import { ChevronLeft, ChevronRight } from "lucide-react";
import { Link, useLocation } from "react-router-dom";
import { useEffect, useMemo, useRef, useState } from "react";
import { getJSON, itemsOrEmpty, readJSONCache, type Category } from "../../api";
import { CategoryIcon } from "../../components/CategoryIcon";
import { FigmaBanner } from "../../components/FigmaBanner";
import { PopularRankList } from "../../components/PopularRankList";
import { RecommendedCard } from "../../components/RecommendedCard";
import { SectionHeader } from "../../components/SectionHeader";
import { MessageBubble } from "../../components/messageStream/MessageBubble";
import { langQuery, useI18n } from "../../i18n";
import { useLocalizedPath } from "../../useLocalizedPath";
import { sourceLanguageQuery } from "../../i18nLanguages";
import { cleanCategoryDisplayName } from "../../utils/categoryDisplay";
import {
  postToResource,
  type PostBackedResource,
} from "../../utils/postResourceAdapter";
import type { Post } from "../../types/post";
import { Reveal } from "../../motion";

const FIGMA_CATEGORY_ORDER = [
  "project-ppt",
  "daily-class",
  "official-announcement",
  "academy-materials",
  "global-evangelism",
  "daily-poster",
  "community-tweets",
  "video-hub",
  "subsidy-policy",
  "how-to",
  "official-assets",
  "media-coverage",
  "academy-video",
  "general",
];

function figmaCategoryRank(category: Category): number {
  const index = FIGMA_CATEGORY_ORDER.indexOf(category.slug);
  return index === -1 ? FIGMA_CATEGORY_ORDER.length : index;
}

type LatestPostColumnItem = {
  post: Post;
  originalIndex: number;
};

function estimateLatestPostHeight(post: Post): number {
  const textLength = (post.text ?? post.title ?? "").length;
  const textRows = Math.ceil(textLength / 72);
  const textHeight = Math.min(180, Math.max(0, textRows * 22));
  const previewHeight = post.linkPreview ? 132 : 0;
  const [firstAttachment] = post.attachments;

  if (!firstAttachment) return 72 + textHeight + previewHeight;

  if (post.attachments.length >= 2) {
    const mediaHeight = firstAttachment.kind === "video" ? 340 : 300;
    return mediaHeight + textHeight + previewHeight + 42;
  }

  if (firstAttachment.kind === "video") {
    return 300 + textHeight + previewHeight + 42;
  }

  if (firstAttachment.kind === "image") {
    return (post.text ? 300 : 260) + textHeight + previewHeight + 42;
  }

  return 96 + post.attachments.length * 72 + textHeight + previewHeight;
}

function splitLatestPostsIntoColumns(
  posts: Post[],
  columnCount: number,
): LatestPostColumnItem[][] {
  const safeColumnCount = Math.max(1, columnCount);
  const columns = Array.from(
    { length: safeColumnCount },
    () => [] as LatestPostColumnItem[],
  );
  const columnHeights = Array.from({ length: safeColumnCount }, () => 0);

  posts.forEach((post, originalIndex) => {
    const targetColumn =
      originalIndex < safeColumnCount
        ? originalIndex
        : columnHeights.indexOf(Math.min(...columnHeights));

    columns[targetColumn].push({ post, originalIndex });
    columnHeights[targetColumn] += estimateLatestPostHeight(post) + 16;
  });

