Added OnChangeAnalytics

README.md

@@ -55,6 +55,34 @@ As most analytics will probably be events without any properties the `AnalyticsD
 
 As a personal preference,  I tend to use `default: return nil` at the end of it. `nil` is returned from the `AnalyticsReducer` for any action/state combination when you don't want it to send analytics. So it is a lot more convenient to wrap them all up in a `default` case at the end of the switch rather than list out all the actions and return `nil` from each.
 
+### On Change Analytics
+
+You can no trigger analytics from the change of state.
+
+If your state is like...
+
+```
+struct State {
+  var count: Int
+}
+```
+
+You can now add analytics when the count changes by adding a `.analyticsOnChange` to your reducer.
+
+```
+Reduce<State, Action> { state, action in
+  // feature reducer 
+}
+.analyticsOnChange(of: \.count) { oldValue, newValue in
+  return .event(
+    name: "countChanged", 
+    properties: [
+    "from": "\(oldValue)",
+    "to": "\(newValue)",
+	)
+}
+```
+
 ## Custom Analytics Clients
 
 This package only provides an analytics client for logging to the console. Accessible as `AnalyticsClient.consoleLogger` but you can very easily add your own custom clients.

Sources/ComposableAnalytics/AnalyticsReducer.swift

@@ -1,6 +1,5 @@
 import Foundation
 import ComposableArchitecture
-import XCTestDynamicOverlay
 
 public struct AnalyticsReducer<State, Action>: Reducer {
 	@usableFromInline

Sources/ComposableAnalytics/OnChangeReducer.swift

@@ -0,0 +1,53 @@
+import Foundation
+import ComposableArchitecture
+
+extension Reducer {
+	@inlinable
+	public func analyticsOnChange<V: Equatable>(
+		of toValue: @escaping (State) -> V,
+		_ toAnalyticsData: @escaping (V, V) -> AnalyticsData
+	) -> _OnChangeAnalyticsReducer<Self, V> {
+		_OnChangeAnalyticsReducer(base: self, toValue: toValue, isDuplicate: ==, toAnalyticsData: toAnalyticsData)
+	}
+}
+
+public struct _OnChangeAnalyticsReducer<Base: Reducer, Value: Equatable>: Reducer {
+	@usableFromInline
+	let base: Base
+
+	@usableFromInline
+	let toValue: (Base.State) -> Value
+
+	@usableFromInline
+	let isDuplicate: (Value, Value) -> Bool
+
+	@usableFromInline
+	@Dependency(\.analyticsClient) var analyticsClient
+
+	@usableFromInline
+	let toAnalyticsData: (Value, Value) -> AnalyticsData
+
+	@usableFromInline
+	init(
+		base: Base,
+		toValue: @escaping (Base.State) -> Value,
+		isDuplicate: @escaping (Value, Value) -> Bool,
+		toAnalyticsData: @escaping (Value, Value) -> AnalyticsData
+	) {
+		self.base = base
+		self.toValue = toValue
+		self.isDuplicate = isDuplicate
+		self.toAnalyticsData = toAnalyticsData
+	}
+
+	@inlinable
+	public func reduce(into state: inout Base.State, action: Base.Action) -> Effect<Base.Action> {
+		let oldValue = toValue(state)
+		let effects = self.base.reduce(into: &state, action: action)
+		let newValue = toValue(state)
+
+		return isDuplicate(oldValue, newValue)
+		? effects
+		: effects.merge(with: .run { _ in analyticsClient.sendAnalytics(toAnalyticsData(oldValue, newValue)) })
+	}
+}