Update section behavior

main.go

@@ -261,6 +261,7 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 	// Determine section index (-1 = whole page).
 	sectionIndex := -1
 	insertBefore := -1
+	sectionSpan := false
 	if editMode {
 		if s := r.URL.Query().Get("section"); s != "" {
 			if n, err := strconv.Atoi(s); err == nil && n >= 0 {
@@ -272,6 +273,7 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 				insertBefore = n
 			}
 		}
+		sectionSpan = r.URL.Query().Has("span")
 	}
 
 	var special *specialPage
@@ -323,7 +325,11 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 	} else if editMode && sectionIndex >= 0 {
 		sections := splitSections(rawMD)
 		if sectionIndex < len(sections) {
-			rawContent = string(sections[sectionIndex])
+			end := sectionIndex + 1
+			if sectionSpan {
+				end = secionSpanEnd(sections, sectionIndex)
+			}
+			rawContent = string(joinSections(sections[sectionIndex:end]))
 		}
 	} else if editMode && rawContent == "" && urlPath != "/" {
 		rawContent = "# " + pageTitle(urlPath) + "\n\n"
@@ -336,6 +342,7 @@ func (h *handler) serveDir(w http.ResponseWriter, r *http.Request, urlPath, fsPa
 		IsRoot:         urlPath == "/",
 		SectionIndex:   sectionIndex,
 		InsertBefore:   insertBefore,
+		Span:           sectionSpan,
 		PostURL:        urlPath,
 		RawContent:     rawContent,
 		Content:        rendered,
@@ -390,11 +397,7 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 	indexPath := filepath.Join(fsPath, "index.md")
 	redirectTarget := urlPath
 
-	// insert_before splices a new section into the file *at* index N rather
-	// than replacing index N (used by the diary "create new day" flow).
-	// section replaces the section at index N (used by per-section edits).
-	// Exactly one of insert_before / section should be set; insert_before
-	// wins if both are present.
+	// handle section saving
 	if s := r.FormValue("insert_before"); s != "" {
 		insertIndex, err := strconv.Atoi(s)
 		if err != nil || insertIndex < 0 {
@@ -431,8 +434,18 @@ func (h *handler) handlePost(w http.ResponseWriter, r *http.Request, urlPath, fs
 			http.Error(w, "section no longer exists — the page changed since you opened the editor", http.StatusConflict)
 			return
 		}
-		sections[sectionIndex] = []byte(content)
-		content = string(joinSections(sections))
+
+		// handling of section editing that spans until the next heading of the same level
+		end := sectionIndex + 1
+		if r.FormValue("span") != "" {
+			end = secionSpanEnd(sections, sectionIndex)
+		}
+		merged := make([][]byte, 0, len(sections)-(end-sectionIndex)+1)
+		merged = append(merged, sections[:sectionIndex]...)
+		merged = append(merged, []byte(content))
+		merged = append(merged, sections[end:]...)
+		content = string(joinSections(merged))
+
 		// Section index ≥ 1 is a heading-anchored section. Redirect to its
 		// anchor so the user lands on the section they just saved, even if
 		// the heading text changed.