  return columns;
}

export function Home() {
  const { t, lang } = useI18n();
  const lp = useLocalizedPath();
  const { hash } = useLocation();
  // Seed from cache on the first render so the categories (and their icons)
  // are present immediately when navigating back to the home page, instead of
  // flashing empty for a frame before the effect re-applies the cached data.
  const [cats, setCats] = useState<Category[]>(() => {
    const cached = readJSONCache<Category[]>(
      `/api/categories?lang=${encodeURIComponent(langQuery(lang))}`,
    );
    return cached ? itemsOrEmpty(cached) : [];
  });
  const [rec, setRec] = useState<PostBackedResource[]>([]);
  const [latestPosts, setLatestPosts] = useState<Post[]>([]);
  const [popular, setPopular] = useState<PostBackedResource[]>([]);
  const [popularPosts, setPopularPosts] = useState<Post[]>([]);
  const [err, setErr] = useState<string | null>(null);
  const recRowRef = useRef<HTMLDivElement>(null);
  const categoryRowRef = useRef<HTMLDivElement>(null);
  const [activeCategoryPage, setActiveCategoryPage] = useState(0);
  const [canScrollRec, setCanScrollRec] = useState(false);
  const [recScroll, setRecScroll] = useState({ ratio: 1, progress: 0 });
  const [latestDesktopColumnCount, setLatestDesktopColumnCount] = useState(
    () =>
      typeof window !== "undefined" &&
      typeof window.matchMedia === "function" &&
      window.matchMedia("(min-width: 1024px)").matches
        ? 3
        : 2,
  );

  useEffect(() => {
    if (typeof window.matchMedia !== "function") return;

    const media = window.matchMedia("(min-width: 1024px)");
    const updateColumnCount = () => {
      setLatestDesktopColumnCount(media.matches ? 3 : 2);
    };

    updateColumnCount();
    media.addEventListener("change", updateColumnCount);
    return () => media.removeEventListener("change", updateColumnCount);
  }, []);

  useEffect(() => {
    let cancelled = false;
    const langParam = encodeURIComponent(langQuery(lang));
    const languageParam = encodeURIComponent(sourceLanguageQuery(lang));
    const catQ = `?lang=${langParam}`;
    const postQ = `?lang=${langParam}&language=${languageParam}`;
    const categoriesUrl = `/api/categories${catQ}`;
    const recommendedUrl = `/api/posts/recommended${postQ}&limit=12`;
    const latestUrl = `/api/posts${postQ}&sort=latest&limit=12`;
    const popularUrl = `/api/posts${postQ}&sort=popular&limit=5`;

    const applyHomeData = (
      c: Category[],
      r: { items: Post[] },
      l: { items: Post[] },
      p: { items: Post[] },
    ) => {
      const categoryItems = itemsOrEmpty(c);
      setCats(categoryItems);
      setRec(
        itemsOrEmpty(r.items).map((post) =>
          postToResource(post, lang, categoryItems),
        ),
      );
      const latestItems = itemsOrEmpty(l.items);
      setLatestPosts(latestItems);
      const popularItems = itemsOrEmpty<Post>(p.items);
      setPopularPosts(popularItems);
      setPopular(
        popularItems.map((post) => postToResource(post, lang, categoryItems)),
      );
    };

    setErr(null);
    const cachedCategories = readJSONCache<Category[]>(categoriesUrl);
    const cachedRecommended = readJSONCache<{ items: Post[] }>(recommendedUrl);
    const cachedLatest = readJSONCache<{ items: Post[] }>(latestUrl);
    const cachedPopular = readJSONCache<{ items: Post[] }>(popularUrl);
    const showedCached = !!(
      cachedCategories &&
      cachedRecommended &&
      cachedLatest
    );

    if (showedCached) {
      applyHomeData(
        cachedCategories,
        cachedRecommended,
        cachedLatest,
        cachedPopular ?? { items: [] },
      );
    }

