input(optimization): replace ev type reflection with table lookup

frontend/device/input.lua

@@ -62,6 +62,8 @@ an interface to get input events
 local Input = {
     -- this depends on keyboard layout and should be overridden:
     event_map = {},
+    -- adapters are post processing functions that transform a given event to another event
+    event_map_adapter = {},
 
     group = {
         Cursor = { "Up", "Down", "Left", "Right" },
@@ -266,8 +268,8 @@ function Input:handleKeyBoardEv(ev)
         return
     end
 
-    if type(keycode) == "function" then
-        return keycode(ev)
+    if self.event_map_adapter[keycode] then
+        return self.event_map_adapter[keycode](ev)
     end
 
     -- take device rotation into account

frontend/device/kobo/device.lua

@@ -129,20 +129,24 @@ function Kobo:init()
     self.input = require("device/input"):new{
         device = self,
         event_map = {
-            [59] = function(ev)
+            [59] = "SleepCover",
+            [90] = "LightButton",
+            [102] = "Home",
+            [116] = "Power",
+        },
+        event_map_adapter = {
+            SleepCover = function(ev)
                 if self.input:isEvKeyPress(ev) then
                     return "SleepCoverClosed"
                 else
                     return "SleepCoverOpened"
                 end
             end,
-            [90] = function(ev)
+            LightButton = function(ev)
                 if self.input:isEvKeyRelease(ev) then
                     return "Light"
                 end
             end,
-            [102] = "Home",
-            [116] = "Power",
         }
     }