Detect existing status line and clean up on exit.

- On startup, determine how many bottom rows of the terminal
  are already reserved by something, and remember this value.

- When resizing, observe this value; set the scrolling region
  such that we protect the existing one.

- When terminating, restore the protection to the original
  one found, or else reset the scrolling region.
  Also bump up the stty rows again; don't leave it trimmed.

1 files changed, 30 insertions, 2 deletions

diff --git a/basta.sh b/basta.sh
index 9c8c932..01b7447 100644
--- a/basta.sh
+++ b/basta.sh
@@ -4,10 +4,22 @@ old_cmdno=${old_cmdno-0}
 old_lines=${old_lines-0}
 old_cols=${old_cols-0}
 
+existing_reserved_rows=${existing_reserved_rows-}
+
+calc_existing_rows()
+{
+  local esc=$(printf "\033")
+  printf "${esc}7$esc[999;999H"
+  local realrows=$(get_current_line)
+  printf "${esc}8"
+  existing_reserved_rows=$((realrows - LINES))
+}
+
 prepare_terminal()
 {
-  stty rows $((LINES - 1))
-  printf "\n\033[1A"
+  [ -n "$existing_reserved_rows" ] || calc_existing_rows
+  stty rows $((LINES - existing_reserved-rows - 1))
+  printf "\n\033[A"
   old_lines=$LINES
   old_cols=$COLUMNS
 }
@@ -76,6 +88,20 @@ update_status_timer()
   done
 }
 
+release_status()
+{
+  local esc=$(printf "\033")
+  local newlines=$((LINES + 1))
+
+  if [ $existing_reserved_rows ] && [ $existing_reserved_rows -gt 0 ] ; then
+    printf "$esc[1;%sr" $((newlines - existing_reserved_rows))
+  else
+    printf "$esc[1r"
+  fi
+
+  stty rows $newlines
+}
+
 PROMPT_COMMAND='update_status_line'
 
 if ! [ $update_status_alarm ] ; then
@@ -85,6 +111,8 @@ if ! [ $update_status_alarm ] ; then
   disown $!
 fi
 
+trap release_status EXIT
+
 # Copyright 2023
 # Kaz Kylheku <kaz@kylheku.com>
 # Vancouver, Canada