self.dataStack = dataStack
+                self.storage = storage
+                self.subscriber = subscriber
+            }
+            
+            
+            // MARK: Subscription
+            
+            func request(_ demand: Subscribers.Demand) {
+                
+                guard demand > 0 else {
+                    
+                    return
+                }
+                var progress: Foundation.Progress?
+                progress = self.dataStack.addStorage(
+                    self.storage,
+                    completion: { [weak self] result in
+                        
+                        guard
+                            let self = self,
+                            let subscriber = self.subscriber
+                        else {
+                            
+                            return
+                        }
+                        switch result {
+                        
+                        case .success(let storage):
+                            _ = subscriber.receive(
+                                .finished(
+                                    storage: storage,
+                                    migrationRequired: progress != nil
+                                )
+                            )
+                            subscriber.receive(
+                                completion: .finished
+                            )
+                            
+                        case .failure(let error):
+                            subscriber.receive(
+                                completion: .failure(error)
+                            )
+                        }
+                    }
+                )
+                guard let progress = progress else {
+                    
+                    return
+                }
+                progress.cs_setProgressHandler { [weak self] progress in
+                    
+                    guard
+                        let self = self,
+                        let subscriber = self.subscriber
+                    else {
+                        
+                        return
+                    }
+                    _ = subscriber.receive(
+                        .migrating(
+                            storage: self.storage,
+                            progressObject: progress
+                        )
+                    )
+                }
+            }
+            
+            
+            // MARK: Cancellable
+            
+            func cancel() {
+                
+                self.subscriber = nil
+            }
+            
+            
+            // MARK: Private
+            
+            private let dataStack: DataStack
+            private let storage: Storage
+            private var subscriber: S?
+        }
+    }
+}
+
+#endif