Read document outlines in the chapter menu

internal/book/chapters.go

@@ -2,6 +2,7 @@ package book
 
 import (
 	"encoding/xml"
+	"os"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -10,7 +11,8 @@ import (
 // Chapter marks the first page of a chapter.
 type Chapter struct {
 	Title string
-	Page  int
+	Page  int // zero-based
+	Depth int // zero-based outline level
 }
 
 type comicInfo struct {
@@ -22,23 +24,49 @@ type comicInfo struct {
 	} `xml:"Pages"`
 }
 
-// Chapters returns EPUB headings/document titles, ComicInfo.xml bookmarks,
-// or top-level archive folder markers. Metadata errors do not fall back to folders.
+// Chapters returns document outlines, headings, comic bookmarks or folder markers.
+// PDF and DJVU extraction runs once and stops when the book closes.
 func (b *Book) Chapters() ([]Chapter, error) {
 	b.chapOnce.Do(func() {
-		b.chaps, b.chapErr = b.comicInfoChapters()
+		b.mu.Lock()
+		if b.closed {
+			b.mu.Unlock()
+			b.chapErr = os.ErrClosed
+			return
+		}
+		ctx, arc := b.contextLocked(), b.arc
+		b.mu.Unlock()
+		if len(b.pages) > 0 {
+			if p, ok := b.pages[0].(toolPage); ok {
+				b.chaps, b.chapErr = p.chapters(ctx, b.Len())
+				return
+			}
+		}
+		b.chaps, b.chapErr = b.comicInfoChapters(arc)
 		if b.chaps == nil && b.chapErr == nil {
 			b.chaps = b.folderChapters()
 		}
 	})
 	return b.chaps, b.chapErr
 }
 
-func (b *Book) comicInfoChapters() ([]Chapter, error) {
-	if b.arc == nil {
+// CurrentChapter returns the nearest preceding destination, regardless of outline order.
+// Later entries win ties, so a subsection takes precedence over its parent.
+func CurrentChapter(chapters []Chapter, page int) int {
+	current := -1
+	for i, c := range chapters {
+		if c.Page <= page && (current < 0 || c.Page >= chapters[current].Page) {
+			current = i
+		}
+	}
+	return current
+}
+
+func (b *Book) comicInfoChapters(arc archive) ([]Chapter, error) {
+	if arc == nil {
 		return nil, nil
 	}
-	for _, f := range b.arc.Entries() {
+	for _, f := range arc.Entries() {
 		if !strings.EqualFold(filepath.Base(f.Name()), "comicinfo.xml") {
 			continue
 		}
@@ -58,12 +86,12 @@ func (b *Book) comicInfoChapters() ([]Chapter, error) {
 		}
 		var chs []Chapter
 		for _, p := range ci.Pages.Page {
-			if p.Bookmark == "" || p.Image < 0 || p.Image >= len(b.pages) {
+			if strings.TrimSpace(p.Bookmark) == "" || p.Image < 0 || p.Image >= len(b.pages) {
 				continue
 			}
 			chs = append(chs, Chapter{Title: p.Bookmark, Page: p.Image})
 		}
-		sort.Slice(chs, func(i, j int) bool { return chs[i].Page < chs[j].Page })
+		sort.SliceStable(chs, func(i, j int) bool { return chs[i].Page < chs[j].Page })
 		return chs, nil
 	}
 	return nil, nil