From 93b6c5447904ce7e383477ae34a11dc9c8f1482b Mon Sep 17 00:00:00 2001
From: Lucien Greathouse <me@lpghatguy.com>
Date: Fri, 18 May 2018 12:27:18 -0700
Subject: [PATCH] Flip middleware execution order

---
 CHANGELOG.md          |  1 +
 docs/api-reference.md | 10 +++++++++-
 lib/Store.lua         |  3 ++-
 lib/Store.spec.lua    | 38 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5fb3509..bdbdae1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@
 	* Thunks are no longer enabled by default, use `Rodux.thunkMiddleware` to add them back.
 	* Added `Rodux.loggerMiddleware` as a simple debugger
 	* The middleware API changed in [#29](https://github.com/Roblox/rodux/pull/29) in a backwards-incompatible way!
+		* Middleware now run left-to-right instead of right-to-left!
 * Errors thrown in `changed` event now have correct stack traces ([#27](https://github.com/Roblox/rodux/pull/27))
 
 ## Public Release (December 13, 2017)
diff --git a/docs/api-reference.md b/docs/api-reference.md
index fb1f508..b56d033 100644
--- a/docs/api-reference.md
+++ b/docs/api-reference.md
@@ -153,7 +153,7 @@ local reducer = createReducer(initialState, {
 ```
 
 ## Middleware
-Rodux provides an API that allows changing the way that actions are dispatched called *middleware*. To attach middlewares to a store, pass a list of middleware as the third argument to `Store.new`.
+Rodux provides an API that allows changing the way that actions are dispatched called *middleware*. To attach middleware to a store, pass a list of middleware as the third argument to `Store.new`.
 
 !!! warn
 	The middleware API changed in [#29](https://github.com/Roblox/rodux/pull/29) -- middleware written against the old API will not work!
@@ -180,6 +180,14 @@ end
 
 Rodux also ships with several middleware that address common use-cases.
 
+To apply middleware, pass a list of middleware as the third argument to `Store.new`:
+
+```lua
+local store = Store.new(reducer, initialState, { simpleLogger })
+```
+
+Middleware runs from left to right when an action is dispatched. That means that if a middleware does not call `nextDispatch` when handling an action, any middleware after it will not run.
+
 ### Rodux.loggerMiddleware
 A middleware that logs actions and the new state that results from them.
 
diff --git a/lib/Store.lua b/lib/Store.lua
index c688540..90aa02f 100644
--- a/lib/Store.lua
+++ b/lib/Store.lua
@@ -53,7 +53,8 @@ function Store.new(reducer, initialState, middlewares)
 			return unboundDispatch(self, ...)
 		end
 
-		for _, middleware in ipairs(middlewares) do
+		for i = #middlewares, 1, -1 do
+			local middleware = middlewares[i]
 			dispatch = middleware(dispatch, self)
 		end
 
diff --git a/lib/Store.spec.lua b/lib/Store.spec.lua
index c7aa014..5e7a5fd 100644
--- a/lib/Store.spec.lua
+++ b/lib/Store.spec.lua
@@ -85,6 +85,44 @@ return function()
 			store:destruct()
 		end)
 
+		it("should execute middleware left-to-right", function()
+			local events = {}
+
+			local function reducer(state)
+				return state
+			end
+
+			local function middlewareA(nextDispatch, store)
+				table.insert(events, "instantiate a")
+				return function(action)
+					table.insert(events, "execute a")
+					return nextDispatch(action)
+				end
+			end
+
+			local function middlewareB(nextDispatch, store)
+				table.insert(events, "instantiate b")
+				return function(action)
+					table.insert(events, "execute b")
+					return nextDispatch(action)
+				end
+			end
+
+			local store = Store.new(reducer, 5, { middlewareA, middlewareB })
+
+			expect(#events).to.equal(2)
+			expect(events[1]).to.equal("instantiate b")
+			expect(events[2]).to.equal("instantiate a")
+
+			store:dispatch({
+				type = "test",
+			})
+
+			expect(#events).to.equal(4)
+			expect(events[3]).to.equal("execute a")
+			expect(events[4]).to.equal("execute b")
+		end)
+
 		it("should send an initial action with a 'type' field", function()
 			local lastAction
 			local callCount = 0