diff --git a/mrblib/xkremap/event_handler.rb b/mrblib/xkremap/event_handler.rb
index fc379ac..223da07 100644
--- a/mrblib/xkremap/event_handler.rb
+++ b/mrblib/xkremap/event_handler.rb
@@ -3,21 +3,33 @@ module Xkremap
     # @param [Xkremap::Config] config
     # @param [Xkremap::Display] display
     def initialize(config, display)
-      @config  = config
-      @display = display
-      XlibWrapper.grab_keys(@display)
+      @key_remap_builder = KeyRemapBuilder.new(config, display)
+      @key_grab_manager  = KeyGrabManager.new(display)
+      remap_keys
     end
 
     def handle_key_press(keycode, state)
+      handler = @key_remap_builder.prebuilt[keycode][state]
+      handler && handler.call
       puts 'Event: key_press'
     end
 
     def handle_property_notify
-      puts 'Event: property_notify'
+      if @key_remap_builder.active_window_changed?
+        remap_keys
+      end
     end
 
     def handle_mapping_notify
-      puts 'Event: mapping_notify'
+      remap_keys
+    end
+
+    private
+
+    def remap_keys
+      @key_remap_builder.build
+      @key_grab_manager.grab_keys
+      puts 'remap keys!'
     end
   end
 end
diff --git a/mrblib/xkremap/key_grab_manager.rb b/mrblib/xkremap/key_grab_manager.rb
new file mode 100644
index 0000000..5d67e3c
--- /dev/null
+++ b/mrblib/xkremap/key_grab_manager.rb
@@ -0,0 +1,13 @@
+module Xkremap
+  class KeyGrabManager
+    # @param [Xkremap::Display] display
+    def initialize(display)
+      @display = display
+    end
+
+    def grab_keys
+      XlibWrapper.ungrab_keys(@display)
+      XlibWrapper.grab_key(@display, 0x0062, 1<<2) # C-b
+    end
+  end
+end
diff --git a/mrblib/xkremap/key_remap_builder.rb b/mrblib/xkremap/key_remap_builder.rb
new file mode 100644
index 0000000..3e11456
--- /dev/null
+++ b/mrblib/xkremap/key_remap_builder.rb
@@ -0,0 +1,33 @@
+module Xkremap
+  class KeyRemapBuilder
+    # @attribute [Hash] prebuilt
+    #   [Fixnum] keycode -> [Fixnum] state -> [Proc] handler
+    attr_reader :prebuilt
+
+    # @param [Xkremap::Config] config
+    # @param [Xkremap::Display] display
+    def initialize(config, display)
+      @config   = config
+      @display  = display
+      @prebuilt = Hash.new { |h, k| h[k] = {} }
+      @current_window = fetch_active_window
+    end
+
+    def build
+      puts 'rebuilt!'
+    end
+
+    def active_window_changed?
+      next_window = fetch_active_window
+      @current_window != next_window
+    ensure
+      @current_window = next_window
+    end
+
+    private
+
+    def fetch_active_window
+      XlibWrapper.fetch_active_window(@display)
+    end
+  end
+end
diff --git a/src/xlib_wrapper.c b/src/xlib_wrapper.c
index 7004160..b56bdfc 100644
--- a/src/xlib_wrapper.c
+++ b/src/xlib_wrapper.c
@@ -5,14 +5,41 @@
 extern Display* extract_x_display(mrb_state *mrb, mrb_value display_obj);
 
 mrb_value
-mrb_xw_grab_keys(mrb_state *mrb, mrb_value self)
+mrb_xw_fetch_active_window(mrb_state *mrb, mrb_value self)
 {
   mrb_value display_obj;
-  mrb_get_args(mrb, "o", &display_obj);
+  mrb_int keycode, state;
+  mrb_get_args(mrb, "o", &display_obj, &keycode, &state);
+
+  Window window;
+  int focus_state;
+  Display *display = extract_x_display(mrb, display_obj);
+  XGetInputFocus(display, &window, &focus_state);
+
+  return mrb_fixnum_value(window);
+}
+
+mrb_value
+mrb_xw_grab_key(mrb_state *mrb, mrb_value self)
+{
+  mrb_value display_obj;
+  mrb_int keycode, state;
+  mrb_get_args(mrb, "oii", &display_obj, &keycode, &state);
+
   Display *display = extract_x_display(mrb, display_obj);
+  XGrabKey(display, XKeysymToKeycode(display, keycode), state, XDefaultRootWindow(display), True, GrabModeAsync, GrabModeAsync);
 
-  Window root = XDefaultRootWindow(display);
-  XGrabKey(display, XKeysymToKeycode(display, XK_b), ControlMask, root, True, GrabModeAsync, GrabModeAsync);
+  return mrb_nil_value();
+}
+
+mrb_value
+mrb_xw_ungrab_keys(mrb_state *mrb, mrb_value self)
+{
+  mrb_value display_obj;
+  mrb_get_args(mrb, "o", &display_obj);
+
+  Display *display = extract_x_display(mrb, display_obj);
+  XUngrabKey(display, AnyKey, AnyModifier, XDefaultRootWindow(display));
 
   return mrb_nil_value();
 }
@@ -21,5 +48,7 @@ void
 mrb_xkremap_xlib_wrapper_init(mrb_state *mrb, struct RClass *mXkremap)
 {
   struct RClass *cXlibWrapper = mrb_define_class_under(mrb, mXkremap, "XlibWrapper", mrb->object_class);
-  mrb_define_class_method(mrb, cXlibWrapper, "grab_keys", mrb_xw_grab_keys, MRB_ARGS_REQ(1));
+  mrb_define_class_method(mrb, cXlibWrapper, "fetch_active_window", mrb_xw_fetch_active_window, MRB_ARGS_REQ(1));
+  mrb_define_class_method(mrb, cXlibWrapper, "grab_key", mrb_xw_grab_key, MRB_ARGS_REQ(3));
+  mrb_define_class_method(mrb, cXlibWrapper, "ungrab_keys", mrb_xw_ungrab_keys, MRB_ARGS_REQ(1));
 }