import { useEffect, useRef } from 'react'
import { useInfiniteQuery, useQuery, useQueryClient } from '@tanstack/react-query'
import { Link, useLocation, useParams, useSearchParams } from 'react-router-dom'
import { getFeed, getSavedCounts, getSyncStatus, listCategories, listChannels } from '../api/client'
import ChannelActivityList from '../components/ChannelActivityList'
import Icon from '../components/Icon'
import VideoCard from '../components/VideoCard'

// The UI exposes exactly two mutually exclusive modes. `long` is the default
// and has no URL parameter; `short` is `?type=short`. The REST endpoint still
// accepts the unfiltered value for future mobile clients, but the UI never
// sends it.
type TypeFilter = 'long' | 'short'

const TYPE_OPTIONS: { value: TypeFilter; label: string }[] = [
  { value: 'long', label: 'Обычные' },
  { value: 'short', label: 'Shorts' },
]

function VideoSkeleton() {
  return <li className="video-card" aria-hidden="true"><div className="skeleton-thumbnail" /><div className="video-info"><div className="skeleton-line wide" /><div className="skeleton-line" /><div className="skeleton-line short" /></div></li>
}

function Feed() {
  const location = useLocation()
  const { categoryId } = useParams<{ categoryId: string }>()
  const [searchParams] = useSearchParams()
  const search = location.pathname === '/search' ? searchParams.get('q')?.trim() ?? '' : ''
  const categoryNumber = categoryId && /^\d+$/.test(categoryId) ? Number(categoryId) : undefined
  const isLocal = location.pathname === '/local'
  const isUncategorized = location.pathname === '/uncategorized'
  const supportsViewToggle = !isLocal && location.pathname !== '/search'
  const isChannelsView = supportsViewToggle && searchParams.get('view') === 'channels'
  // Any value other than `short` (missing, `all`, `long`, garbage) is
  // normalized to the default `long` mode.
  const videoType: TypeFilter = searchParams.get('type') === 'short' ? 'short' : 'long'
  // Query params carried across sidebar/mobile-category links: the view mode
  // and the video-type filter. Only `?type=short` is ever written; `long` is
  // the default and has no parameter. `?new=1` stays feed-specific.
  const preservedParams = new URLSearchParams()
  if (isChannelsView) preservedParams.set('view', 'channels')
  if (videoType === 'short') preservedParams.set('type', 'short')
  const preservedQuery = preservedParams.toString()
  const withPreserved = (path: string) => (preservedQuery ? `${path}${path.includes('?') ? '&' : '?'}${preservedQuery}` : path)
  // "На сервере" has no channels view, so the view mode must not leak into its
  // URL; keep only the type filter.
  const localNavPath = `/local${videoType === 'short' ? '?type=short' : ''}`
  const typeLink = (value: TypeFilter) => {
    const params = new URLSearchParams(location.search)
    if (value === 'short') params.set('type', 'short')
    else params.delete('type')
    const qs = params.toString()
    return { pathname: location.pathname, search: qs ? `?${qs}` : '' }
  }
  const feedViewLink = () => {
    const params = new URLSearchParams()
    if (videoType === 'short') params.set('type', 'short')
    const qs = params.toString()
    return { pathname: location.pathname, search: qs ? `?${qs}` : '' }
  }
  const channelsViewSearch = new URLSearchParams({ view: 'channels' })
  // The filter is not applied in the channels view; carrying `?type=short`
  // only restores the user's choice when they switch back to the feed.
  if (videoType === 'short') channelsViewSearch.set('type', 'short')
  const newOnly = categoryNumber !== undefined && searchParams.get('new') === '1'
  const localCategoryRaw = isLocal ? searchParams.get('category') : null
  const localCategory = localCategoryRaw && /^\d+$/.test(localCategoryRaw) ? Number(localCategoryRaw) : undefined
  const localUncategorized = isLocal && searchParams.get('uncategorized') === 'true'
  const queryClient = useQueryClient()
  const categoriesQuery = useQuery({ queryKey: ['categories'], queryFn: listCategories })
  const category = categoriesQuery.data?.find((item) => item.id === categoryNumber)
  const savedCountsQuery = useQuery({ queryKey: ['feed', 'saved-counts'], queryFn: getSavedCounts, enabled: isLocal })
  const countQuery = useQuery({
    queryKey: ['channels', isUncategorized ? 'uncategorized-count' : 'all-for-counts'],
