From a2e36cab153433cd9a4b3f03b826554b07efd168 Mon Sep 17 00:00:00 2001
From: Jan <jan@example.com>
Date: Tue, 7 Apr 2026 16:14:53 +0200
Subject: [PATCH] ingest: share decoder pcm helpers

---
 internal/ingest/decoder/helpers.go           | 58 ++++++++++++++++++++
 internal/ingest/decoder/mp3/decoder.go       | 31 +++--------
 internal/ingest/decoder/oggvorbis/decoder.go | 43 +++------------
 3 files changed, 74 insertions(+), 58 deletions(-)
 create mode 100644 internal/ingest/decoder/helpers.go

diff --git a/internal/ingest/decoder/helpers.go b/internal/ingest/decoder/helpers.go
new file mode 100644
index 0000000..4443038
--- /dev/null
+++ b/internal/ingest/decoder/helpers.go
@@ -0,0 +1,58 @@
+package decoder
+
+import (
+	"encoding/binary"
+	"math"
+	"time"
+
+	"github.com/jan/fm-rds-tx/internal/ingest"
+)
+
+const defaultSampleRateHz = 44100
+
+func ResolveSampleRate(decodedSampleRateHz int, meta StreamMeta) int {
+	if decodedSampleRateHz > 0 {
+		return decodedSampleRateHz
+	}
+	if meta.SampleRateHz > 0 {
+		return meta.SampleRateHz
+	}
+	return defaultSampleRateHz
+}
+
+func BuildChunk(samples []int32, channels, sampleRateHz int, seq uint64, sourceID string) ingest.PCMChunk {
+	return ingest.PCMChunk{
+		Samples:      samples,
+		Channels:     channels,
+		SampleRateHz: sampleRateHz,
+		Sequence:     seq,
+		Timestamp:    time.Now(),
+		SourceID:     sourceID,
+	}
+}
+
+func PCM16LEToPCM32(in []byte) []int32 {
+	out := make([]int32, 0, len(in)/2)
+	for i := 0; i+1 < len(in); i += 2 {
+		v := int16(binary.LittleEndian.Uint16(in[i : i+2]))
+		out = append(out, int32(v)<<16)
+	}
+	return out
+}
+
+func Float32ToPCM32(in []float32) []int32 {
+	out := make([]int32, len(in))
+	for i, sample := range in {
+		if sample > 1 {
+			sample = 1
+		} else if sample < -1 {
+			sample = -1
+		}
+		if sample == -1 {
+			out[i] = math.MinInt32
+			continue
+		}
+		out[i] = int32(sample * math.MaxInt32)
+	}
+	return out
+}
diff --git a/internal/ingest/decoder/mp3/decoder.go b/internal/ingest/decoder/mp3/decoder.go
index 2c7d46e..4d2a71e 100644
--- a/internal/ingest/decoder/mp3/decoder.go
+++ b/internal/ingest/decoder/mp3/decoder.go
@@ -2,10 +2,8 @@ package mp3
 
 import (
 	"context"
-	"encoding/binary"
 	"fmt"
 	"io"
-	"time"
 
 	gomp3 "github.com/hajimehoshi/go-mp3"
 	"github.com/jan/fm-rds-tx/internal/ingest"
@@ -32,14 +30,7 @@ func (d *Decoder) DecodeStream(ctx context.Context, r io.Reader, meta decoder.St
 	}
 
 	const channels = 2 // go-mp3 always decodes to stereo s16le
-	sampleRate := dec.SampleRate()
-	if sampleRate <= 0 {
-		if meta.SampleRateHz > 0 {
-			sampleRate = meta.SampleRateHz
-		} else {
-			sampleRate = 44100
-		}
-	}
+	sampleRate := decoder.ResolveSampleRate(dec.SampleRate(), meta)
 
 	const chunkFrames = 1024
 	const frameBytes = channels * 2
@@ -74,17 +65,11 @@ func (d *Decoder) DecodeStream(ctx context.Context, r io.Reader, meta decoder.St
 }
 
 func emitChunk(data []byte, seq uint64, sampleRate int, sourceID string, emit func(ingest.PCMChunk) error) error {
-	samples := make([]int32, 0, len(data)/2)
-	for i := 0; i+1 < len(data); i += 2 {
-		v := int16(binary.LittleEndian.Uint16(data[i : i+2]))
-		samples = append(samples, int32(v)<<16)
-	}
-	return emit(ingest.PCMChunk{
-		Samples:      samples,
-		Channels:     2,
-		SampleRateHz: sampleRate,
-		Sequence:     seq,
-		Timestamp:    time.Now(),
-		SourceID:     sourceID,
-	})
+	return emit(decoder.BuildChunk(
+		decoder.PCM16LEToPCM32(data),
+		2,
+		sampleRate,
+		seq,
+		sourceID,
+	))
 }
diff --git a/internal/ingest/decoder/oggvorbis/decoder.go b/internal/ingest/decoder/oggvorbis/decoder.go
index c3de4da..ef1dca0 100644
--- a/internal/ingest/decoder/oggvorbis/decoder.go
+++ b/internal/ingest/decoder/oggvorbis/decoder.go
@@ -4,8 +4,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"math"
-	"time"
 
 	"github.com/jan/fm-rds-tx/internal/ingest"
 	"github.com/jan/fm-rds-tx/internal/ingest/decoder"
@@ -40,14 +38,7 @@ func (d *Decoder) DecodeStream(ctx context.Context, r io.Reader, meta decoder.St
 		}
 	}
 
-	sampleRate := dec.SampleRate()
-	if sampleRate <= 0 {
-		if meta.SampleRateHz > 0 {
-			sampleRate = meta.SampleRateHz
-		} else {
-			sampleRate = 44100
-		}
-	}
+	sampleRate := decoder.ResolveSampleRate(dec.SampleRate(), meta)
 
 	const chunkFrames = 1024
 	buf := make([]float32, chunkFrames*channels)
@@ -62,14 +53,13 @@ func (d *Decoder) DecodeStream(ctx context.Context, r io.Reader, meta decoder.St
 
 		n, readErr := dec.Read(buf)
 		if n > 0 {
-			chunk := ingest.PCMChunk{
-				Samples:      float32ToPCM32(buf[:n]),
-				Channels:     channels,
-				SampleRateHz: sampleRate,
-				Sequence:     seq,
-				Timestamp:    time.Now(),
-				SourceID:     meta.SourceID,
-			}
+			chunk := decoder.BuildChunk(
+				decoder.Float32ToPCM32(buf[:n]),
+				channels,
+				sampleRate,
+				seq,
+				meta.SourceID,
+			)
 			if err := emit(chunk); err != nil {
 				return err
 			}
@@ -84,20 +74,3 @@ func (d *Decoder) DecodeStream(ctx context.Context, r io.Reader, meta decoder.St
 		}
 	}
 }
-
-func float32ToPCM32(in []float32) []int32 {
-	out := make([]int32, len(in))
-	for i, sample := range in {
-		if sample > 1 {
-			sample = 1
-		} else if sample < -1 {
-			sample = -1
-		}
-		if sample == -1 {
-			out[i] = math.MinInt32
-			continue
-		}
-		out[i] = int32(sample * math.MaxInt32)
-	}
-	return out
-}