works, basically

lib/stopwatch/hooks.rb

@@ -0,0 +1,11 @@
+module Stopwatch
+  class Hooks < Redmine::Hook::ViewListener
+    render_on :view_layouts_base_html_head,
+      partial: 'stopwatch/hooks/layouts_base_html_head'
+    render_on :view_layouts_base_body_bottom,
+      partial: 'stopwatch/hooks/layouts_base_body_bottom'
+    render_on :view_time_entries_context_menu_start,
+      partial: 'stopwatch/hooks/time_entries_context_menu_start'
+
+  end
+end

lib/stopwatch/start_timer.rb

@@ -9,16 +9,20 @@ module Stopwatch
     end
 
     def call
-      if @time_entry.project && @user.allowed_to?(:log_time, @time_entry.project)
+      if @time_entry.project && !@user.allowed_to?(:log_time, @time_entry.project)
         return Result.new(error: :unauthorized)
       end
 
-      stop_existing_timer
+      StopTimer.new(user: @user).call
 
       @time_entry.hours = 0 if @time_entry.hours.nil?
+      # we want to start tracking time if this is an existing time entry, or a
+      # new entry with 0 hours was created.
+      # new entries with hours > 0 are just saved as is.
+      start_timer = !@time_entry.new_record? || @time_entry.hours == 0
 
       if @time_entry.save
-        start_new_timer
+        start_new_timer if start_timer
         return Result.new(success: true)
       else
         Rails.logger.error("could not save time entry: \n#{@time_entry.errors.inspect}")
@@ -33,12 +37,5 @@ module Stopwatch
       timer.start @time_entry
     end
 
-    def stop_existing_timer
-      timer = Timer.new @user
-      if timer.running?
-        timer.stop
-      end
-    end
-
   end
 end

lib/stopwatch/stop_timer.rb

@@ -0,0 +1,20 @@
+module Stopwatch
+  class StopTimer
+
+    Result = ImmutableStruct.new(:success?, :error)
+
+    def initialize(user: User.current)
+      @user = user
+    end
+
+    def call
+      timer = Timer.new @user
+      if timer.running?
+        timer.stop
+      end
+      return Result.new(success: true)
+    end
+
+  end
+end
+

lib/stopwatch/timer.rb

@@ -21,7 +21,7 @@ module Stopwatch
 
     def stop
       if hours = runtime_hours and
-          time_entry = TimeEntry.find_by_id(data[:time_entry_id])
+          time_entry = TimeEntry.find_by_id(time_entry_id)
 
         time_entry.update_column :hours, time_entry.hours + hours
       end
@@ -29,11 +29,22 @@ module Stopwatch
       save
     end
 
+    def to_json
+      {
+        time_entry_id: time_entry_id,
+        running: running?
+      }.to_json
+    end
+
     def save
       user.pref[:current_timer] = data.to_json
       user.pref.save
     end
 
+    def time_entry_id
+      data[:time_entry_id]
+    end
+
     private
 
     def data

lib/stopwatch/user_patch.rb

@@ -7,5 +7,10 @@ module Stopwatch
     def timer_running?
       Stopwatch::Timer.new(self).running?
     end
+
+    def is_running_timer?(time_entry)
+      timer = Stopwatch::Timer.new(self)
+      timer.running? and timer.time_entry_id == time_entry.id
+    end
   end
 end