chore: prepare for docs sidebar

lib/load/docs/order.js

@@ -0,0 +1,34 @@
+// build the docs meta such as next, previous, category and sidebar
+module.exports = function createOrder(allSidebars = {}) {
+  const order = {};
+  if (!allSidebars) {
+    return order;
+  }
+  Object.keys(allSidebars).forEach(sidebar => {
+    const categories = allSidebars[sidebar];
+
+    let ids = [];
+    const categoryOrder = [];
+    Object.keys(categories).forEach(category => {
+      ids = ids.concat(categories[category]);
+      for (let i = 0; i < categories[category].length; i++) {
+        categoryOrder.push(category);
+      }
+    });
+
+    for (let i = 0; i < ids.length; i++) {
+      const id = ids[i];
+      let previous;
+      let next;
+      if (i > 0) previous = ids[i - 1];
+      if (i < ids.length - 1) next = ids[i + 1];
+      order[id] = {
+        previous,
+        next,
+        sidebar,
+        category: categoryOrder[i]
+      };
+    }
+  });
+  return order;
+};