refactor(lyrics): share pointer helpers via gg.Clone and gg.If

Add a nil-safe generic gg.Clone[T](*T) *T to utils/gg alongside the existing
V and If helpers, and route the lyrics package's bespoke pointer-copy helpers
through it: ptrOrNil (model/lyrics.go) and cloneTTMLCue (model/lyrics_ttml.go)
are removed in favor of gg.Clone. Also replaces the local positiveOrDefault
helper with gg.If at its three TTML timing-param call sites.

This removes duplicated single-purpose plumbing in favor of shared, generic
utilities. Behavior is unchanged. Adds tests for gg.Clone covering copy,
non-aliasing, and nil input.

model/lyrics.go

@@ -10,6 +10,7 @@ import (
 	"unicode"
 
 	"github.com/navidrome/navidrome/log"
+	"github.com/navidrome/navidrome/utils/gg"
 	"github.com/navidrome/navidrome/utils/str"
 )
 
@@ -542,7 +543,7 @@ func NormalizeCueEnds(cues []Cue, fallbackEnd *int64) []Cue {
 		if end != nil && out[i].Start != nil && *end < *out[i].Start {
 			end = out[i].Start
 		}
-		out[i].End = ptrOrNil(end)
+		out[i].End = gg.Clone(end)
 	}
 
 	for i := range out {
@@ -555,13 +556,3 @@ func NormalizeCueEnds(cues []Cue, fallbackEnd *int64) []Cue {
 	}
 	return out
 }
-
-// ptrOrNil returns a fresh copy of *v so callers never alias another cue's
-// Start/End pointer into the result.
-func ptrOrNil(v *int64) *int64 {
-	if v == nil {
-		return nil
-	}
-	c := *v
-	return &c
-}

model/lyrics_ttml.go

@@ -13,6 +13,7 @@ import (
 	"unicode"
 
 	"github.com/navidrome/navidrome/log"
+	"github.com/navidrome/navidrome/utils/gg"
 	"github.com/navidrome/navidrome/utils/str"
 )
 
@@ -487,7 +488,7 @@ func splitTTMLPiecesByNewline(pieces []ttmlPiece) [][]ttmlPiece {
 			if start < i {
 				lines[len(lines)-1] = append(lines[len(lines)-1], ttmlPiece{
 					raw: raw[start:i],
-					cue: cloneTTMLCue(piece.cue),
+					cue: gg.Clone(piece.cue),
 				})
 			}
 			lines = append(lines, []ttmlPiece{})
@@ -496,7 +497,7 @@ func splitTTMLPiecesByNewline(pieces []ttmlPiece) [][]ttmlPiece {
 		if start < len(raw) {
 			lines[len(lines)-1] = append(lines[len(lines)-1], ttmlPiece{
 				raw: raw[start:],
-				cue: cloneTTMLCue(piece.cue),
+				cue: gg.Clone(piece.cue),
 			})
 		}
 	}
@@ -562,15 +563,6 @@ func ttmlPiecesContainCue(pieces []ttmlPiece) bool {
 	return false
 }
 
-func cloneTTMLCue(cue *Cue) *Cue {
-	if cue == nil {
-		return nil
-	}
-
-	cloned := *cue
-	return &cloned
-}
-
 func (p *ttmlParser) toLyricList() LyricList {
 	res := make(LyricList, 0, len(p.mainLangOrder)+len(p.translationLangOrder)+len(p.pronunciationLangOrder))
 	for _, lang := range p.mainLangOrder {
@@ -979,9 +971,9 @@ func (p *ttmlParser) updateTimingParams(attrs []xml.Attr) {
 		}
 	}
 
-	p.params.frameRate = positiveOrDefault(frameRate, defaultTTMLFrameRate)
-	p.params.subFrameRate = positiveOrDefault(subFrameRate, defaultTTMLSubFrameRate)
-	p.params.tickRate = positiveOrDefault(tickRate, defaultTTMLTickRate)
+	p.params.frameRate = gg.If(frameRate > 0, frameRate, defaultTTMLFrameRate)
+	p.params.subFrameRate = gg.If(subFrameRate > 0, subFrameRate, defaultTTMLSubFrameRate)
+	p.params.tickRate = gg.If(tickRate > 0, tickRate, defaultTTMLTickRate)
 }
 
 func parseTTMLDurationExpression(expr string, params ttmlTimingParams) (int64, bool) {
@@ -1262,10 +1254,3 @@ func linesAreSynced(lines []Line) bool {
 	}
 	return false
 }
-
-func positiveOrDefault(v float64, fallback float64) float64 {
-	if v <= 0 {
-		return fallback
-	}
-	return v
-}

utils/gg/gg.go

@@ -16,3 +16,13 @@ func If[T any](cond bool, v1, v2 T) T {
 	}
 	return v2
 }
+
+// Clone returns a pointer to a fresh copy of *p, or nil if p is nil. Use it to
+// avoid aliasing the pointed-to value when a separate *T is needed.
+func Clone[T any](p *T) *T {
+	if p == nil {
+		return nil
+	}
+	v := *p
+	return &v
+}

utils/gg/gg_test.go

@@ -46,4 +46,25 @@ var _ = Describe("GG", func() {
 			Expect(gg.If(false, 1.1, 2.2)).To(Equal(2.2))
 		})
 	})
+
+	Describe("Clone", func() {
+		It("returns a pointer to a copy of the value", func() {
+			original := 123
+			cloned := gg.Clone(&original)
+			Expect(cloned).To(HaveValue(Equal(123)))
+			Expect(cloned).NotTo(BeIdenticalTo(&original))
+		})
+
+		It("does not alias the original value", func() {
+			original := 123
+			cloned := gg.Clone(&original)
+			original = 456
+			Expect(*cloned).To(Equal(123))
+		})
+
+		It("returns nil when the input is nil", func() {
+			var v *int
+			Expect(gg.Clone(v)).To(BeNil())
+		})
+	})
 })