From 998938490cb15fd5d1f5ae8a8e13ad338ad5cf7e Mon Sep 17 00:00:00 2001
From: John Estropia <rommel.estropia@gmail.com>
Date: Fri, 25 Oct 2019 19:16:38 +0900
Subject: [PATCH] Make ObjectPublishers even lighter by lazy-loading observers

---
 .../NSManagedObjectContext+CoreStore.swift    |  6 +++
 Sources/ObjectPublisher.swift                 | 41 +++++++++++--------
 Sources/ObjectSnapshot.swift                  | 28 +++++++++----
 3 files changed, 49 insertions(+), 26 deletions(-)

diff --git a/Sources/NSManagedObjectContext+CoreStore.swift b/Sources/NSManagedObjectContext+CoreStore.swift
index 1e1b6d8..1e3a636 100644
--- a/Sources/NSManagedObjectContext+CoreStore.swift
+++ b/Sources/NSManagedObjectContext+CoreStore.swift
@@ -145,6 +145,12 @@ extension NSManagedObjectContext {
             )
         }
     }
+
+    @nonobjc
+    internal func objectsDidChangeObserver<U: AnyObject>(remove: U) {
+
+        _ = self.userInfo(for: .objectsChangeObserver(U.self), initialize: { nil as Any? })
+    }
     
     
     // MARK: Private
diff --git a/Sources/ObjectPublisher.swift b/Sources/ObjectPublisher.swift
index be59366..98718f5 100644
--- a/Sources/ObjectPublisher.swift
+++ b/Sources/ObjectPublisher.swift
@@ -195,6 +195,7 @@ public final class ObjectPublisher<O: DynamicObject>: ObjectRepresentation, Hash
 
     deinit {
 
+        self.context.objectsDidChangeObserver(remove: self)
         self.observers.removeAllObjects()
     }
 
@@ -221,30 +222,36 @@ public final class ObjectPublisher<O: DynamicObject>: ObjectRepresentation, Hash
 
             self.rawObjectWillChange = nil
         }
-        self.$lazySnapshot.initialize({ initializer(objectID, context) })
-        
-        context.objectsDidChangeObserver(for: self).addObserver(self) { [weak self] (updatedIDs, deletedIDs) in
+        self.$lazySnapshot.initialize { [weak self] in
 
             guard let self = self else {
 
-                return
+                return initializer(objectID, context)
             }
-            if deletedIDs.contains(objectID) {
+            context.objectsDidChangeObserver(for: self).addObserver(self) { [weak self] (updatedIDs, deletedIDs) in
 
-                self.object = nil
+                guard let self = self else {
 
-                self.willChange()
-                self.$lazySnapshot.reset({ nil })
-                self.didChange()
-                self.notifyObservers()
-            }
-            else if updatedIDs.contains(objectID) {
-
-                self.willChange()
-                self.$lazySnapshot.reset({ initializer(objectID, context) })
-                self.didChange()
-                self.notifyObservers()
+                    return
+                }
+                if deletedIDs.contains(objectID) {
+
+                    self.object = nil
+
+                    self.willChange()
+                    self.$lazySnapshot.reset({ nil })
+                    self.didChange()
+                    self.notifyObservers()
+                }
+                else if updatedIDs.contains(objectID) {
+
+                    self.willChange()
+                    self.$lazySnapshot.reset({ initializer(objectID, context) })
+                    self.didChange()
+                    self.notifyObservers()
+                }
             }
+            return initializer(objectID, context)
         }
     }
 
diff --git a/Sources/ObjectSnapshot.swift b/Sources/ObjectSnapshot.swift
index 811cbda..92dd900 100644
--- a/Sources/ObjectSnapshot.swift
+++ b/Sources/ObjectSnapshot.swift
@@ -107,6 +107,7 @@ public struct ObjectSnapshot<O: DynamicObject>: ObjectRepresentation, Hashable {
             return nil
         }
         self.id = objectID
+        self.context = context
         self.values = values
     }
 
@@ -114,6 +115,7 @@ public struct ObjectSnapshot<O: DynamicObject>: ObjectRepresentation, Hashable {
     // MARK: Private
 
     private let id: O.ObjectID
+    private let context: NSManagedObjectContext
     private var values: [String: Any]
 
     private var valuesRef: NSDictionary {
@@ -214,51 +216,59 @@ extension ObjectSnapshot where O: CoreStoreObject {
     /**
      Returns the value for the property identified by a given key.
      */
-    public subscript<OBase, D>(dynamicMember member: KeyPath<O, RelationshipContainer<OBase>.ToOne<D>>) -> D.ObjectID? {
+    public subscript<OBase, D>(dynamicMember member: KeyPath<O, RelationshipContainer<OBase>.ToOne<D>>) -> ObjectPublisher<D>? {
 
         get {
 
             let key = String(keyPath: member)
-            return self.values[key] as! D.ObjectID?
+            guard let id = self.values[key] as! D.ObjectID? else {
+
+                return nil
+            }
+            return self.context.objectPublisher(objectID: id)
         }
         set {
 
             let key = String(keyPath: member)
-            self.values[key] = newValue
+            self.values[key] = newValue?.objectID()
         }
     }
 
     /**
      Returns the value for the property identified by a given key.
      */
-    public subscript<OBase, D>(dynamicMember member: KeyPath<O, RelationshipContainer<OBase>.ToManyOrdered<D>>) -> [D.ObjectID] {
+    public subscript<OBase, D>(dynamicMember member: KeyPath<O, RelationshipContainer<OBase>.ToManyOrdered<D>>) -> [ObjectPublisher<D>] {
 
         get {
 
             let key = String(keyPath: member)
-            return self.values[key] as! [D.ObjectID]
+            let context = self.context
+            let ids = self.values[key] as! [D.ObjectID]
+            return ids.map(context.objectPublisher(objectID:))
         }
         set {
 
             let key = String(keyPath: member)
-            self.values[key] = newValue
+            self.values[key] = newValue.map({ $0.objectID() })
         }
     }
 
     /**
      Returns the value for the property identified by a given key.
      */
-    public subscript<OBase, D>(dynamicMember member: KeyPath<O, RelationshipContainer<OBase>.ToManyUnordered<D>>) -> Set<D.ObjectID> {
+    public subscript<OBase, D>(dynamicMember member: KeyPath<O, RelationshipContainer<OBase>.ToManyUnordered<D>>) -> Set<ObjectPublisher<D>> {
 
         get {
 
             let key = String(keyPath: member)
-            return self.values[key] as! Set<D.ObjectID>
+            let context = self.context
+            let ids = self.values[key] as! Set<D.ObjectID>
+            return Set(ids.map(context.objectPublisher(objectID:)))
         }
         set {
 
             let key = String(keyPath: member)
-            self.values[key] = newValue
+            self.values[key] = Set(newValue.map({ $0.objectID() }))
         }
     }
 }