"use client";

import { useState, useMemo, useRef } from "react";
import Link from "next/link";
import { usePathname, useSearchParams } from "next/navigation";
import { Card, CardContent } from "@/components/ui/card";
import { Badge } from "@/components/ui/badge";
import { buttonVariants } from "@/components/ui/button";
import { cn } from "@/lib/utils";
import { ChevronLeft, ChevronRight, Menu, Calendar, Clock, MapPin } from "lucide-react";
import { PlayAudioButton } from "@/app/(app)/(reader)/transcriptions/[slug]/play-audio-button";
import { parseChapter, parseVerse } from "@/lib/book-reference";
import {
  Drawer,
  DrawerClose,
  DrawerContent,
  DrawerHeader,
  DrawerTitle,
  DrawerTrigger,
} from "@/components/ui/drawer";

// ---------------------------------------------------------------------------
// Types
// ---------------------------------------------------------------------------

export type TranscriptionItem = {
  slug: string;
  name: string;
  type: string;
  date: string | null;
  year: number | null;
  month: number | null;
  day: number | null;
  place: string | null;
  context: string | null;
  reference: string | null;
  durationMinutes: number | null;
  participants: string[];
  audioUrl: string | null;
};

type ChapterGroup = {
  key: string;
  label: string;
  transcriptions: TranscriptionItem[];
};

// A section is a canto (SB) or līlā (CC). Books without that level produce a
// single section with a null label (rendered without a heading).
type SectionGroup = {
  key: string;
  label: string | null;
  chapters: ChapterGroup[];
};

// ---------------------------------------------------------------------------
// Grouping
// ---------------------------------------------------------------------------

// Group all of a book's transcripts into sections (canto/līlā) → chapters,
// ordered by the parsed sort tuple. Books without a canto/līlā level collapse
// into a single section with a null label. Only sections/chapters that have
// transcripts appear. Transcripts arrive already sorted chronologically.
function buildSections(
  transcriptions: TranscriptionItem[],
  code: string,
): SectionGroup[] {
  const sections = new Map<
    string,
    {
      label: string | null;
      order: number;
      chapters: Map<
        string,
        { label: string; sort: [number, number]; items: TranscriptionItem[] }
      >;
    }
  >();

  for (const t of transcriptions) {
    const ch = parseChapter(code, t.reference);
    const secKey = ch.section ? ch.section.key : "__flat__";
    if (!sections.has(secKey)) {
      sections.set(secKey, {
        label: ch.section ? ch.section.label : null,
        order: ch.section ? ch.section.order : 0,
        chapters: new Map(),
      });
    }
    const sec = sections.get(secKey)!;
    if (!sec.chapters.has(ch.key)) {
      sec.chapters.set(ch.key, { label: ch.label, sort: ch.sort, items: [] });
    }
    sec.chapters.get(ch.key)!.items.push(t);
  }

  return Array.from(sections.entries())
    .sort((a, b) => a[1].order - b[1].order)
    .map(([key, s]) => ({
      key,
      label: s.label,
      chapters: Array.from(s.chapters.entries())
        .sort(
          (a, b) => a[1].sort[0] - b[1].sort[0] || a[1].sort[1] - b[1].sort[1],
        )
        .map(([k, v]) => ({
          key: k,
          label: v.label,
          // Order lectures by verse ascending (e.g. 2.1, 2.3, 2.4…),
          // irrespective of year. Stable sort keeps year order within a verse.
          transcriptions: v.items
            .slice()
            .sort((a, b) => parseVerse(a.reference) - parseVerse(b.reference)),
        })),
    }));
}

// Flatten sections into a linear chapter list for prev/next navigation and
// active-chapter lookup, carrying each chapter's section label for display.
type FlatChapter = { sectionLabel: string | null; chapter: ChapterGroup };

function flattenChapters(sections: SectionGroup[]): FlatChapter[] {
  return sections.flatMap((s) =>
    s.chapters.map((chapter) => ({ sectionLabel: s.label, chapter })),
  );
}

// ---------------------------------------------------------------------------
// Chapter nav list (shared by sidebar + mobile drawer)
// ---------------------------------------------------------------------------

function ChapterNavList({
  sections,
  activeKey,
  onSelect,
}: {
  sections: SectionGroup[];
  activeKey: string;
  onSelect: (key: string) => void;
}) {
  return (
    <nav className="flex flex-col gap-3">
      {sections.map((section) => (
        <div key={section.key} className="flex flex-col gap-0.5">
          {section.label && (
            <div className="px-2 pt-1 pb-0.5 text-xs font-bold uppercase tracking-wider text-muted-foreground/80">
              {section.label}
            </div>
          )}
          {section.chapters.map((ch) => {
            const isActive = ch.key === activeKey;
            return (
              <button
                key={ch.key}
                onClick={() => onSelect(ch.key)}
                className={cn(
                  "flex items-center justify-between gap-2 px-2 py-1.5 rounded-md text-sm transition-colors text-left",
                  isActive
                    ? "bg-primary/10 text-primary font-medium"
                    : "text-muted-foreground hover:bg-muted hover:text-foreground",
                )}
              >
                <span className="truncate">{ch.label}</span>
                <span
                  className={cn(
                    "text-xs tabular-nums shrink-0",
                    isActive ? "text-primary/70" : "text-muted-foreground/60",
                  )}
                >
                  {ch.transcriptions.length}
                </span>
              </button>
            );
          })}
        </div>
      ))}
    </nav>
  );
}

