fix(subsonic): emit agent-specific cueLine values (#5679)

* fix(subsonic): emit agent-specific cue line values

* fix(subsonic): preserve cue line edge text

server/subsonic/lyrics.go

@@ -114,12 +114,17 @@ func buildCueLines(line model.Line, index int32, agents lyricAgents) []responses
 
 	cueLines := make([]responses.CueLine, 0, len(agentOrder))
 	for _, agentID := range agentOrder {
+		value := line.Value
+		cues := cuesByAgent[agentID]
+		if len(agentOrder) > 1 {
+			value, cues = buildAgentCueLineValue(line.Value, cues, line.Cue, agentID)
+		}
 		cueLine := responses.CueLine{
 			Index: index,
 			Start: line.Start,
 			End:   line.End,
-			Value: line.Value,
-			Cue:   buildLyricCues(cuesByAgent[agentID], line.End),
+			Value: value,
+			Cue:   buildLyricCues(cues, line.End),
 		}
 		if agentID != "" {
 			cueLine.AgentID = agentID
@@ -149,6 +154,85 @@ func (a lyricAgents) less(left, right string, origI, origJ int) bool {
 	return origI < origJ
 }
 
+func buildAgentCueLineValue(lineValue string, cues, allCues []model.Cue, agentID string) (string, []model.Cue) {
+	if len(cues) == 0 {
+		return "", nil
+	}
+
+	remapped := slices.Clone(cues)
+	var value strings.Builder
+	leadingGap := cueLineGap(lineValue, 0, remapped[0].ByteStart, allCues, agentID)
+	if strings.TrimSpace(leadingGap) != "" {
+		value.WriteString(leadingGap)
+	}
+
+	previousEnd := -1
+	for i := range remapped {
+		originalStart := remapped[i].ByteStart
+		originalEnd := remapped[i].ByteEnd
+		if i > 0 {
+			value.WriteString(cueLineGap(lineValue, previousEnd+1, originalStart, allCues, agentID))
+		}
+
+		remapped[i].ByteStart = value.Len()
+		value.WriteString(remapped[i].Value)
+		remapped[i].ByteEnd = value.Len() - 1
+		previousEnd = originalEnd
+	}
+
+	trailingGap := cueLineGap(lineValue, previousEnd+1, len(lineValue), allCues, agentID)
+	if strings.TrimSpace(trailingGap) != "" {
+		value.WriteString(trailingGap)
+	}
+	return value.String(), remapped
+}
+
+type byteRange struct {
+	start int
+	end   int
+}
+
+func cueLineGap(source string, start, end int, allCues []model.Cue, agentID string) string {
+	start = max(start, 0)
+	end = min(end, len(source))
+	if start >= end {
+		return ""
+	}
+
+	excluded := make([]byteRange, 0, 1)
+	for _, cue := range allCues {
+		if strings.TrimSpace(cue.AgentID) == agentID {
+			continue
+		}
+		cueStart := max(cue.ByteStart, start)
+		cueEnd := min(cue.ByteEnd+1, end)
+		if cueStart < cueEnd {
+			excluded = append(excluded, byteRange{start: cueStart, end: cueEnd})
+		}
+	}
+
+	if len(excluded) == 0 {
+		return source[start:end]
+	}
+
+	sort.SliceStable(excluded, func(i, j int) bool {
+		return excluded[i].start < excluded[j].start
+	})
+
+	var gap strings.Builder
+	cursor := start
+	for _, r := range excluded {
+		if r.start > cursor {
+			gap.WriteString(source[cursor:r.start])
+		}
+		cursor = max(cursor, r.end)
+	}
+	if cursor < end {
+		gap.WriteString(source[cursor:end])
+	}
+	return gap.String()
+}
+
 func buildLyricCues(cues []model.Cue, lineEnd *int64) []responses.LyricCue {
 	if len(cues) == 0 {
 		return nil

server/subsonic/lyrics_test.go

@@ -431,7 +431,7 @@ var _ = Describe("GetLyricsBySongId", func() {
 							Index:   0,
 							Start:   &lineStart,
 							End:     &lineEnd,
-							Value:   "Hello echo",
+							Value:   "Hello",
 							AgentID: "lead",
 							Cue: []responses.LyricCue{
 								{
@@ -447,14 +447,14 @@ var _ = Describe("GetLyricsBySongId", func() {
 							Index:   0,
 							Start:   &lineStart,
 							End:     &lineEnd,
-							Value:   "Hello echo",
+							Value:   "echo",
 							AgentID: "__nd_bg__|lead",
 							Cue: []responses.LyricCue{
 								{
 									Start:     tokenStartB,
 									End:       &tokenEndB,
-									ByteStart: 6,
-									ByteEnd:   9,
+									ByteStart: 0,
+									ByteEnd:   3,
 									Value:     "echo",
 								},
 							},
@@ -465,6 +465,220 @@ var _ = Describe("GetLyricsBySongId", func() {
 		})
 	})
 
