Implement basic lightbox with gallery support

ts/components/LightboxGallery.md

@@ -0,0 +1,16 @@
+```js
+const noop = () => {};
+
+const items = [
+  { objectURL: 'https://placekitten.com/800/600', contentType: 'image/jpeg' },
+  { objectURL: 'https://placekitten.com/900/600', contentType: 'image/jpeg' },
+  { objectURL: 'https://placekitten.com/1000/800', contentType: 'image/jpeg' },
+];
+
+<div style={{position: 'relative', width: '100%', height: 500}}>
+  <LightboxGallery
+    items={items}
+    onSave={noop}
+  />
+</div>
+```

ts/components/LightboxGallery.tsx

@@ -0,0 +1,79 @@
+/**
+ * @prettier
+ */
+import React from 'react';
+
+import * as MIME from '../types/MIME';
+import { Lightbox } from './Lightbox';
+
+interface Item {
+  objectURL: string;
+  contentType: MIME.MIMEType | undefined;
+}
+
+interface Props {
+  close: () => void;
+  items: Array<Item>;
+  // onNext?: () => void;
+  // onPrevious?: () => void;
+  onSave?: () => void;
+  selectedIndex: number;
+}
+
+interface State {
+  selectedIndex: number;
+}
+
+export class LightboxGallery extends React.Component<Props, State> {
+  public static defaultProps: Partial<Props> = {
+    selectedIndex: 0,
+  };
+
+  constructor(props: Props) {
+    super(props);
+
+    this.state = {
+      selectedIndex: this.props.selectedIndex,
+    };
+  }
+
+  public render() {
+    const { close, items, onSave } = this.props;
+    const { selectedIndex } = this.state;
+
+    const selectedItem: Item = items[selectedIndex];
+
+    const firstIndex = 0;
+    const onPrevious =
+      selectedIndex > firstIndex ? this.handlePrevious : undefined;
+
+    const lastIndex = items.length - 1;
+    const onNext = selectedIndex < lastIndex ? this.handleNext : undefined;
+
+    return (
+      <Lightbox
+        close={close}
+        onPrevious={onPrevious}
+        onNext={onNext}
+        onSave={onSave}
+        objectURL={selectedItem.objectURL}
+        contentType={selectedItem.contentType}
+      />
+    );
+  }
+
+  private handlePrevious = () => {
+    this.setState(prevState => ({
+      selectedIndex: Math.max(prevState.selectedIndex - 1, 0),
+    }));
+  };
+
+  private handleNext = () => {
+    this.setState((prevState, props) => ({
+      selectedIndex: Math.min(
+        prevState.selectedIndex + 1,
+        props.items.length - 1
+      ),
+    }));
+  };
+}