    Promise.all([
      getJSON<Category[]>(categoriesUrl),
      getJSON<{ items: Post[] }>(recommendedUrl),
      getJSON<{ items: Post[] }>(latestUrl),
      getJSON<{ items: Post[] }>(popularUrl).catch(
        (): { items: Post[] } => cachedPopular ?? { items: [] },
      ),
    ])
      .then(([c, r, l, p]) => {
        if (cancelled) return;
        applyHomeData(c, r, l, p);
      })
      .catch((e) => {
        if (!cancelled && !showedCached) setErr(String(e));
      });

    return () => {
      cancelled = true;
    };
  }, [lang]);

  const figmaOrderedCategories = [...cats].sort(
    (a, b) => figmaCategoryRank(a) - figmaCategoryRank(b),
  );

  const categoryPages: Category[][] = [];
  for (let index = 0; index < figmaOrderedCategories.length; index += 9) {
    categoryPages.push(figmaOrderedCategories.slice(index, index + 9));
  }
  // Use the tallest page so the carousel height doesn't shrink between
  // pages — otherwise the section below jumps up when swiping to a page
  // with fewer categories.
  const maxCategoryRows = categoryPages.reduce(
    (max, page) => Math.max(max, Math.ceil(page.length / 3)),
    0,
  );
  const mobileCategoryHeight =
    maxCategoryRows * 88 + Math.max(0, maxCategoryRows - 1) * 8;

  useEffect(() => {
    const row = categoryRowRef.current;
    if (!row) return;

    const update = () => {
      const width = row.clientWidth || 1;
      const next = Math.round(row.scrollLeft / width);
      setActiveCategoryPage((prev) => (prev === next ? prev : next));
    };

    update();
    row.addEventListener("scroll", update, { passive: true });
    return () => row.removeEventListener("scroll", update);
  }, [cats.length]);

  useEffect(() => {
    setActiveCategoryPage(0);
    categoryRowRef.current?.scrollTo({ left: 0 });
  }, [lang]);

  useEffect(() => {
    const row = recRowRef.current;
    if (!row) {
      setCanScrollRec(false);
      return;
    }

    const update = () => {
      const overflow = row.scrollWidth > row.clientWidth + 1;
      setCanScrollRec(overflow);
      const ratio = overflow ? row.clientWidth / row.scrollWidth : 1;
      const maxScroll = Math.max(1, row.scrollWidth - row.clientWidth);
      const progress = overflow ? row.scrollLeft / maxScroll : 0;
      setRecScroll({
        ratio: Math.min(1, Math.max(0.15, ratio)),
        progress: Math.min(1, Math.max(0, progress)),
      });
    };

    update();
    const resizeObserver = new ResizeObserver(update);
    resizeObserver.observe(row);
    row.addEventListener("scroll", update, { passive: true });
    return () => {
      resizeObserver.disconnect();
      row.removeEventListener("scroll", update);
    };
  }, [rec.length]);

  // Reveal one more card per click, fully, inside the arrow "lanes" (the left
  // and right padding the arrows float in) so the edge card is never half-shown
  // or tucked under an arrow.
  //  - Right arrow: bring the first card clipped on the right so its RIGHT edge
  //    rests just left of the right arrow.
  //  - Left arrow: bring the last card clipped on the left so its LEFT edge
  //    rests just right of the left arrow.
  const scrollRec = (dir: 1 | -1) => {
    const row = recRowRef.current;
    if (!row) return;
    const children = Array.from(row.children) as HTMLElement[];
    if (children.length === 0) return;
    const rowLeft = row.getBoundingClientRect().left;
    const style = getComputedStyle(row);
    const padLeft = parseFloat(style.paddingLeft) || 0;
    const padRight = parseFloat(style.paddingRight) || 0;
    const epsilon = 2;
    let delta: number;
    if (dir === 1) {
      const laneRight = row.clientWidth - padRight;
      const next = children
        .map((c) => c.getBoundingClientRect().right - rowLeft)
        .find((right) => right > laneRight + epsilon);
      delta = next !== undefined ? next - laneRight : 0;
    } else {
      const lefts = children
        .map((c) => c.getBoundingClientRect().left - rowLeft)
        .filter((left) => left < padLeft - epsilon);
      delta = lefts.length
        ? lefts[lefts.length - 1] - padLeft
        : -row.scrollLeft;
    }
    const maxScroll = Math.max(0, row.scrollWidth - row.clientWidth);
    const target = Math.max(0, Math.min(maxScroll, row.scrollLeft + delta));
    row.scrollTo({ left: target, behavior: "smooth" });
  };

