import Link from "next/link";
import { notFound } from "next/navigation";
import {
  getSvaContent,
  getSvaSidebarItems,
  type SvaChapter,
  type SvaSidebarItem,
} from "@/lib/sva";
import { PageHeader } from "@/components/page-header";
import { Card, CardContent } from "@/components/ui/card";
import { buttonVariants } from "@/components/ui/button";
import { ChevronLeft, ChevronRight } from "lucide-react";
import { cn } from "@/lib/utils";
import { MobileNav, type MobileNavGroup } from "@/components/mobile-nav";

// ---------------------------------------------------------------------------
// Page
// ---------------------------------------------------------------------------

export default async function SvaChapterPage({
  params,
}: {
  params: Promise<{ chapter: string }>;
}) {
  const { chapter: slug } = await params;

  const content = await getSvaContent(slug);
  if (!content) notFound();

  const sidebarItems = await getSvaSidebarItems();
  const currentIdx = sidebarItems.findIndex((item) => item.slug === slug);

  const prev = currentIdx > 0 ? sidebarItems[currentIdx - 1] : null;
  const next =
    currentIdx < sidebarItems.length - 1 ? sidebarItems[currentIdx + 1] : null;

  // Build the page title
  const isChapter =
    "chapter" in content &&
    typeof (content as SvaChapter).chapter === "number" &&
    (content as SvaChapter).chapter !== null;
  const chapterNum = isChapter ? (content as SvaChapter).chapter : null;

  return (
    <div className="min-h-screen bg-background">
      <PageHeader sticky wide>
        <Link
          href="/books/sva"
          className="text-sm text-muted-foreground hover:text-foreground transition-colors"
        >
          &larr; Songs of the Vaiṣṇava Ācāryas
        </Link>
        <h1 className="mt-3 text-2xl font-bold text-foreground">
          {chapterNum != null && (
            <span className="text-primary">Part {chapterNum}: </span>
          )}
          {content.title}
        </h1>
      </PageHeader>

      <div className="w-full md:max-w-6xl mx-auto flex">
        {/* Left sidebar */}
        <SvaSidebar items={sidebarItems} currentSlug={slug} />

        {/* Main content */}
        <main className="flex-1 min-w-0 px-6 py-8 space-y-8">
          {/* Top navigation */}
          <SvaNav
            prev={prev}
            next={next}
            sidebarItems={sidebarItems}
            currentSlug={slug}
          />

          {/* Content */}
          <Card>
            <CardContent className="py-8 px-6 sm:px-8">
              <div className="space-y-4">
                {content.paragraphs.map((paragraph, i) => (
                  <div
                    key={i}
                    className="text-base text-foreground leading-relaxed"
                    dangerouslySetInnerHTML={{ __html: paragraph }}
                  />
                ))}
              </div>
            </CardContent>
          </Card>

          {/* Bottom navigation */}
          <SvaNav
            prev={prev}
            next={next}
            sidebarItems={sidebarItems}
            currentSlug={slug}
          />
        </main>
      </div>
    </div>
  );
}

// ---------------------------------------------------------------------------
// Sidebar
// ---------------------------------------------------------------------------

function SvaSidebar({
  items,
  currentSlug,
}: {
  items: SvaSidebarItem[];
  currentSlug: string;
}) {
  const frontMatterItems: SvaSidebarItem[] = [];
  const chapterItems: SvaSidebarItem[] = [];
  const backMatterItems: SvaSidebarItem[] = [];

  let pastChapters = false;

  for (const item of items) {
    if (item.type === "chapter") {
      pastChapters = true;
      chapterItems.push(item);
    } else if (!pastChapters) {
      frontMatterItems.push(item);
    } else {
      backMatterItems.push(item);
    }
  }

  return (
    <aside className="hidden lg:block w-56 shrink-0 sticky top-[89px] self-start max-h-[calc(100vh-89px)] overflow-y-auto py-8 pr-4">
      {/* Front Matter */}
      {frontMatterItems.length > 0 && (
        <>
          <h2 className="text-xs font-bold uppercase tracking-wider text-muted-foreground mb-3 px-2">
            Front Matter
          </h2>
          <nav className="flex flex-col gap-0.5 mb-4">
            {frontMatterItems.map((item) => (
              <SidebarLink
                key={item.slug}
                item={item}
                isActive={item.slug === currentSlug}
              />
            ))}
          </nav>
        </>
      )}