function ChapterSidebar(props: {
  sections: SectionGroup[];
  activeKey: string;
  onSelect: (key: string) => void;
}) {
  return (
    <aside className="hidden lg:block w-60 shrink-0 sticky top-[89px] self-start max-h-[calc(100vh-89px)] overflow-y-auto py-8 pr-4">
      <h2 className="text-xs font-bold uppercase tracking-wider text-muted-foreground mb-3 px-2">
        Chapters
      </h2>
      <ChapterNavList {...props} />
    </aside>
  );
}

function ChapterMobileNav({
  sections,
  activeKey,
  onSelect,
  title,
}: {
  sections: SectionGroup[];
  activeKey: string;
  onSelect: (key: string) => void;
  title: string;
}) {
  const [open, setOpen] = useState(false);

  return (
    <Drawer open={open} onOpenChange={setOpen} direction="left">
      <DrawerTrigger
        className={cn(
          buttonVariants({ variant: "outline", size: "sm" }),
          "lg:hidden gap-1.5",
        )}
      >
        <Menu className="size-4" />
        <span className="hidden sm:inline">Chapters</span>
      </DrawerTrigger>
      <DrawerContent direction="left" className="h-full">
        <DrawerHeader className="text-left border-b border-border pb-4 mb-2">
          <DrawerTitle>{title}</DrawerTitle>
        </DrawerHeader>
        <div className="overflow-y-auto px-4 pb-6 pt-2">
          <ChapterNavList
            sections={sections}
            activeKey={activeKey}
            onSelect={(key) => {
              onSelect(key);
              setOpen(false);
            }}
          />
        </div>
      </DrawerContent>
    </Drawer>
  );
}

// ---------------------------------------------------------------------------
// Prev / Next nav
// ---------------------------------------------------------------------------

function ChapterNav({
  prev,
  next,
  sections,
  activeKey,
  onSelect,
  drawerTitle,
}: {
  prev: FlatChapter | null;
  next: FlatChapter | null;
  sections: SectionGroup[];
  activeKey: string;
  onSelect: (key: string) => void;
  drawerTitle: string;
}) {
  return (
    <div className="flex items-center justify-between gap-3">
      <div className="flex items-center gap-2">
        <ChapterMobileNav
          sections={sections}
          activeKey={activeKey}
          onSelect={onSelect}
          title={drawerTitle}
        />

        {prev ? (
          <button
            onClick={() => onSelect(prev.chapter.key)}
            className={cn(
              buttonVariants({ variant: "outline", size: "sm" }),
              "gap-1.5",
            )}
          >
            <ChevronLeft className="size-4" />
            <span className="hidden sm:inline truncate max-w-[180px]">
              {prev.chapter.label}
            </span>
            <span className="sm:hidden">Previous</span>
          </button>
        ) : (
          <div className="hidden lg:block" />
        )}
      </div>

      {next ? (
        <button
          onClick={() => onSelect(next.chapter.key)}
          className={cn(
            buttonVariants({ variant: "outline", size: "sm" }),
            "gap-1.5",
          )}
        >
          <span className="hidden sm:inline truncate max-w-[180px]">
            {next.chapter.label}
          </span>
          <span className="sm:hidden">Next</span>
          <ChevronRight className="size-4" />
        </button>
      ) : (
        <div />
      )}
    </div>
  );
}

// ---------------------------------------------------------------------------
// Lecture row
// ---------------------------------------------------------------------------

function LectureRow({ t }: { t: TranscriptionItem }) {
  return (
    <Link
      href={`/transcriptions/${t.slug}`}
      className="flex items-center px-5 py-3.5 gap-3 hover:bg-muted transition-colors"
    >
      <div className="min-w-0 flex-1">
        <div className="flex items-center gap-2 flex-wrap">
          <p className="font-medium text-foreground text-sm">{t.name}</p>
          <Badge
            variant={t.type === "lecture" ? "default" : "secondary"}
            className="text-[10px] px-1.5 py-0"
          >
            {t.type === "lecture" ? "Lecture" : "Conversation"}
          </Badge>
        </div>
        <div className="flex flex-wrap items-center gap-x-3 gap-y-1 mt-1 text-xs text-muted-foreground">
          {t.date && (
            <span className="flex items-center gap-1">
              <Calendar className="size-3" />
              {t.date}
            </span>
          )}
          {t.place && (
            <span className="flex items-center gap-1">
              <MapPin className="size-3" />
              {t.place}
            </span>
          )}
          {t.reference && (
            <span className="text-primary/70">{t.reference}</span>
          )}
          {t.durationMinutes && t.durationMinutes > 0 && (
            <span className="flex items-center gap-1">
              <Clock className="size-3" />
              {t.durationMinutes} min
            </span>
          )}
        </div>
      </div>
      {t.audioUrl && (
        <PlayAudioButton
          audioUrl={t.audioUrl}
          title={t.name}
          subtitle={[t.date, t.place].filter(Boolean).join(" · ")}
          sourceUrl={`/transcriptions/${t.slug}`}
          type={t.type}
          variant="compact"
        />
      )}
    </Link>
  );
}