    queryFn: () => listChannels({ subscribed: true, uncategorized: isUncategorized }),
    enabled: isUncategorized || (!categoryNumber && !isLocal && !search),
  })
  const feedQuery = useInfiniteQuery({
    queryKey: ['feed', location.pathname, search, localCategory, localUncategorized, newOnly, videoType],
    queryFn: ({ pageParam }) => getFeed({
      categoryId: isLocal ? localCategory : categoryNumber,
      uncategorized: isUncategorized || localUncategorized,
      downloaded: isLocal,
      search,
      newOnly,
      type: videoType,
      cursor: pageParam,
    }),
    initialPageParam: undefined as string | undefined,
    getNextPageParam: (lastPage) => lastPage.next_cursor ?? undefined,
    enabled: (!categoryId || categoryNumber !== undefined) && !isChannelsView,
  })
  const syncStatusQuery = useQuery({
    queryKey: ['sync-status'], queryFn: getSyncStatus,
    refetchInterval: (query) => query.state.data?.videos.running ? 2000 : 60_000,
  })
  const syncRunning = Boolean(syncStatusQuery.data?.subscriptions.running || syncStatusQuery.data?.videos.running)
  const finishedAt = syncStatusQuery.data?.videos.finished_at
  const previousFinished = useRef(finishedAt)
  useEffect(() => {
    if (finishedAt && previousFinished.current !== finishedAt) {
      queryClient.invalidateQueries({ queryKey: ['feed'] })
      queryClient.invalidateQueries({ queryKey: ['channel-activity'] })
    }
    previousFinished.current = finishedAt
  }, [finishedAt, queryClient])
  const subscriptionsFinished = syncStatusQuery.data?.subscriptions.finished_at
  const previousSubscriptionsFinished = useRef(subscriptionsFinished)
  useEffect(() => {
    if (subscriptionsFinished && previousSubscriptionsFinished.current !== subscriptionsFinished) {
      queryClient.invalidateQueries({ queryKey: ['channels'] })
      queryClient.invalidateQueries({ queryKey: ['channel-activity'] })
    }
    previousSubscriptionsFinished.current = subscriptionsFinished
  }, [subscriptionsFinished, queryClient])
  const title = search ? `Поиск: ${search}` : isLocal ? 'На сервере' : isUncategorized ? 'Без категории' : categoryId ? category?.name ?? 'Категория' : 'Все видео'
  const subtitle = newOnly ? 'Только новые видео' : search ? 'Результаты в вашей ленте' : isLocal ? 'Видео, которые вы сохранили для просмотра' : isUncategorized ? `${countQuery.data?.length ?? '…'} каналов пока без категории` : category ? `${category.channel_count} каналов в категории` : isChannelsView ? 'Каналы, отсортированные по свежести видео' : `${countQuery.data?.length ?? '…'} подписок в вашей ленте`
  const items = feedQuery.data?.pages.flatMap((page) => page.items) ?? []
  useEffect(() => {
    if (isChannelsView || feedQuery.isLoading) return
    const key = `feed-scroll:${location.pathname + location.search}`
    const saved = sessionStorage.getItem(key)
    if (saved) {
      sessionStorage.removeItem(key)
      requestAnimationFrame(() => window.scrollTo(0, Number(saved)))
    }
  }, [isChannelsView, feedQuery.isLoading, location.pathname, location.search])
  const hasInvalidCategory = Boolean(categoryId && !categoryNumber)
  // Empty-state content is derived from the active type filter together with
  // the context, so the heading and the hint never contradict each other.
  const typeEmptyTitle = videoType === 'short' ? 'Здесь пока нет Shorts' : 'Здесь пока нет обычных видео'
  const typeEmptyText = videoType === 'short' ? 'Короткие ролики появятся здесь, когда попадут в ленту.' : 'Обычные ролики появятся здесь, когда попадут в ленту.'
  // Offer switching to the other type when this context does have content,
  // just not of the selected type.
  const otherTypeLink = videoType === 'short' ? typeLink('long') : typeLink('short')
  const otherTypeLabel = videoType === 'short' ? 'Смотреть обычные' : 'Смотреть Shorts'
  // `/local`: tell "nothing saved at all" apart from "nothing of this type".
  const noSavedVideos = savedCountsQuery.data?.all === 0
  // `/uncategorized`: tell "all channels already categorized" apart from
  // "uncategorized channels exist but have no videos of this type".
  const noUncategorizedChannels = countQuery.data !== undefined && countQuery.data.length === 0
  // Root feed with zero subscriptions: onboarding takes priority over the
  // type-specific empty-state.
  const noSubscriptions = location.pathname === '/' && countQuery.data !== undefined && countQuery.data.length === 0

