feat: add excluded filetypes config opt

• Users may now choose to pass a list of filetypes for Tidy
      to ignore to the setup function. It is not required and
      will be ignored if it does not exist.

    Resolves #5

lua/tidy/init.lua

@@ -1,35 +1,58 @@
 local M = {}
 
-function M.setup()
+local function is_excluded_ft(opts)
+    if not opts.filetype_exclude then
+        return false
+    end
+
+    local ft = vim.api.nvim_buf_get_option(0, "filetype")
+
+    for _, entry in ipairs(opts.filetype_exclude) do
+        if entry == ft then
+            return true
+        end
+    end
+
+    return false
+end
+
+local function reset_cursor_pos(pos)
+    local num_rows = vim.api.nvim_buf_line_count(0)
+
+    --[[
+        if the row value in the original cursor
+        position tuple is greater than the
+        line count after empty line deletion
+        (meaning that the cursor was inside of
+        the group of empty lines at the end of
+        the file when they were deleted), set
+        the cursor row to the last line.
+    ]]
+    if pos[1] > num_rows then
+        pos[1] = num_rows
+    end
+
+    vim.api.nvim_win_set_cursor(0, pos)
+end
+
+function M.setup(opts)
     local tidy_grp = vim.api.nvim_create_augroup("tidy", { clear = true })
 
     vim.api.nvim_create_autocmd("BufWritePre", {
         group = tidy_grp,
         callback = function()
-            local pos = vim.api.nvim_win_get_cursor(0)
+            if is_excluded_ft(opts) then
+                return false
+            end
+
+            local cursor_pos = vim.api.nvim_win_get_cursor(0)
 
             vim.cmd([[:keepjumps keeppatterns %s/\s\+$//e]])
 
             -- delete all lines at end of buffer, see source 2
             vim.cmd([[:keepjumps keeppatterns silent! 0;/^\%(\n*.\)\@!/,$d]])
 
-            -- get row count after line deletion
-            local last_row = vim.api.nvim_buf_line_count(0)
-
-            --[[
-                if the row value in the original cursor
-                position tuple is greater than the
-                line count after empty line deletion
-                (meaning that the cursor was inside of
-                the group of empty lines at the end of
-                the file when they were deleted), set
-                the cursor row to the last line.
-            ]]
-            if pos[1] > last_row then
-                pos[1] = last_row
-            end
-
-            vim.api.nvim_win_set_cursor(0, pos)
+            reset_cursor_pos(cursor_pos)
         end,
     })
 end