From 138695208e06a733d6b27673338fd3ca8de7fe62 Mon Sep 17 00:00:00 2001
From: Paul Buetow <paul@buetow.org>
Date: Tue, 21 Apr 2026 10:45:38 +0300
Subject: fix o7: keep comic section splitting UTF-8 safe

---
 internal/comic/artist.go     |  5 +++--
 internal/comic/comic_test.go | 29 +++++++++++++++++++++++++++++
 internal/comic/helpers.go    |  7 ++++---
 3 files changed, 36 insertions(+), 5 deletions(-)

(limited to 'internal')

diff --git a/internal/comic/artist.go b/internal/comic/artist.go
index 248e8c4..aa1dd5f 100644
--- a/internal/comic/artist.go
+++ b/internal/comic/artist.go
@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"strings"
 	"time"
+	"unicode/utf8"
 
 	"codeberg.org/snonux/comicforge/internal/provider"
 )
@@ -377,8 +378,8 @@ func buildPanelLayout(section string, pagePanels []string, panelCount int) strin
 	}
 
 	excerpt := strings.TrimSpace(section)
-	if len(excerpt) > comicPromptMaxChars {
-		excerpt = excerpt[:comicPromptMaxChars]
+	if utf8.RuneCountInString(excerpt) > comicPromptMaxChars {
+		excerpt = string([]rune(excerpt)[:comicPromptMaxChars])
 		if idx := strings.LastIndex(excerpt, " "); idx > 0 {
 			excerpt = excerpt[:idx]
 		}
diff --git a/internal/comic/comic_test.go b/internal/comic/comic_test.go
index 020fba5..0acccb0 100644
--- a/internal/comic/comic_test.go
+++ b/internal/comic/comic_test.go
@@ -8,6 +8,7 @@ import (
 	"strings"
 	"testing"
 	"time"
+	"unicode/utf8"
 )
 
 func TestSlugify(t *testing.T) {
@@ -55,6 +56,34 @@ func TestBuildPanelLayoutUsesFallbackExcerpt(t *testing.T) {
 	}
 }
 
+func TestSplitIntoSectionsUsesRuneBoundaries(t *testing.T) {
+	t.Parallel()
+
+	text := strings.Repeat("Български текст за проверка на разделянето. ", 80)
+	sections := splitIntoSections(text, 4)
+	if len(sections) != 4 {
+		t.Fatalf("splitIntoSections() sections = %d, want 4", len(sections))
+	}
+	for i, section := range sections {
+		if !utf8.ValidString(section) {
+			t.Fatalf("splitIntoSections() section %d is not valid UTF-8: %q", i, section)
+		}
+	}
+}
+
+func TestBuildPanelLayoutTruncatesCyrillicOnRuneBoundaries(t *testing.T) {
+	t.Parallel()
+
+	text := strings.Repeat("абвгдежзийклмно", 70)
+	got := buildPanelLayout(text, nil, 2)
+	if !utf8.ValidString(got) {
+		t.Fatalf("buildPanelLayout() returned invalid UTF-8: %q", got)
+	}
+	if !strings.Contains(got, "…") {
+		t.Fatalf("buildPanelLayout() = %q, want truncation ellipsis", got)
+	}
+}
+
 func TestParseGenerateResultUsesConfiguredDimensions(t *testing.T) {
 	t.Parallel()
 
diff --git a/internal/comic/helpers.go b/internal/comic/helpers.go
index 0458db5..6f5b5a8 100644
--- a/internal/comic/helpers.go
+++ b/internal/comic/helpers.go
@@ -64,15 +64,16 @@ func distributeParagraphs(paragraphs []string, n int) []string {
 }
 
 func splitByChars(text string, n int) []string {
-	size := len(text) / n
+	runes := []rune(text)
+	size := len(runes) / n
 	sections := make([]string, n)
 	for i := range n {
 		start := i * size
 		end := start + size
 		if i == n-1 {
-			end = len(text)
+			end = len(runes)
 		}
-		sections[i] = strings.TrimSpace(text[start:end])
+		sections[i] = strings.TrimSpace(string(runes[start:end]))
 	}
 	return sections
 }
-- 
cgit v1.2.3