feat(latest): extract per-site covers (#58)

backend/internal/latest/sites.go

@@ -1,6 +1,7 @@
 package latest
 
 import (
+	"html"
 	"net/url"
 	"regexp"
 	"strconv"
@@ -146,3 +147,79 @@ func latestChapterFrom(site, seriesURL, body string) (latestChapter, bool) {
 	}
 	return best, found
 }
+
+var metaTagRe = regexp.MustCompile(`(?is)<meta\b[^>]*>`)
+var doubleQuotedMetaAttrRe = regexp.MustCompile(`(?is)([a-z][a-z0-9:_-]*)\s*=\s*"([^"]*)"`)
+var singleQuotedMetaAttrRe = regexp.MustCompile(`(?is)([a-z][a-z0-9:_-]*)\s*=\s*'([^']*)'`)
+
+// comix stores its cover in the target series object in the page state rather
+// than an HTML metadata tag. The medium rendition is deliberately selected
+// instead of deriving a URL for a thumbnail or retaining the larger rendition.
+var comixHIDRe = regexp.MustCompile(`"hid"\s*:\s*"[^"]+"`)
+var comixPosterMediumRe = regexp.MustCompile(`(?s)"poster"\s*:\s*\{.*?"medium"\s*:\s*"([^"]+)"`)
+
+// kagane's browser-fetched series response carries this published cover URL.
+// Match the cover field, not merely an image-shaped URL elsewhere in JSON.
+var kaganeCoverFieldRe = regexp.MustCompile(`"cover"\s*:\s*"([^"]+)"`)
+
+func comixCoverURL(seriesURL, body string) string {
+	m := comixSlugRe.FindStringSubmatch(seriesURL)
+	if m == nil {
+		return ""
+	}
+	id := m[1]
+	if i := strings.Index(id, "-"); i != -1 {
+		id = id[:i]
+	}
+	hidRe := regexp.MustCompile(`"hid"\s*:\s*"` + regexp.QuoteMeta(id) + `"`)
+	hid := hidRe.FindStringIndex(body)
+	if hid == nil {
+		return ""
+	}
+	end := len(body)
+	if next := comixHIDRe.FindStringIndex(body[hid[1]:]); next != nil {
+		end = hid[1] + next[0]
+	}
+	if m := comixPosterMediumRe.FindStringSubmatch(body[hid[0]:end]); m != nil {
+		return publishedCoverURL(m[1])
+	}
+	return ""
+}
+
+func coverFrom(site, seriesURL, body string) (string, bool) {
+	var cover string
+	switch site {
+	case "asura", "demonic", "lightnovelworld":
+		cover = metaContent(body, "property", "og:image")
+	case "novelfull":
+		cover = metaContent(body, "name", "image")
+	case "comix":
+		cover = comixCoverURL(seriesURL, body)
+	case "kagane":
+		if m := kaganeCoverFieldRe.FindStringSubmatch(body); m != nil {
+			cover = publishedCoverURL(m[1])
+		}
+	}
+	return cover, cover != ""
+}
+
+func metaContent(body, attrName, attrValue string) string {
+	for _, tag := range metaTagRe.FindAllString(body, -1) {
+		attrs := make(map[string]string)
+		for _, m := range doubleQuotedMetaAttrRe.FindAllStringSubmatch(tag, -1) {
+			attrs[strings.ToLower(m[1])] = m[2]
+		}
+		for _, m := range singleQuotedMetaAttrRe.FindAllStringSubmatch(tag, -1) {
+			attrs[strings.ToLower(m[1])] = m[2]
+		}
+		if strings.EqualFold(attrs[strings.ToLower(attrName)], attrValue) {
+			return publishedCoverURL(attrs["content"])
+		}
+	}
+	return ""
+}
+
+func publishedCoverURL(value string) string {
+	value = strings.TrimSpace(html.UnescapeString(value))
+	return strings.ReplaceAll(value, " ", "%20")
+}

backend/internal/latest/sites_test.go

@@ -79,6 +79,107 @@ const lnwSeriesFixture = `
 <a href="https://lightnovelworld.net/overgeared-chapter-9999/">Chapter 9999</a>
 `
 
