diff --git a/lua/cmp_path/init.lua b/lua/cmp_path/init.lua
index 7bd094a..8886914 100644
--- a/lua/cmp_path/init.lua
+++ b/lua/cmp_path/init.lua
@@ -1,4 +1,4 @@
-local cmp = require'cmp'
+local cmp = require 'cmp'
 
 local NAME_REGEX = '\\%([^/\\\\:\\*?<>\'"`\\|]\\)'
 local PATH_REGEX = vim.regex(([[\%(/PAT*[^/\\\\:\\*?<>\'"`\\| ]\)*/\zePAT*$]]):gsub('PAT', NAME_REGEX))
@@ -9,10 +9,11 @@ local constants = {
   max_lines = 20,
 }
 
----@class cmp_path.Options
+---@class cmp_path.Option
 ---@field public trailing_slash boolean
+---@field public get_cwd fun(): string
 
----@type cmp_buffer.Options
+---@type cmp_path.Option
 local defaults = {
   trailing_slash = false,
   get_cwd = function(params)
@@ -24,34 +25,24 @@ source.new = function()
   return setmetatable({}, { __index = source })
 end
 
----@return cmp_buffer.Options
-source._validate_options = function(_, params)
-  local opts = vim.tbl_deep_extend('keep', params.option, defaults)
-  vim.validate({
-    trailing_slash = { opts.trailing_slash, 'boolean' },
-    get_cwd = { opts.get_cwd, 'function' },
-  })
-  return opts
-end
-
 source.get_trigger_characters = function()
   return { '/', '.' }
 end
 
-source.get_keyword_pattern = function()
+source.get_keyword_pattern = function(self, params)
   return NAME_REGEX .. '*'
 end
 
 source.complete = function(self, params, callback)
-  local opts = self:_validate_options(params)
+  local option = self:_validate_option(params)
 
-  local dirname = self:_dirname(params, opts)
+  local dirname = self:_dirname(params, option)
   if not dirname then
     return callback()
   end
 
   local include_hidden = string.sub(params.context.cursor_before_line, params.offset, params.offset) == '.'
-  self:_candidates(dirname, include_hidden, opts, function(err, candidates)
+  self:_candidates(dirname, include_hidden, option, function(err, candidates)
     if err then
       return callback()
     end
@@ -59,7 +50,20 @@ source.complete = function(self, params, callback)
   end)
 end
 
-source._dirname = function(self, params, opts)
+source.resolve = function(self, completion_item, callback)
+  local data = completion_item.data
+  if data.stat and data.stat.type == 'file' then
+    local ok, documentation = pcall(function()
+      return self:_get_documentation(data.path, constants.max_lines)
+    end)
+    if ok then
+      completion_item.documentation = documentation
+    end
+  end
+  callback(completion_item)
+end
+
+source._dirname = function(self, params, option)
   local s = PATH_REGEX:match_str(params.context.cursor_before_line)
   if not s then
     return nil
@@ -68,7 +72,7 @@ source._dirname = function(self, params, opts)
   local dirname = string.gsub(string.sub(params.context.cursor_before_line, s + 2), '%a*$', '') -- exclude '/'
   local prefix = string.sub(params.context.cursor_before_line, 1, s + 1) -- include '/'
 
-  local buf_dirname = opts.get_cwd(params)
+  local buf_dirname = option.get_cwd(params)
   if vim.api.nvim_get_mode().mode == 'c' then
     buf_dirname = vim.fn.getcwd()
   end
@@ -107,24 +111,7 @@ source._dirname = function(self, params, opts)
   return nil
 end
 
-local function lines_from(file, count)
-  local bfile = assert(io.open(file, 'rb'))
-  local first_k = bfile:read(1024)
-  if first_k:find('\0') then
-    return { kind = cmp.lsp.MarkupKind.PlainText, value = 'binary file' }
-  end
-  local lines = { '```' .. (vim.filetype.match { filename = file } or '') }
-  for line in first_k:gmatch("[^\r\n]+") do
-    lines[#lines + 1] = line
-    if count ~= nil and #lines >= count then
-     break
-    end
-  end
-  lines[#lines + 1] = '```'
-  return { kind = cmp.lsp.MarkupKind.Markdown, value = table.concat(lines, '\n') }
-end
-
-source._candidates = function(_, dirname, include_hidden, opts, callback)
+source._candidates = function(_, dirname, include_hidden, option, callback)
   local fs, err = vim.loop.fs_scandir(dirname)
   if err then
     return callback(err, nil)
@@ -168,7 +155,7 @@ source._candidates = function(_, dirname, include_hidden, opts, callback)
       item.kind = cmp.lsp.CompletionItemKind.Folder
       item.label = name .. '/'
       item.insertText = name .. '/'
-      if not opts.trailing_slash then
+      if not option.trailing_slash then
         item.word = name
       end
     end
@@ -198,15 +185,39 @@ source._is_slash_comment = function(_)
   return is_slash_comment and not no_filetype
 end
 
-function source:resolve(completion_item, callback)
-  local data = completion_item.data
-  if data.stat and data.stat.type == 'file' then
-    local ok, preview_lines = pcall(lines_from, data.path, constants.max_lines)
-    if ok then
-      completion_item.documentation = preview_lines
+---@return cmp_path.Option
+source._validate_option = function(_, params)
+  local option = vim.tbl_deep_extend('keep', params.option, defaults)
+  vim.validate({
+    trailing_slash = { option.trailing_slash, 'boolean' },
+    get_cwd = { option.get_cwd, 'function' },
+  })
+  return option
+end
+
+source._get_documentation = function(_, filename, count)
+  local binary = assert(io.open(filename, 'rb'))
+  local first_kb = binary:read(1024)
+  if first_kb:find('\0') then
+    return { kind = cmp.lsp.MarkupKind.PlainText, value = 'binary file' }
+  end
+
+  local contents = {}
+  for content in first_kb:gmatch("[^\r\n]+") do
+    table.insert(contents, content)
+    if count ~= nil and #contents >= count then
+      break
     end
   end
-  callback(completion_item)
+
+  local filetype = vim.filetype.match({ filename = filename })
+  if not filetype then
+    return { kind = cmp.lsp.MarkupKind.PlainText, value = table.concat(contents, '\n') }
+  end
+
+  table.insert(contents, 1, '```' .. filetype)
+  table.insert(contents, '```')
+  return { kind = cmp.lsp.MarkupKind.Markdown, value = table.concat(contents, '\n') }
 end
 
 return source