support markdown link

Author: Paul Alonte

src/index.ts

@@ -1,2 +1,3 @@
 export { default as md2hast } from "./md2hast.js";
 export { default as preprocessor } from "./preprocessor.js";
+export { default as interpolationToLink } from "./interpolationToLink.js";

src/interpolationToLink.ts

@@ -0,0 +1,50 @@
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { visit } from "unist-util-visit";
+import type { Node, Element } from "hast";
+
+type Field = {
+  value: string;
+};
+
+function interpolationToLink(
+  options: { fields: Record<string, Field> } = { fields: {} },
+) {
+  return (tree: Node) => {
+    visit(tree, "element", (node: Element) => {
+      if (
+        node.tagName === "a" &&
+        node.properties?.href &&
+        typeof node.properties.href === "string"
+      ) {
+        // Decode potential URL-encoded curly braces
+        // e.g [site](http://site.com/%7B%7Bfield%7B%7B)
+        // replace and becomes [site](http://site.com/{{field}})
+        const href = node.properties.href
+          .replace(/%7B%7B/gi, "{{")
+          .replace(/%7D%7D/gi, "}}");
+
+        // // Only apply regex if the pattern exists
+        const interpolationRegex = /{{\s*(\w+)\s*}}/;
+
+        if (interpolationRegex.test(href)) {
+          const match = interpolationRegex.exec(href);
+
+          if (match) {
+            // we get the key from the string e.g. {{field}}
+            const key = match[1];
+
+            if (options?.fields[key] === undefined) return;
+            // get the value based from the fields object using the key
+            const replacement = options?.fields[key]?.value;
+            const resolvedHref = href.replace(interpolationRegex, replacement);
+
+            // eslint-disable-next-line no-param-reassign
+            node.properties.href = resolvedHref;
+          }
+        }
+      }
+    });
+  };
+}
+
+export default interpolationToLink;