import Link from "next/link";
import { notFound } from "next/navigation";
import {
  getSsrContent,
  getSsrSidebarItems,
  type SsrChapter,
  type SsrSidebarItem,
} from "@/lib/ssr";
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 SsrChapterPage({
  params,
}: {
  params: Promise<{ chapter: string }>;
}) {
  const { chapter: slug } = await params;

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

  const sidebarItems = await getSsrSidebarItems();

  // Build a flat list of navigable items (skip "parent" type — they're labels, not pages)
  const navigableItems = sidebarItems.filter((item) => item.type !== "parent");
  const currentIdx = navigableItems.findIndex((item) => item.slug === slug);

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

  // Determine if this is a sub-chapter (has parentChapter and is type "chapter"/"sub-chapter")
  const isSubChapter =
    "parentChapter" in content &&
    typeof (content as SsrChapter).parentChapter === "number";
  const parentChapterNum = isSubChapter
    ? (content as SsrChapter).parentChapter
    : null;

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

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

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

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

function SsrSidebar({
  items,
  currentSlug,
}: {
  items: SsrSidebarItem[];
  currentSlug: string;
}) {
  // Split items by section
  const frontMatter = items.filter(
    (i) => i.type === "intro-segment" && i.slug !== "intro-about-the-author",
  );
  const parents = items.filter((i) => i.type === "parent");
  const subChapters = items.filter((i) => i.type === "sub-chapter");
  const backMatter = items.filter((i) => i.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 */}
      {frontMatter.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">
            {frontMatter.map((item) => (
              <SidebarLink
                key={item.slug}
                item={item}
                isActive={item.slug === currentSlug}
              />
            ))}
          </nav>
        </>
      )}

      {/* Chapters — grouped by parent */}
      {parents.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 mb-4">
            {parents.map((parent) => (
              <div key={parent.slug}>
                {/* Parent heading — not a link, just a bold label */}
                <div className="px-2 py-1.5 text-xs font-bold text-muted-foreground mt-3 first:mt-0">
                  {parent.label}
                </div>
                {/* Sub-chapters indented */}
                {subChapters
                  .filter((sub) => sub.parentChapter === parent.parentChapter)
                  .map((sub) => {
                    const isActive = sub.slug === currentSlug;
                    return (
                      <Link
                        key={sub.slug}
                        href={`/books/ssr/${sub.slug}`}
                        className={cn(
                          "pl-4 px-2 py-1.5 rounded-md text-sm transition-colors truncate block",
                          isActive
                            ? "bg-primary/10 text-primary font-medium"
                            : "text-muted-foreground hover:bg-muted hover:text-foreground",
                        )}
                        title={sub.label}
                      >
                        {sub.label}
                      </Link>
                    );
                  })}
              </div>
            ))}
          </nav>
        </>
      )}

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

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

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