  useEffect(() => {
    if (!hash) return;
    const id = hash.slice(1);
    if (!id) return;
    const frame = window.requestAnimationFrame(() => {
      document.getElementById(id)?.scrollIntoView({
        block: id === "latest" ? "center" : "start",
      });
    });
    return () => window.cancelAnimationFrame(frame);
  }, [hash, cats.length, rec.length, latestPosts.length, popular.length]);

  const hasPopular = popular.length > 0 || popularPosts.length > 0;
  const recommendedDotCount = rec.length;
  const activeRecommendedDot =
    recommendedDotCount > 0
      ? Math.min(
          recommendedDotCount - 1,
          Math.round(recScroll.progress * (recommendedDotCount - 1)),
        )
      : 0;
  const latestDesktopColumns = useMemo(
    () => splitLatestPostsIntoColumns(latestPosts, latestDesktopColumnCount),
    [latestPosts, latestDesktopColumnCount],
  );
  // Hide the arrow that points to an edge we're already at.
  const recAtStart = recScroll.progress <= 0.01;
  const recAtEnd = recScroll.progress >= 0.99;

  if (err) {
    return (
      <div className="mt-6 rounded-xl border border-red-900 bg-red-950/40 p-4 text-red-200 md:mt-0">
        {err}
      </div>
    );
  }

  return (
    <div className="space-y-2.5 pb-4 md:space-y-10 md:pb-16 xl:space-y-[34px]">
      <section className="md:mt-0">
        <FigmaBanner />
      </section>

      <Reveal delay={0}>
        <section id="categories" className="scroll-mt-16 md:scroll-mt-24">
          <div className="mx-auto max-w-full md:max-w-[820px] lg:max-w-[1080px] xl:max-w-[1180px]">
            <div className="px-4 md:px-0">
              <SectionHeader
                title={t("categorySection")}
                viewAllTo={lp("/categories")}
                viewAllLabel={t("viewAll")}
              />
            </div>

            <div className="mt-2.5 md:hidden">
              <div
                ref={categoryRowRef}
                className="flex snap-x snap-mandatory items-start overflow-x-auto overflow-y-hidden scroll-smooth [-ms-overflow-style:none] [scrollbar-width:none] [&::-webkit-scrollbar]:hidden"
                style={{ height: `${mobileCategoryHeight}px` }}
                aria-label={t("categorySection")}
              >
                {categoryPages.map((page, pageIndex) => (
                  <div
                    key={`category-page-${pageIndex}`}
                    className="grid w-full shrink-0 snap-start grid-cols-3 gap-2 px-4"
                  >
                    {page.map((c) => (
                      <Link
                        key={c.id}
                        to={lp(`/category/${encodeURIComponent(c.slug)}`)}
                        className="flex h-[88px] min-w-0 flex-col items-center justify-center gap-2 rounded-xl border border-[#27292E] bg-[#1D1E23] px-4 py-3 text-center outline-none transition hover:border-ark-gold/55 hover:bg-[#252630] focus-visible:ring-2 focus-visible:ring-ark-gold/80 focus-visible:ring-offset-2 focus-visible:ring-offset-ark-bg"
                      >
                        <CategoryIcon
                          iconKey={c.iconKey}
                          categorySlug={c.slug}
                          className="h-9 w-9 shrink-0 text-ark-gold"
                        />
                        <div className="w-full truncate text-[13px] font-medium leading-[19.5px] text-white">
                          {cleanCategoryDisplayName(c.name)}
                        </div>
                      </Link>
                    ))}
                  </div>
                ))}
              </div>

