nvim: add mapping for inserting include guards in C files

config/nvim/after/ftplugin/c.lua

@@ -1 +1,27 @@
 vim.bo.commentstring = "// %s"
+
+local insert_include_guards = function(bufnr)
+  bufnr = bufnr or 0
+
+  -- foo.h -> FOO_H_
+  local guard = string.gsub(string.upper(vim.fn.expand("%:t")), "%.", "_") .. "_"
+
+  vim.api.nvim_buf_set_lines(bufnr, 0, 0, true, {
+    string.format("#ifndef %s", guard),
+    string.format("#define %s", guard),
+    "",
+  })
+
+  local last_lineno = vim.api.nvim_buf_line_count(bufnr)
+  vim.api.nvim_buf_set_lines(bufnr, last_lineno, last_lineno, true, {
+    "",
+    string.format("#endif  // %s", guard),
+  })
+end
+
+vim.keymap.set(
+  "n",
+  "<localleader>ig",
+  insert_include_guards,
+  { desc = "Add include guards", buffer = true, silent = true }
+)