Docs: Add Explore guide for plugins (#24547)

* Add Explore guide for plugins

* Fix review comments

docs/sources/developers/plugins/add-support-for-explore-queries.md

++++
+title = "Add support for Explore queries"
+type = "docs"
++++
+
+# Add support for Explore queries
+
+This guide explains how to add support for [Explore]({{< relref "../../features/explore.md" >}}) to an existing data source plugin.
+
+This guide assumes that you're already familiar with how to [Build a data source plugin]({{< relref "../../../../../tutorials/build-a-data-source-plugin.md" >}}).
+
+By adding support for Explore to your data source, users can make ad-hoc queries without the new of a dashboard. This is useful when users want to troubleshoot or to learn more about the data.
+
+To support Explore, your plugin needs to define a _query editor_ for Explore. Optionally, your plugin can also define a _start page_ for Explore.
+
+## Add a query editor for Explore
+
+The query editor for Explore is similar to the query editor for the data source itself. In fact, you'll probably reuse the same components for both query editors.
+
+1. Create a file `ExploreQueryEditor.tsx` in the `src` directory of your plugin, with the following content:
+
+   ```ts
+   import React from 'react';
+
+   import { ExploreQueryFieldProps } from '@grafana/data';
+   import { QueryField } from '@grafana/ui';
+   import { DataSource } from './DataSource';
+   import { MyQuery, MyDataSourceOptions } from './types';
+
+   export type Props = ExploreQueryFieldProps<DataSource, MyQuery, MyDataSourceOptions>;
+
+   export default (props: Props) => {
+     return (
+       <h2>My query editor</h2>
+     );
+   };
+   ```
+
+1. Configure the plugin to use the `ExploreQueryEditor`.
+
+   ```ts
+   import ExploreQueryEditor from './ExploreQueryEditor';
+   ```
+
+   ```ts
+   export const plugin = new DataSourcePlugin<DataSource, MyQuery, MyDataSourceOptions>(DataSource)
+     .setConfigEditor(ConfigEditor)
+     .setQueryEditor(QueryEditor)
+     .setExploreQueryField(ExploreQueryEditor);
+   ```
+
+1. Add a [QueryField]({{< relref "../../packages_api/ui/queryfield.md" >}}) to `ExploreQueryEditor`.
+
+   ```ts
+   import { QueryField } from '@grafana/ui';
+   ```
+
+   ```ts
+   export default (props: Props) => {
+     const { query } = props;
+
+     const onQueryChange = (value: string, override?: boolean) => {
+       const { query, onChange, onRunQuery } = props;
+
+       if (onChange) {
+         // Update the query whenever the query field changes.
+         onChange({ ...query, queryText: value });
+
+         // Run the query on Enter.
+         if (override && onRunQuery) {
+           onRunQuery();
+         }
+       }
+     };
+
+     return (
+       <QueryField
+         portalOrigin="mock-origin"
+         onChange={onQueryChange}
+         onRunQuery={props.onRunQuery}
+         onBlur={props.onBlur}
+         query={query.queryText || ''}
+         placeholder="Enter a query"
+       />
+     );
+   };
+   ```
+
+## Add a start page for Explore
+
+By adding an Explore start page for your plugin, you can for example create "cheat sheets" with commonly used queries. When the user clicks on one of the examples, it automatically updates the query editor, and runs the query. It's a great way to increase productivity for your users.
+
+1. Create a file `ExploreStartPage.tsx` in the `src` directory of your plugin, with the following content:
+
+   ```ts
+   import React from 'react';
+   import { ExploreStartPageProps } from '@grafana/data';
+
+   export default (props: ExploreStartPageProps) => {
+     return (
+       <h2>My start page</h2>
+     );
+   };
+   ```
+
+1. Configure the plugin to use the `ExploreStartPage`.
+
+   ```ts
+   import ExploreStartPage from './ExploreStartPage';
+   ```
+
+   ```ts
+   export const plugin = new DataSourcePlugin<DataSource, MyQuery, MyDataSourceOptions>(DataSource)
+     .setConfigEditor(ConfigEditor)
+     .setQueryEditor(QueryEditor)
+     .setExploreQueryField(ExploreQueryEditor)
+     .setExploreStartPage(ExploreStartPage);
+   ```
+
+1. Create a few examples.
+
+   ```ts
+   import React from 'react';
+   import { ExploreStartPageProps, DataQuery } from '@grafana/data';
+
+   const examples = [
+     {
+       title: 'Addition',
+       expression: '1 + 2',
+       label: 'Add two integers',
+     },
+     {
+       title: 'Subtraction',
+       expression: '2 - 1',
+       label: 'Subtract an integer from another',
+     },
+   ];
+
+   export default (props: ExploreStartPageProps) => {
+     return (
+       <div>
+         <h2>Cheat Sheet</h2>
+         {examples.map((item, index) => (
+           <div className="cheat-sheet-item" key={index}>
+             <div className="cheat-sheet-item__title">{item.title}</div>
+             {item.expression ? (
+               <div
+                 className="cheat-sheet-item__example"
+                 onClick={e => props.onClickExample({ refId: 'A', queryText: item.expression } as DataQuery)}
+               >
+                 <code>{item.expression}</code>
+               </div>
+             ) : null}
+             <div className="cheat-sheet-item__label">{item.label}</div>
+           </div>
+         ))}
+       </div>
+     );
+   };
+   ```
+
+## Support multiple Explore modes
+
+Explore lets you query any data source, regardless of whether it returns metrics or logs. You can change which type of query you want to make, by setting the _Explore mode_.
+
+The query modes that the plugin supports are defined in the [plugin.json]({{< relref "metadata.md" >}}) file.
+
+The query mode is available on the `props` object for both the query editor and the start page. For example, here's how you can change the query editor based on the currently selected mode:
+
+```
+export default (props: Props) => {
+  const { query, exploreMode } = props;
+
+  switch (exploreMode) {
+    case ExploreMode.Metrics:
+      return <MetricsQueryField query={query} />;
+    case ExploreMode.Logs:
+      return <LogsQueryField query={query} />;
+    default:
+      return <p>Unsupported mode</p>;
+  }
+}
+```

docs/sources/menu.yaml

@@ -364,6 +364,8 @@
           link: /developers/plugins/add-support-for-variables/
         - name: Add support for annotations
           link: /developers/plugins/add-support-for-annotations/
+        - name: Add support for Explore queries
+          link: /developers/plugins/add-support-for-explore-queries
         - name: Build a logs data source
           link: /developers/plugins/build-a-logs-data-source/
         - name: Authentication