From 7c33c37e1017024b8c53a0ea4453ff48f81ced22 Mon Sep 17 00:00:00 2001
From: Nolan Woods <nolan@i2labs.ca>
Date: Sun, 16 Feb 2020 16:29:36 -0800
Subject: [PATCH] Change Dir to interface and add NewLazyDir()

---
 fs/dir.go | 87 +++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 69 insertions(+), 18 deletions(-)

diff --git a/fs/dir.go b/fs/dir.go
index d876d89a61a0b..e63dc32ca2ae2 100644
--- a/fs/dir.go
+++ b/fs/dir.go
@@ -6,7 +6,16 @@ import (
 )
 
 // Dir describes an unspecialized directory for directory/container/bucket lists
-type Dir struct {
+
+type Dir interface {
+	Directory
+	SetRemote(string) Dir
+	SetID(string) Dir
+	SetSize(int64) Dir
+	SetItems(int64) Dir
+}
+
+type dir struct {
 	remote  string    // name of the directory
 	modTime time.Time // modification or creation time - IsZero for unknown
 	size    int64     // size of directory and contents or -1 if unknown
@@ -14,9 +23,9 @@ type Dir struct {
 	id      string    // optional ID
 }
 
-// NewDir creates an unspecialized Directory object
-func NewDir(remote string, modTime time.Time) *Dir {
-	return &Dir{
+// NewDir creates an unspecialized *dir object
+func NewDir(remote string, modTime time.Time) Dir {
+	return &dir{
 		remote:  remote,
 		modTime: modTime,
 		size:    -1,
@@ -24,47 +33,88 @@ func NewDir(remote string, modTime time.Time) *Dir {
 	}
 }
 
+type lazyDir struct {
+	dir
+	sizeGetter  func() int64
+	itemsGetter func() int64
+}
+
 // NewDirCopy creates an unspecialized copy of the Directory object passed in
-func NewDirCopy(ctx context.Context, d Directory) *Dir {
-	return &Dir{
+func NewDirCopy(ctx context.Context, d Directory) Dir {
+	dir := dir{
 		remote:  d.Remote(),
 		modTime: d.ModTime(ctx),
 		size:    d.Size(),
 		items:   d.Items(),
 		id:      d.ID(),
 	}
+	if l, ok := d.(*lazyDir); ok {
+		return &lazyDir{
+			dir:         dir,
+			sizeGetter:  l.sizeGetter,
+			itemsGetter: l.itemsGetter,
+		}
+	}
+	return &dir
+}
+
+func (d *lazyDir) Size() int64 {
+	if d.dir.Size() == -1 {
+		d.SetSize(d.sizeGetter())
+	}
+	return d.dir.Size()
+}
+
+func (d *lazyDir) Items() int64 {
+	if d.dir.Items() == -1 {
+		d.SetItems(d.itemsGetter())
+	}
+	return d.dir.Items()
+}
+
+func NewLazyDir(remote string, modTime time.Time, sizeGetter func() int64, itemsGetter func() int64) Dir {
+	return &lazyDir{
+		dir: dir{
+			remote:  remote,
+			modTime: modTime,
+			size:    -1,
+			items:   -1,
+		},
+		sizeGetter:  sizeGetter,
+		itemsGetter: itemsGetter,
+	}
 }
 
 // String returns the name
-func (d *Dir) String() string {
+func (d *dir) String() string {
 	return d.remote
 }
 
 // Remote returns the remote path
-func (d *Dir) Remote() string {
+func (d *dir) Remote() string {
 	return d.remote
 }
 
 // SetRemote sets the remote
-func (d *Dir) SetRemote(remote string) *Dir {
+func (d *dir) SetRemote(remote string) Dir {
 	d.remote = remote
 	return d
 }
 
 // ID gets the optional ID
-func (d *Dir) ID() string {
+func (d *dir) ID() string {
 	return d.id
 }
 
 // SetID sets the optional ID
-func (d *Dir) SetID(id string) *Dir {
+func (d *dir) SetID(id string) Dir {
 	d.id = id
 	return d
 }
 
 // ModTime returns the modification date of the file
 // It should return a best guess if one isn't available
-func (d *Dir) ModTime(ctx context.Context) time.Time {
+func (d *dir) ModTime(ctx context.Context) time.Time {
 	if !d.modTime.IsZero() {
 		return d.modTime
 	}
@@ -72,30 +122,31 @@ func (d *Dir) ModTime(ctx context.Context) time.Time {
 }
 
 // Size returns the size of the file
-func (d *Dir) Size() int64 {
+func (d *dir) Size() int64 {
 	return d.size
 }
 
 // SetSize sets the size of the directory
-func (d *Dir) SetSize(size int64) *Dir {
+func (d *dir) SetSize(size int64) Dir {
 	d.size = size
 	return d
 }
 
 // Items returns the count of items in this directory or this
 // directory and subdirectories if known, -1 for unknown
-func (d *Dir) Items() int64 {
+func (d *dir) Items() int64 {
 	return d.items
 }
 
 // SetItems sets the number of items in the directory
-func (d *Dir) SetItems(items int64) *Dir {
+func (d *dir) SetItems(items int64) Dir {
 	d.items = items
 	return d
 }
 
 // Check interfaces
 var (
-	_ DirEntry  = (*Dir)(nil)
-	_ Directory = (*Dir)(nil)
+	_ Dir       = (*dir)(nil)
+	_ DirEntry  = (*dir)(nil)
+	_ Directory = (*dir)(nil)
 )