diff --git a/lua/Trans/core/backend.lua b/lua/Trans/core/backend.lua
index 1074539..fec610c 100644
--- a/lua/Trans/core/backend.lua
+++ b/lua/Trans/core/backend.lua
@@ -71,7 +71,6 @@ if file then
 end
 
 -- WARNING : [Breaking change] 'Trans.json' should use json object instead of array
-
 ---@class Trans
 ---@field backend TransBackendCore
 return setmetatable(M, {
diff --git a/lua/Trans/core/data.lua b/lua/Trans/core/data.lua
index 512913a..dcc939d 100644
--- a/lua/Trans/core/data.lua
+++ b/lua/Trans/core/data.lua
@@ -1,55 +1,39 @@
 local Trans = require 'Trans'
 
-
----@class TransData
+---@class TransData: TransDataOption
+---@field mode string @The mode of the str
 ---@field from string @Source language type
 ---@field to string @Target language type
----@field is_word boolean @Is the str a word
 ---@field str string @The original string
----@field mode string @The mode of the str
 ---@field result table<string, TransResult|nil|false> @The result of the translation
 ---@field frontend TransFrontend
+---@field is_word? boolean @Is the str a word
 ---@field trace table<string, string> debug message
 ---@field backends TransBackend[]
 local M = {}
 M.__index = M
 
 ---TransData constructor
----@param opts table
+---@param opts TransDataOption
 ---@return TransData
 function M.new(opts)
-    local mode = opts.mode
-    local str  = opts.str
-
 
+    ---@cast opts TransData
+    local mode     = opts.mode
+    opts.result    = {}
+    opts.trace     = {}
     local strategy = Trans.conf.strategy[mode]
-    local data = setmetatable({
-        str    = str,
-        mode   = mode,
-        result = {},
-        trace  = {},
-    }, M)
 
 
-    data.frontend = Trans.frontend[strategy.frontend].new()
-    data.backends = {}
+    ---@cast opts TransData
+    setmetatable(opts, M)
 
-    -- FIXME :
-    -- for i, name in ipairs(strategy.backend) do
-    --     data.backends[i] = Trans.backend[name]
-    -- end
 
-    if Trans.util.is_english(str) then
-        data.from = 'en'
-        data.to = 'zh'
-    else
-        data.from = 'zh'
-        data.to = 'en'
-    end
-
-    data.is_word = Trans.util.is_word(str)
+    -- NOTE : whether should we use the default strategy
+    opts.frontend = Trans.frontend[strategy.frontend].new()
+    opts.backends = {}
 
-    return data
+    return opts
 end
 
 ---@class TransResult
@@ -69,12 +53,8 @@ end
 ---@return string? backend.name
 function M:get_available_result()
     local result = self.result
-
-    if result['offline'] then return result['offline'], 'offline' end
-
     for _, backend in ipairs(self.backends) do
         if result[backend.name] then
-            ---@diagnostic disable-next-line: return-type-mismatch
             return result[backend.name], backend.name
         end
     end
diff --git a/lua/Trans/core/debug.lua b/lua/Trans/core/debug.lua
new file mode 100644
index 0000000..9ad53d8
--- /dev/null
+++ b/lua/Trans/core/debug.lua
@@ -0,0 +1,8 @@
+---@class Trans
+---@field debug fun(message: string, level: number?)
+
+return function (message, level)
+    level = level or vim.log.levels.INFO
+    -- TODO : custom messaage filter
+    vim.notify(message, level)
+end
diff --git a/lua/Trans/core/frontend.lua b/lua/Trans/core/frontend.lua
index 67f0a09..ecaefb2 100644
--- a/lua/Trans/core/frontend.lua
+++ b/lua/Trans/core/frontend.lua
@@ -6,9 +6,9 @@ local default_frontend = {
     query     = 'fallback',
     border    = 'rounded',
     title     = vim.fn.has 'nvim-0.9' == 1 and {
-        { '',       'TransTitleRound' },
+        { '', 'TransTitleRound' },
         { ' Trans', 'TransTitle' },
-        { '',       'TransTitleRound' },
+        { '', 'TransTitleRound' },
     } or nil, -- need nvim-0.9+
     ---@type {open: string | boolean, close: string | boolean, interval: integer} Window Animation
     animation = {
@@ -16,26 +16,38 @@ local default_frontend = {
         close = 'slid',
         interval = 12,
     },
-    timeout   = 2000, -- only for online backend query 
+    timeout   = 2000, -- only for online backend query
 }
 
 if Trans.conf.frontend.default then
     default_frontend = vim.tbl_extend('force', default_frontend, Trans.conf.frontend.default)
 end
 
+local function empty_method(method)
+    return function() error('Method [' .. method .. '] not implemented') end
+end
+
 
