From e8d67e4003cc25d50fc20293b38d90ba5fc93059 Mon Sep 17 00:00:00 2001
From: SukkaW <isukkaw@gmail.com>
Date: Sun, 21 Jan 2024 17:59:48 +0800
Subject: [PATCH] refactor: re-implement `useNextLink`

---
 src/use-next-link-props/index.ts | 174 ++++++++++++++++++++++++++-----
 1 file changed, 150 insertions(+), 24 deletions(-)

diff --git a/src/use-next-link-props/index.ts b/src/use-next-link-props/index.ts
index 4112ae0b..69e95c87 100644
--- a/src/use-next-link-props/index.ts
+++ b/src/use-next-link-props/index.ts
@@ -1,31 +1,157 @@
 import 'client-only';
 
+import type { UrlObject } from 'url';
 import type { LinkProps } from 'next/link';
-import { useCallback, useEffect, useMemo, useState } from 'react';
-import type { MouseEvent } from 'react';
-import { usePathname } from 'next/navigation';
+import { useCallback, useMemo, useState, useTransition } from 'react';
+import { useRouter } from 'next/navigation';
 
-export interface ExtraProps {
-  isPending: boolean
+import { formatUrl } from 'next/dist/shared/lib/router/utils/format-url';
+import { useIntersection } from '../use-intersection';
+import { noop } from '@/noop';
+
+export interface UseNextLinkOptions extends Omit<LinkProps,
+  | 'as' // Next.js App Router doesn't encourage to use `as` prop (it is only retained for the legacy puprpose)
+  | 'href' // `href` is passed in as a separate argument (for easier usage)
+  | 'legacyBehavior' // Dropping `legacyBehavior` prop can simplify things a lot
+  | 'shallow' // `shallow` is only for Next.js Pages Router
+  | 'passHref' // Also `legacyBehavior`
+  | 'locale' // For Next.js Pages Router's built-in i18n only, Next.js App Router doesn't implement i18n yet
+> {
+  ref?: React.RefObject<HTMLAnchorElement> | React.RefCallback<HTMLAnchorElement> | null
+}
+
+export interface UseNextLinkReturnProps extends Partial<JSX.IntrinsicElements['a']> {
+  ref: React.RefCallback<HTMLAnchorElement>,
+  onTouchStart: React.TouchEventHandler<HTMLAnchorElement>,
+  onMouseEnter: React.MouseEventHandler<HTMLAnchorElement>,
+  onClick: React.MouseEventHandler<HTMLAnchorElement>,
+  href?: string
 }
 
-export const useNextLink = (props: LinkProps): LinkProps & ExtraProps => {
-  const pathname = usePathname();
-  const [targetPathname, setTargetPathname] = useState(() => pathname);
-  useEffect(() => {
-    setTargetPathname(pathname);
-  }, [pathname]);
-  const onClickProp = props.onClick;
-  const onClick = useCallback((event: MouseEvent<HTMLAnchorElement>) => {
-    setTargetPathname(new URL(event.currentTarget.href).pathname);
-    return onClickProp?.(event);
-  }, [onClickProp]);
-  const isPending = targetPathname !== pathname;
-  return useMemo(() => {
-    return {
-      ...props,
-      onClick,
-      isPending
-    };
-  }, [props, onClick, isPending]);
+const isModifiedEvent = (event: React.MouseEvent) => {
+  const eventTarget = event.target as HTMLElement;
+  const target = eventTarget.getAttribute('target');
+  return (
+    (target && target !== '_self')
+    || event.metaKey
+    || event.ctrlKey
+    || event.shiftKey
+    || event.altKey // triggers resource download
+    || (event.nativeEvent && event.nativeEvent.which === 2)
+  );
+};
+
+export const useNextLink = (
+  hrefProp: string | UrlObject,
+  {
+    prefetch = true,
+    ref,
+    onClick,
+    onMouseEnter,
+    onTouchStart,
+    scroll: routerScroll = true,
+    replace = false,
+    ...restProps // Record<string, never>
+  }: UseNextLinkOptions
+): [isPending: boolean, linkProps: UseNextLinkReturnProps] => {
+  // Type guard to make sure there is no more props left in restProps
+  if (process.env.NODE_ENV === 'development') {
+    const _: Record<string, never> = restProps;
+  }
+
+  const router = useRouter();
+
+  const [isPending, startTransition] = useTransition();
+
+  const [setIntersectionRef, isVisible, resetVisible] = useIntersection({
+    rootMargin: '200px'
+  });
+
+  const resolvedHref = useMemo(() => (typeof hrefProp === 'string' ? hrefProp : formatUrl(hrefProp)), [hrefProp]);
+  const [previousResolvedHref, setPreviousResolvedHref] = useState<string>(resolvedHref);
+
+  if (previousResolvedHref !== resolvedHref) {
+    // It is safe to set the state during render, as long as it won't trigger an infinite render loop.
+    // React will render the component with the current state, then throws away the render result
+    // and immediately re-executes the component function with the updated state.
+    setPreviousResolvedHref(resolvedHref);
+    resetVisible();
+  }
+
+  const callbackRef: React.RefCallback<HTMLAnchorElement> = useCallback((el: HTMLAnchorElement | null) => {
+    // track the element visibility
+    setIntersectionRef(el);
+
+    if (typeof ref === 'function') {
+      ref(el);
+    } else if (ref && el) {
+      // We are acting on React behalf to assign the passed-in ref
+      (ref as React.MutableRefObject<HTMLAnchorElement>).current = el;
+    }
+  }, [ref, setIntersectionRef]);
+
+  const childProps: UseNextLinkReturnProps = {
+    ref: callbackRef,
+    onClick(e) {
+      if (typeof onClick === 'function') {
+        onClick(e);
+      }
+      if (e.defaultPrevented) {
+        return;
+      }
+
+      const { nodeName } = e.currentTarget;
+      // anchors inside an svg have a lowercase nodeName
+      if (
+        nodeName.toUpperCase() === 'A'
+        && isModifiedEvent(e)
+      ) {
+        // app-router supports external urls out of the box
+        // ignore click for browser’s default behavior
+        return;
+      }
+
+      e.preventDefault();
+
+      startTransition(() => {
+        router[replace ? 'replace' : 'push'](resolvedHref, { scroll: routerScroll });
+      });
+    },
+    onMouseEnter(e) {
+      if (typeof onMouseEnter === 'function') {
+        onMouseEnter(e);
+      }
+      // Always disable prefetching during the development
+      if (process.env.NODE_ENV === 'development') {
+        return;
+      }
+      if (!prefetch) {
+        return;
+      }
+
+      // TODO-SUKKA: bring up prefetch
+      noop(e);
+    },
+    onTouchStart(e) {
+      if (typeof onTouchStart === 'function') {
+        onTouchStart(e);
+      }
+      // Always disable prefetching during the development
+      if (process.env.NODE_ENV === 'development') {
+        return;
+      }
+      if (!prefetch) {
+        return;
+      }
+
+      // TODO-SUKKA: bring up prefetch
+      noop(e);
+    },
+    ...restProps
+  };
+
+  return [
+    isPending,
+    childProps
+  ] as const;
 };