add night mode option that inverts screen color

frontend/apps/filemanager/filemanagermenu.lua

@@ -81,6 +81,15 @@ function FileManagerMenu:setUpdateItemTable()
         ReaderFrontLight:addToMainMenu(self.tab_item_table)
     end
 
+    table.insert(self.tab_item_table.main, {
+        text = _("Night mode"),
+        checked_func = function() return G_reader_settings:readSetting("night_mode") end,
+        callback = function()
+            local night_mode = G_reader_settings:readSetting("night_mode") or false
+            Screen.bb:invert()
+            G_reader_settings:saveSetting("night_mode", not night_mode)
+        end
+    })
     table.insert(self.tab_item_table.main, Language:getLangMenuTable())
     table.insert(self.tab_item_table.main, {
         text = _("Version"),

frontend/apps/reader/modules/readermenu.lua

@@ -71,6 +71,15 @@ function ReaderMenu:setUpdateItemTable()
         widget:addToMainMenu(self.tab_item_table)
     end
 
+    table.insert(self.tab_item_table.main, {
+        text = _("Night mode"),
+        checked_func = function() return G_reader_settings:readSetting("night_mode") end,
+        callback = function()
+            local night_mode = G_reader_settings:readSetting("night_mode") or false
+            Screen.bb:invert()
+            G_reader_settings:saveSetting("night_mode", not night_mode)
+        end
+    })
     table.insert(self.tab_item_table.main, Language:getLangMenuTable())
     table.insert(self.tab_item_table.main, {
         text = _("Version"),

reader.lua

@@ -173,10 +173,10 @@ end
 local last_file = G_reader_settings:readSetting("lastfile")
 -- load last opened file
 local open_last = G_reader_settings:readSetting("open_last")
-
-
---@TODO we can read version here, refer to commit in master tree:   (houqp)
---87712cf0e43fed624f8a9f610be42b1fe174b9fe
+-- night mode
+if G_reader_settings:readSetting("night_mode") then
+    Screen.bb:invert()
+end
 
 do
     local powerd = Device:getPowerDevice()