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;
+};

lib/load/docs/sidebars.js

@@ -0,0 +1,34 @@
+const fs = require('fs-extra');
+const path = require('path');
+const {idx} = require('../utils');
+
+module.exports = function loadSidebars({siteDir, env}) {
+  let allSidebars = {};
+
+  // current sidebars
+  const sidebarsJSONFile = path.join(siteDir, 'sidebars.json');
+  if (fs.existsSync(sidebarsJSONFile)) {
+    allSidebars = require(sidebarsJSONFile);
+  }
+
+  // versioned sidebars
+  if (idx(env, ['versioning', 'enabled'])) {
+    const versions = idx(env, ['versioning', 'versions']);
+    versions &&
+      versions.forEach(version => {
+        const versionedSidebarsJSONFile = path.join(
+          siteDir,
+          'versioned_sidebars',
+          `version-${version}-sidebars.json`
+        );
+        if (fs.existsSync(versionedSidebarsJSONFile)) {
+          const sidebar = require(versionedSidebarsJSONFile);
+          Object.assign(allSidebars, sidebar);
+        } else {
+          const missingFile = path.relative(siteDir, versionedSidebarsJSONFile);
+          throw new Error(`Failed to load ${missingFile}. It does not exist.`);
+        }
+      });
+  }
+  return allSidebars;
+};