Webhooks: use external meeting ID as key in the mappings

It changes less than the internal meeting ID. An application can subscribe
to an external ID and use the hook for several different meetings that will
have the same external ID but different internal IDs.

labs/bbb-callback/meeting_id_map.coffee

@@ -3,33 +3,36 @@ redis = require("redis")
 
 config = require("./config")
 
-# The database of mappings. Format:
-# { internalMeetingID: externalMeetingID }
+# The database of mappings. Uses the externalID as key because it changes less than
+# the internal ID (e.g. the internalID can change for different meetings in the same
+# room). Format:
+#   { externalMeetingID: internalMeetingID }
 db = {}
 
 # A simple model to store mappings for meeting IDs.
 module.exports = class MeetingIDMap
 
   @addOrUpdateMapping = (internalMeetingID, externalMeetingID) ->
-    db[internalMeetingID] = externalMeetingID
-    console.log "MeetingIDMap: added or changed meeting mapping to the list { #{internalMeetingID}: #{db[internalMeetingID]} }"
+    db[externalMeetingID] = internalMeetingID
+    console.log "MeetingIDMap: added or changed meeting mapping to the list { #{externalMeetingID}: #{db[externalMeetingID]} }"
     MeetingIDMap.updateRedis()
 
   @removeMapping = (internalMeetingID) ->
-    if internalMeetingID in _.keys(db)
-      console.log "MeetingIDMap: removing meeting mapping from the list { #{internalMeetingID}: #{db[internalMeetingID]} }"
-      delete db[internalMeetingID]
-      db[internalMeetingID] = null
+    for external, internal of db
+      if internalMeetingID is internal
+        console.log "MeetingIDMap: removing meeting mapping from the list { #{external}: #{db[external]} }"
+        delete db[external]
+        db[external] = null
         MeetingIDMap.updateRedis()
 
   @getInternalMeetingID = (externalMeetingID) ->
-    for internal, external of db
-      if external is externalMeetingID
-        return internal
-    null
+    db[externalMeetingID]
 
   @getExternalMeetingID = (internalMeetingID) ->
-    db[internalMeetingID]
+    for external, internal of db
+      if internal is internalMeetingID
+        return external
+    null
 
   @initialize = (callback) ->
     MeetingIDMap.resync(callback)