From 44c79e225673f3f7fd74a420273d23f94227ec91 Mon Sep 17 00:00:00 2001
From: saxon <saxon.milton@gmail.com>
Date: Mon, 21 Jan 2019 15:41:49 +1030
Subject: [PATCH] av/stream/flac: wrote decode function and test to see if we
 can get wav.

---
 stream/flac/decode.go    | 108 +++++++++++++++++++++++++++++++++++++++
 stream/flac/flac_test.go |  31 +++++++++++
 2 files changed, 139 insertions(+)

diff --git a/stream/flac/decode.go b/stream/flac/decode.go
index e69de29b..2ecfb737 100644
--- a/stream/flac/decode.go
+++ b/stream/flac/decode.go
@@ -0,0 +1,108 @@
+package flac
+
+import (
+	"bytes"
+	"errors"
+	"io"
+
+	"github.com/go-audio/audio"
+	"github.com/go-audio/wav"
+	"github.com/mewkiz/flac"
+)
+
+const wavAudioFormat = 1
+
+type buffer struct {
+	Buffer bytes.Buffer
+	Index  int64
+}
+
+func (b *buffer) Bytes() []byte {
+	return b.Buffer.Bytes()
+}
+
+func (b *buffer) Read(p []byte) (int, error) {
+	n, err := bytes.NewBuffer(b.Buffer.Bytes()[b.Index:]).Read(p)
+
+	if err == nil {
+		if b.Index+int64(len(p)) < int64(b.Buffer.Len()) {
+			b.Index += int64(len(p))
+		} else {
+			b.Index = int64(b.Buffer.Len())
+		}
+	}
+
+	return n, err
+}
+
+func (b *buffer) Write(p []byte) (int, error) {
+	n, err := b.Buffer.Write(p)
+
+	if err == nil {
+		b.Index = int64(b.Buffer.Len())
+	}
+
+	return n, err
+}
+
+func (b *buffer) Seek(offset int64, whence int) (int64, error) {
+	var err error
+	var Index int64 = 0
+
+	switch whence {
+	case 0:
+		if offset >= int64(b.Buffer.Len()) || offset < 0 {
+			err = errors.New("Invalid Offset.")
+		} else {
+			b.Index = offset
+			Index = offset
+		}
+	default:
+		err = errors.New("Unsupported Seek Method.")
+	}
+
+	return Index, err
+}
+
+// Decode takes a slice of flac and decodes to wav
+func Decode(buf []byte) ([]byte, error) {
+	r := bytes.NewReader(buf)
+	stream, err := flac.Parse(r)
+	if err != nil {
+		return nil, errors.New("Could not parse FLAC")
+	}
+	fb := &buffer{}
+	enc := wav.NewEncoder(fb, int(stream.Info.SampleRate), int(stream.Info.BitsPerSample), int(stream.Info.NChannels), wavAudioFormat)
+	defer enc.Close()
+	var data []int
+	for {
+		// Decode FLAC audio samples.
+		frame, err := stream.ParseNext()
+		if err != nil {
+			if err == io.EOF {
+				break
+			}
+			return nil, err
+		}
+
+		// Encode WAV audio samples.
+		data = data[:0]
+		for i := 0; i < frame.Subframes[0].NSamples; i++ {
+			for _, subframe := range frame.Subframes {
+				data = append(data, int(subframe.Samples[i]))
+			}
+		}
+		buf := &audio.IntBuffer{
+			Format: &audio.Format{
+				NumChannels: int(stream.Info.NChannels),
+				SampleRate:  int(stream.Info.SampleRate),
+			},
+			Data:           data,
+			SourceBitDepth: int(stream.Info.BitsPerSample),
+		}
+		if err := enc.Write(buf); err != nil {
+			return nil, err
+		}
+	}
+	return fb.Bytes(), nil
+}
diff --git a/stream/flac/flac_test.go b/stream/flac/flac_test.go
index e69de29b..763731d4 100644
--- a/stream/flac/flac_test.go
+++ b/stream/flac/flac_test.go
@@ -0,0 +1,31 @@
+package flac
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+const (
+	testFile = "/home/saxon/Desktop/robot.flac"
+	outFile  = "out.wav"
+)
+
+func TestDecodeFlac(t *testing.T) {
+	b, err := ioutil.ReadFile(testFile)
+	if err != nil {
+		t.Fatalf("Could not read test file, failed with err: %v", err.Error())
+	}
+	out, err := Decode(b)
+	if err != nil {
+		t.Errorf("Could not decode, failed with err: %v", err.Error())
+	}
+	f, err := os.Create(outFile)
+	if err != nil {
+		t.Fatalf("Could not create output file, failed with err: %v", err.Error())
+	}
+	_, err = f.Write(out)
+	if err != nil {
+		t.Fatalf("Could not write to output file, failed with err: %v", err.Error())
+	}
+}