feat(thunder): add offline download tool (#7673)

* feat(thunder): add offline download tool

* fix(thunder): improve error handling and parse file size in status response

---------

Co-authored-by: Andy Hsu <i@nn.ci>

internal/offline_download/thunder/util.go

@@ -0,0 +1,42 @@
+package thunder
+
+import (
+	"context"
+	"time"
+
+	"github.com/Xhofe/go-cache"
+	"github.com/alist-org/alist/v3/drivers/thunder"
+	"github.com/alist-org/alist/v3/internal/op"
+	"github.com/alist-org/alist/v3/pkg/singleflight"
+)
+
+var taskCache = cache.NewMemCache(cache.WithShards[[]thunder.OfflineTask](16))
+var taskG singleflight.Group[[]thunder.OfflineTask]
+
+func (t *Thunder) GetTasks(thunderDriver *thunder.Thunder) ([]thunder.OfflineTask, error) {
+	key := op.Key(thunderDriver, "/drive/v1/task")
+	if !t.refreshTaskCache {
+		if tasks, ok := taskCache.Get(key); ok {
+			return tasks, nil
+		}
+	}
+	t.refreshTaskCache = false
+	tasks, err, _ := taskG.Do(key, func() ([]thunder.OfflineTask, error) {
+		ctx := context.Background()
+		tasks, err := thunderDriver.OfflineList(ctx, "")
+		if err != nil {
+			return nil, err
+		}
+		// 添加缓存 10s
+		if len(tasks) > 0 {
+			taskCache.Set(key, tasks, cache.WithEx[[]thunder.OfflineTask](time.Second*10))
+		} else {
+			taskCache.Del(key)
+		}
+		return tasks, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return tasks, nil
+}