supersonic/ui/widgets/gridview.go

package widgets

import (
	"context"
	"image"
	"log"
	"sync"

	"github.com/dweymouth/supersonic/backend/mediaprovider"
	"github.com/dweymouth/supersonic/sharedutil"

	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/widget"
	xwidget "fyne.io/x/fyne/widget"
)

const batchFetchSize = 6

type BatchingIterator struct {
	iter mediaprovider.AlbumIterator
}

func NewBatchingIterator(iter mediaprovider.AlbumIterator) BatchingIterator {
	return BatchingIterator{iter}
}

func (b *BatchingIterator) NextN(n int) []*mediaprovider.Album {
	results := make([]*mediaprovider.Album, 0, n)
	i := 0
	for i < n {
		album := b.iter.Next()
		if album == nil {
			break
		}
		results = append(results, album)
		i++
	}
	return results
}

type ImageFetcher interface {
	GetCoverThumbnailFromCache(string) (image.Image, bool)
	GetCoverThumbnail(string) (image.Image, error)
}

type GridViewIterator interface {
	NextN(int) []GridViewItemModel
}

type gridViewAlbumIterator struct {
	iter BatchingIterator
}

func (g gridViewAlbumIterator) NextN(n int) []GridViewItemModel {
	albums := g.iter.NextN(n)
	return sharedutil.MapSlice(albums, func(al *mediaprovider.Album) GridViewItemModel {
		return GridViewItemModel{
			Name:        al.Name,
			ID:          al.ID,
			CoverArtID:  al.CoverArtID,
			Secondary:   al.ArtistNames[0],
			SecondaryID: al.ArtistIDs[0],
		}
	})
}

func NewGridViewAlbumIterator(iter mediaprovider.AlbumIterator) GridViewIterator {
	return gridViewAlbumIterator{iter: NewBatchingIterator(iter)}
}

type GridView struct {
	widget.BaseWidget

	stateMutex  sync.RWMutex
	fetchCancel context.CancelFunc
	GridViewState

	grid *xwidget.GridWrap
}

type GridViewState struct {
	items        []GridViewItemModel
	iter         GridViewIterator
	imageFetcher ImageFetcher
	placeholder  fyne.Resource
	highestShown int
	done         bool

	OnPlay              func(id string, shuffle bool)
	OnAddToQueue        func(id string)
	OnAddToPlaylist     func(id string)
	OnDownload          func(id string)
	OnShowItemPage      func(id string)
	OnShowSecondaryPage func(id string)

	scrollPos float32
}

var _ fyne.Widget = (*GridView)(nil)

func NewFixedGridView(items []GridViewItemModel, fetch ImageFetcher, placeholder fyne.Resource) *GridView {
	g := &GridView{
		GridViewState: GridViewState{
			items:        items,
			done:         true,
			imageFetcher: fetch,
			placeholder:  placeholder,
		},
	}
	g.ExtendBaseWidget(g)
	g.createGridWrap()
	return g
}

func NewGridView(iter GridViewIterator, fetch ImageFetcher, placeholder fyne.Resource) *GridView {
	g := &GridView{
		GridViewState: GridViewState{
			iter:         iter,
			imageFetcher: fetch,
			placeholder:  placeholder,
		},
	}
	g.ExtendBaseWidget(g)
	g.createGridWrap()

	// fetch initial items
	g.fetchMoreItems(36)
	return g
}

func (g *GridView) SaveToState() *GridViewState {
	g.stateMutex.RLock()
	s := g.GridViewState
	g.stateMutex.RUnlock()
	s.scrollPos = g.grid.GetScrollOffset()
	return &s
}

func NewGridViewFromState(state *GridViewState) *GridView {
	g := &GridView{GridViewState: *state}
	g.ExtendBaseWidget(g)
	g.createGridWrap()
	g.Refresh() // needed to initialize the widget
	g.grid.ScrollToOffset(state.scrollPos)
	return g
}

func (g *GridView) Clear() {
	if g.fetchCancel != nil {
		g.fetchCancel()
		g.fetchCancel = nil
	}
	g.stateMutex.Lock()
	defer g.stateMutex.Unlock()
	g.items = nil
	g.done = true
}

func (g *GridView) Reset(iter GridViewIterator) {
	if g.fetchCancel != nil {
		g.fetchCancel()
		g.fetchCancel = nil
	}
	g.stateMutex.Lock()
	g.items = nil
	g.done = false
	g.highestShown = 0
	g.iter = iter
	g.stateMutex.Unlock()
	g.fetchMoreItems(36)
	g.Refresh()
}

func (g *GridView) ResetFromState(state *GridViewState) {
	if g.fetchCancel != nil {
		g.fetchCancel()
		g.fetchCancel = nil
	}
	g.stateMutex.Lock()
	g.GridViewState = *state
	g.stateMutex.Unlock()
	g.grid.Refresh()
	g.grid.ScrollToOffset(state.scrollPos)
	g.grid.Refresh()
}