+	It("should preserve shared edge text when remapping agent cue lines", func() {
+		lineStart := int64(1000)
+		lineEnd := int64(2000)
+		cueStart := int64(1200)
+		cueEnd := int64(1800)
+
+		cueLines := buildCueLines(model.Line{
+			Start: &lineStart,
+			End:   &lineEnd,
+			Value: "(Hello)",
+			Cue: []model.Cue{
+				{
+					Start:     &cueStart,
+					End:       &cueEnd,
+					Value:     "Hello",
+					ByteStart: 1,
+					ByteEnd:   5,
+					AgentID:   "lead",
+				},
+				{
+					Start:     &cueStart,
+					End:       &cueEnd,
+					Value:     "Hello",
+					ByteStart: 1,
+					ByteEnd:   5,
+					AgentID:   "__nd_bg__|lead",
+				},
+			},
+		}, 0, newLyricAgents([]model.Agent{
+			{ID: "lead", Role: "main"},
+			{ID: "__nd_bg__|lead", Role: "bg"},
+		}))
+
+		Expect(cueLines).To(Equal([]responses.CueLine{
+			{
+				Index:   0,
+				Start:   &lineStart,
+				End:     &lineEnd,
+				Value:   "(Hello)",
+				AgentID: "lead",
+				Cue: []responses.LyricCue{
+					{
+						Start:     cueStart,
+						End:       &cueEnd,
+						Value:     "Hello",
+						ByteStart: 1,
+						ByteEnd:   5,
+					},
+				},
+			},
+			{
+				Index:   0,
+				Start:   &lineStart,
+				End:     &lineEnd,
+				Value:   "(Hello)",
+				AgentID: "__nd_bg__|lead",
+				Cue: []responses.LyricCue{
+					{
+						Start:     cueStart,
+						End:       &cueEnd,
+						Value:     "Hello",
+						ByteStart: 1,
+						ByteEnd:   5,
+					},
+				},
+			},
+		}))
+	})
+
+	It("should remap cue offsets for interleaved agent cue lines", func() {
+		r := newGetRequest("id=1&enhanced=true")
+
+		lineStart := int64(82889)
+		lineEnd := int64(86859)
+		realStart := int64(85593)
+		realEnd := int64(85934)
+		slowStart := int64(85934)
+		slowEnd := int64(86751)
+		bgStartA := int64(83881)
+		bgEndA := int64(84243)
+		bgStartB := int64(86232)
+		bgEndB := int64(86859)
+		lyricsJSON, err := json.Marshal(model.LyricList{
+			{
+				Lang:   "eng",
+				Agents: []model.Agent{{ID: "v2", Role: "main"}, {ID: "__nd_bg__|v2", Role: "bg"}},
+				Synced: true,
+				Line: []model.Line{
+					{
+						Start: &lineStart,
+						End:   &lineEnd,
+						Value: "real slow (When you slide)",
+						Cue: []model.Cue{
+							{
+								Start:     &realStart,
+								End:       &realEnd,
+								Value:     "real",
+								ByteStart: 0,
+								ByteEnd:   3,
+								AgentID:   "v2",
+							},
+							{
+								Start:     &slowStart,
+								End:       &slowEnd,
+								Value:     "slow",
+								ByteStart: 5,
+								ByteEnd:   8,
+								AgentID:   "v2",
+							},
+							{
+								Start:     &bgStartA,
+								End:       &bgEndA,
+								Value:     "(When you",
+								ByteStart: 10,
+								ByteEnd:   18,
+								AgentID:   "__nd_bg__|v2",
+							},
+							{
+								Start:     &bgStartB,
+								End:       &bgEndB,
+								Value:     "slide)",
+								ByteStart: 20,
+								ByteEnd:   25,
+								AgentID:   "__nd_bg__|v2",
+							},
+						},
+					},
+				},
+			},
+		})
+		Expect(err).ToNot(HaveOccurred())
+
+		mockRepo.SetData(model.MediaFiles{
+			{
+				ID:     "1",
+				Artist: "Rick Astley",
+				Title:  "Never Gonna Give You Up",
+				Lyrics: string(lyricsJSON),
+			},
+		})
+
+		response, err := router.GetLyricsBySongId(r)
+		Expect(err).ToNot(HaveOccurred())
+		compareResponses(response.LyricsList, responses.LyricsList{
+			StructuredLyrics: responses.StructuredLyrics{
+				{
+					DisplayArtist: "Rick Astley",
+					DisplayTitle:  "Never Gonna Give You Up",
+					Kind:          "main",
+					Lang:          "eng",
+					Synced:        true,
+					Agents: []responses.Agent{
+						{ID: "v2", Role: "main"},
+						{ID: "__nd_bg__|v2", Role: "bg"},
+					},
+					Line: []responses.Line{
+						{
+							Start: &lineStart,
+							Value: "real slow (When you slide)",
+						},
+					},
+					CueLine: []responses.CueLine{
+						{
+							Index:   0,
+							Start:   &lineStart,
+							End:     &lineEnd,
+							Value:   "real slow",
+							AgentID: "v2",
+							Cue: []responses.LyricCue{
+								{
+									Start:     realStart,
+									End:       &realEnd,
+									ByteStart: 0,
+									ByteEnd:   3,
+									Value:     "real",
+								},
+								{
+									Start:     slowStart,
+									End:       &slowEnd,
+									ByteStart: 5,
+									ByteEnd:   8,
+									Value:     "slow",
+								},
+							},
+						},
+						{
+							Index:   0,
+							Start:   &lineStart,
+							End:     &lineEnd,
+							Value:   "(When you slide)",
+							AgentID: "__nd_bg__|v2",
+							Cue: []responses.LyricCue{
+								{
+									Start:     bgStartA,
+									End:       &bgEndA,
+									ByteStart: 0,
+									ByteEnd:   8,
+									Value:     "(When you",
+								},
+								{
+									Start:     bgStartB,
+									End:       &bgEndB,
+									ByteStart: 10,
+									ByteEnd:   15,
+									Value:     "slide)",
+								},
+							},
+						},
+					},
+				},
+			},
+		})
+	})
+
 	It("should keep enhanced line-level lyrics when no cue data is available", func() {
 		r := newGetRequest("id=1&enhanced=true")