 ---@class TransFrontend
 ---@field opts? TransFrontendOpts options which user can set
 ---@field get_active_instance fun():TransFrontend?
----@field process fun(self: TransFrontend, data: TransData) @render backend result
 ---@field wait fun(self: TransFrontend): fun(backend: TransBackend): boolean Update wait status
 ---@field execute fun(action: string) @Execute action for frontend instance
----@field fallback fun() @Fallback method when no result
 ---@field setup? fun() @Setup method for frontend [optional] **NOTE: This method will be called when frontend is first used**
+local M = {
+    ---@type fun() @Fallback method when no result
+    fallback = empty_method 'fallback',
+    ---@type fun(self: TransFrontend, data: TransData) @render backend result
+    process = empty_method 'process',
+}
+
+
+
+
 
 ---@class Trans
 ---@field frontend TransFrontend
-return setmetatable({}, {
+return setmetatable(M, {
     __index = function(self, name)
         ---@type TransFrontend
         local frontend = require('Trans.frontend.' .. name)
diff --git a/lua/Trans/core/init.lua b/lua/Trans/core/init.lua
new file mode 100644
index 0000000..fe169f8
--- /dev/null
+++ b/lua/Trans/core/init.lua
@@ -0,0 +1,7 @@
+-- Return Core module
+local M = {}
+
+
+
+
+return M
diff --git a/lua/Trans/core/translate.lua b/lua/Trans/core/translate.lua
index 244426a..93fcab4 100644
--- a/lua/Trans/core/translate.lua
+++ b/lua/Trans/core/translate.lua
@@ -1,22 +1,43 @@
 local Trans = require 'Trans'
 
--- HACK : Core process logic
 local function process(opts)
     opts = opts or {}
     opts.mode = opts.mode or vim.fn.mode()
     local str = Trans.util.get_str(opts.mode)
     opts.str = str
 
-    if not str or str == '' then return end
+
+    if not str or str == '' then
+        Trans.debug 'No string to translate'
+        return
+    end
+
+
+    if opts.from == nil and opts.to == nil then
+        -- INFO : Default support [zh -> en] or [en -> zh]
+        if Trans.util.is_english(str) then
+            opts.from = 'en'
+            opts.to = 'zh'
+        else
+            opts.from = 'zh'
+            opts.to = 'en'
+        end
+    end
+    assert(opts.from and opts.to, 'opts.from and opts.to must be set at the same time')
+
+    opts.is_word = opts.is_word or Trans.util.is_word(str)
 
 
     -- Find in cache
     if Trans.cache[str] then
         local data = Trans.cache[str]
-        data.frontend:process(data)
-        return
+        return data.frontend:process(data)
     end
 
+
+
+
+    -- Create new data
     local data = Trans.data.new(opts)
     if Trans.strategy[data.frontend.opts.query](data) then
         Trans.cache[data.str] = data
@@ -26,9 +47,18 @@ local function process(opts)
     end
 end
 
----@class Trans
----@field translate fun(opts: { frontend: string?, mode: string?}?) Translate string core function
 
-return function(opts)
-    coroutine.wrap(process)(opts)
-end
+---@class TransDataOption
+---@field mode string?
+---@field frontend string?
+---@field from string? @Source language type
+---@field to string? @Target language type
+---@field is_word? boolean @Is the str a word
+
+
+
+--- NOTE : Use coroutine to stop and resume the process (for animation)
+
+---@class Trans
+---@field translate fun(opts: TransDataOption?) Translate string core function
+return function(...) coroutine.wrap(process)(...) end
diff --git a/lua/Trans/core/util.lua b/lua/Trans/core/util.lua
index 4d50638..8c934b4 100644
--- a/lua/Trans/core/util.lua
+++ b/lua/Trans/core/util.lua
@@ -38,21 +38,21 @@ end
 ---Get selected text
 ---@return string
 function M.get_lines()
-  local _start = vim.fn.getpos 'v'
-  local _end = vim.fn.getpos '.'
+    local _start = vim.fn.getpos 'v'
+    local _end = vim.fn.getpos '.'
 
-  if _start[2] > _end[2] then
-    _start, _end = _end, _start
-  end
+    if _start[2] > _end[2] then
+        _start, _end = _end, _start
+    end
 
-  local s_row, e_row = _start[2], _end[2]
+    local s_row, e_row = _start[2], _end[2]
 
-  if s_row == e_row then
-    return vim.fn.getline(s_row)
-  else
-    local lines = vim.fn.getline(s_row, e_row)
-    return table.concat(lines, " ")
-  end
+    if s_row == e_row then
+        return vim.fn.getline(s_row)
+    else
+        local lines = vim.fn.getline(s_row, e_row)
+        return table.concat(lines, ' ')
+    end
 end
 
 ---Get Text which need to be translated
@@ -224,6 +224,13 @@ function M.list_fields(list, field)
     return ret
 end
 
+-- function M.checker(method, ...)
+--     -- TODO :Use function programming to simplify the code
+--     local params = { ... }
+
+-- end
+
+
 ---@class Trans
 ---@field util TransUtil
 return M