Large "query" plug refactor into "directive"

plugs/directive/eval_directive.ts

@@ -0,0 +1,60 @@
+// This is some shocking stuff. My profession would kill me for this.
+
+import { YAML } from "../../common/deps.ts";
+import { jsonToMDTable, renderTemplate } from "./util.ts";
+
+// Enables plugName.functionName(arg1, arg2) syntax in JS expressions
+function translateJs(js: string): string {
+  return js.replaceAll(
+    /(\w+\.\w+)\s*\(/g,
+    'await invokeFunction("$1", ',
+  );
+}
+
+// Syntaxes to support:
+// - random JS expression
+// - random JS expression render [[some/template]]
+const expressionRegex = /(.+?)(\s+render\s+\[\[([^\]]+)\]\])?$/;
+
+// This is rather scary and fragile stuff, but it works.
+export async function evalDirectiveRenderer(
+  _directive: string,
+  _pageName: string,
+  expression: string,
+): Promise<string> {
+  console.log("Got JS expression", expression);
+  const match = expressionRegex.exec(expression);
+  if (!match) {
+    throw new Error(`Invalid eval directive: ${expression}`);
+  }
+  let template = "";
+  if (match[3]) {
+    // This is the template reference
+    expression = match[1];
+    template = match[3];
+  }
+  try {
+    // Why the weird "eval" call? https://esbuild.github.io/content-types/#direct-eval
+    const result = await (0, eval)(
+      `(async () => { 
+        function invokeFunction(name, ...args) {
+          return syscall("system.invokeFunction", "server", name, ...args);
+        }
+        return ${translateJs(expression)};
+      })()`,
+    );
+    if (template) {
+      return await renderTemplate(template, result);
+    }
+    if (typeof result === "string") {
+      return result;
+    } else if (typeof result === "number") {
+      return "" + result;
+    } else if (Array.isArray(result)) {
+      return jsonToMDTable(result);
+    }
+    return YAML.stringify(result);
+  } catch (e: any) {
+    return `**ERROR:** ${e.message}`;
+  }
+}