Add :Tac command to replace :!tac & be cross-platform

plugin/commands.lua

@@ -165,3 +165,27 @@ vim.api.nvim_create_user_command('CheckboxToggle', function(opts)
   if x == 'x' then x = ' ' else x = 'x' end
   vim.fn.setline(linenr, string.sub(line, 1, pos) .. x .. string.sub(line, pos + 2))
 end, {})
+
+-- :Tac reverse the order of lines in the selected range or the whole file if
+-- no range is specificed, works as if executing :!tac but purely in Lua making
+-- it cross-platform.
+vim.api.nvim_create_user_command('Tac', function(opts)
+  local buffer = vim.api.nvim_get_current_buf()
+  local line1 = opts.line1 - 1
+  local line2 = opts.line2
+  if opts.range == 0 then
+    line1 = 0
+    line2 = -1
+  end
+  print(opts.range, line1, line2)
+  local lines = vim.api.nvim_buf_get_lines(buffer, line1, line2, false)
+  if lines and #lines > 1 then
+    local temp = nil
+    for n = 1, math.floor(#lines / 2) do
+      temp = lines[n]
+      lines[n] = lines[#lines - (n - 1)]
+      lines[#lines - (n - 1)] = temp
+    end
+    vim.api.nvim_buf_set_lines(buffer, line1, line2, true, lines)
+  end
+end, { range = true })