Screensaver option on Kindle devices (#2734)

* Screensaver on Kindle devices

frontend/apps/filemanager/filemanagermenu.lua

@@ -96,7 +96,7 @@ function FileManagerMenu:setUpdateItemTable()
             G_reader_settings:flush()
         end
     }
-    if Device.isKobo() then
+    if Device.isKobo() or Device.isKindle() then
         self.menu_items.screensaver = {
             text = _("Screensaver"),
             sub_item_table = {

frontend/apps/reader/modules/readermenu.lua

@@ -145,8 +145,27 @@ function ReaderMenu:setUpdateItemTable()
                 }
             }
         }
+    elseif Device:isKindle() then
+        self.menu_items.screensaver = {
+            text = _("Screensaver"),
+            sub_item_table = {
+                {
+                    text = _("Use book's cover as screensaver"),
+                    checked_func = Screensaver.isUsingBookCover,
+                    callback = function()
+                        if Screensaver:isUsingBookCover() then
+                            G_reader_settings:saveSetting(
+                                "use_lastfile_as_screensaver", false)
+                        else
+                            G_reader_settings:delSetting(
+                                "use_lastfile_as_screensaver")
+                        end
+                        G_reader_settings:flush()
+                    end
+                }
+            }
+        }
     end
-
     -- main menu tab
     -- insert common info
     for id, common_setting in pairs(require("ui/elements/common_info_menu_table")) do

frontend/device/kindle/device.lua

@@ -46,6 +46,9 @@ function Kindle:usbPlugIn()
 end
 
 function Kindle:intoScreenSaver()
+    if require("ui/screensaver").isUsingBookCover then
+        require("ui/screensaver"):show("suspend")
+    end
     self.powerd:beforeSuspend()
     if self.charging_mode == false and self.screen_saver_mode == false then
         self.screen:saveCurrentBB()
@@ -64,6 +67,9 @@ function Kindle:outofScreenSaver()
         if os.getenv("AWESOME_STOPPED") == "yes" then
             os.execute("killall -stop awesome")
         end
+        if require("ui/screensaver").isUsingBookCover then
+            require("ui/screensaver"):close()
+        end
         -- wait for native system update screen before we recover saved
         -- Blitbuffer.
         util.usleep(1500000)

frontend/ui/screensaver.lua

@@ -129,8 +129,10 @@ function Screensaver:show(kind, default_msg)
     -- fallback to message box
     if not self.left_msg then
         local msg = screensaver_settings.message or default_msg
-        self.left_msg = InfoMessage:new{ text = msg }
-        UIManager:show(self.left_msg)
+        if msg then
+            self.left_msg = InfoMessage:new{ text = msg }
+            UIManager:show(self.left_msg)
+        end
     else
         -- refresh whole screen for other types
         UIManager:show(self.left_msg, "full")