func (g *GridView) ResetFixed(items []GridViewItemModel) {
	if g.fetchCancel != nil {
		g.fetchCancel()
		g.fetchCancel = nil
	}
	g.stateMutex.Lock()
	g.items = items
	g.done = true
	g.highestShown = 0
	g.iter = nil
	g.stateMutex.Unlock()
	g.Refresh()
}

func (g *GridView) GetScrollOffset() float32 {
	return g.grid.GetScrollOffset()
}

func (g *GridView) ScrollToOffset(offs float32) {
	g.grid.ScrollToOffset(offs)
}

func (g *GridView) createGridWrap() {
	g.grid = xwidget.NewGridWrap(
		func() int {
			return g.lenItems()
		},
		// create func
		func() fyne.CanvasObject {
			card := NewGridViewItem(g.placeholder)
			card.OnPlay = func(shuffle bool) {
				if g.OnPlay != nil {
					g.OnPlay(card.ItemID(), shuffle)
				}
			}
			card.OnAddToQueue = func() {
				if g.OnAddToQueue != nil {
					g.OnAddToQueue(card.ItemID())
				}
			}
			card.OnShowSecondaryPage = func() {
				if g.OnShowSecondaryPage != nil {
					g.OnShowSecondaryPage(card.SecondaryID())
				}
			}
			card.OnShowItemPage = func() {
				if g.OnShowItemPage != nil {
					g.OnShowItemPage(card.ItemID())
				}
			}
			card.OnAddToPlaylist = func() {
				if g.OnAddToPlaylist != nil {
					g.OnAddToPlaylist(card.ItemID())
				}
			}
			card.OnDownload = func() {
				if g.OnDownload != nil {
					g.OnDownload(card.ItemID())
				}
			}
			return card
		},
		// update func
		func(itemID xwidget.GridWrapItemID, obj fyne.CanvasObject) {
			ac := obj.(*GridViewItem)
			g.doUpdateItemCard(int(itemID), ac)
		},
	)
}

func (g *GridView) doUpdateItemCard(itemIdx int, card *GridViewItem) {
	if itemIdx > g.highestShown {
		g.highestShown = itemIdx
	}
	var item GridViewItemModel
	g.stateMutex.RLock()
	// itemIdx can rarely be out of range if the data is being updated
	// as the view is requested to refresh
	if itemIdx < len(g.items) {
		item = g.items[itemIdx]
	}
	g.stateMutex.RUnlock()
	if card.PrevID == item.ID {
		// nothing to do
		return
	}
	card.Update(item)
	card.PrevID = item.ID
	// cancel any previous image fetch
	if card.ImgLoadCancel != nil {
		card.ImgLoadCancel()
		card.ImgLoadCancel = nil
	}
	if item.CoverArtID != "" {
		if img, ok := g.imageFetcher.GetCoverThumbnailFromCache(item.CoverArtID); ok {
			card.Cover.SetImage(img)
		} else {
			card.Cover.SetImage(nil)
			// asynchronously fetch cover image
			ctx, cancel := context.WithCancel(context.Background())
			card.ImgLoadCancel = cancel
			go func(ctx context.Context) {
				i, err := g.imageFetcher.GetCoverThumbnail(item.CoverArtID)
				select {
				case <-ctx.Done():
					return
				default:
					if err == nil {
						card.Cover.SetImage(i)
					} else {
						log.Printf("error fetching image: %s", err.Error())
					}
				}
			}(ctx)
		}
	} else {
		// use the placeholder for an item that has no cover art ID
		card.Cover.SetImage(nil)
	}

	// if user has scrolled near the bottom, fetch more
	if !g.done && g.fetchCancel == nil && itemIdx > g.lenItems()-10 {
		g.fetchMoreItems(20)
	}
}

func (g *GridView) lenItems() int {
	g.stateMutex.RLock()
	defer g.stateMutex.RUnlock()
	return len(g.items)
}

// fetches at least count more items
func (g *GridView) fetchMoreItems(count int) {
	if g.iter == nil {
		g.done = true
		return
	}
	ctx, cancel := context.WithCancel(context.Background())
	g.fetchCancel = cancel
	go func() {
		// keep repeating the fetch task as long as the user
		// has scrolled near the bottom
		for !g.done && g.highestShown >= g.lenItems()-10 {
			n := 0
			for !g.done && n < count {
				items := g.iter.NextN(batchFetchSize)
				select {
				case <-ctx.Done():
					return
				default:
					g.stateMutex.Lock()
					g.items = append(g.items, items...)
					g.stateMutex.Unlock()
					if len(items) < batchFetchSize {
						g.done = true
					}
					n += len(items)
					if len(items) > 0 {
						g.grid.Refresh()
					}
				}
			}
		}
		g.fetchCancel = nil
	}()
}

func (g *GridView) CreateRenderer() fyne.WidgetRenderer {
	return widget.NewSimpleRenderer(g.grid)
}