From fe86cfda472d8a2ceb0334fcfbc9a76018fa0e9a Mon Sep 17 00:00:00 2001
From: Drew Weymouth <dweymouth@gmail.com>
Date: Sat, 28 Jan 2023 09:04:17 -0800
Subject: [PATCH] batch-add albums to infinite scroll grid to slightly improve
 smoothness

---
 backend/albumiterator.go | 55 +++++++++++++++-------------------------
 ui/widgets/albumgrid.go  | 33 ++++++++++--------------
 2 files changed, 34 insertions(+), 54 deletions(-)

diff --git a/backend/albumiterator.go b/backend/albumiterator.go
index c065434..6ef2c76 100644
--- a/backend/albumiterator.go
+++ b/backend/albumiterator.go
@@ -10,7 +10,6 @@ import (
 
 type AlbumIterator interface {
 	Next() *subsonic.AlbumID3
-	NextN(int, func(*subsonic.AlbumID3))
 }
 
 type LibraryManager struct {
@@ -164,18 +163,6 @@ func (r *baseIter) Next() *subsonic.AlbumID3 {
 	return r.prefetched[0]
 }
 
-func (r *baseIter) NextN(n int, cb func(*subsonic.AlbumID3)) {
-	go func() {
-		for i := 0; i < n; i++ {
-			a := r.Next()
-			cb(a)
-			if a == nil {
-				break
-			}
-		}
-	}()
-}
-
 type searchIter struct {
 	query         string
 	artistOffset  int
@@ -263,18 +250,6 @@ func (s *searchIter) Next() *subsonic.AlbumID3 {
 	return nil
 }
 
-func (s *searchIter) NextN(n int, cb func(*subsonic.AlbumID3)) {
-	go func() {
-		for i := 0; i < n; i++ {
-			a := s.Next()
-			cb(a)
-			if a == nil {
-				break
-			}
-		}
-	}()
-}
-
 func (s *searchIter) addNewAlbums(al []*subsonic.AlbumID3) {
 	for _, album := range al {
 		if _, have := s.albumIDset[album.ID]; have {
@@ -386,14 +361,24 @@ func (r *randomIter) Next() *subsonic.AlbumID3 {
 	return nil
 }
 
-func (r *randomIter) NextN(n int, cb func(*subsonic.AlbumID3)) {
-	go func() {
-		for i := 0; i < n; i++ {
-			a := r.Next()
-			cb(a)
-			if a == nil {
-				break
-			}
-		}
-	}()
+type BatchingIterator struct {
+	iter AlbumIterator
+}
+
+func NewBatchingIterator(iter AlbumIterator) *BatchingIterator {
+	return &BatchingIterator{iter}
+}
+
+func (b *BatchingIterator) NextN(n int) []*subsonic.AlbumID3 {
+	results := make([]*subsonic.AlbumID3, 0, n)
+	i := 0
+	for i < n {
+		album := b.iter.Next()
+		if album == nil {
+			break
+		}
+		results = append(results, album)
+		i++
+	}
+	return results
 }
diff --git a/ui/widgets/albumgrid.go b/ui/widgets/albumgrid.go
index 64ecd0e..ba1d6e0 100644
--- a/ui/widgets/albumgrid.go
+++ b/ui/widgets/albumgrid.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"image"
 	"log"
+	"supersonic/backend"
 
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/widget"
@@ -15,10 +16,6 @@ type ImageFetcher interface {
 	GetAlbumThumbnail(string) (image.Image, error)
 }
 
-type AlbumIterator interface {
-	NextN(int, func(*subsonic.AlbumID3))
-}
-
 type AlbumGrid struct {
 	widget.BaseWidget
 
@@ -29,7 +26,7 @@ type AlbumGrid struct {
 
 type AlbumGridState struct {
 	albums   []*subsonic.AlbumID3
-	iter     AlbumIterator
+	iter     *backend.BatchingIterator
 	fetching bool
 	done     bool
 	showYear bool
@@ -58,10 +55,10 @@ func NewFixedAlbumGrid(albums []*subsonic.AlbumID3, fetch ImageFetcher, showYear
 	return ag
 }
 
-func NewAlbumGrid(iter AlbumIterator, fetch ImageFetcher, showYear bool) *AlbumGrid {
+func NewAlbumGrid(iter backend.AlbumIterator, fetch ImageFetcher, showYear bool) *AlbumGrid {
 	ag := &AlbumGrid{
 		AlbumGridState: AlbumGridState{
-			iter:         iter,
+			iter:         backend.NewBatchingIterator(iter),
 			imageFetcher: fetch,
 		},
 	}
@@ -94,11 +91,11 @@ func (ag *AlbumGrid) Clear() {
 	ag.done = true
 }
 
-func (ag *AlbumGrid) Reset(iter AlbumIterator) {
+func (ag *AlbumGrid) Reset(iter backend.AlbumIterator) {
 	ag.albums = nil
 	ag.fetching = false
 	ag.done = false
-	ag.iter = iter
+	ag.iter = backend.NewBatchingIterator(iter)
 	ag.fetchMoreAlbums(36)
 }
 
@@ -182,20 +179,18 @@ func (a *AlbumGrid) fetchMoreAlbums(count int) {
 	if a.iter == nil {
 		a.done = true
 	}
-	i := 0
 	a.fetching = true
-	a.iter.NextN(count, func(al *subsonic.AlbumID3) {
-		if al == nil {
+	go func() {
+		albums := a.iter.NextN(count)
+		a.albums = append(a.albums, albums...)
+		if len(albums) < count {
 			a.done = true
-			return
 		}
-		a.albums = append(a.albums, al)
-		i++
-		if i == count {
-			a.fetching = false
+		a.fetching = false
+		if len(albums) > 0 {
+			a.Refresh()
 		}
-		a.Refresh()
-	})
+	}()
 }
 
 func (a *AlbumGrid) CreateRenderer() fyne.WidgetRenderer {