              {categoryPages.length > 1 ? (
                <div
                  className="flex h-[30px] items-center justify-center gap-1.5"
                  aria-label="Category pagination"
                >
                  {categoryPages.map((_, index) => (
                    <button
                      key={`category-dot-${index}`}
                      type="button"
                      aria-label={`Go to category page ${index + 1}`}
                      aria-current={activeCategoryPage === index}
                      onClick={() => {
                        const row = categoryRowRef.current;
                        if (!row) return;
                        row.scrollTo({
                          left: row.clientWidth * index,
                          behavior: "smooth",
                        });
                        setActiveCategoryPage(index);
                      }}
                      className={`h-1.5 rounded-full transition-all ${
                        activeCategoryPage === index
                          ? "w-6 bg-ark-gold"
                          : "w-1.5 bg-[#7C7C7C]"
                      }`}
                    />
                  ))}
                </div>
              ) : null}
            </div>

            <div className="mt-7 hidden grid-cols-3 gap-3 min-[440px]:gap-3.5 md:grid md:grid-cols-5 md:gap-3 lg:grid-cols-6 xl:grid-cols-7 xl:gap-4">
              {figmaOrderedCategories.map((c, index) => (
                <Reveal key={c.id} delay={Math.min(index, 8) * 0.05}>
                  <Link
                    to={lp(`/category/${encodeURIComponent(c.slug)}`)}
                    className="flex h-[88px] min-w-0 flex-col items-center justify-center gap-2 rounded-xl border border-[#27292E] bg-[#1D1E23] px-4 py-3 text-center outline-none transition hover:border-ark-gold/55 hover:bg-[#252630] focus-visible:ring-2 focus-visible:ring-ark-gold/80 focus-visible:ring-offset-2 focus-visible:ring-offset-ark-bg"
                  >
                    <CategoryIcon
                      iconKey={c.iconKey}
                      categorySlug={c.slug}
                      className="h-9 w-9 shrink-0 text-ark-gold"
                    />
                    <div className="w-full text-center text-[13px] font-medium leading-[19.5px] text-white line-clamp-2">
                      {cleanCategoryDisplayName(c.name)}
                    </div>
                  </Link>
                </Reveal>
              ))}
            </div>
          </div>
        </section>
      </Reveal>

      <Reveal>
        <section id="official" className="scroll-mt-16 md:scroll-mt-24">
          <div className="mx-auto max-w-full md:max-w-[820px] lg:max-w-[1080px] xl:max-w-[1180px]">
            <div className="px-4 md:px-0">
              <SectionHeader
                title={t("officialSection")}
                viewAllTo={lp("/official-recommendations")}
                viewAllLabel={t("viewAll")}
              />
            </div>
            <div className="relative">
              <div
                ref={recRowRef}
                className="mt-2.5 flex gap-3 overflow-x-auto overflow-y-hidden px-4 pb-0 pr-4 scroll-smooth [-ms-overflow-style:none] [scrollbar-width:none] md:mt-7 md:gap-4 md:px-0 md:pr-0 md:pb-5 [&::-webkit-scrollbar]:hidden"
              >
                {rec.map((r, index) => (
                  <div key={r.id}>
                    <Reveal delay={Math.min(index, 8) * 0.05}>
                      <RecommendedCard
                        r={r}
                        visualIndex={index}
                        useFigmaDesign
                      />
                    </Reveal>
                  </div>
                ))}
              </div>
              <div
                className="flex h-[30px] items-center justify-center gap-1.5"
                aria-label="Recommended pagination"
              >
                {Array.from({ length: recommendedDotCount }).map((_, index) => (
                  <button
                    key={`recommended-dot-${index}`}
                    type="button"
                    aria-label={`Go to recommendation page ${index + 1}`}
                    aria-current={activeRecommendedDot === index}
                    onClick={() => {
                      const row = recRowRef.current;
                      if (!row) return;
                      const maxScroll = Math.max(
                        0,
                        row.scrollWidth - row.clientWidth,
                      );
                      row.scrollTo({
                        left:
                          recommendedDotCount === 1
                            ? 0
                            : (maxScroll * index) / (recommendedDotCount - 1),
                        behavior: "smooth",
                      });
                    }}
                    className={`h-1.5 rounded-full transition-all ${
                      activeRecommendedDot === index
                        ? "w-6 bg-ark-gold"
                        : "w-1.5 bg-[#7C7C7C]"
                    }`}
                  />
                ))}
              </div>
              {canScrollRec && !recAtStart ? (
                <button
                  type="button"
                  onClick={() => scrollRec(-1)}
                  className="absolute left-0 top-[45%] hidden h-9 w-9 -translate-y-1/2 items-center justify-center rounded-lg border border-ark-line bg-[#292a31]/95 text-neutral-200 shadow-lg backdrop-blur transition hover:border-ark-gold hover:text-ark-gold md:flex"
                  aria-label="Previous recommendations"
                >
                  <ChevronLeft className="h-5 w-5" />
                </button>
              ) : null}
              {canScrollRec && !recAtEnd ? (
                <button
                  type="button"
                  onClick={() => scrollRec(1)}
                  className="absolute right-0 top-[45%] hidden h-9 w-9 -translate-y-1/2 items-center justify-center rounded-lg border border-ark-line bg-[#292a31]/95 text-neutral-200 shadow-lg backdrop-blur transition hover:border-ark-gold hover:text-ark-gold md:flex"
                  aria-label="Next recommendations"
                >
                  <ChevronRight className="h-5 w-5" />
                </button>
              ) : null}
            </div>
          </div>
        </section>
      </Reveal>

