fix: considers folded lines near EoF (#8)

* fix: considers folded lines near EoF (fix #7)

* refactor: code readability

* perf: avoid calculations when far away from EoF

* Linting. Only change topline in `winrestview()`

---------

Co-authored-by: Aasim-A <23695024+Aasim-A@users.noreply.github.com>

lua/scrollEOF.lua

@@ -3,20 +3,50 @@ local M = {}
 local mode_disabled = false
 local filetype_disabled = false
 
+---Counts the number of folded lines between two line numbers
+---@param lnum1 number
+---@param lnum2 number
+---@return number
+local function folded_lines_between(lnum1, lnum2)
+  local next_fold_end_ln = -1
+  local folded_lines = 0
+
+  for ln = lnum1, lnum2, 1 do
+    if ln > next_fold_end_ln then -- skip folded lines we already added to the count
+      next_fold_end_ln = vim.fn.foldclosedend(ln)
+      local is_folded_line = next_fold_end_ln ~= -1
+      if is_folded_line then
+        local fold_size = next_fold_end_ln - ln
+        folded_lines = folded_lines + fold_size
+      end
+    end
+  end
+
+  return folded_lines
+end
+
 local function check_eof_scrolloff()
   if mode_disabled or filetype_disabled then
     return
   end
 
   local win_height = vim.api.nvim_win_get_height(0)
+  local last_line = vim.fn.line('$')
+  local win_last_line = vim.fn.line('w$')
+
+  -- PERF avoid calculations when far away from the end of file
+  if win_last_line + win_height < last_line then return end
+
   local win_view = vim.fn.winsaveview()
   local scrolloff = math.min(vim.o.scrolloff, math.floor(win_height / 2))
-  local scrolloff_line_count = win_height - (vim.fn.line('w$') - win_view.topline + 1)
-  local distance_to_last_line = vim.fn.line('$') - win_view.lnum
+  local cur_line = win_view.lnum
+  local win_top_line = win_view.topline
+  local visual_distance_to_eof = last_line - cur_line - folded_lines_between(cur_line, last_line)
+  local visual_last_line_in_win = win_last_line - folded_lines_between(win_top_line, win_last_line)
+  local scrolloff_line_count = win_height - (visual_last_line_in_win - win_top_line + 1)
 
-  if distance_to_last_line < scrolloff and scrolloff_line_count + distance_to_last_line < scrolloff then
-    win_view.topline = win_view.topline + scrolloff - (scrolloff_line_count + distance_to_last_line)
-    vim.fn.winrestview(win_view)
+  if visual_distance_to_eof < scrolloff and scrolloff_line_count + visual_distance_to_eof < scrolloff then
+    vim.fn.winrestview({ topline = win_view.topline + scrolloff - (scrolloff_line_count + visual_distance_to_eof) })
   end
 end