From ca3be9f2587fab9d814c4ce6392e2ec71ea6db05 Mon Sep 17 00:00:00 2001
From: Jan Svabenik <jan@svabi.ch>
Date: Sun, 22 Mar 2026 21:15:24 +0100
Subject: [PATCH] recorder: add stereo pilot lock test

---
 internal/recorder/streamer_test.go | 77 ++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 internal/recorder/streamer_test.go

diff --git a/internal/recorder/streamer_test.go b/internal/recorder/streamer_test.go
new file mode 100644
index 0000000..67ad9c9
--- /dev/null
+++ b/internal/recorder/streamer_test.go
@@ -0,0 +1,77 @@
+package recorder
+
+import (
+	"math"
+	"testing"
+)
+
+func TestStereoDecodeStatefulPilotLock(t *testing.T) {
+	const (
+		sampleRate = 192000
+		blockSize  = 4096
+		blocks     = 10
+		pilotAmp   = 0.1
+		toneL      = 440.0
+		toneR      = 880.0
+	)
+
+	sess := &streamSession{}
+	var out []float32
+	locked := false
+
+	for b := 0; b < blocks; b++ {
+		mono := make([]float32, blockSize)
+		base := b * blockSize
+		for i := 0; i < blockSize; i++ {
+			t := float64(base+i) / float64(sampleRate)
+			l := math.Sin(2 * math.Pi * toneL * t)
+			r := math.Sin(2 * math.Pi * toneR * t)
+			lpr := 0.5 * (l + r)
+			lmr := 0.5 * (l - r)
+			composite := lpr + lmr*math.Cos(2*math.Pi*38000*t) + pilotAmp*math.Sin(2*math.Pi*19000*t)
+			mono[i] = float32(composite)
+		}
+		out, locked = sess.stereoDecodeStateful(mono, sampleRate)
+	}
+
+	if !locked {
+		t.Fatalf("expected pilot lock after warmup blocks")
+	}
+	if len(out) != blockSize*2 {
+		t.Fatalf("unexpected output size: got %d, want %d", len(out), blockSize*2)
+	}
+
+	left := make([]float32, blockSize)
+	right := make([]float32, blockSize)
+	for i := 0; i < blockSize; i++ {
+		left[i] = out[i*2]
+		right[i] = out[i*2+1]
+	}
+
+	magL440 := toneMagnitude(left, toneL, sampleRate)
+	magL880 := toneMagnitude(left, toneR, sampleRate)
+	magR440 := toneMagnitude(right, toneL, sampleRate)
+	magR880 := toneMagnitude(right, toneR, sampleRate)
+
+	if magL440 < 0.05 || magR880 < 0.05 {
+		t.Fatalf("decoded tones too weak: L440=%.3f R880=%.3f", magL440, magR880)
+	}
+	leftIsL := magL440 >= magL880*1.3 && magR880 >= magR440*1.3
+	rightIsL := magL880 >= magL440*1.3 && magR440 >= magR880*1.3
+	if !leftIsL && !rightIsL {
+		t.Fatalf(
+			"channels not cleanly separated: L440=%.3f L880=%.3f R440=%.3f R880=%.3f",
+			magL440, magL880, magR440, magR880,
+		)
+	}
+}
+
+func toneMagnitude(x []float32, freq float64, sampleRate int) float64 {
+	var iSum, qSum float64
+	for n, v := range x {
+		angle := 2 * math.Pi * freq * float64(n) / float64(sampleRate)
+		iSum += float64(v) * math.Cos(angle)
+		qSum += float64(v) * math.Sin(angle)
+	}
+	return math.Hypot(iSum, qSum) / float64(len(x))
+}