From 080b231ceb51ca8ce995d46492833d9b5530162b Mon Sep 17 00:00:00 2001
From: Arnout Roemers <roemers@zorgdomein.nl>
Date: Fri, 24 Jul 2020 20:39:58 +0200
Subject: [PATCH] Skip redefinition of defstate when active

---
 CHANGELOG.md         |  7 +++++++
 README.md            |  2 ++
 project.clj          |  2 +-
 src/redelay/core.clj | 20 +++++++++++++++-----
 4 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2a79b7d..a7a2228 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # Change Log
 
+## 1.0.3
+
+### Added
+
+- Trying to redefine an active (i.e. realized) `defstate` is skipped and yields a warning.
+
+
 ## 1.0.2
 
 ### Fixed
diff --git a/README.md b/README.md
index 67129a3..0100530 100644
--- a/README.md
+++ b/README.md
@@ -118,6 +118,8 @@ Therefore the above can also be written as follows:
 ```
 
 Users of [mount](https://github.com/tolitius/mount) or [mount-lite](https://github.com/aroemers/mount-lite) will recognize above syntax.
+Trying to redefine a `defstate` which is active (i.e. realized) is skipped.
+
 The `defstate` macro fully supports metadata on the name, a docstring and an attribute map.
 Note that this metadata is set on the var.
 If you want metadata on a State, you can use **a `:meta` expression** in the body of the `state` macro, or use Clojure's `with-meta` on it.
diff --git a/project.clj b/project.clj
index 0a5a6f5..1555b11 100644
--- a/project.clj
+++ b/project.clj
@@ -1,4 +1,4 @@
-(defproject functionalbytes/redelay "1.0.2"
+(defproject functionalbytes/redelay "1.0.3"
   :description "Clojure library for first class lifecycle-managed state."
   :url "https://github.com/aroemers/redelay"
   :license {:name "EPL-2.0 OR GPL-2.0-or-later WITH Classpath-exception-2.0"
diff --git a/src/redelay/core.clj b/src/redelay/core.clj
index d4421ee..a5f3048 100644
--- a/src/redelay/core.clj
+++ b/src/redelay/core.clj
@@ -87,9 +87,15 @@
           (recur qualifiers (rest exprs) qualifier (update qualified qualifier (fnil conj []) expr))))
       qualified)))
 
+(declare state?)
+
+(defn- skip-defstate? [ns name]
+  (let [state (some-> (ns-resolve ns name) deref)]
+    (and (state? state) (realized? state))))
+
 ;;; Public API
 
-(defn  state*
+(defn state*
   "Low-level function to create a State object. All keys are optional.
   The `:start-fn` value must be a 0-arity function. The `:stop-fn`
   value must be a 1-arity function. The `:meta` value must be a map."
@@ -131,12 +137,16 @@
   "Create a State object, using the optional :start, :stop and :meta
   expressions, and bind it to a var with the given name in the current
   namespace. Supports metadata on the name, a docstring and an
-  attribute map."
+  attribute map. Trying to redefine an active (i.e. realized) defstate
+  is skipped."
   {:arglists '([name doc-string? attr-map? body])}
   [name & exprs]
-  (let [[name exprs] (name-with-exprs name exprs)]
-    `(def ~name
-       (state ~@exprs :name ~(symbol (str *ns*) (str name))))))
+  (if (skip-defstate? *ns* name)
+    (binding [*out* *err*]
+      (println "WARNING: skipping redefinition of active defstate" name))
+    (let [[name exprs] (name-with-exprs name exprs)]
+      `(def ~name
+         (state ~@exprs :name ~(symbol (str *ns*) (str name)))))))
 
 ;;; Default management.