Proof of concept: Auto execute on "# => " snippet expansion

Needs to be cleaned up, this was just to see if it is possible, which it is.
I'm committing it on a branch to maybe prompt consideration in the snippets package.
It seems like maybe the way to do this for real would be for the snippets package
to emit an event for did-expand-snippet. Though I don't fully grasp how all the
pieces fit together.

For context, see:
  #25
  atom/snippets#221

lib/seeing-is-believing.coffee

@@ -43,10 +43,25 @@ module.exports = SeeingIsBelieving =
   activate: ->
     @notifications = []
     @subscriptions = new CompositeDisposable
+    # The snippets package subscribes to "atom-text-editor"
+    # what's the difference? Sounds like it's what we actually want and would let
+    # us get rid fo teh `return unless editor` check down below
     @subscriptions.add atom.commands.add 'atom-workspace',
       'seeing-is-believing:annotate-document':       => @run [],
       'seeing-is-believing:annotate-magic-comments': => @run ['--xmpfilter-style'],
       'seeing-is-believing:remove-annotations':      => @run ['--clean']
+    @subscriptions.add atom.commands.onDidDispatch (event) =>
+      return unless event.type == "snippets:expand"
+      editor = atom.workspace.getActiveTextEditor()         # I think we can assume this since snippets:expand did dispatch, note they use @getModel, to do this, but a quick glance around didn't locate it, so maybe look for it if I keep this
+      scope  = editor.getLastCursor().getScopeDescriptor()
+      scopes = scope?.getScopesArray?()                     # IDK if I need the ?s, just cargo culting their work: https://github.com/atom/snippets/blob/c93956cc7306632beede152d77a7d4f757bc70a9/lib/snippets.coffee#L193
+      return unless scopes && scopes.includes("source.ruby")
+      didExpand = false
+      editor.getCursors().forEach (cursor) =>
+        {row, column} = cursor.getBufferPosition()
+        text = editor.getTextInRange([{row, column: column-5}, {row, column: column}])
+        console.log(text)
+        @run ['--xmpfilter-style'] if text == "# => "
 
   deactivate: ->
     @subscriptions.dispose()