From 5cdc82a1932ad892a46e5d9aa9bebcf6a8946f42 Mon Sep 17 00:00:00 2001
From: cnt0 <4948391+cnt0@users.noreply.github.com>
Date: Fri, 8 Feb 2019 20:04:46 +0500
Subject: [PATCH] add ChapterFrame type for CHAP frames

---
 chapter_frame.go | 116 +++++++++++++++++++++++++++++++++++++++++++++++
 common_ids.go    |   5 +-
 sequence.go      |   2 +
 tag.go           |   5 ++
 4 files changed, 127 insertions(+), 1 deletion(-)
 create mode 100644 chapter_frame.go

diff --git a/chapter_frame.go b/chapter_frame.go
new file mode 100644
index 0000000..5181b55
--- /dev/null
+++ b/chapter_frame.go
@@ -0,0 +1,116 @@
+package id3v2
+
+import (
+	"encoding/binary"
+	"io"
+	"time"
+)
+
+const (
+	nanosInMillis = 1000000
+	IgnoredOffset = 0xFFFFFFFF
+)
+
+// ChapterFrame is used to work with CHAP frames
+// according to spec from http://id3.org/id3v2-chapters-1.0
+// This implementation only supports single TIT2 subframe (Title field).
+// All other subframes are ignored.
+// If StartOffset or EndOffset == id3v2.IgnoredOffset, then it should be ignored
+// and StartTime or EndTime should be utilized
+type ChapterFrame struct {
+	ElementID   string
+	StartTime   time.Duration
+	EndTime     time.Duration
+	StartOffset uint32
+	EndOffset   uint32
+	Title       string
+}
+
+func (cf ChapterFrame) Size() int {
+	titleFrame := TextFrame{
+		Encoding: EncodingUTF8,
+		Text:     cf.Title,
+	}
+	return encodedSize(cf.ElementID, EncodingISO) +
+		1 + // trailing zero after ElementID
+		4 + 4 + 4 + 4 + // (Start, End) (Time, Offset)
+		frameHeaderSize + // Title frame header size
+		titleFrame.Size()
+}
+
+func (cf ChapterFrame) WriteTo(w io.Writer) (n int64, err error) {
+	return useBufWriter(w, func(bw *bufWriter) {
+		bw.EncodeAndWriteText(cf.ElementID, EncodingISO)
+		bw.WriteByte(0)
+		// nanoseconds => milliseconds
+		binary.Write(bw, binary.BigEndian, int32(cf.StartTime/nanosInMillis))
+		binary.Write(bw, binary.BigEndian, int32(cf.EndTime/nanosInMillis))
+
+		binary.Write(bw, binary.BigEndian, cf.StartOffset)
+		binary.Write(bw, binary.BigEndian, cf.EndOffset)
+
+		titleFrame := TextFrame{
+			Encoding: EncodingUTF8,
+			Text:     cf.Title,
+		}
+		writeFrame(bw, "TIT2", titleFrame, true)
+	})
+}
+
+func parseChapterFrame(br *bufReader) (Framer, error) {
+	ElementID := br.ReadText(EncodingISO)
+	chapterTime := make([]int32, 2)
+	for i := range chapterTime {
+		if err := binary.Read(br, binary.BigEndian, &chapterTime[i]); err != nil {
+			return nil, err
+		}
+	}
+	chapterOffset := make([]uint32, 2)
+	for i := range chapterOffset {
+		if err := binary.Read(br, binary.BigEndian, &chapterOffset[i]); err != nil {
+			return nil, err
+		}
+	}
+	var title string
+
+	// borrowed from parse.go
+	buf := getByteSlice(32 * 1024)
+	defer putByteSlice(buf)
+	for {
+		// no way to determine whether this should be true or not
+		// this is likely should be fixed
+		header, err := parseFrameHeader(buf, br, true)
+		if err == io.EOF || err == errBlankFrame || err == ErrInvalidSizeFormat {
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+		id, bodySize := header.ID, header.BodySize
+		if id == "TIT2" {
+			bodyRd := getLimitedReader(br, bodySize)
+			br2 := newBufReader(bodyRd)
+			frame, err := parseTextFrame(br2)
+			if err != nil {
+				putLimitedReader(bodyRd)
+				return nil, err
+			}
+			title = frame.(TextFrame).Text
+
+			putLimitedReader(bodyRd)
+			break
+		}
+	}
+
+	cf := ChapterFrame{
+		ElementID: string(ElementID),
+		// StartTime is given in milliseconds, so we should convert it to nanoseconds
+		// for time.Duration
+		StartTime:   time.Duration(chapterTime[0] * nanosInMillis),
+		EndTime:     time.Duration(chapterTime[1] * nanosInMillis),
+		StartOffset: chapterOffset[0],
+		EndOffset:   chapterOffset[1],
+		Title:       title,
+	}
+	return cf, nil
+}
diff --git a/common_ids.go b/common_ids.go
index 1677b7a..cfa0a60 100644
--- a/common_ids.go
+++ b/common_ids.go
@@ -8,6 +8,7 @@ package id3v2
 var (
 	V23CommonIDs = map[string]string{
 		"Attached picture":                   "APIC",
+		"Chapters":                           "CHAP",
 		"Comments":                           "COMM",
 		"Album/Movie/Show title":             "TALB",
 		"BPM":                                "TBPM",
@@ -59,6 +60,7 @@ var (
 
 	V24CommonIDs = map[string]string{
 		"Attached picture":                   "APIC",
+		"Chapters":                           "CHAP",
 		"Comments":                           "COMM",
 		"Album/Movie/Show title":             "TALB",
 		"BPM":                                "TBPM",
@@ -133,6 +135,7 @@ var (
 //	}
 var parsers = map[string]func(*bufReader) (Framer, error){
 	"APIC": parsePictureFrame,
+	"CHAP": parseChapterFrame,
 	"COMM": parseCommentFrame,
 	"TXXX": parseUserDefinedTextFrame,
 	"UFID": parseUFIDFrame,
@@ -143,7 +146,7 @@ var parsers = map[string]func(*bufReader) (Framer, error){
 // be added to sequence.
 func mustFrameBeInSequence(id string) bool {
 	switch id {
-	case "APIC", "COMM", "TXXX", "USLT":
+	case "APIC", "CHAP", "COMM", "TXXX", "USLT":
 		return true
 	}
 	return false
diff --git a/sequence.go b/sequence.go
index 2abc942..26794c7 100644
--- a/sequence.go
+++ b/sequence.go
@@ -27,6 +27,8 @@ func (s *sequence) AddFrame(f Framer) {
 		id = uslf.Language + uslf.ContentDescriptor
 	} else if udtf, ok := f.(UserDefinedTextFrame); ok {
 		id = udtf.Description
+	} else if cf, ok := f.(ChapterFrame); ok {
+		id = cf.ElementID
 	} else {
 		panic("sequence: unknown type of Framer")
 	}
diff --git a/tag.go b/tag.go
index de0418c..a15a590 100644
--- a/tag.go
+++ b/tag.go
@@ -51,6 +51,11 @@ func (tag *Tag) AddAttachedPicture(pf PictureFrame) {
 	tag.AddFrame(tag.CommonID("Attached picture"), pf)
 }
 
+// AddChapterFrame adds the chapter frame to tag.
+func (tag *Tag) AddChapterFrame(cf ChapterFrame) {
+	tag.AddFrame(tag.CommonID("Chapters"), cf)
+}
+
 // AddCommentFrame adds the comment frame to tag.
 func (tag *Tag) AddCommentFrame(cf CommentFrame) {
 	tag.AddFrame(tag.CommonID("Comments"), cf)