feat(invoice): add send route

pkg/invoice/report/html.go

@@ -0,0 +1,43 @@
+package report
+
+import (
+	"fmt"
+	"html/template"
+	"regexp"
+	"strconv"
+)
+
+// OffsetHTags offsets all <h1>-<h6> tags in the HTML by the given amount.
+// If the resulting heading level exceeds 6, it is capped at 6.
+func offsetHTags(amount int, html template.HTML) template.HTML {
+	// Regular expression to match opening and closing h tags, e.g., <h1> or </h2>
+	re := regexp.MustCompile(`(?i)<(/?)h([1-6])(\s[^>]*)?>`)
+
+	// Replace all matches
+	result := re.ReplaceAllStringFunc(string(html), func(tag string) string {
+		matches := re.FindStringSubmatch(tag)
+		if len(matches) < 4 {
+			return tag
+		}
+
+		closingSlash := matches[1] // "/" if closing tag
+		levelStr := matches[2]     // heading level
+		attrs := matches[3]        // attributes like ' class="foo"'
+
+		level, err := strconv.Atoi(levelStr)
+		if err != nil {
+			return tag
+		}
+
+		newLevel := level + amount
+		if newLevel < 1 {
+			newLevel = 1
+		} else if newLevel > 6 {
+			newLevel = 6
+		}
+
+		return fmt.Sprintf("<%sh%d%s>", closingSlash, newLevel, attrs)
+	})
+
+	return template.HTML(result)
+}