devout: replay relevant events to new subscriber

pkgs/devout/devout.fnl

@@ -53,6 +53,9 @@
      :add (fn [_ event-string] (record-event db subscribers event-string))
      :at-path (fn [_ path] (. db path))
      :subscribe (fn [_ id callback terms]
+                  (let [past-events (find-in-database db terms)]
+                    (each [_ e (pairs past-events)]
+                      (callback e)))
                   (tset subscribers id {: callback : terms }))
      :unsubscribe (fn [_ id] (tset subscribers id nil))
      }))

pkgs/devout/test.fnl

@@ -126,6 +126,16 @@ MINOR=17")
    (db:add sdb1-remove)
    (expect= (# received) 2)))
 
+(example
+ "Subscribers get notifications of prior events for present devices"
+ (var received [])
+ (let [db (database)
+       subscriber (fn [e] (table.insert received e))]
+   (db:add sdb1-insert)
+   (db:add sda-uevent)
+   (db:subscribe :me subscriber {:devname "/dev/sdb1"})
+   (expect= (# received) 1)))
+
 (example
  "I can unsubscribe after subscribing"
  (var received [])