OptimizedImage - wrapper for CDN-optimized image

Objective:
- Get appropriately sized images to improve performance and Core Vitals score.
- Ensure images using "objectFit=cover" doesn't get stretched out if the source is large enough.
- Peg to 100px increments for better caching.

Notes:
- Skip images hosted in '/public'. If we really want to optimize it, then we'll need to provide the full path in the code, otherwise CDN lookup will fail.

ui/component/optimizedImage/index.js

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+import OptimizedImage from './view';
+export default OptimizedImage;

ui/component/optimizedImage/view.jsx

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+// @flow
+import React from 'react';
+import { getThumbnailCdnUrl } from 'util/thumbnail';
+
+function scaleToDevicePixelRatio(value: number, window: any) {
+  const devicePixelRatio = window.devicePixelRatio || 1.0;
+  return Math.ceil(value * devicePixelRatio);
+}
+
+type Props = {
+  src: string,
+  objectFit?: string,
+};
+
+function OptimizedImage(props: Props) {
+  const { objectFit, src, ...imgProps } = props;
+  const [optimizedSrc, setOptimizedSrc] = React.useState('');
+  const ref = React.useRef<any>();
+
+  function getOptimizedImgUrl(url, width, height) {
+    let optimizedUrl = url;
+    if (url && !url.startsWith('/public/')) {
+      optimizedUrl = url.trim().replace(/^http:\/\//i, 'https://');
+
+      // @if TARGET='web'
+      if (!optimizedUrl.endsWith('.gif')) {
+        optimizedUrl = getThumbnailCdnUrl({ thumbnail: optimizedUrl, width, height, quality: 85 });
+      }
+      // @endif
+    }
+    return optimizedUrl;
+  }
+
+  function getOptimumSize(elem) {
+    if (!elem || !elem.parentElement || !elem.parentElement.clientWidth || !elem.parentElement.clientHeight) {
+      return null;
+    }
+
+    let width = elem.parentElement.clientWidth;
+    let height = elem.parentElement.clientHeight;
+
+    width = scaleToDevicePixelRatio(width, window);
+    height = scaleToDevicePixelRatio(height, window);
+
+    // Round to next 100px for better caching
+    width = Math.ceil(width / 100) * 100;
+    height = Math.ceil(height / 100) * 100;
+
+    // Reminder: CDN expects integers.
+    return { width, height };
+  }
+
+  function adjustOptimizationIfNeeded(elem, objectFit, origSrc) {
+    if (objectFit === 'cover' && elem) {
+      const containerSize = getOptimumSize(elem);
+      if (containerSize) {
+        // $FlowFixMe
+        if (elem.naturalWidth < containerSize.width) {
+          // For 'cover', we don't want to stretch the image. We started off by
+          // filling up the container height, but the width still has a gap for
+          // this instance (usually due to aspect ratio mismatch).
+          // If the original image is much larger, we can request for a larger
+          // image so that "objectFit=cover" will center it without stretching and
+          // making it blur. The double fetch might seem wasteful, but on
+          // average the total transferred bytes is still less than the original.
+          const probablyMaxedOut = elem.naturalHeight < containerSize.height;
+          if (!probablyMaxedOut) {
+            const newOptimizedSrc = getOptimizedImgUrl(origSrc, containerSize.width, 0);
+            if (newOptimizedSrc && newOptimizedSrc !== optimizedSrc) {
+              setOptimizedSrc(newOptimizedSrc);
+            }
+          }
+        }
+      }
+    }
+  }
+
+  React.useEffect(() => {
+    const containerSize = getOptimumSize(ref.current);
+    if (containerSize) {
+      const width = 0; // The CDN will fill the zeroed attribute per image's aspect ratio.
+      const height = containerSize.height;
+
+      const newOptimizedSrc = getOptimizedImgUrl(src, width, height);
+
+      if (newOptimizedSrc !== optimizedSrc) {
+        setOptimizedSrc(newOptimizedSrc);
+      }
+    } else {
+      setOptimizedSrc(src);
+    }
+  }, []); // eslint-disable-line react-hooks/exhaustive-deps
+
+  if (!src) {
+    return null;
+  }
+
+  return (
+    <img
+      ref={ref}
+      {...imgProps}
+      src={optimizedSrc}
+      onLoad={() => adjustOptimizationIfNeeded(ref.current, objectFit, src)}
+    />
+  );
+}
+
+export default OptimizedImage;