+// Trimmed from https://asurascans.com/comics/chronicles-of-the-demon-faction-00dcbf97 on 2026-08-10.
+const asuraCoverFixture = `<meta property="og:image" content="https://cdn.asurascans.com/asura-images/covers/chronicles-of-the-demon-faction.d4dcb8.webp">`
+
+// Trimmed from https://demonicscans.org/manga/Catastrophic-Necromancer on 2026-08-10.
+// The source publishes the raw space in this URL.
+const demonicCoverFixture = `<meta property="og:image" content="https://readermc.org/images/thumbnails/Catastrophic Necromancer.webp">`
+
+// Trimmed from https://comix.to/title/n8we-dungeons-and-crayons on 2026-08-10.
+// comix publishes medium and large renditions in its state blob, with no og:image.
+const comixCoverFixture = `{"hid":"recommended","poster":{"medium":"https://static.comix.to/recommended@280.jpg","large":"https://static.comix.to/recommended.jpg"},"hid":"n8we","poster":{"medium":"https://static.comix.to/039d/i/1/34/6a6742bf15736@280.jpg","large":"https://static.comix.to/039d/i/1/34/6a6742bf15736.jpg"}}`
+
+// Trimmed from GET https://kagane.to/api/v2/series/019f84bc-9ba0-7ed9-86f5-8b905ec7c28b on 2026-08-09.
+const kaganeCoverFixture = `{"image":"https://kagane.to/api/v2/image/00000000-0000-0000-0000-000000000000/compressed","cover":"https://kagane.to/api/v2/image/019f84bc-9ba0-7ed9-86f5-8b905ec7c28b/compressed"}`
+
+// Trimmed from https://novelfull.com/reverend-insanity.html on 2026-08-10.
+const novelfullCoverFixture = `<meta name="image" content="https://novelfull.com/uploads/webp/novel/reverend-insanity-82661d911a.webp">`
+
+// Trimmed from https://lightnovelworld.net/novel/a-will-eternal/ on 2026-08-10.
+const lnwCoverFixture = `<meta content='https://lightnovelworld.net/wp-content/uploads/2026/03/a-will-eternal-1.webp' property='og:image'>`
+
+func TestCoverFrom(t *testing.T) {
+	const comixURL = "https://comix.to/title/n8we-dungeons-and-crayons"
+	tests := []struct {
+		name      string
+		site      string
+		seriesURL string
+		body      string
+		wantOK    bool
+		wantCover string
+	}{
+		{
+			name: "asura uses published metadata URL",
+			site: "asura", body: asuraCoverFixture, wantOK: true,
+			wantCover: "https://cdn.asurascans.com/asura-images/covers/chronicles-of-the-demon-faction.d4dcb8.webp",
+		},
+		{
+			name: "demonic escapes raw spaces",
+			site: "demonic", body: demonicCoverFixture, wantOK: true,
+			wantCover: "https://readermc.org/images/thumbnails/Catastrophic%20Necromancer.webp",
+		},
+		{
+			name: "comix takes target medium poster",
+			site: "comix", seriesURL: comixURL, body: comixCoverFixture, wantOK: true,
+			wantCover: "https://static.comix.to/039d/i/1/34/6a6742bf15736@280.jpg",
+		},
+		{
+			name: "kagane reads API cover field",
+			site: "kagane", body: kaganeCoverFixture, wantOK: true,
+			wantCover: "https://kagane.to/api/v2/image/019f84bc-9ba0-7ed9-86f5-8b905ec7c28b/compressed",
+		},
+		{
+			name: "novelfull reads image metadata",
+			site: "novelfull", body: novelfullCoverFixture, wantOK: true,
+			wantCover: "https://novelfull.com/uploads/webp/novel/reverend-insanity-82661d911a.webp",
+		},
+		{
+			name: "lightnovelworld reads og image",
+			site: "lightnovelworld", body: lnwCoverFixture, wantOK: true,
+			wantCover: "https://lightnovelworld.net/wp-content/uploads/2026/03/a-will-eternal-1.webp",
+		},
+		{
+			name: "page without cover is empty",
+			site: "asura", body: `<meta property="og:title" content="No Cover">`,
+		},
+		{
+			name: "unknown site is empty",
+			site: "unknown", body: asuraCoverFixture,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, ok := coverFrom(tt.site, tt.seriesURL, tt.body)
+			if ok != tt.wantOK {
+				t.Fatalf("ok = %v, want %v (got %q)", ok, tt.wantOK, got)
+			}
+			if got != tt.wantCover {
+				t.Errorf("cover = %q, want %q", got, tt.wantCover)
+			}
+		})
+	}
+}
+
+func TestCoverFromChallenge(t *testing.T) {
+	seriesURLs := map[string]string{
+		"asura":           "https://asurascans.com/comics/chronicles-of-the-demon-faction-f886a8af",
+		"demonic":         "https://demonicscans.org/manga/Catastrophic-Necromancer",
+		"comix":           "https://comix.to/title/n8we-dungeons-and-crayons",
+		"kagane":          "https://kagane.to/series/019f84bc-9ba0-7ed9-86f5-8b905ec7c28b",
+		"novelfull":       "https://novelfull.com/reverend-insanity.html",
+		"lightnovelworld": "https://lightnovelworld.net/novel/a-will-eternal/",
+	}
+	for site, seriesURL := range seriesURLs {
+		t.Run(site, func(t *testing.T) {
+			if got, ok := coverFrom(site, seriesURL, challengeFixture); ok || got != "" {
+				t.Fatalf("cover = %q, ok = %v, want empty", got, ok)
+			}
+		})
+	}
+}
+
 func TestLatestChapterFrom(t *testing.T) {
 	const asuraURL = "https://asurascans.com/comics/chronicles-of-the-demon-faction-f886a8af"
 	const demonicURL = "https://demonicscans.org/manga/Catastrophic-Necromancer"