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
+}