      <Reveal>
        <section id="latest" className="scroll-mt-16 md:scroll-mt-24">
          <div className="mx-auto max-w-full md:max-w-[820px] lg:max-w-[1080px] xl:max-w-[1180px]">
            <div className="px-4 md:px-0">
              <SectionHeader
                title={t("latestSection")}
                viewAllTo={lp("/browse")}
                viewAllLabel={t("viewAll")}
              />
            </div>
            <div className="mt-2.5 flex flex-col gap-3 md:hidden">
              {latestPosts.slice(0, 5).map((post, index) => (
                <Reveal key={post.id} delay={Math.min(index, 8) * 0.05}>
                  <MessageBubble post={post} />
                </Reveal>
              ))}
            </div>
            {/* Desktop: explicit balanced columns avoid the uneven gaps that
                CSS multi-column masonry can create with variable-height cards. */}
            <div className="mt-7 hidden gap-4 px-4 md:grid md:grid-cols-2 lg:grid-cols-3 lg:px-0">
              {latestDesktopColumns.map((column, columnIndex) => (
                <div
                  key={`latest-desktop-column-${columnIndex}`}
                  className="flex min-w-0 flex-col gap-4"
                >
                  {column.map(({ post, originalIndex }) => (
                    <Reveal
                      key={post.id}
                      delay={Math.min(originalIndex, 8) * 0.05}
                    >
                      <MessageBubble post={post} fluid />
                    </Reveal>
                  ))}
                </div>
              ))}
            </div>
          </div>
        </section>
      </Reveal>

      {hasPopular ? (
        <Reveal>
          <section id="popular" className="scroll-mt-16 md:scroll-mt-24">
            <div className="mx-auto max-w-full md:max-w-[820px] lg:max-w-[1080px] xl:max-w-[1180px]">
              <div className="px-4 md:px-0">
                <SectionHeader
                  title={t("popularSection")}
                  viewAllTo={lp("/browse?sort=popular")}
                  viewAllLabel={t("viewAll")}
                />
              </div>
              <div className="mt-2.5 md:mt-7">
                <PopularRankList posts={popularPosts} categories={cats} />
              </div>
            </div>
          </section>
        </Reveal>
      ) : null}
    </div>
  );
}