From 8b2e284fc32016101ed9fdb1706c3da02c2e42ef Mon Sep 17 00:00:00 2001
From: BennettJames <bennettsala@gmail.com>
Date: Sun, 7 Feb 2016 22:08:43 -0800
Subject: [PATCH] Added automatic discovery mechanism for partials

---
 hbs.js | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/hbs.js b/hbs.js
index 2cd32c6..131f7c6 100644
--- a/hbs.js
+++ b/hbs.js
@@ -4,7 +4,49 @@ import Handlebars from 'handlebars';
 
 const handlebarsRuntimePath = System.normalizeSync('handlebars/handlebars.runtime', __moduleName);
 
+/**
+ * Attaches the precompiled Handlebars template in a CommonJs module,
+ * and attaches any depended partials on `load` for system.js to
+ * fetch. Also registers the partials as such on the Handlebars
+ * runtime.
+ */
 export function translate(load) {
-  var precompiled = Handlebars.precompile(load.source);
-  load.source = `module.exports = require('${handlebarsRuntimePath}').template(${precompiled});`;
+
+  let ast = Handlebars.parse(load.source);
+  let partials = findPartials(ast);
+  load.metadata.deps = partials;
+
+  let precompiled = Handlebars.precompile(load.source); 
+  let partialReqs = partials.map(dep =>
+      `Handlebars.registerPartial('${dep}', require('${dep}'));`);
+  
+  load.source = `
+  var Handlebars = require('${handlebarsRuntimePath}');
+  ${partialReqs.join('\n')};
+  module.exports = Handlebars.template(${precompiled});
+  `;
+}
+
+/**
+ * Recursively trawls a Handlebars AST, providing the string names of
+ * all invoked partials.
+ */
+function findPartials(astRoot) {
+  let partials = [];
+
+  let recurse = function(ast) {
+    if (!ast) {
+      return;
+    } else if (Array.isArray(ast)) {
+      ast.forEach(n => recurse(n));
+    } else if (ast.type === 'PartialStatement') {
+      partials.push(ast.name.original);
+    } else if (typeof ast === 'object') {
+      let subnodes = Object.keys(ast).map(k => ast[k]);
+      subnodes.forEach(n => recurse(n));
+    }
+  };
+  recurse(astRoot);
+
+  return partials;
 }