feat(v2): Algolia search theme (#1440)

* feat(v2): Algolia search plugin

* patch PR #1440 (#1441)

* alternative implementation

* typo

* refactor noop

* rename SearchAlgolia -> SearchBar

* changes.md

packages/docusaurus-theme-search-algolia/src/index.js

@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const path = require('path');
+
+const DEFAULT_OPTIONS = {};
+
+class DocusaurusThemeSearchAlgolia {
+  constructor(context, opts) {
+    this.options = {...DEFAULT_OPTIONS, ...opts};
+    this.context = context;
+  }
+
+  getName() {
+    return 'docusaurus-theme-search-algolia';
+  }
+
+  getThemePath() {
+    return path.resolve(__dirname, './theme');
+  }
+}
+
+module.exports = DocusaurusThemeSearchAlgolia;

packages/docusaurus-theme-search-algolia/src/theme/SearchBar/index.js

@@ -0,0 +1,67 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import React from 'react';
+
+import DocusaurusContext from '@docusaurus/context';
+
+import './styles.css';
+
+class Search extends React.Component {
+  constructor(props) {
+    super(props);
+    this.state = {
+      enabled: true,
+    };
+  }
+
+  componentDidMount() {
+    const {siteConfig = {}, metadata = {}} = this.context;
+    const {version: thisVersion, language: thisLanguage} = metadata;
+    const {
+      themeConfig: {algolia},
+    } = siteConfig;
+
+    // https://github.com/algolia/docsearch/issues/352
+    const isClient = typeof window !== 'undefined';
+    if (isClient) {
+      import('docsearch.js').then(({default: docsearch}) => {
+        docsearch({
+          appId: algolia.appId,
+          apiKey: algolia.apiKey,
+          indexName: algolia.indexName,
+          inputSelector: '#search_input_react',
+          algoliaOptions: JSON.parse(
+            JSON.stringify(algolia.algoliaOptions)
+              .replace('VERSION', thisVersion)
+              .replace('LANGUAGE', thisLanguage),
+          ),
+        });
+      });
+    } else {
+      console.warn('Search has failed to load and now is being disabled');
+      this.setState({enabled: false});
+    }
+  }
+
+  render() {
+    const {enabled} = this.state;
+
+    return enabled ? (
+      <input
+        id="search_input_react"
+        type="search"
+        placeholder="Search docs"
+        aria-label="Search docs"
+      />
+    ) : null;
+  }
+}
+
+Search.contextType = DocusaurusContext;
+
+export default Search;