link.tsx

import React from 'react'
import { UrlObject } from 'url'
import {
  isLocalURL,
  NextRouter,
  PrefetchOptions,
  resolveHref,
} from '../shared/lib/router/router'
import { addLocale } from './add-locale'
import { RouterContext } from '../shared/lib/router-context'
import {
  AppRouterContext,
  AppRouterInstance,
} from '../shared/lib/app-router-context'
import { useIntersection } from './use-intersection'
import { getDomainLocale } from './get-domain-locale'
import { addBasePath } from './add-base-path'

type Url = string | UrlObject
type RequiredKeys<T> = {
  [K in keyof T]-?: {} extends Pick<T, K> ? never : K
}[keyof T]
type OptionalKeys<T> = {
  [K in keyof T]-?: {} extends Pick<T, K> ? K : never
}[keyof T]

type InternalLinkProps = {
  href: Url
  as?: Url
  replace?: boolean
  scroll?: boolean
  shallow?: boolean
  passHref?: boolean
  prefetch?: boolean
  locale?: string | false
  legacyBehavior?: boolean
  // e: any because as it would otherwise overlap with existing types
  /**
   * requires experimental.newNextLinkBehavior
   */
  onMouseEnter?: (e: any) => void
  // e: any because as it would otherwise overlap with existing types
  /**
   * requires experimental.newNextLinkBehavior
   */
  onTouchStart?: (e: any) => void
  // e: any because as it would otherwise overlap with existing types
  /**
   * requires experimental.newNextLinkBehavior
   */
  onClick?: (e: any) => void
}

// TODO-APP: Include the full set of Anchor props
// adding this to the publicly exported type currently breaks existing apps
export type LinkProps = InternalLinkProps
type LinkPropsRequired = RequiredKeys<LinkProps>
type LinkPropsOptional = OptionalKeys<InternalLinkProps>

const prefetched: { [cacheKey: string]: boolean } = {}

function prefetch(
  router: NextRouter,
  href: string,
  as: string,
  options?: PrefetchOptions
): void {
  if (typeof window === 'undefined' || !router) return
  if (!isLocalURL(href)) return
  // Prefetch the JSON page if asked (only in the client)
  // We need to handle a prefetch error here since we may be
  // loading with priority which can reject but we don't
  // want to force navigation since this is only a prefetch
  Promise.resolve(router.prefetch(href, as, options)).catch((err) => {
    if (process.env.NODE_ENV !== 'production') {
      // rethrow to show invalid URL errors
      throw err
    }
  })
  const curLocale =
    options && typeof options.locale !== 'undefined'
      ? options.locale
      : router && router.locale

  // Join on an invalid URI character
  prefetched[href + '%' + as + (curLocale ? '%' + curLocale : '')] = true
}

function isModifiedEvent(event: React.MouseEvent): boolean {
  const { target } = event.currentTarget as HTMLAnchorElement
  return (
    (target && target !== '_self') ||
    event.metaKey ||
    event.ctrlKey ||
    event.shiftKey ||
    event.altKey || // triggers resource download
    (event.nativeEvent && event.nativeEvent.which === 2)
  )
}

function linkClicked(
  e: React.MouseEvent,
  router: NextRouter | AppRouterInstance,
  href: string,
  as: string,
  replace?: boolean,
  shallow?: boolean,
  scroll?: boolean,
  locale?: string | false,
  isAppRouter?: boolean,
  prefetchEnabled?: boolean
): void {
  const { nodeName } = e.currentTarget

  // anchors inside an svg have a lowercase nodeName
  const isAnchorNodeName = nodeName.toUpperCase() === 'A'

  if (isAnchorNodeName && (isModifiedEvent(e) || !isLocalURL(href))) {
    // ignore click for browser’s default behavior
    return
  }

  e.preventDefault()

  const navigate = () => {
    // If the router is an NextRouter instance it will have `beforePopState`
    if ('beforePopState' in router) {
      router[replace ? 'replace' : 'push'](href, as, {
        shallow,
        locale,
        scroll,
      })
    } else {
      // If `beforePopState` doesn't exist on the router it's the AppRouter.
      const method: keyof AppRouterInstance = replace ? 'replace' : 'push'

      router[method](href, { forceOptimisticNavigation: !prefetchEnabled })
    }
  }

  if (isAppRouter) {
    // @ts-expect-error startTransition exists.
    React.startTransition(navigate)
  } else {
    navigate()
  }
}

type LinkPropsReal = React.PropsWithChildren<
  Omit<React.AnchorHTMLAttributes<HTMLAnchorElement>, keyof LinkProps> &
    LinkProps
>

const Link = React.forwardRef<HTMLAnchorElement, LinkPropsReal>(
  function LinkComponent(props, forwardedRef) {
    if (process.env.NODE_ENV !== 'production') {
      function createPropError(args: {
        key: string
        expected: string
        actual: string
      }) {
        return new Error(
          `Failed prop type: The prop \`${args.key}\` expects a ${args.expected} in \`<Link>\`, but got \`${args.actual}\` instead.` +
            (typeof window !== 'undefined'
              ? "\nOpen your browser's console to view the Component stack trace."
              : '')
        )
      }

