add proper events and make the notifier class generic

Expand the event system to have explicit Event objects and potentially
many Notifiers. Previously they was only one notifier and one (implied)
event.

A lot of this is stolen from preservim#358.

Author: scrooloose

autoload/nerdtree.vim

@@ -74,10 +74,11 @@ function! nerdtree#loadClassFiles()
     runtime lib/nerdtree/tree_dir_node.vim
     runtime lib/nerdtree/opener.vim
     runtime lib/nerdtree/creator.vim
-    runtime lib/nerdtree/refresh_notifier.vim
     runtime lib/nerdtree/flag_set.vim
     runtime lib/nerdtree/nerdtree.vim
     runtime lib/nerdtree/ui.vim
+    runtime lib/nerdtree/event.vim
+    runtime lib/nerdtree/notifier.vim
 endfunction
 
 " FUNCTION: nerdtree#postSourceActions() {{{2

lib/nerdtree/event.vim

@@ -0,0 +1,13 @@
+"CLASS: Event
+"============================================================
+let s:Event = {}
+let g:NERDTreeEvent = s:Event
+
+function! s:Event.New(nerdtree, subject, action, params) abort
+    let newObj = copy(self)
+    let newObj.nerdtree = a:nerdtree
+    let newObj.subject = a:subject
+    let newObj.action = a:action
+    let newObj.params = a:params
+    return newObj
+endfunction

lib/nerdtree/notifier.vim

@@ -0,0 +1,35 @@
+"CLASS: Notifier
+"============================================================
+let s:Notifier = {}
+
+function! s:Notifier.AddListener(event, funcname)
+    let listeners = s:Notifier.GetListenersForEvent(a:event)
+    if listeners == []
+        let listenersMap = s:Notifier.GetListenersMap()
+        let listenersMap[a:event] = listeners
+    endif
+    call add(listeners, a:funcname)
+endfunction
+
+function! s:Notifier.NotifyListeners(event, path, params)
+    let event = g:NERDTreeEvent.New(b:NERDTree, a:path, a:event, a:params)
+
+    for listener in s:Notifier.GetListenersForEvent(a:event)
+        call {listener}(event)
+    endfor
+endfunction
+
+function! s:Notifier.GetListenersMap()
+    if !exists("s:refreshListenersMap")
+        let s:refreshListenersMap = {}
+    endif
+    return s:refreshListenersMap
+endfunction
+
+function! s:Notifier.GetListenersForEvent(name)
+    let listenersMap = s:Notifier.GetListenersMap()
+    return get(listenersMap, a:name, [])
+endfunction
+
+let g:NERDTreePathNotifier = deepcopy(s:Notifier)
+

lib/nerdtree/path.vim

@@ -549,13 +549,13 @@ endfunction
 "FUNCTION: Path.refresh() {{{1
 function! s:Path.refresh()
     call self.readInfoFromDisk(self.str())
-    call g:NERDTreeRefreshNotifier.NotifyListeners(self)
+    call g:NERDTreePathNotifier.NotifyListeners('refresh', self, {})
     call self.cacheDisplayString()
 endfunction
 
 "FUNCTION: Path.refreshFlags() {{{1
 function! s:Path.refreshFlags()
-    call g:NERDTreeRefreshNotifier.NotifyListeners(self)
+    call g:NERDTreePathNotifier.NotifyListeners('refreshFlags', self, {})
     call self.cacheDisplayString()
 endfunction
 

lib/nerdtree/refresh_notifier.vim

@@ -252,7 +252,7 @@ function! s:TreeDirNode._initChildren(silent)
             try
                 let path = g:NERDTreePath.New(i)
                 call self.createChild(path, 0)
-                call g:NERDTreeRefreshNotifier.NotifyListeners(path)
+                call g:NERDTreePathNotifier.NotifyListeners('init', path, {})
             catch /^NERDTree.\(InvalidArguments\|InvalidFiletype\)Error/
                 let invalidFilesFound += 1
             endtry