Add __get_current_window_index internal helper function

lib/layout-helpers.sh

@@ -313,6 +313,15 @@ __get_first_window_index() {
   fi
 }
 
+__get_current_window_index() {
+  local lookup=$(tmuxifier-tmux list-windows -t "$session:" \
+    -F "#{window_active}:#{window_index}" 2>/dev/null | grep "^1:")
+
+  if [ -n "$lookup" ]; then
+    echo "${lookup/1:}"
+  fi
+}
+
 __go_to_session() {
   if [ -z "$TMUX" ]; then
     tmuxifier-tmux -u attach-session -t "$session:"

test/lib/layout-helpers/__get_current_window_index.test.sh

@@ -0,0 +1,48 @@
+#! /usr/bin/env bash
+source "../../test-helper.sh"
+source "${root}/lib/layout-helpers.sh"
+
+#
+# __get_current_window_index() tests.
+#
+
+# When current window is the first and only window.
+create-test-session
+assert "__get_current_window_index" "0"
+kill-test-session
+
+# When creating a second window.
+create-test-session
+test-socket-tmux new-window -t "$session:1"
+assert "__get_current_window_index" "1"
+kill-test-session
+
+# When creating a second window and then switching back to the first window.
+create-test-session
+test-socket-tmux new-window -t "$session:1"
+test-socket-tmux select-window -t "$session:0"
+assert "__get_current_window_index" "0"
+kill-test-session
+
+# When creating multiples windows and switching between them randomly.
+create-test-session
+assert "__get_current_window_index" "0"
+test-socket-tmux new-window -t "$session:1"
+assert "__get_current_window_index" "1"
+test-socket-tmux new-window -t "$session:2"
+assert "__get_current_window_index" "2"
+test-socket-tmux new-window -t "$session:3"
+assert "__get_current_window_index" "3"
+test-socket-tmux select-window -t "$session:1"
+assert "__get_current_window_index" "1"
+test-socket-tmux select-window -t "$session:0"
+assert "__get_current_window_index" "0"
+test-socket-tmux select-window -t "$session:3"
+assert "__get_current_window_index" "3"
+test-socket-tmux select-window -t "$session:2"
+assert "__get_current_window_index" "2"
+kill-test-session
+
+
+# End of tests.
+assert_end "__get_current_window_index()"