      // TypeScript trick for type-guarding:
      const requiredPropsGuard: Record<LinkPropsRequired, true> = {
        href: true,
      } as const
      const requiredProps: LinkPropsRequired[] = Object.keys(
        requiredPropsGuard
      ) as LinkPropsRequired[]
      requiredProps.forEach((key: LinkPropsRequired) => {
        if (key === 'href') {
          if (
            props[key] == null ||
            (typeof props[key] !== 'string' && typeof props[key] !== 'object')
          ) {
            throw createPropError({
              key,
              expected: '`string` or `object`',
              actual: props[key] === null ? 'null' : typeof props[key],
            })
          }
        } else {
          // TypeScript trick for type-guarding:
          // eslint-disable-next-line @typescript-eslint/no-unused-vars
          const _: never = key
        }
      })

      // TypeScript trick for type-guarding:
      const optionalPropsGuard: Record<LinkPropsOptional, true> = {
        as: true,
        replace: true,
        scroll: true,
        shallow: true,
        passHref: true,
        prefetch: true,
        locale: true,
        onClick: true,
        onMouseEnter: true,
        onTouchStart: true,
        legacyBehavior: true,
      } as const
      const optionalProps: LinkPropsOptional[] = Object.keys(
        optionalPropsGuard
      ) as LinkPropsOptional[]
      optionalProps.forEach((key: LinkPropsOptional) => {
        const valType = typeof props[key]

        if (key === 'as') {
          if (props[key] && valType !== 'string' && valType !== 'object') {
            throw createPropError({
              key,
              expected: '`string` or `object`',
              actual: valType,
            })
          }
        } else if (key === 'locale') {
          if (props[key] && valType !== 'string') {
            throw createPropError({
              key,
              expected: '`string`',
              actual: valType,
            })
          }
        } else if (
          key === 'onClick' ||
          key === 'onMouseEnter' ||
          key === 'onTouchStart'
        ) {
          if (props[key] && valType !== 'function') {
            throw createPropError({
              key,
              expected: '`function`',
              actual: valType,
            })
          }
        } else if (
          key === 'replace' ||
          key === 'scroll' ||
          key === 'shallow' ||
          key === 'passHref' ||
          key === 'prefetch' ||
          key === 'legacyBehavior'
        ) {
          if (props[key] != null && valType !== 'boolean') {
            throw createPropError({
              key,
              expected: '`boolean`',
              actual: valType,
            })
          }
        } else {
          // TypeScript trick for type-guarding:
          // eslint-disable-next-line @typescript-eslint/no-unused-vars
          const _: never = key
        }
      })

      // This hook is in a conditional but that is ok because `process.env.NODE_ENV` never changes
      // eslint-disable-next-line react-hooks/rules-of-hooks
      const hasWarned = React.useRef(false)
      if (props.prefetch && !hasWarned.current) {
        hasWarned.current = true
        console.warn(
          'Next.js auto-prefetches automatically based on viewport. The prefetch attribute is no longer needed. More: https://nextjs.org/docs/messages/prefetch-true-deprecated'
        )
      }
    }

    let children: React.ReactNode

    const {
      href: hrefProp,
      as: asProp,
      children: childrenProp,
      prefetch: prefetchProp,
      passHref,
      replace,
      shallow,
      scroll,
      locale,
      onClick,
      onMouseEnter,
      onTouchStart,
      legacyBehavior = Boolean(process.env.__NEXT_NEW_LINK_BEHAVIOR) !== true,
      ...restProps
    } = props

    children = childrenProp

    if (
      legacyBehavior &&
      (typeof children === 'string' || typeof children === 'number')
    ) {
      children = <a>{children}</a>
    }

    const p = prefetchProp !== false
    let router = React.useContext(RouterContext)

    // TODO-APP: type error. Remove `as any`
    const appRouter = React.useContext(AppRouterContext) as any
    if (appRouter) {
      router = appRouter
    }

    const { href, as } = React.useMemo(() => {
      const [resolvedHref, resolvedAs] = resolveHref(router, hrefProp, true)
      return {
        href: resolvedHref,
        as: asProp ? resolveHref(router, asProp) : resolvedAs || resolvedHref,
      }
    }, [router, hrefProp, asProp])

    const previousHref = React.useRef<string>(href)
    const previousAs = React.useRef<string>(as)

