dbserver: fix CDJ-saved cue colour showing orange instead of green

dbserver/cuepoints.go

@@ -59,14 +59,7 @@ func ParseCueBlob(blob []byte, trackID uint32) (*CuePoint, error) {
 		Status: binary.LittleEndian.Uint32(blob[0x18:]),
 		LoopMs: int32(binary.LittleEndian.Uint32(blob[0x20:])),
 	}
-	// 124-byte blobs put the picker palette index at byte 0x4e (with RGB
-	// at 0x4f-0x51), and reserve 0x34 as a fixed 0x42 marker. 76-byte
-	// blobs put the raw palette index directly at 0x34.
-	if len(blob) >= 124 && blob[0x34] == 0x42 {
-		cue.ColorID = uint32(blob[0x4e])
-	} else {
-		cue.ColorID = binary.LittleEndian.Uint32(blob[0x34:])
-	}
+	cue.ColorID = cueColorFromBlob(blob)
 
 	log.Printf("cuestore: parsed cue #%d type=%d time=%dms loop=%d color_id=%d (0x%x) track=%d",
 		cue.Number, cue.Type, cue.TimeMs, cue.LoopMs, cue.ColorID, cue.ColorID, trackID)
@@ -159,6 +152,43 @@ func cueColorRGB(idx uint32) (r, g, b byte) {
 	return 0xff, 0x6a, 0x00
 }
 
+// cueColorFromBlob extracts the palette color_id from a cue blob. 124-byte NXS2
+// blobs carry the picker index at 0x4e; when that index is 0 the real colour is
+// in the RGB bytes (0x4f-0x51) — the CDJ encodes its default hot-cue green that
+// way, and taking idx 0 alone would paint it Pioneer orange (palette 0x00) — so
+// recover the nearest palette id from the RGB. 76-byte blobs store the raw index
+// directly at 0x34. Callers must ensure len(blob) >= 76.
+func cueColorFromBlob(blob []byte) uint32 {
+	if len(blob) >= 124 && blob[0x34] == 0x42 {
+		if idx := uint32(blob[0x4e]); idx != 0 {
+			return idx
+		}
+		if r, g, b := blob[0x4f], blob[0x50], blob[0x51]; r|g|b != 0 {
+			return nearestCueColorID(r, g, b)
+		}
+		return 0
+	}
+	return binary.LittleEndian.Uint32(blob[0x34:])
+}
+
+// nearestCueColorID returns the palette color_id whose RGB is closest to the
+// given triplet (squared-Euclidean distance; ties resolve to the lower id so
+// the result is deterministic). Used when the CDJ hands us a cue with a zero
+// palette index but a real colour in the RGB bytes, so the stored color_id —
+// and the web UI swatch — reflect the colour the deck paints.
+func nearestCueColorID(r, g, b byte) uint32 {
+	best := uint32(0)
+	bestDist := -1
+	for idx, c := range cueColorPalette {
+		dr, dg, db := int(c[0])-int(r), int(c[1])-int(g), int(c[2])-int(b)
+		d := dr*dr + dg*dg + db*db
+		if bestDist < 0 || d < bestDist || (d == bestDist && idx < best) {
+			bestDist, best = d, idx
+		}
+	}
+	return best
+}
+
 var cueColorPalette = map[uint32][3]byte{
 	0x00: {0xff, 0x6a, 0x00},
 	0x01: {0x30, 0x5a, 0xff}, 0x02: {0x50, 0x73, 0xff}, 0x03: {0x50, 0x8c, 0xff}, 0x04: {0x50, 0xa0, 0xff},
@@ -365,6 +395,20 @@ func (cs *CueStore) loadAll() {
 			cs.rawBlobs[bTrackID][bCueNum] = data
 		}
 	}
+
+	// Re-derive the colour of CDJ-saved cues from their raw blob. Cues stored
+	// before the RGB-colour recovery kept whatever color_id was persisted (a
+	// default green came through as 0 → orange); re-reading the blob now applies
+	// the fix on load. Web-UI/synthesized cues have no blob (or a stub), so they
+	// keep their stored colour.
+	for trackID, cues := range cs.data {
+		blobs := cs.rawBlobs[trackID]
+		for i := range cues {
+			if raw := blobs[cues[i].Number]; len(raw) >= 76 {
+				cues[i].ColorID = cueColorFromBlob(raw)
+			}
+		}
+	}
 }
 