      {/* Parts */}
      {chapterItems.length > 0 && (
        <>
          <h2 className="text-xs font-bold uppercase tracking-wider text-muted-foreground mb-3 px-2">
            Parts
          </h2>
          <nav className="flex flex-col gap-0.5 mb-4">
            {chapterItems.map((item) => (
              <SidebarLink
                key={item.slug}
                item={item}
                isActive={item.slug === currentSlug}
              />
            ))}
          </nav>
        </>
      )}

      {/* Back Matter */}
      {backMatterItems.length > 0 && (
        <nav className="flex flex-col gap-0.5">
          {backMatterItems.map((item) => (
            <SidebarLink
              key={item.slug}
              item={item}
              isActive={item.slug === currentSlug}
            />
          ))}
        </nav>
      )}
    </aside>
  );
}

function SidebarLink({
  item,
  isActive,
}: {
  item: SvaSidebarItem;
  isActive: boolean;
}) {
  let label: string;
  if (item.type === "chapter" && item.chapter != null) {
    // Extract just the title portion after "Part N: "
    const titlePart = item.label.replace(/^Part \d+:\s*/, "");
    label = `${item.chapter}. ${titlePart}`;
  } else {
    label = item.label;
  }

  return (
    <Link
      href={`/books/sva/${item.slug}`}
      className={cn(
        "px-2 py-1.5 rounded-md text-sm transition-colors truncate",
        isActive
          ? "bg-primary/10 text-primary font-medium"
          : "text-muted-foreground hover:bg-muted hover:text-foreground",
      )}
      title={label}
    >
      {label}
    </Link>
  );
}

// ---------------------------------------------------------------------------
// Prev / Next navigation
// ---------------------------------------------------------------------------

function SvaNav({
  prev,
  next,
  sidebarItems,
  currentSlug,
}: {
  prev: SvaSidebarItem | null;
  next: SvaSidebarItem | null;
  sidebarItems: SvaSidebarItem[];
  currentSlug: string;
}) {
  const mobileNavGroups: MobileNavGroup[] = [];

  const frontMatterItems: SvaSidebarItem[] = [];
  const chapterItems: SvaSidebarItem[] = [];
  const backMatterItems: SvaSidebarItem[] = [];
  let pastChapters = false;

  for (const item of sidebarItems) {
    if (item.type === "chapter") {
      pastChapters = true;
      chapterItems.push(item);
    } else if (!pastChapters) {
      frontMatterItems.push(item);
    } else {
      backMatterItems.push(item);
    }
  }

  if (frontMatterItems.length > 0) {
    mobileNavGroups.push({
      title: "Front Matter",
      items: frontMatterItems.map((i) => ({
        slug: i.slug,
        label: i.label,
        href: `/books/sva/${i.slug}`,
        type: i.type,
      })),
    });
  }

  if (chapterItems.length > 0) {
    mobileNavGroups.push({
      title: "Parts",
      items: chapterItems.map((i) => ({
        slug: i.slug,
        label: i.label,
        href: `/books/sva/${i.slug}`,
        type: i.type,
      })),
    });
  }

  if (backMatterItems.length > 0) {
    mobileNavGroups.push({
      title: "Back Matter",
      items: backMatterItems.map((i) => ({
        slug: i.slug,
        label: i.label,
        href: `/books/sva/${i.slug}`,
        type: i.type,
      })),
    });
  }

  return (
    <div className="flex items-center justify-between gap-3">
      <div className="flex items-center gap-2">
        <MobileNav
          groups={mobileNavGroups}
          currentSlug={currentSlug}
          bookTitle="Songs of the Vaiṣṇava Ācāryas"
        />
        {prev ? (
          <Link
            href={`/books/sva/${prev.slug}`}
            className={cn(
              buttonVariants({ variant: "outline", size: "sm" }),
              "gap-1.5",
            )}
          >
            <ChevronLeft className="size-4" />
            <span className="hidden sm:inline truncate max-w-[180px]">
              {prev.type === "chapter" && prev.chapter != null
                ? `Part ${prev.chapter}`
                : prev.label}
            </span>
            <span className="sm:hidden">Previous</span>
          </Link>
        ) : (
          <div className="hidden lg:block" />
        )}
      </div>

      {next ? (
        <Link
          href={`/books/sva/${next.slug}`}
          className={cn(
            buttonVariants({ variant: "outline", size: "sm" }),
            "gap-1.5",
          )}
        >
          <span className="hidden sm:inline truncate max-w-[180px]">
            {next.type === "chapter" && next.chapter != null
              ? `Part ${next.chapter}`
              : next.label}
          </span>
          <span className="sm:hidden">Next</span>
          <ChevronRight className="size-4" />
        </Link>
      ) : (
        <div />
      )}
    </div>
  );
}