    // This will return the first child, if multiple are provided it will throw an error
    let child: any
    if (legacyBehavior) {
      if (process.env.NODE_ENV === 'development') {
        if (onClick) {
          console.warn(
            `"onClick" was passed to <Link> with \`href\` of \`${hrefProp}\` but "legacyBehavior" was set. The legacy behavior requires onClick be set on the child of next/link`
          )
        }
        if (onMouseEnter) {
          console.warn(
            `"onMouseEnter" was passed to <Link> with \`href\` of \`${hrefProp}\` but "legacyBehavior" was set. The legacy behavior requires onMouseEnter be set on the child of next/link`
          )
        }
        try {
          child = React.Children.only(children)
        } catch (err) {
          if (!children) {
            throw new Error(
              `No children were passed to <Link> with \`href\` of \`${hrefProp}\` but one child is required https://nextjs.org/docs/messages/link-no-children`
            )
          }
          throw new Error(
            `Multiple children were passed to <Link> with \`href\` of \`${hrefProp}\` but only one child is supported https://nextjs.org/docs/messages/link-multiple-children` +
              (typeof window !== 'undefined'
                ? " \nOpen your browser's console to view the Component stack trace."
                : '')
          )
        }
      } else {
        child = React.Children.only(children)
      }
    }

    const childRef: any = legacyBehavior
      ? child && typeof child === 'object' && child.ref
      : forwardedRef

    const [setIntersectionRef, isVisible, resetVisible] = useIntersection({
      rootMargin: '200px',
    })

    const setRef = React.useCallback(
      (el: Element) => {
        // Before the link getting observed, check if visible state need to be reset
        if (previousAs.current !== as || previousHref.current !== href) {
          resetVisible()
          previousAs.current = as
          previousHref.current = href
        }

        setIntersectionRef(el)
        if (childRef) {
          if (typeof childRef === 'function') childRef(el)
          else if (typeof childRef === 'object') {
            childRef.current = el
          }
        }
      },
      [as, childRef, href, resetVisible, setIntersectionRef]
    )
    React.useEffect(() => {
      const shouldPrefetch = isVisible && p && isLocalURL(href)
      const curLocale =
        typeof locale !== 'undefined' ? locale : router && router.locale
      const isPrefetched =
        prefetched[href + '%' + as + (curLocale ? '%' + curLocale : '')]
      if (shouldPrefetch && !isPrefetched) {
        prefetch(router, href, as, {
          locale: curLocale,
        })
      }
    }, [as, href, isVisible, locale, p, router])

    const childProps: {
      onTouchStart: React.TouchEventHandler
      onMouseEnter: React.MouseEventHandler
      onClick: React.MouseEventHandler
      href?: string
      ref?: any
    } = {
      ref: setRef,
      onClick: (e: React.MouseEvent) => {
        if (process.env.NODE_ENV !== 'production') {
          if (!e) {
            throw new Error(
              `Component rendered inside next/link has to pass click event to "onClick" prop.`
            )
          }
        }

        if (!legacyBehavior && typeof onClick === 'function') {
          onClick(e)
        }
        if (
          legacyBehavior &&
          child.props &&
          typeof child.props.onClick === 'function'
        ) {
          child.props.onClick(e)
        }
        if (!e.defaultPrevented) {
          linkClicked(
            e,
            router,
            href,
            as,
            replace,
            shallow,
            scroll,
            locale,
            Boolean(appRouter),
            p
          )
        }
      },
      onMouseEnter: (e: React.MouseEvent) => {
        if (!legacyBehavior && typeof onMouseEnter === 'function') {
          onMouseEnter(e)
        }
        if (
          legacyBehavior &&
          child.props &&
          typeof child.props.onMouseEnter === 'function'
        ) {
          child.props.onMouseEnter(e)
        }

        // Check for not prefetch disabled in page using appRouter
        if (!(!p && appRouter)) {
          if (isLocalURL(href)) {
            prefetch(router, href, as, { priority: true })
          }
        }
      },
      onTouchStart: (e: React.TouchEvent<HTMLAnchorElement>) => {
        if (!legacyBehavior && typeof onTouchStart === 'function') {
          onTouchStart(e)
        }

        if (
          legacyBehavior &&
          child.props &&
          typeof child.props.onTouchStart === 'function'
        ) {
          child.props.onTouchStart(e)
        }

        // Check for not prefetch disabled in page using appRouter
        if (!(!p && appRouter)) {
          if (isLocalURL(href)) {
            prefetch(router, href, as, { priority: true })
          }
        }
      },
    }

    // If child is an <a> tag and doesn't have a href attribute, or if the 'passHref' property is
    // defined, we specify the current 'href', so that repetition is not needed by the user
    if (
      !legacyBehavior ||
      passHref ||
      (child.type === 'a' && !('href' in child.props))
    ) {
      const curLocale =
        typeof locale !== 'undefined' ? locale : router && router.locale

      // we only render domain locales if we are currently on a domain locale
      // so that locale links are still visitable in development/preview envs
      const localeDomain =
        router &&
        router.isLocaleDomain &&
        getDomainLocale(as, curLocale, router.locales, router.domainLocales)

      childProps.href =
        localeDomain ||
        addBasePath(addLocale(as, curLocale, router && router.defaultLocale))
    }

    return legacyBehavior ? (
      React.cloneElement(child, childProps)
    ) : (
      <a {...restProps} {...childProps}>
        {children}
      </a>
    )
  }
)

export default Link