From bc6cec22f2580e7413336b2ec13c2c01f2653ffa Mon Sep 17 00:00:00 2001
From: Alex Usbergo <alexusbergo@alexusbergo-imacpro.roam.corp.google.com>
Date: Tue, 19 May 2020 10:19:05 +0200
Subject: [PATCH] Template Actions

---
 Sources/Store/TemplateActions.swift | 68 +++++++++++++++++------------
 1 file changed, 40 insertions(+), 28 deletions(-)

diff --git a/Sources/Store/TemplateActions.swift b/Sources/Store/TemplateActions.swift
index be28a8f..e588882 100644
--- a/Sources/Store/TemplateActions.swift
+++ b/Sources/Store/TemplateActions.swift
@@ -3,68 +3,60 @@ import os.log
 
 // MARK: - Template Actions
 
+public enum KeyPath<M, V> {
+  /// A non-optional writeable keyPath.
+  case value(keyPath: WritableKeyPath<M, V>)
+  /// A optional writeable keyPath.
+  case optional(keyPath: WritableKeyPath<M, V?>)
+}
 
 /// General-purpose actions that can be applied to any store.
 public struct TemplateAction {
-  
-  public struct AssignKeyPath<M, V>: ActionProtocol {
-    public let keyPath: WritableKeyPath<M, V>
-    public let value: V
 
-    public func reduce(context: TransactionContext<Store<M>, Self>) {
-      defer { context.fulfill() }
-      context.reduceModel { model in model[keyPath: keyPath] = value }
-    }
-  }
-  
-  public struct AssignOptionalKeyPath<M, V>: ActionProtocol {
-    public let keyPath: WritableKeyPath<M, V?>
+  public struct AssignKeyPath<M, V>: ActionProtocol {
+    public let keyPath: KeyPath<M, V>
     public let value: V?
 
     public func reduce(context: TransactionContext<Store<M>, Self>) {
       defer { context.fulfill() }
-      context.reduceModel { model in model[keyPath: keyPath] = value }
+      context.reduceModel { model in
+        _assignKeyPath(object: &model, keyPath: keyPath, value: value)
+      }
     }
   }
   
   public struct Filter<M, V: Collection, T>: ActionProtocol where V.Element == T {
-    public let keyPath: WritableKeyPath<M, V>
+    public let keyPath: KeyPath<M, V>
     public let isIncluded: (T) -> Bool
     
     public func reduce(context: TransactionContext<Store<M>, Self>) {
       defer { context.fulfill() }
       context.reduceModel { model in
-        _mutateArray(object: &model, keyPath: keyPath) { array in
-          array = array.filter(isIncluded)
-        }
+        _mutateArray(object: &model, keyPath: keyPath) { $0 = $0.filter(isIncluded) }
       }
     }
   }
   
   public struct RemoveAtIndex<M, V: Collection, T>: ActionProtocol where V.Element == T {
-    public let keyPath: WritableKeyPath<M, V>
+    public let keyPath: KeyPath<M, V>
     public let index: Int
     
     public func reduce(context: TransactionContext<Store<M>, Self>) {
       defer { context.fulfill() }
       context.reduceModel { model in
-        _mutateArray(object: &model, keyPath: keyPath) { array in
-          array.remove(at: index)
-        }
+        _mutateArray(object: &model, keyPath: keyPath) { $0.remove(at: index) }
       }
     }
   }
   
   public struct Push<M, V: Collection, T>: ActionProtocol where V.Element == T {
-    public let keyPath: WritableKeyPath<M, V>
+    public let keyPath: KeyPath<M, V>
     public let object: T
 
     public func reduce(context: TransactionContext<Store<M>, Self>) {
       defer { context.fulfill() }
       context.reduceModel { model in
-        _mutateArray(object: &model, keyPath: keyPath) { array in
-          array.append(object)
-        }
+        _mutateArray(object: &model, keyPath: keyPath) { $0.append(object) }
       }
     }
   }
@@ -72,15 +64,35 @@ public struct TemplateAction {
 
 private func _mutateArray<M, V: Collection, T>(
   object: inout M,
-  keyPath: WritableKeyPath<M, V>,
+  keyPath: KeyPath<M, V>,
   mutate: (inout [T]) -> Void
 ) where V.Element == T  {
-  guard var array = object[keyPath: keyPath] as? [T] else {
+  var value: V
+  switch keyPath {
+  case .value(let keyPath): value = object[keyPath: keyPath]
+  case .optional(let keyPath):
+    guard let unwrapped = object[keyPath: keyPath] else { return }
+    value = unwrapped
+  }
+  guard var array = value as? [T] else {
     os_log(.error, log: OSLog.primary, " Arrays are the only collection type supported.")
     return
   }
   mutate(&array)
   // Trivial cast.
   guard let collection = array as? V else { return }
-  object[keyPath: keyPath] = collection
+  switch keyPath {
+  case .value(let keyPath): object[keyPath: keyPath] = collection
+  case .optional(let keyPath): object[keyPath: keyPath] = collection
+  }
+}
+
+private func _assignKeyPath<M, V>(object: inout M, keyPath: KeyPath<M, V>, value: V?) {
+  switch keyPath {
+  case .value(let keyPath):
+    guard let value = value else { return }
+    object[keyPath: keyPath] = value
+  case .optional(let keyPath):
+    object[keyPath: keyPath] = value
+  }
 }