1 files changed, 29 insertions, 4 deletions
diff --git a/app/models/concerns/taskable.rb b/app/models/concerns/taskable.rb
index 660e58b876d..df2a9e3e84b 100644
--- a/app/models/concerns/taskable.rb
+++ b/app/models/concerns/taskable.rb
@@ -7,14 +7,39 @@ require 'task_list/filter'
 #
 # Used by MergeRequest and Issue
 module Taskable
+  COMPLETED    = 'completed'.freeze
+  INCOMPLETE   = 'incomplete'.freeze
+  ITEM_PATTERN = /
+    ^
+    (?:\s*[-+*]|(?:\d+\.))? # optional list prefix
+    \s*                     # optional whitespace prefix
+    (\[\s\]|\[[xX]\])       # checkbox
+    (\s.+)                  # followed by whitespace and some text.
+  /x
+
+  def self.get_tasks(content)
+    content.to_s.scan(ITEM_PATTERN).map do |checkbox, label|
+      # ITEM_PATTERN strips out the hyphen, but Item requires it. Rabble rabble.
+      TaskList::Item.new("- #{checkbox}", label.strip)
+    end
+  end
+
+  def self.get_updated_tasks(old_content:, new_content:)
+    old_tasks, new_tasks = get_tasks(old_content), get_tasks(new_content)
+
+    new_tasks.select.with_index do |new_task, i|
+      old_task = old_tasks[i]
+      next unless old_task
+
+      new_task.source == old_task.source && new_task.complete? != old_task.complete?
+    end
+  end
+
   # Called by `TaskList::Summary`
   def task_list_items
     return [] if description.blank?
 
-    @task_list_items ||= description.scan(TaskList::Filter::ItemPattern).collect do |item|
-      # ItemPattern strips out the hyphen, but Item requires it. Rabble rabble.
-      TaskList::Item.new("- #{item}")
-    end
+    @task_list_items ||= Taskable.get_tasks(description)
   end
 
   def tasks