From 2eef88a269572754a1379120acb72a16e633f75c Mon Sep 17 00:00:00 2001
From: Brent Vukmer <brent.vukmer@gmail.com>
Date: Thu, 29 Apr 2021 12:22:42 -0400
Subject: [PATCH] Resolves #4; guards synchronize operation inside
 schema.core/converge against the case where c1 is from a remote node.

---
 src/schism/core.cljc       | 13 ++++++++++++-
 test/schism/core_test.cljc | 16 +++++++++++++++-
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/schism/core.cljc b/src/schism/core.cljc
index af43c3d..dff5f3b 100644
--- a/src/schism/core.cljc
+++ b/src/schism/core.cljc
@@ -57,6 +57,15 @@
   [& args]
   (apply nvector/new-vector args))
 
+(defn- is-local-node?
+      [n]
+      "Checks the most recent update in this entity's vector clock. Returns true if that most recent update is not from most-recent schism.node/*current-node*"
+      (let [most-recent (->> (into [] (sp/get-clock n))
+                             (sort-by second)
+                             last
+                             first)]
+           (= most-recent schism.node/*current-node*)))
+
 (defn converge
   "Return a converged copy of `c1` containing the modifications of
   `c2`. Convergence is defined on a per-type basis. If `c1` has
@@ -71,7 +80,9 @@
   - The current value of `schism.node/*current-node*` is shared with
   another node making modifications to the same logical collection."
   [c1 c2]
-  (sp/synchronize c1 c2))
+      (if (is-local-node? c1)
+        (sp/synchronize c1 c2)
+        (throw (IllegalArgumentException. "The most recent update in c1's vector clock is not from the local node. schism.core/converge expects the c1 param to be the local node and the c2 param to be the remote node. Please check whether you have reversed that order."))))
 
 (def initialize-node!
   "Initialize the current node to an edn serializable value if
diff --git a/test/schism/core_test.cljc b/test/schism/core_test.cljc
index 50c9852..69b400c 100644
--- a/test/schism/core_test.cljc
+++ b/test/schism/core_test.cljc
@@ -29,7 +29,21 @@
   #?(:cljs (gen/such-that #(not (js/Number.isNaN %)) gen/any)
      :clj gen/any))
 
-
+(deftest handles-non-local-copy-as-first-param
+         (let [m1 (schism/with-node "LOCAL" (schism/convergent-map :foo "bar", :a "b"))
+               _ (Thread/sleep 1)
+               m2 (schism/with-node "NOT LOCAL" (schism/convergent-map :y 2, :z 3, :x 1))]
+              (testing "FIXME, I fail."
+                       (is
+                         (thrown-with-msg? IllegalArgumentException
+                                           #"The most recent update in c1's vector clock is not from the local node. schism.core/converge expects the c1 param to be the local node and the c2 param to be the remote node. Please check whether you have reversed that order."
+                                           (schism/with-node "LOCAL" (schism/converge m2 m1))))
+                       ;; We haven't broken existing code in the case where the order is correct (c1 is the local node)
+                       (is (= {:y 2, :z 3, :x 1}
+                              (->>
+                                (schism/with-node "LOCAL" (schism/converge m1 m2))
+                                seq
+                                (into {})))))))
 
 (defspec convergent-set-is-equivalent-to-hash-set
   50