toot-toot: stop clobbering existing files

I've been reluctant to do this until now because it makes it more
difficult to grant an app the ideal permissions. Here's what I use:

  return string.find(filename, 'toot') == 1

But I'm also trying to keep people from looking to the app to figure out
what permissions to give it :/

toot-toot.tlv

@@ -969,3 +969,65 @@
  > {'^w', 'write to "toot"'},
  > {'^f|^b', 'scroll'},
  >}
+- __teliva_timestamp:
+ >Thu Mar 31 08:42:19 2022
+ update:
+ >function update(window)
+ > local key = window:getch()
+ > local h, w = window:getmaxyx()
+ > if key == curses.KEY_LEFT then
+ > if cursor > 1 then
+ > cursor = cursor-1
+ > end
+ > elseif key == curses.KEY_RIGHT then
+ > if cursor <= #prose then
+ > cursor = cursor+1
+ > end
+ > elseif key == curses.KEY_DOWN then
+ > cursor = cursor_down(prose, cursor, w)
+ > elseif key == curses.KEY_UP then
+ > cursor = cursor_up(prose, cursor, w)
+ > elseif key == curses.KEY_BACKSPACE or key == 8 or key == 127 then -- ctrl-h, ctrl-?, delete
+ > if cursor > 1 then
+ > cursor = cursor-1
+ > prose = prose:remove(cursor)
+ > end
+ > elseif key == 6 then -- ctrl-f
+ > first_toot = first_toot+1
+ > elseif key == 2 then -- ctrl-b
+ > if first_toot > 1 then
+ > first_toot = first_toot-1
+ > end
+ > elseif key == 23 then -- ctrl-w
+ > local out = io.open(next_toot(), 'w')
+ > if out ~= nil then
+ > out:write(prose, '\n')
+ > out:close()
+ > end
+ > elseif key == 10 or (key >= 32 and key < 127) then
+ > prose = prose:insert(string.char(key), cursor-1)
+ > cursor = cursor+1
+ > end
+ >end
+- __teliva_timestamp:
+ >Thu Mar 31 08:44:19 2022
+ next_toot:
+ >-- pick the first filename starting with 'toot' that doesn't exist yet
+ >function next_toot()
+ > if not file_exists('toot') then return 'toot' end
+ > local idx = 1
+ > while true do
+ > local curr = 'toot'..str(idx)
+ > if not file_exists(curr) then
+ > return curr
+ > end
+ > idx = idx+1
+ > end
+ >end
+- __teliva_timestamp:
+ >Thu Mar 31 08:46:27 2022
+ file_exists:
+ >function file_exists(filename)
+ > local f = io.open(filename, 'r')
+ > return f ~= nil
+ >end