[change] Image - extract useSource hook

Move the image loading effect here
Changed the original logic slightly for less nesting
Changed to cover cases where passing the same headers object was
starting new loads, as it was treated as a different value due to
referential equality

Author: kidroca

packages/react-native-web/src/exports/Image/index.js

@@ -185,18 +185,10 @@ const Image: React.AbstractComponent<
       );
     }
   }
-  const [loadedUri, setLoadedUri] = React.useState('');
-  const [state, updateState] = React.useState(() => {
-    const uri = resolveAssetUri(source);
-    if (uri != null) {
-      const isLoaded = ImageLoader.has(uri);
-      if (isLoaded) {
-        return LOADED;
-      }
-    }
-    return IDLE;
-  });
-
+  const { state, loadedUri } = useSource(
+    { onLoad, onLoadStart, onLoadEnd, onError },
+    source
+  );
   const [layout, updateLayout] = React.useState({});
   const hasTextAncestor = React.useContext(TextAncestorContext);
   const hiddenImageRef = React.useRef(null);
@@ -254,53 +246,6 @@ const Image: React.AbstractComponent<
     }
   }
 
-  // Image loading
-  const uri = resolveAssetUri(source);
-  let headers;
-  if (source && typeof source.headers === 'object') {
-    headers = ((source.headers: any): { [key: string]: string });
-  }
-
-  React.useEffect(() => {
-    if (uri != null) {
-      updateState(LOADING);
-      if (onLoadStart) onLoadStart();
-
-      const requestId = ImageLoader.load(
-        { uri, headers },
-        function load(result) {
-          updateState(LOADED);
-          setLoadedUri(result.uri);
-          if (onLoad) {
-            onLoad(result);
-          }
-          if (onLoadEnd) {
-            onLoadEnd();
-          }
-        },
-        function error() {
-          updateState(ERRORED);
-          if (onError) {
-            onError({
-              nativeEvent: {
-                error: `Failed to load resource ${uri} (404)`
-              }
-            });
-          }
-          if (onLoadEnd) {
-            onLoadEnd();
-          }
-        }
-      );
-
-      const effectCleanup = () => {
-        if (requestId) ImageLoader.release(requestId);
-      };
-
-      return effectCleanup;
-    }
-  }, [updateState, onError, onLoad, onLoadEnd, onLoadStart, uri, headers]);
-
   return (
     <View
       {...rest}
@@ -351,6 +296,83 @@ ImageWithStatics.queryCache = function (uris) {
   return ImageLoader.queryCache(uris);
 };
 
+type UseSourceParams = {
+  onLoad?: Function,
+  onLoadStart?: Function,
+  onLoadEnd?: Function,
+  onError?: Function
+};
+
+/**
+ * Image loading/state management hook
+ * @param params
+ * @param source
+ * @returns {{state: string, uri: string}}
+ */
+const useSource = (
+  { onLoad, onLoadStart, onLoadEnd, onError }: UseSourceParams,
+  source: ?Source
+): { state: string, uri: string } => {
+  const [loadedUri, setLoadedUri] = React.useState('');
+  const [state, updateState] = React.useState(() => {
+    const uri = resolveAssetUri(source);
+    if (uri != null) {
+      const isLoaded = ImageLoader.has(uri);
+      if (isLoaded) return LOADED;
+    }
+    return IDLE;
+  });
+
+  const loadInput = React.useRef(null);
+
+  React.useEffect(() => {
+    const uri = resolveAssetUri(source);
+    if (uri == null) return;
+
+    let headers;
+    if (source && typeof source.headers === 'object') {
+      headers = ((source.headers: any): { [key: string]: string });
+    }
+
+    const nextInput = { uri, headers };
+    const currentInput = loadInput.current;
+    if (JSON.stringify(nextInput) === JSON.stringify(currentInput)) return;
+
+    updateState(LOADING);
+    if (onLoadStart) onLoadStart();
+
+    loadInput.current = nextInput;
+    const requestId = ImageLoader.load(
+      nextInput,
+      function load(result) {
+        updateState(LOADED);
+        setLoadedUri(result.uri);
+        if (onLoad) onLoad(result);
+        if (onLoadEnd) onLoadEnd();
+      },
+      function error() {
+        updateState(ERRORED);
+        if (onError) {
+          onError({
+            nativeEvent: {
+              error: `Failed to load resource ${uri} (404)`
+            }
+          });
+        }
+        if (onLoadEnd) onLoadEnd();
+      }
+    );
+
+    const effectCleanup = () => ImageLoader.release(requestId);
+    return effectCleanup;
+  }, [updateState, onError, onLoad, onLoadEnd, onLoadStart, source]);
+
+  return {
+    state,
+    loadedUri
+  };
+};
+
 const styles = StyleSheet.create({
   root: {
     flexBasis: 'auto',