new framework

lib/bbs/focus_manager.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+module BBS
+  # Tracks which widget within a Container currently has focus.
+  # Tab / Shift-Tab cycle through its focusable descendants.
+  class FocusManager
+    attr_reader :focused
+
+    def initialize(container)
+      @container = container
+      @focused   = nil
+      focus_first
+    end
+
+    def candidates
+      @container.focusable_descendants.select { |w| w.enabled }
+    end
+
+    def focus_first
+      first = candidates.first
+      set_focus(first)
+    end
+
+    def focus(widget)
+      set_focus(widget) if widget && widget.focusable? && widget.enabled
+    end
+
+    def next_focus
+      list = candidates
+      return if list.empty?
+      idx = list.index(@focused) || -1
+      set_focus(list[(idx + 1) % list.size])
+    end
+
+    def prev_focus
+      list = candidates
+      return if list.empty?
+      idx = list.index(@focused) || 0
+      set_focus(list[(idx - 1) % list.size])
+    end
+
+    def handle_focus_key(event)
+      return false unless event.key?
+      case event.key
+      when :tab
+        next_focus
+        true
+      when :shift_tab
+        prev_focus
+        true
+      else
+        false
+      end
+    end
+
+    def dispatch(event)
+      return nil unless @focused
+      @focused.handle_event(event)
+    end
+
+    private
+
+    def set_focus(widget)
+      return if widget == @focused
+      if @focused
+        @focused.focused = false
+        @focused.on_blur
+      end
+      @focused = widget
+      if widget
+        widget.focused = true
+        widget.on_focus
+      end
+    end
+  end
+end