fix(copilot): show token output in chat

Thanks to @GitMurf for this original PR in #623

lua/codecompanion/adapters/copilot.lua

@@ -99,6 +99,17 @@ local function authorize_token()
   return _github_token
 end
 
+---Prepare data to be parsed as JSON
+---@param data string | { body: string }
+---@return string
+local prepare_data_for_json = function(data)
+  if type(data) == "table" then
+    return data.body
+  end
+  local find_json_start = string.find(data, "{") or 1
+  return string.sub(data, find_json_start)
+end
+
 ---@class Copilot.Adapter: CodeCompanion.Adapter
 return {
   name = "copilot",
@@ -166,7 +177,21 @@ return {
       return openai.handlers.form_messages(self, messages)
     end,
     tokens = function(self, data)
-      return openai.handlers.tokens(self, data)
+      if data and data ~= "" then
+        local data_mod = prepare_data_for_json(data)
+        local ok, json = pcall(vim.json.decode, data_mod, { luanil = { object = true } })
+
+        if ok then
+          if json.usage then
+            local total_tokens = json.usage.total_tokens or 0
+            local completion_tokens = json.usage.completion_tokens or 0
+            local prompt_tokens = json.usage.prompt_tokens or 0
+            local tokens = total_tokens > 0 and total_tokens or completion_tokens + prompt_tokens
+            log:trace("Tokens: %s", tokens)
+            return tokens
+          end
+        end
+      end
     end,
     chat_output = function(self, data)
       return openai.handlers.chat_output(self, data)