 // MarshalCueResponse builds the cue point response for 0x2104.

dbserver/cuepoints_test.go

@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package dbserver
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// makeNXS2CueBlob builds a minimal 124-byte NXS2 cue blob with the given cue
+// number, palette index (0x4e), and RGB (0x4f-0x51), matching what
+// ParseCueBlob reads.
+func makeNXS2CueBlob(number uint16, idx, r, g, b byte) []byte {
+	blob := make([]byte, 124)
+	blob[0x04] = byte(number)
+	blob[0x06] = 1    // type = cue
+	blob[0x34] = 0x42 // NXS2 picker-coloured marker
+	blob[0x4e] = idx
+	blob[0x4f], blob[0x50], blob[0x51] = r, g, b
+	return blob
+}
+
+func TestParseCueBlobCDJDefaultGreen(t *testing.T) {
+	// A default hot cue set on the CDJ arrives as palette idx 0 + RGB 00ff30
+	// (green). Taking idx 0 alone would paint it Pioneer orange; the RGB must
+	// win so the web UI shows green.
+	cue, err := ParseCueBlob(makeNXS2CueBlob(5, 0x00, 0x00, 0xff, 0x30), 42)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cue.ColorID != 0x16 {
+		t.Errorf("CDJ green cue: color_id = %#x, want 0x16 (green), not orange", cue.ColorID)
+	}
+}
+
+func TestParseCueBlobHonoursPaletteIndex(t *testing.T) {
+	// A non-zero palette index is authoritative; RGB is not consulted.
+	cue, _ := ParseCueBlob(makeNXS2CueBlob(1, 0x2a, 0x00, 0x00, 0x00), 42)
+	if cue.ColorID != 0x2a {
+		t.Errorf("color_id = %#x, want 0x2a (index honoured)", cue.ColorID)
+	}
+}
+
+func TestParseCueBlobNoColour(t *testing.T) {
+	// idx 0 with all-zero RGB is a genuinely uncoloured cue → stays 0.
+	cue, _ := ParseCueBlob(makeNXS2CueBlob(1, 0x00, 0x00, 0x00, 0x00), 42)
+	if cue.ColorID != 0 {
+		t.Errorf("color_id = %#x, want 0 (no colour)", cue.ColorID)
+	}
+}
+
+func TestLoadAllRederivesCueColour(t *testing.T) {
+	dir := t.TempDir()
+	// A cue stored before the fix: the JSON has color_id 0, but the raw CDJ
+	// blob carries green in its RGB bytes. Loading should re-derive green.
+	if err := os.WriteFile(filepath.Join(dir, "cues_7.json"),
+		[]byte(`[{"number":5,"type":1,"time_ms":0,"loop_ms":-1,"status":1,"color_id":0}]`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "cue_7_5.bin"),
+		makeNXS2CueBlob(5, 0x00, 0x00, 0xff, 0x30), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	cues := NewCueStore(dir).GetCues(7)
+	if len(cues) != 1 || cues[0].ColorID != 0x16 {
+		t.Fatalf("re-derived colour = %+v, want one cue with color_id 0x16", cues)
+	}
+}
+
+func TestNearestCueColorID(t *testing.T) {
+	cases := []struct {
+		r, g, b byte
+		want    uint32
+		name    string
+	}{
+		{0x28, 0xe2, 0x14, 0x16, "exact palette green round-trips"},
+		{0x00, 0xff, 0x30, 0x16, "CDJ's brighter green maps to our green"},
+		{0xff, 0x6a, 0x00, 0x00, "orange maps back to idx 0"},
+	}
+	for _, c := range cases {
+		if got := nearestCueColorID(c.r, c.g, c.b); got != c.want {
+			t.Errorf("%s: nearest(%#x,%#x,%#x) = %#x, want %#x", c.name, c.r, c.g, c.b, got, c.want)
+		}
+	}
+}