Properly create reactive cursor.

We should be patching SynchronousCursor's forEach and count only, but
from SynchronousCursor one cannot access observeChanges. So we have to
patch Cursor itself.

Author: mitar

package.js

@@ -20,6 +20,13 @@ Package.onUse(function (api) {
     'peerlibrary:server-autorun@0.2.2'
   ], 'server');
 
+  // Package can be used without PeerDB. But if PeerDB is available, make
+  // sure it is loaded before this package so that PeerDB adds "exists"
+  // to the cursor before we make it reactive.
+  api.use([
+    'peerlibrary:peerdb@0.19.1'
+  ], 'server', {'weak': true});
+
   api.addFiles([
     'server.coffee'
   ], 'server');

server.coffee

@@ -1,9 +1,13 @@
 MeteorCursor = Object.getPrototypeOf(MongoInternals.defaultRemoteCollectionDriver().mongo.find()).constructor
 
 originalObserveChanges = MeteorCursor::observeChanges
-originalForEach = MeteorCursor::forEach
 originalCount = MeteorCursor::count
 
+# This is a PeerDB extension. It might not exist if the package is used without PeerDB.
+# But we defined a week dependency on PeerDB so that it is loaded before this package
+# to that PeerDB adds this extension before we get here.
+originalExists = MeteorCursor::exists
+
 MeteorCursor::_isReactive = ->
   # By default we make all cursors reactive. But you can
   # still disable that, the same as on the client.
@@ -37,20 +41,32 @@ MeteorCursor::observeChanges = (options) ->
       handle.stop()
   handle
 
-MeteorCursor::forEach = (args...) ->
-  if @_isReactive()
-    @_depend
-      addedBefore: true
-      removed: true
-      changed: true
-      movedBefore: true
+for method in ['forEach', 'map', 'fetch']
+  do (method) ->
+    originalMethod = MeteorCursor::[method]
+    MeteorCursor::[method] = (args...) ->
+      if @_isReactive()
+        @_depend
+          addedBefore: true
+          removed: true
+          changed: true
+          movedBefore: true
 
-   originalForEach.apply @, args
+      originalMethod.apply @, args
 
 MeteorCursor::count = (args...) ->
   if @_isReactive()
     @_depend
       added: true
       removed: true
 
-   originalCount.apply @, args
+  originalCount.apply @, args
+
+if originalExists
+  MeteorCursor::exists = (args...) ->
+    if @_isReactive()
+      @_depend
+        added: true
+        removed: true
+
+    originalExists.apply @, args