import { useState, startTransition } from 'react'
import { useHasTmdbKey } from '../hooks/use-external'
import LazyMount from '../components/ui/LazyMount'
import { usePreferencesStore } from '../stores/preferences-store'
import { regionForUser } from '../lib/format'
import DiscoverFilters, {
  DEFAULT_FILTERS,
  hasAnyActiveFilters,
  type DiscoverFilterState,
} from '../components/discover/DiscoverFilters'
import TonightHero from '../components/discover/TonightHero'
import { MoodChips, MoodRow } from '../components/discover/MoodChips'
import Roulette from '../components/discover/Roulette'
import DecadeStrip from '../components/discover/DecadeStrip'
import CanonicalLists from '../components/discover/CanonicalLists'
import OnThisDay from '../components/discover/OnThisDay'
import LibraryGapFinder from '../components/discover/LibraryGapFinder'
import {
  BrowseSection,
  genreTiles,
  languageTiles,
  studioTiles,
  networkTiles,
  type BrowseKey,
} from '../components/discover/BrowseGrid'
import { NoKey, Hero } from './discover/chrome'
import { FilteredGrid } from './discover/filtered-grid'
import {
  TrendingDayRow,
  TrendingWeekRow,
  PopularMoviesRow,
  PopularTvRow,
  UpcomingMoviesRow,
  TopRatedMoviesRow,
  TopRatedTvRow,
  CultClassicsRow,
} from './discover/rows'

/**
 * Discover page - intent-driven entry to TMDB content the user doesn't
 * already have.
 *
 * Layout:
 *   1. Compact page header
 *   2. Sticky filter bar (movie/tv + advanced filters)
 *   3. Editorial spotlight - one big "pick of the day"
 *   4. Mood chips - 10 vibes that resolve to a single content row
 *   5. 3-4 curated rows (Trending / Acclaimed / Coming soon / etc.)
 *   6. Browse-by sections: genre, language, studio, network - compact
 *      tile grids with inline expansion when a tile is clicked
 *
 * Active filters take over the page with the existing FilteredGrid - that
 * mode is unchanged so the filter workflow stays familiar.
 */
export default function DiscoverPage() {
  const hasTmdb = useHasTmdbKey()
  const prefs = usePreferencesStore()
  const region = prefs.region || regionForUser()
  const [filters, setFilters] = useState<DiscoverFilterState>(() => ({
    ...DEFAULT_FILTERS,
    watchRegion: region,
  }))
  const [moodId, setMoodId] = useState<string | null>(null)
  const [decade, setDecade] = useState<string | null>(null)
  const [expanded, setExpanded] = useState<BrowseKey | null>(null)

  if (!hasTmdb) return <NoKey />

  const filterMode = hasAnyActiveFilters(filters)
  const kind = filters.kind

  // Reset the mood / expansion when toggling movie<->tv since both are
  // kind-scoped and the previously-active mood may not exist on the
  // other side.
  function onFiltersChange(next: DiscoverFilterState) {
    if (next.kind !== filters.kind) {
      setMoodId(null)
      setDecade(null)
      setExpanded(null)
    }
    setFilters(next)
  }

  return (
    <div className="pb-12 overflow-x-hidden" style={{ isolation: 'isolate' }}>
      <Hero />

      <div
        className="sticky top-0 py-3 -mt-1 mb-3 border-b border-border/60"
        style={{ zIndex: 25, backgroundColor: 'var(--color-void)' }}
      >
        <DiscoverFilters filters={filters} onChange={onFiltersChange} region={region} />
      </div>

      {filterMode ? (
        <FilteredGrid filters={filters} />
      ) : (
        <>
          <TonightHero kind={kind} />

          <div className="px-7 mb-2 flex items-center justify-end">
            <Roulette kind={kind} moodId={moodId} />
          </div>

          <MoodChips activeId={moodId} onChange={setMoodId} kind={kind} />

          {moodId && (
            <div className="mb-4">
              <MoodRow moodId={moodId} kind={kind} />
            </div>
          )}

          <DecadeStrip kind={kind} active={decade} onChange={setDecade} />

          <div className="relative z-10">
            {kind === 'movie' ? (
              <>
                <TrendingDayRow />
                <LazyMount mountMargin="1600px"><PopularMoviesRow /></LazyMount>
                <LazyMount mountMargin="1600px"><UpcomingMoviesRow region={region} /></LazyMount>
                <LazyMount mountMargin="1600px"><TopRatedMoviesRow /></LazyMount>
                <LazyMount mountMargin="1600px"><CultClassicsRow /></LazyMount>
              </>
            ) : (
              <>
                <TrendingWeekRow />
                <LazyMount mountMargin="1600px"><PopularTvRow /></LazyMount>
                <LazyMount mountMargin="1600px"><TopRatedTvRow /></LazyMount>
              </>
            )}
          </div>

          {kind === 'movie' && <LazyMount mountMargin="1600px"><OnThisDay /></LazyMount>}

          {kind === 'movie' && <LazyMount mountMargin="1600px"><LibraryGapFinder /></LazyMount>}

          {kind === 'movie' && <LazyMount mountMargin="1600px"><CanonicalLists /></LazyMount>}

          <div className="mt-4 mb-2 px-7">
            <div className="flex items-center gap-3 text-text-4">
              <span className="flex-1 h-px bg-border" />
              <span className="text-[10.5px] uppercase tracking-[0.2em] font-semibold">Browse by</span>
              <span className="flex-1 h-px bg-border" />
            </div>
          </div>

          <BrowseSection
            eyebrow="By genre"
            title="Genres"
            subtitle="Top of each genre, missing from your shelves"
            tiles={genreTiles()}
            expanded={expanded}
            onSelect={k => startTransition(() => setExpanded(k))}
          />

          {kind === 'movie' && (
            <BrowseSection
              eyebrow="By language"
              title="Around the world"
              subtitle="Top-rated cinema by original language"
              tiles={languageTiles()}
              expanded={expanded}
              onSelect={k => startTransition(() => setExpanded(k))}
            />
          )}

          {kind === 'movie' && (
            <BrowseSection
              eyebrow="By studio"
              title="From the studios"
              subtitle="Films grouped by who made them"
              tiles={studioTiles()}
              expanded={expanded}
              onSelect={k => startTransition(() => setExpanded(k))}
            />
          )}

          {kind === 'tv' && (
            <BrowseSection
              eyebrow="By network"
              title="On the networks"
              subtitle="Shows grouped by where they air"
              tiles={networkTiles()}
              expanded={expanded}
              onSelect={k => startTransition(() => setExpanded(k))}
            />
          )}
        </>
      )}
    </div>
  )
}