  return <section className="page">
    <div className="page-heading">
      <div><p className="eyebrow">Моя лента</p><h1>{title}</h1><p className="page-subtitle">{subtitle}{newOnly && <> · <Link to={withPreserved(`/category/${categoryNumber}`)}>Показать все</Link></>}</p></div>
      <div className="page-controls">
        {!isChannelsView && <div className="type-toggle" role="group" aria-label="Тип видео">
          {TYPE_OPTIONS.map((option) => <Link key={option.value} to={typeLink(option.value)} className={videoType === option.value ? 'active' : ''} aria-current={videoType === option.value ? 'page' : undefined}>{option.label}</Link>)}
        </div>}
        {supportsViewToggle && <div className="view-toggle" role="group" aria-label="Режим просмотра">
          <Link to={feedViewLink()} className={!isChannelsView ? 'active' : ''} aria-current={!isChannelsView ? 'page' : undefined}>Лента</Link>
          <Link to={{ pathname: location.pathname, search: `?${channelsViewSearch.toString()}` }} className={isChannelsView ? 'active' : ''} aria-current={isChannelsView ? 'page' : undefined}>Каналы</Link>
        </div>}
      </div>
    </div>
    <nav className="mobile-category-nav" aria-label="Категории">
      <Link to={withPreserved('/')} className={location.pathname === '/' ? 'active' : ''}>Все</Link>
      <Link to={withPreserved('/uncategorized')} className={isUncategorized ? 'active' : ''}>Без категории</Link>
      <Link to={localNavPath} className={isLocal ? 'active' : ''}>На сервере</Link>
      {categoriesQuery.data?.map((item) => <Link key={item.id} to={withPreserved(`/category/${item.id}`)} className={categoryNumber === item.id ? 'active' : ''}>{item.name}</Link>)}
    </nav>
    {isLocal && <nav className="local-filter-nav" aria-label="Фильтр сохранённых видео">
      <Link to={withPreserved('/local')} className={!localCategory && !localUncategorized ? 'active' : ''}>Все <span>{savedCountsQuery.data?.all ?? '…'}</span></Link>
      <Link to={withPreserved('/local?uncategorized=true')} className={localUncategorized ? 'active' : ''}>Без категории <span>{savedCountsQuery.data?.uncategorized ?? '…'}</span></Link>
      {categoriesQuery.data?.map((item) => <Link key={item.id} to={withPreserved(`/local?category=${item.id}`)} className={localCategory === item.id ? 'active' : ''}>{item.name} <span>{savedCountsQuery.data?.categories[String(item.id)] ?? 0}</span></Link>)}
    </nav>}
    {syncStatusQuery.data?.videos.status === 'failed' && <div className="notice error-notice" role="status"><Icon name="alert" size={18} />Последнее обновление видео завершилось ошибкой. Попробуйте позже.</div>}
    {location.pathname === '/' && (countQuery.data?.length ?? 0) > 0 && categoriesQuery.data?.length === 0 && <div className="notice onboarding-notice"><Icon name="folder" size={19} /><span>Каналы уже в ленте. Разложи их по темам, чтобы быстрее находить видео.</span><Link to="/channels">Настроить категории <Icon name="chevron" size={15} /></Link></div>}
    {hasInvalidCategory || (categoryId && categoriesQuery.data && !category) ? <div className="empty-state"><h2>Категория не найдена</h2><Link className="button-primary" to="/">Ко всем видео</Link></div> : isChannelsView ? <ChannelActivityList categoryId={categoryNumber} uncategorized={isUncategorized} syncRunning={syncRunning} /> : <>
      {feedQuery.isLoading && <ul className="video-grid">{Array.from({ length: 8 }, (_, index) => <VideoSkeleton key={index} />)}</ul>}
      {feedQuery.isError && <div className="empty-state" role="alert"><Icon name="alert" size={28} /><h2>Не удалось загрузить видео</h2><p>Проверь соединение и попробуй ещё раз.</p><button className="button-primary" onClick={() => feedQuery.refetch()}>Повторить</button></div>}
      {!feedQuery.isLoading && !feedQuery.isError && items.length > 0 && <ul className="video-grid">{items.map((video) => <VideoCard key={video.youtube_video_id} video={video} showActions={isLocal} />)}</ul>}
      {!feedQuery.isLoading && !feedQuery.isError && items.length === 0 && <div className="empty-state"><span className="empty-icon"><Icon name={syncRunning ? 'refresh' : isLocal ? 'server' : search ? 'search' : 'folder'} size={28} /></span><h2>{syncRunning ? 'Загружаем новые видео' : search ? 'Ничего не найдено' : isLocal ? (noSavedVideos ? 'Пока нет сохранённых видео' : typeEmptyTitle) : isUncategorized ? (noUncategorizedChannels ? 'Все каналы распределены' : typeEmptyTitle) : noSubscriptions ? 'Здесь пока нет видео' : typeEmptyTitle}</h2><p>{syncRunning ? 'Подписки и лента обновляются. Видео появятся здесь автоматически.' : search ? 'Попробуй другой запрос.' : isLocal ? (noSavedVideos ? 'Нажми «Скачать» у понравившегося ролика, и он появится здесь.' : typeEmptyText) : isUncategorized ? (noUncategorizedChannels ? 'Все каналы уже распределены по категориям.' : typeEmptyText) : noSubscriptions ? 'Добавь каналы в категорию или обнови ленту.' : typeEmptyText}</p>{!search && !syncRunning && (isLocal ? (!noSavedVideos && <Link className="button-primary" to={otherTypeLink}>{otherTypeLabel}</Link>) : noSubscriptions ? <Link className="button-primary" to="/channels">Перейти к каналам</Link> : isUncategorized && noUncategorizedChannels ? null : <Link className="button-primary" to={otherTypeLink}>{otherTypeLabel}</Link>)}</div>}
      {feedQuery.hasNextPage && <button className="button-secondary load-more" onClick={() => feedQuery.fetchNextPage()} disabled={feedQuery.isFetchingNextPage}>{feedQuery.isFetchingNextPage ? 'Загрузка…' : 'Показать ещё'}</button>}
    </>}
  </section>
}

export default Feed