From 2b20c780f4983023c6cebc9eb51532b27c7a0aa8 Mon Sep 17 00:00:00 2001
From: Jay Zawrotny <jayzawrotny@gmail.com>
Date: Thu, 13 Dec 2018 12:57:41 -0500
Subject: [PATCH] Setup middleware to warn user and fail-safely if
 cognitect.rebl is not found.

---
 src/nrebl/middleware.clj | 50 ++++++++++++++++++++++++++--------------
 1 file changed, 33 insertions(+), 17 deletions(-)

diff --git a/src/nrebl/middleware.clj b/src/nrebl/middleware.clj
index a7d3961..91fb346 100644
--- a/src/nrebl/middleware.clj
+++ b/src/nrebl/middleware.clj
@@ -1,13 +1,25 @@
 (ns nrebl.middleware
-  (:require [nrepl
+  ;; TODO: Please look at my lein-2.8.1 branch for cleanup of imports and
+  ;;       supporting legacy lein with dynamic imports.
+  (:require [clojure.tools.nrepl
              [middleware :refer [set-descriptor!]]
              [transport :as transport]]
-            [nrepl.middleware.interruptible-eval :as ev]
-            [cognitect.rebl.ui :as ui]
-            [cognitect.rebl :as rebl]
             [clojure.datafy :refer [datafy]])
   (:import
-   nrepl.transport.Transport))
+   clojure.tools.nrepl.transport.Transport))
+
+(def rebl-exists?
+  (try
+    (require '[cognitect.rebl :as rebl])
+    true
+    (catch java.io.FileNotFoundException _
+        false)))
+
+;; Ensure cognitect.rebl namespace exists
+(when-not rebl-exists?
+  (create-ns 'rebl)
+  (intern 'rebl 'submit identity)
+  (intern 'rebl 'ui identity))
 
 (defn send-to-rebl! [{:keys [code] :as req} {:keys [value] :as resp}]
   (when-let [value (datafy value)]
@@ -17,7 +29,7 @@
 (defn- wrap-rebl-sender
   "Wraps a `Transport` with code which prints the value of messages sent to
   it using the provided function."
-  [{:keys [id op ^Transport transport] :as request} ]
+  [{:keys [id op ^Transport transport] :as request}]
   (reify Transport
     (recv [this]
       (.recv transport))
@@ -28,11 +40,16 @@
              (send-to-rebl! request resp))
       this)))
 
-(defn wrap-nrebl [handler]
-  (fn [{:keys [id op transport] :as request}]
-    (if (= op "start-rebl-ui")
-      (rebl/ui)
-      (handler (assoc request :transport (wrap-rebl-sender request))))))
+(defn wrap-nrebl
+  [handler]
+  (if rebl-exists?
+    (fn [{:keys [id op transport] :as request}]
+      (cond
+        (= op "start-rebl-ui") (rebl/ui)
+        :else (handler (assoc request :transport (wrap-rebl-sender request)))))
+    (do
+      (println "WARNING: cognitect.rebl namespace was not found on classpath. nrebl.middlware could not be started.")
+      handler)))
 
 (set-descriptor! #'wrap-nrebl
                  {:requires #{}
@@ -49,17 +66,16 @@
      (-> (nrepl/client conn 1000)    ; message receive timeout required
          ;(nrepl/message {:op "inspect-nrebl" :code "[1 2 3 4 5 6 7 8 9 10 {:a :b :c :d :e #{5 6 7 8 9 10}}]"})
          (nrepl/message {:op "eval" :code "(do {:a :b :c [1 2 3 4] :d #{5 6 7 8} :e (range 20)})"})
-         nrepl/response-values
-         ))
+         nrepl/response-values))
+
 
   (with-open [conn (nrepl/connect :port 52756)]
      (-> (nrepl/client conn 1000)    ; message receive timeout required
          (nrepl/message {:op "start-rebl-ui"})
-         nrepl/response-values
-         ))
+         nrepl/response-values))
+
 
   (require '[nrepl.server :as ser])
 
   (def nrep (ser/start-server :port 55804
-                              :handler (ser/default-handler #'wrap-nrebl)))
-  )
+                              :handler (ser/default-handler #'wrap-nrebl))))