add reorder tracks options to playlist page context menu

sharedutil/sharedutil.go

@@ -1,6 +1,11 @@
 package sharedutil
 
-import "github.com/dweymouth/go-subsonic/subsonic"
+import (
+	"math"
+	"sort"
+
+	"github.com/dweymouth/go-subsonic/subsonic"
+)
 
 func StringSliceContains(slice []string, str string) bool {
 	for _, s := range slice {
@@ -11,6 +16,15 @@ func StringSliceContains(slice []string, str string) bool {
 	return false
 }
 
+func IntSliceContains(slice []int, i int) bool {
+	for _, x := range slice {
+		if x == i {
+			return true
+		}
+	}
+	return false
+}
+
 func FindTrackByID(id string, tracks []*subsonic.Child) *subsonic.Child {
 	for _, tr := range tracks {
 		if id == tr.ID {
@@ -26,3 +40,89 @@ func TrackIDOrEmptyStr(track *subsonic.Child) string {
 	}
 	return track.ID
 }
+
+type TrackReorderOp int
+
+const (
+	MoveToTop TrackReorderOp = iota
+	MoveToBottom
+	MoveUp
+	MoveDown
+)
+
+// Reorder tracks and return a new track slice.
+// idxToMove must contain only valid indexes into tracks, and no repeats
+func ReorderTracks(tracks []*subsonic.Child, idxToMove []int, op TrackReorderOp) []*subsonic.Child {
+	newTracks := make([]*subsonic.Child, len(tracks))
+	switch op {
+	case MoveToTop:
+		topIdx := 0
+		botIdx := len(idxToMove)
+		for i, t := range tracks {
+			if IntSliceContains(idxToMove, i) {
+				newTracks[topIdx] = t
+				topIdx++
+			} else {
+				newTracks[botIdx] = t
+				botIdx++
+			}
+		}
+	case MoveToBottom:
+		topIdx := 0
+		botIdx := len(tracks) - len(idxToMove)
+		for i, t := range tracks {
+			if IntSliceContains(idxToMove, i) {
+				newTracks[botIdx] = t
+				botIdx++
+			} else {
+				newTracks[topIdx] = t
+				topIdx++
+			}
+		}
+	case MoveUp:
+		first := firstIdxCanMoveUp(idxToMove)
+		copy(newTracks, tracks)
+		for _, i := range idxToMove {
+			if i < first {
+				continue
+			}
+			newTracks[i-1], newTracks[i] = newTracks[i], newTracks[i-1]
+		}
+	case MoveDown:
+		last := lastIdxCanMoveDown(idxToMove, len(tracks))
+		copy(newTracks, tracks)
+		for i := len(idxToMove) - 1; i >= 0; i-- {
+			idx := idxToMove[i]
+			if idx > last {
+				continue
+			}
+			newTracks[idx+1], newTracks[idx] = newTracks[idx], newTracks[idx+1]
+		}
+	}
+	return newTracks
+}
+
+func firstIdxCanMoveUp(idxs []int) int {
+	prevIdx := -1
+	sort.Ints(idxs)
+	for _, idx := range idxs {
+		if idx > prevIdx+1 {
+			return idx
+		}
+		prevIdx = idx
+	}
+	return math.MaxInt
+}
+
+func lastIdxCanMoveDown(idxs []int, lenSlice int) int {
+	prevIdx := lenSlice
+	sort.Ints(idxs)
+	for i := len(idxs) - 1; i >= 0; i-- {
+		idx := idxs[i]
+		if idx < prevIdx-1 {
+			return idx
+		}
+		prevIdx = idx
+	}
+	return -1
+}

sharedutil/sharedutil_test.go

@@ -0,0 +1,91 @@
+package sharedutil
+
+import (
+	"testing"
+
+	"github.com/dweymouth/go-subsonic/subsonic"
+)
+
+func Test_ReorderTracks(t *testing.T) {
+	tracks := []*subsonic.Child{
+		{ID: "a"}, // 0
+		{ID: "b"}, // 1
+		{ID: "c"}, // 2
+		{ID: "d"}, // 3
+		{ID: "e"}, // 4
+		{ID: "f"}, // 5
+	}
+
+	// test MoveToTop:
+	idxToMove := []int{0, 2, 3, 5}
+	want := []*subsonic.Child{
+		{ID: "a"},
+		{ID: "c"},
+		{ID: "d"},
+		{ID: "f"},
+		{ID: "b"},
+		{ID: "e"},
+	}
+	newTracks := ReorderTracks(tracks, idxToMove, MoveToTop)
+	if !tracklistsEqual(t, newTracks, want) {
+		t.Error("ReorderTracks: MoveToTop order incorrect")
+	}
+
+	// test MoveToBottom:
+	idxToMove = []int{0, 2, 5}
+	want = []*subsonic.Child{
+		{ID: "b"},
+		{ID: "d"},
+		{ID: "e"},
+		{ID: "a"},
+		{ID: "c"},
+		{ID: "f"},
+	}
+	newTracks = ReorderTracks(tracks, idxToMove, MoveToBottom)
+	if !tracklistsEqual(t, newTracks, want) {
+		t.Error("ReorderTracks: MoveToBottom order incorrect")
+	}
+
+	// test MoveUp:
+	idxToMove = []int{0, 1, 3, 5}
+	want = []*subsonic.Child{
+		{ID: "a"},
+		{ID: "b"},
+		{ID: "d"},
+		{ID: "c"},
+		{ID: "f"},
+		{ID: "e"},
+	}
+	newTracks = ReorderTracks(tracks, idxToMove, MoveUp)
+	if !tracklistsEqual(t, newTracks, want) {
+		t.Error("ReorderTracks: MoveUp order incorrect")
+	}
+
+	// test MoveDown:
+	idxToMove = []int{2, 4, 5}
+	want = []*subsonic.Child{
+		{ID: "a"},
+		{ID: "b"},
+		{ID: "d"},
+		{ID: "c"},
+		{ID: "e"},
+		{ID: "f"},
+	}
+	newTracks = ReorderTracks(tracks, idxToMove, MoveDown)
+	if !tracklistsEqual(t, newTracks, want) {
+		t.Error("ReorderTracks: MoveDown order incorrect")
+	}
+}
+
+func tracklistsEqual(t *testing.T, a, b []*subsonic.Child) bool {
+	t.Helper()
+	if len(a) != len(b) {
+		return false
+	}
+	for i, _ := range a {
+		if a[i].ID != b[i].ID {
+			return false
+		}
+	}
+	return true
+}