Add new handlebars helper

Author: ptmt

documentation/pages/custom-html.md

@@ -272,6 +272,22 @@ Include partials:
 {{include "partials/sidebar.hbs"}}
 ```
 
+### `md` (inline markdown)
+
+Render inline Markdown from a string (links, bold, italics, ~~strikethrough~~):
+
+```handlebars
+{{{md post.metadata.captionText}}}
+```
+
+Useful for nested frontmatter fields, e.g.:
+
+```handlebars
+{{#each post.metadata.timeline}}
+  <span class="caption-text">{{{md captionText}}}</span>
+{{/each}}
+```
+
 ### `datasource`
 
 All templates receive a `datasource` object that mirrors the generated JSON files, so you can render galleries, quote blocks, or entity lists during server-side rendering without additional fetches:

resources/META-INF/services/com.potomushto.statik.template.helpers.HandlebarsHelperRegistrar

@@ -7,6 +7,7 @@ com.potomushto.statik.template.helpers.FormatDateHelperRegistrar
 com.potomushto.statik.template.helpers.GroupByHelperRegistrar
 com.potomushto.statik.template.helpers.IncludeHelperRegistrar
 com.potomushto.statik.template.helpers.LimitHelperRegistrar
+com.potomushto.statik.template.helpers.MarkdownHelperRegistrar
 com.potomushto.statik.template.helpers.SafeHelperRegistrar
 com.potomushto.statik.template.helpers.SortByHelperRegistrar
 com.potomushto.statik.template.helpers.SubstringHelperRegistrar

src/com/potomushto/statik/template/helpers/MarkdownHelperRegistrar.kt

@@ -0,0 +1,56 @@
+package com.potomushto.statik.template.helpers
+
+import com.github.jknack.handlebars.Handlebars
+import com.github.jknack.handlebars.Helper
+import com.vladsch.flexmark.ext.autolink.AutolinkExtension
+import com.vladsch.flexmark.ext.gfm.strikethrough.StrikethroughExtension
+import com.vladsch.flexmark.html.HtmlRenderer
+import com.vladsch.flexmark.parser.Parser
+
+class MarkdownHelperRegistrar : HandlebarsHelperRegistrar {
+    private val parser = Parser.builder()
+        .extensions(listOf(
+            AutolinkExtension.create(),
+            StrikethroughExtension.create()
+        ))
+        .build()
+
+    private val renderer = HtmlRenderer.builder()
+        .extensions(listOf(
+            AutolinkExtension.create(),
+            StrikethroughExtension.create()
+        ))
+        .build()
+
+    override fun register(handlebars: Handlebars, context: HelperRegistrationContext) {
+        handlebars.registerHelper("md", Helper<Any?> { value, _ ->
+            val text = value?.toString()?.trim().orEmpty()
+            if (text.isEmpty()) {
+                return@Helper ""
+            }
+
+            val html = renderer.render(parser.parse(text))
+            val inline = stripSingleParagraph(html)
+            Handlebars.SafeString(inline)
+        })
+    }
+
+    private fun stripSingleParagraph(html: String): String {
+        val trimmed = html.trim()
+        if (!trimmed.startsWith("<p>") || !trimmed.endsWith("</p>")) {
+            return trimmed
+        }
+
+        val firstClose = trimmed.indexOf("</p>")
+        if (firstClose != trimmed.length - 4) {
+            return trimmed
+        }
+
+        val nextOpen = trimmed.indexOf("<p>", startIndex = 3)
+        if (nextOpen != -1) {
+            return trimmed
+        }
+
+        return trimmed.substring(3, trimmed.length - 4).trim()
+    }
+}