import Link from "next/link";
import { notFound } from "next/navigation";
import {
  getHkhContent,
  getHkhSidebarItems,
  type HkhChapter,
  type HkhSidebarItem,
} from "@/lib/hkh";
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";

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

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

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

  const sidebarItems = await getHkhSidebarItems();
  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 HkhChapter).chapter === "number" &&
    (content as HkhChapter).chapter !== null;
  const chapterNum = isChapter ? (content as HkhChapter).chapter : null;

  return (
    <div className="min-h-screen bg-background">
      <PageHeader sticky wide>
        <Link
          href="/books/hkh"
          className="text-sm text-muted-foreground hover:text-foreground transition-colors"
        >
          &larr; The Kṛṣṇa Consciousness Handbook
        </Link>
        <h1 className="mt-3 text-2xl font-bold text-foreground">
          {chapterNum != null && (
            <span className="text-primary">Chapter {chapterNum}: </span>
          )}
          {content.title}
        </h1>
      </PageHeader>

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

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

          {/* 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-foreground leading-relaxed"
                    dangerouslySetInnerHTML={{ __html: paragraph }}
                  />
                ))}
              </div>
            </CardContent>
          </Card>

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

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

function HkhSidebar({
  items,
  currentSlug,
}: {
  items: HkhSidebarItem[];
  currentSlug: string;
}) {
  const introItems = items.filter((item) => item.type === "intro-segment");
  const chapterItems = items.filter((item) => item.type === "chapter");

  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 */}
      {introItems.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">
            {introItems.map((item) => (
              <SidebarLink
                key={item.slug}
                item={item}
                isActive={item.slug === currentSlug}
              />
            ))}
          </nav>
        </>
      )}

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

function SidebarLink({
  item,
  isActive,
}: {
  item: HkhSidebarItem;
  isActive: boolean;
}) {
  return (
    <Link
      href={`/books/hkh/${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 HkhNav({
  prev,
  next,
}: {
  prev: HkhSidebarItem | null;
  next: HkhSidebarItem | null;
}) {
  return (
    <div className="flex items-center justify-between gap-3">
      {prev ? (
        <Link
          href={`/books/hkh/${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
              ? `Ch. ${prev.chapter}`
              : prev.label}
          </span>
          <span className="sm:hidden">Previous</span>
        </Link>
      ) : (
        <div />
      )}

      {next ? (
        <Link
          href={`/books/hkh/${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
              ? `Ch. ${next.chapter}`
              : next.label}
          </span>
          <span className="sm:hidden">Next</span>
          <ChevronRight className="size-4" />
        </Link>
      ) : (
        <div />
      )}
    </div>
  );
}