import Link from "next/link";
import { notFound } from "next/navigation";
import {
  getIsoContent,
  getIsoSidebarItems,
  type IsoVerse,
  type IsoIntroSegment,
  type IsoSidebarItem,
} from "@/lib/iso";
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";

// ---------------------------------------------------------------------------
// Type guards
// ---------------------------------------------------------------------------

function isVerse(content: IsoVerse | IsoIntroSegment): content is IsoVerse {
  return "mantra" in content && "devanagari" in content;
}

function isIntroSegment(
  content: IsoVerse | IsoIntroSegment,
): content is IsoIntroSegment {
  return "paragraphs" in content && "order" in content;
}

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

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

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

  const sidebarItems = await getIsoSidebarItems();
  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 for the header
  const verse = isVerse(content) ? content : null;
  const intro = isIntroSegment(content) ? content : null;

  return (
    <div className="min-h-screen bg-background">
      <PageHeader sticky wide>
        <Link
          href="/books/iso"
          className="text-sm text-muted-foreground hover:text-foreground transition-colors"
        >
          &larr; Śrī Īśopaniṣad
        </Link>
        <h1 className="mt-3 text-2xl font-bold text-foreground">
          {verse && (
            <>
              <span className="text-primary">{verse.reference}: </span>
              {verse.title}
            </>
          )}
          {intro && intro.title}
        </h1>
      </PageHeader>

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

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

          {/* Content */}
          {verse && <VerseContent verse={verse} />}
          {intro && <IntroContent intro={intro} />}

          {/* Bottom navigation */}
          <IsoNav prev={prev} next={next} />
        </main>
      </div>
    </div>
  );
}

// ---------------------------------------------------------------------------
// Verse content (Devanagari, transliteration, synonyms, translation, purport)
// ---------------------------------------------------------------------------

function VerseContent({ verse }: { verse: IsoVerse }) {
  return (
    <Card>
      <CardContent className="py-8 px-6 sm:px-8 space-y-8">
        {/* Devanagari */}
        <section>
          <div className="text-xl leading-relaxed text-foreground whitespace-pre-line font-serif text-center">
            {verse.devanagari}
          </div>
        </section>

        {/* Transliteration */}
        <section>
          <div className="text-foreground/80 italic whitespace-pre-line leading-relaxed text-center">
            {verse.transliteration}
          </div>
        </section>

        {/* Synonyms */}
        {verse.synonyms.length > 0 && (
          <section>
            <h2 className="text-xs font-bold uppercase tracking-wider text-muted-foreground mb-3">
              Synonyms
            </h2>
            <div className="text-sm text-foreground/70 leading-relaxed">
              {verse.synonyms.map((s, i) => (
                <span key={i}>
                  {i > 0 && "; "}
                  <span className="font-medium text-foreground/90">
                    {s.word}
                  </span>
                  {"—"}
                  {s.meanings.join(", ")}
                </span>
              ))}
            </div>
          </section>
        )}

        {/* Translation */}
        <section>
          <h2 className="text-xs font-bold uppercase tracking-wider text-muted-foreground mb-3">
            Translation
          </h2>
          <div
            className="text-foreground font-medium leading-relaxed"
            dangerouslySetInnerHTML={{ __html: verse.translation }}
          />
        </section>

        {/* Purport */}
        {verse.purport.length > 0 && (
          <section>
            <h2 className="text-xs font-bold uppercase tracking-wider text-muted-foreground mb-3">
              Purport
            </h2>
            <div className="space-y-4">
              {verse.purport.map((p, i) => (
                <div
                  key={i}
                  className="text-foreground leading-relaxed"
                  dangerouslySetInnerHTML={{ __html: p }}
                />
              ))}
            </div>
          </section>
        )}
      </CardContent>
    </Card>
  );
}

// ---------------------------------------------------------------------------
// Intro segment content (paragraphs)
// ---------------------------------------------------------------------------

function IntroContent({ intro }: { intro: IsoIntroSegment }) {
  return (
    <Card>
      <CardContent className="py-8 px-6 sm:px-8">
        <div className="space-y-4">
          {intro.paragraphs.map((paragraph, i) => (
            <div
              key={i}
              className="text-foreground leading-relaxed"
              dangerouslySetInnerHTML={{ __html: paragraph }}
            />
          ))}
        </div>
      </CardContent>
    </Card>
  );
}

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

function IsoSidebar({
  items,
  currentSlug,
}: {
  items: IsoSidebarItem[];
  currentSlug: string;
}) {
  // Front matter items (front-pages + introduction)
  const frontMatterItems = items.filter(
    (item) =>
      item.slug === "intro-front-pages" || item.slug === "intro-introduction",
  );
  // Mantras = invocation + 1-18
  const mantraItems = items.filter((item) => item.type === "verse");
  // about-the-author comes last
  const aboutAuthorItem = items.find(
    (item) => item.slug === "intro-about-the-author",
  );

  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>
        </>
      )}

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

      {/* About the Author */}
      {aboutAuthorItem && (
        <nav className="flex flex-col gap-0.5">
          <SidebarLink
            item={aboutAuthorItem}
            isActive={aboutAuthorItem.slug === currentSlug}
          />
        </nav>
      )}
    </aside>
  );
}

function SidebarLink({
  item,
  isActive,
}: {
  item: IsoSidebarItem;
  isActive: boolean;
}) {
  return (
    <Link
      href={`/books/iso/${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={item.label}
    >
      {item.label}
    </Link>
  );
}

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

function IsoNav({
  prev,
  next,
}: {
  prev: IsoSidebarItem | null;
  next: IsoSidebarItem | null;
}) {
  return (
    <div className="flex items-center justify-between gap-3">
      {prev ? (
        <Link
          href={`/books/iso/${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 === "verse" && prev.mantra != null && prev.mantra > 0
              ? `Mantra ${prev.mantra}`
              : prev.label}
          </span>
          <span className="sm:hidden">Previous</span>
        </Link>
      ) : (
        <div />
      )}

      {next ? (
        <Link
          href={`/books/iso/${next.slug}`}
          className={cn(
            buttonVariants({ variant: "outline", size: "sm" }),
            "gap-1.5",
          )}
        >
          <span className="hidden sm:inline truncate max-w-[180px]">
            {next.type === "verse" && next.mantra != null && next.mantra > 0
              ? `Mantra ${next.mantra}`
              : next.label}
          </span>
          <span className="sm:hidden">Next</span>
          <ChevronRight className="size-4" />
        </Link>
      ) : (
        <div />
      )}
    </div>
  );
}