From 0eb8ade0e9c0eb878b4c39f5614c840433468277 Mon Sep 17 00:00:00 2001
From: Emmm Monster <58943012+emmmx@users.noreply.github.com>
Date: Sat, 26 Dec 2020 04:38:23 +0800
Subject: [PATCH] Add XM Decoder

---
 algo/xm/xm.go | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 algo/xm/xm.go

diff --git a/algo/xm/xm.go b/algo/xm/xm.go
new file mode 100644
index 0000000..25efe16
--- /dev/null
+++ b/algo/xm/xm.go
@@ -0,0 +1,90 @@
+package xm
+
+import (
+	"bytes"
+	"errors"
+	"github.com/umlock-music/cli/algo/common"
+	"github.com/umlock-music/cli/internal/logging"
+	"go.uber.org/zap"
+)
+
+var (
+	xmMagicHeader    = []byte{'i', 'f', 'm', 't'}
+	xmMagicHeader2   = []byte{0xfe, 0xfe, 0xfe, 0xfe}
+	xmHeaders        map[string]string
+	ErrXmFileSize    = errors.New("xm invalid file size")
+	ErrXmMagicHeader = errors.New("xm magic header not matched")
+)
+
+func init() {
+	xmHeaders = map[string]string{
+		" WAV": "wav",
+		"FLAC": "flac",
+		" MP3": "mp3",
+		" A4M": "m4a",
+	}
+}
+
+type Decoder struct {
+	data      []byte
+	headerLen uint32
+	outputExt string
+	mask      byte
+	audio     []byte
+}
+
+func (d *Decoder) GetCoverImage() []byte {
+	return nil
+}
+
+func (d *Decoder) GetAudioData() []byte {
+	return d.audio
+}
+
+func (d *Decoder) GetAudioExt() string {
+	return d.outputExt
+}
+
+func (d *Decoder) GetMeta() common.Meta {
+	return nil
+}
+
+func NewDecoder(data []byte) *Decoder {
+	return &Decoder{data: data}
+}
+
+func (d *Decoder) Validate() error {
+	lenData := len(d.data)
+	if lenData < 16 {
+		return ErrXmFileSize
+	}
+	if !bytes.Equal(xmMagicHeader, d.data[:4]) ||
+		!bytes.Equal(xmMagicHeader2, d.data[8:12]) {
+		return ErrXmMagicHeader
+	}
+
+	var ok bool
+	d.outputExt, ok = xmHeaders[string(d.data[4:8])]
+	if !ok {
+		return errors.New("detect unknown xm file type: " + string(d.data[4:8]))
+	}
+
+	if d.data[14] != 0 {
+		logging.Log().Warn("not a simple xm file", zap.Uint8("b[14]", d.data[14]))
+	}
+	d.headerLen = uint32(d.data[12]) | uint32(d.data[13])<<8 | uint32(d.data[14])<<16 // LittleEndian Unit24
+	if d.headerLen+16 > uint32(lenData) {
+		return ErrXmFileSize
+	}
+	return nil
+}
+
+func (d *Decoder) Decode() error {
+	d.mask = d.data[15]
+	d.audio = d.data[16:]
+	dataLen := uint32(len(d.audio))
+	for i := d.headerLen; i < dataLen; i++ {
+		d.audio[i] = ^(d.audio[i] - d.mask)
+	}
+	return nil
+}