fix(sync): trigger auth then resume operation when not authenticated (#69)

* fix(sync): trigger auth then resume operation when not authenticated

Problem: `get_access_token()` called `auth()` then immediately tried to
load tokens, but `auth()` is async (TCP server + browser redirect), so
tokens were never present at that point. All sync operations silently
aborted when unauthenticated.

Solution: Remove the inline auth attempt from `get_access_token()` and
add an `on_complete` callback to `auth()` / `_exchange_code()`. Add a
`with_token(callback)` helper in `gtasks.lua` and `gcal.lua` that
triggers auth with the sync operation as the continuation, so
`push`/`pull`/`sync` resume automatically after the OAuth flow
completes.

* ci: format

lua/pending/sync/gcal.lua

@@ -136,17 +136,31 @@ local function delete_event(access_token, calendar_id, event_id)
   return err
 end
 
+---@param callback fun(access_token: string): nil
+local function with_token(callback)
+  oauth.async(function()
+    local token = client:get_access_token()
+    if not token then
+      client:auth(function()
+        oauth.async(function()
+          local fresh = client:get_access_token()
+          if fresh then
+            callback(fresh)
+          end
+        end)
+      end)
+      return
+    end
+    callback(token)
+  end)
+end
+
 function M.auth()
   client:auth()
 end
 
 function M.push()
-  oauth.async(function()
-    local access_token = client:get_access_token()
-    if not access_token then
-      return
-    end
-
+  with_token(function(access_token)
     local calendars, cal_err = get_all_calendars(access_token)
     if cal_err or not calendars then
       log.error(cal_err or 'failed to fetch calendars')

lua/pending/sync/gtasks.lua

@@ -337,23 +337,38 @@ local function pull_pass(access_token, tasklists, s, now_ts, by_gtasks_id)
   return created, updated
 end
 
----@return string? access_token
+---@param access_token string
 ---@return table<string, string>? tasklists
----@return pending.Store? store
+---@return pending.Store? s
 ---@return string? now_ts
-local function sync_setup()
-  local access_token = client:get_access_token()
-  if not access_token then
-    return nil
-  end
+local function sync_setup(access_token)
   local tasklists, tl_err = get_all_tasklists(access_token)
   if tl_err or not tasklists then
     log.error(tl_err or 'failed to fetch task lists')
-    return nil
+    return nil, nil, nil
   end
   local s = require('pending').store()
   local now_ts = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]]
-  return access_token, tasklists, s, now_ts
+  return tasklists, s, now_ts
+end
+
+---@param callback fun(access_token: string): nil
+local function with_token(callback)
+  oauth.async(function()
+    local token = client:get_access_token()
+    if not token then
+      client:auth(function()
+        oauth.async(function()
+          local fresh = client:get_access_token()
+          if fresh then
+            callback(fresh)
+          end
+        end)
+      end)
+      return
+    end
+    callback(token)
+  end)
 end
 
 function M.auth()
@@ -361,12 +376,11 @@ function M.auth()
 end
 
 function M.push()
-  oauth.async(function()
-    local access_token, tasklists, s, now_ts = sync_setup()
-    if not access_token then
+  with_token(function(access_token)
+    local tasklists, s, now_ts = sync_setup(access_token)
+    if not tasklists then
       return
     end
-    ---@cast tasklists table<string, string>
     ---@cast s pending.Store
     ---@cast now_ts string
     local by_gtasks_id = build_id_index(s)
@@ -382,12 +396,11 @@ function M.push()
 end
 
 function M.pull()
-  oauth.async(function()
-    local access_token, tasklists, s, now_ts = sync_setup()
-    if not access_token then
+  with_token(function(access_token)
+    local tasklists, s, now_ts = sync_setup(access_token)
+    if not tasklists then
       return
     end
-    ---@cast tasklists table<string, string>
     ---@cast s pending.Store
     ---@cast now_ts string
     local by_gtasks_id = build_id_index(s)
@@ -403,12 +416,11 @@ function M.pull()
 end
 
 function M.sync()
-  oauth.async(function()
-    local access_token, tasklists, s, now_ts = sync_setup()
-    if not access_token then
+  with_token(function(access_token)
+    local tasklists, s, now_ts = sync_setup(access_token)
+    if not tasklists then
       return
     end
-    ---@cast tasklists table<string, string>
     ---@cast s pending.Store
     ---@cast now_ts string
     local by_gtasks_id = build_id_index(s)

lua/pending/sync/oauth.lua

@@ -236,11 +236,7 @@ function OAuthClient:get_access_token()
   local creds = self:resolve_credentials()
   local tokens = self:load_tokens()
   if not tokens or not tokens.refresh_token then
-    self:auth()
-    tokens = self:load_tokens()
-    if not tokens then
-      return nil
-    end
+    return nil
   end
   local now = os.time()
   local obtained = tokens.obtained_at or 0
@@ -255,8 +251,9 @@ function OAuthClient:get_access_token()
   return tokens.access_token
 end
 
+---@param on_complete? fun(): nil
 ---@return nil
-function OAuthClient:auth()
+function OAuthClient:auth(on_complete)
   local creds = self:resolve_credentials()
   local port = self.port
 
@@ -329,7 +326,7 @@ function OAuthClient:auth()
       close_server()
       if code then
         vim.schedule(function()
-          self:_exchange_code(creds, code, code_verifier, port)
+          self:_exchange_code(creds, code, code_verifier, port, on_complete)
         end)
       end
     end)
@@ -347,8 +344,9 @@ end
 ---@param code string
 ---@param code_verifier string
 ---@param port integer
+---@param on_complete? fun(): nil
 ---@return nil
-function OAuthClient:_exchange_code(creds, code, code_verifier, port)
+function OAuthClient:_exchange_code(creds, code, code_verifier, port, on_complete)
   local body = 'client_id='
     .. M.url_encode(creds.client_id)
     .. '&client_secret='
@@ -387,6 +385,9 @@ function OAuthClient:_exchange_code(creds, code, code_verifier, port)
   decoded.obtained_at = os.time()
   self:save_tokens(decoded)
   log.info(self.name .. ' authorized successfully.')
+  if on_complete then
+    on_complete()
+  end
 end
 
 ---@param opts { name: string, scope: string, port: integer, config_key: string }