From ffc36fce369aa6e48ce28e9bae4e69a11c9348bb Mon Sep 17 00:00:00 2001
From: Tommi Reiman <tommi@iki.fi>
Date: Sun, 18 Nov 2018 22:19:30 +0200
Subject: [PATCH] Support composable transformations of mw/interceptor chain

* fixes #167
---
 CHANGELOG.md                                  |  4 ++++
 .../reitit-core/src/reitit/interceptor.cljc   | 11 +++++----
 .../reitit-core/src/reitit/middleware.cljc    | 13 +++++-----
 test/cljc/reitit/interceptor_test.cljc        | 24 +++++++++++++------
 test/cljc/reitit/middleware_test.cljc         |  7 +++++-
 5 files changed, 40 insertions(+), 19 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2924dc91..b64b1820 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 ## UNRELEASED
 
+## `reitit-core`
+
+* Added support for composing middleware & interceptor transformations, fixes [#167](https://github.com/metosin/reitit/issues/167).
+
 ## `reitit-spec`
 
 * Spec problems are exposed as-is into request & response coercion errors, enabling pretty-printers like [expound](https://github.com/bhb/expound) to be used:
diff --git a/modules/reitit-core/src/reitit/interceptor.cljc b/modules/reitit-core/src/reitit/interceptor.cljc
index f45fe74c..c1829e49 100644
--- a/modules/reitit-core/src/reitit/interceptor.cljc
+++ b/modules/reitit-core/src/reitit/interceptor.cljc
@@ -110,11 +110,12 @@
   ([interceptors data]
    (chain interceptors data nil))
   ([interceptors data {:keys [::transform] :or {transform identity} :as opts}]
-   (->> interceptors
-        (keep #(into-interceptor % data opts))
-        (transform)
-        (keep #(into-interceptor % data opts))
-        (into []))))
+   (let [transform (if (vector? transform) (apply comp (reverse transform)) transform)]
+     (->> interceptors
+          (keep #(into-interceptor % data opts))
+          (transform)
+          (keep #(into-interceptor % data opts))
+          (into [])))))
 
 (defn compile-result
   ([route opts]
diff --git a/modules/reitit-core/src/reitit/middleware.cljc b/modules/reitit-core/src/reitit/middleware.cljc
index f429aac1..d9bdc66d 100644
--- a/modules/reitit-core/src/reitit/middleware.cljc
+++ b/modules/reitit-core/src/reitit/middleware.cljc
@@ -84,12 +84,13 @@
 
 (defn- expand-and-transform
   [middleware data {:keys [::transform] :or {transform identity} :as opts}]
-  (->> middleware
-       (keep #(into-middleware % data opts))
-       (into [])
-       (transform)
-       (keep #(into-middleware % data opts))
-       (into [])))
+  (let [transform (if (vector? transform) (apply comp (reverse transform)) transform)]
+    (->> middleware
+         (keep #(into-middleware % data opts))
+         (into [])
+         (transform)
+         (keep #(into-middleware % data opts))
+         (into []))))
 
 (defn- compile-handler [middleware handler]
   ((apply comp identity (keep :wrap middleware)) handler))
diff --git a/test/cljc/reitit/interceptor_test.cljc b/test/cljc/reitit/interceptor_test.cljc
index 639db51d..3eed9ae7 100644
--- a/test/cljc/reitit/interceptor_test.cljc
+++ b/test/cljc/reitit/interceptor_test.cljc
@@ -222,19 +222,29 @@
                                               (enter ::kerran)
                                               (enter ::avaruus)]
                                :handler handler}]
-                     options)))]
+                     options)))
+        inject-debug (fn [interceptors]
+                       (concat
+                         (interleave (butlast interceptors) (repeat debug-i))
+                         [(last interceptors)]))
+        sort-interceptors (fn [interceptors]
+                            (concat
+                              (sort-by :name (butlast interceptors))
+                              [(last interceptors)]))]
 
     (testing "by default, all interceptors are applied in order"
       (let [app (create nil)]
         (is (= [::olipa ::kerran ::avaruus :ok] (app "/ping")))))
 
     (testing "interceptors can be re-ordered"
-      (let [app (create {::interceptor/transform (fn [interceptors]
-                                                   (concat
-                                                     (sort-by :name (butlast interceptors))
-                                                     [(last interceptors)]))})]
+      (let [app (create {::interceptor/transform sort-interceptors})]
         (is (= [::avaruus ::kerran ::olipa :ok] (app "/ping")))))
 
     (testing "adding debug interceptor between interceptors"
-      (let [app (create {::interceptor/transform #(interleave % (repeat debug-i))})]
-        (is (= [::olipa ::debug ::kerran ::debug ::avaruus ::debug :ok] (app "/ping")))))))
+      (let [app (create {::interceptor/transform inject-debug})]
+        (is (= [::olipa ::debug ::kerran ::debug ::avaruus ::debug :ok] (app "/ping")))))
+
+    (testing "vector of transformations"
+      (let [app (create {::interceptor/transform [inject-debug
+                                                  sort-interceptors]})]
+        (is (= [::avaruus ::debug ::debug ::debug ::kerran ::olipa :ok] (app "/ping")))))))
diff --git a/test/cljc/reitit/middleware_test.cljc b/test/cljc/reitit/middleware_test.cljc
index 11f75c7f..7933ed2b 100644
--- a/test/cljc/reitit/middleware_test.cljc
+++ b/test/cljc/reitit/middleware_test.cljc
@@ -254,4 +254,9 @@
 
     (testing "adding debug middleware between middleware"
       (let [app (create {::middleware/transform #(interleave % (repeat debug-mw))})]
-        (is (= [::olipa ::debug ::kerran ::debug ::avaruus ::debug :ok] (app "/ping")))))))
+        (is (= [::olipa ::debug ::kerran ::debug ::avaruus ::debug :ok] (app "/ping")))))
+
+    (testing "vector of transformations"
+      (let [app (create {::middleware/transform [#(interleave % (repeat debug-mw))
+                                                 (partial sort-by :name)]})]
+        (is (= [::avaruus ::debug ::debug ::debug ::kerran ::olipa :ok] (app "/ping")))))))