feat: multiple search indexes (#2514)

* refactor: abstract search interface

* wip: ~

* fix cycle import

* objs update hook

* wip: ~

* Delete search/none

* auto update index while cache changed

* db searcher

TODO: bleve init issue

cannot open index, metadata missing

* fix size type

why float64??

* fix typo

* fix nil pointer using

* api adapt ui

* bleve: fix clear & change struct

internal/fs/walk.go

@@ -0,0 +1,45 @@
+package fs
+
+import (
+	"context"
+	"path"
+	"path/filepath"
+
+	"github.com/alist-org/alist/v3/internal/db"
+	"github.com/alist-org/alist/v3/internal/model"
+)
+
+// WalkFS traverses filesystem fs starting at name up to depth levels.
+//
+// WalkFS will stop when current depth > `depth`. For each visited node,
+// WalkFS calls walkFn. If a visited file system node is a directory and
+// walkFn returns path.SkipDir, walkFS will skip traversal of this node.
+func WalkFS(ctx context.Context, depth int, name string, info model.Obj, walkFn func(reqPath string, info model.Obj, err error) error) error {
+	// This implementation is based on Walk's code in the standard path/path package.
+	walkFnErr := walkFn(name, info, nil)
+	if walkFnErr != nil {
+		if info.IsDir() && walkFnErr == filepath.SkipDir {
+			return nil
+		}
+		return walkFnErr
+	}
+	if !info.IsDir() || depth == 0 {
+		return nil
+	}
+	meta, _ := db.GetNearestMeta(name)
+	// Read directory names.
+	objs, err := List(context.WithValue(ctx, "meta", meta), name)
+	if err != nil {
+		return walkFnErr
+	}
+	for _, fileInfo := range objs {
+		filename := path.Join(name, fileInfo.GetName())
+		if err := WalkFS(ctx, depth-1, filename, fileInfo, walkFn); err != nil {
+			if err == filepath.SkipDir {
+				break
+			}
+			return err
+		}
+	}
+	return nil
+}