// ---------------------------------------------------------------------------
// Main component
// ---------------------------------------------------------------------------

export function TranscriptionBookBrowser({
  transcriptions,
  code,
  title,
  totalCount,
}: {
  transcriptions: TranscriptionItem[];
  code: string;
  title: string;
  totalCount: number;
}) {
  const sections = useMemo(
    () => buildSections(transcriptions, code),
    [transcriptions, code],
  );

  const flat = useMemo(() => flattenChapters(sections), [sections]);

  // The active chapter lives in the URL (?chapter=<key>) so it's bookmarkable
  // and survives back-navigation: opening a lecture then pressing Back returns
  // to the chapter you were on rather than resetting to the first one. We seed
  // local state from the URL on mount and keep the URL in sync on selection.
  const pathname = usePathname();
  const searchParams = useSearchParams();

  const [activeKeyRaw, setActiveKey] = useState<string>(() => {
    const fromUrl = searchParams.get("chapter");
    if (fromUrl && flat.find((f) => f.chapter.key === fromUrl)) return fromUrl;
    return flat.length > 0 ? flat[0].chapter.key : "";
  });

  // Derive a safe active chapter key (the data could change underneath us).
  const activeKey = useMemo(() => {
    if (flat.length === 0) return activeKeyRaw;
    if (flat.find((f) => f.chapter.key === activeKeyRaw)) return activeKeyRaw;
    return flat[0].chapter.key;
  }, [flat, activeKeyRaw]);

  const contentRef = useRef<HTMLDivElement>(null);

  const handleSelect = (key: string) => {
    setActiveKey(key);
    // Reflect the choice in the URL without a new history entry (so Back leaves
    // the page rather than cycling chapters) or a server round-trip.
    const params = new URLSearchParams(Array.from(searchParams.entries()));
    params.set("chapter", key);
    window.history.replaceState(null, "", `${pathname}?${params.toString()}`);
    contentRef.current?.scrollIntoView({ behavior: "smooth", block: "start" });
  };

  const activeIdx = flat.findIndex((f) => f.chapter.key === activeKey);
  const active = activeIdx >= 0 ? flat[activeIdx] : null;
  const prev = activeIdx > 0 ? flat[activeIdx - 1] : null;
  const next =
    activeIdx >= 0 && activeIdx < flat.length - 1 ? flat[activeIdx + 1] : null;

  const activeFullLabel = active
    ? active.sectionLabel
      ? `${active.sectionLabel} · ${active.chapter.label}`
      : active.chapter.label
    : "";
  const activeCount = active?.chapter.transcriptions.length ?? 0;

  return (
    <>
      {/* Header */}
      <header className="border-b border-border bg-card px-6 py-4 sticky top-0 z-20">
        <div className="max-w-5xl mx-auto">
          <Link
            href="/transcriptions?view=book"
            className="text-sm text-muted-foreground hover:text-foreground transition-colors"
          >
            &larr; Transcriptions by Book
          </Link>
          <h1 className="mt-3 text-2xl font-bold text-foreground">
            <span className="text-primary">{title}</span>
            {activeFullLabel ? `: ${activeFullLabel}` : ""}
          </h1>
          <p className="mt-1 text-muted-foreground">
            {activeCount} {activeCount === 1 ? "lecture" : "lectures"} in this
            chapter · {totalCount} total
          </p>
        </div>
      </header>

      {/* Sidebar + Main */}
      <div className="max-w-5xl mx-auto flex">
        {/* Left sidebar — chapters */}
        <ChapterSidebar
          sections={sections}
          activeKey={activeKey}
          onSelect={handleSelect}
        />

        {/* Main content */}
        <main ref={contentRef} className="flex-1 min-w-0 px-6 py-8 space-y-8">
          {/* Top navigation */}
          <ChapterNav
            prev={prev}
            next={next}
            sections={sections}
            activeKey={activeKey}
            onSelect={handleSelect}
            drawerTitle={title}
          />

          {/* Content — every lecture of the active chapter (all years/places) */}
          {!active || active.chapter.transcriptions.length === 0 ? (
            <div className="py-12 text-center text-muted-foreground">
              <p className="text-lg font-medium">
                No transcriptions for this chapter
              </p>
            </div>
          ) : (
            <Card className="overflow-hidden">
              <CardContent className="p-0 divide-y divide-border">
                {active.chapter.transcriptions.map((t) => (
                  <LectureRow key={t.slug} t={t} />
                ))}
              </CardContent>
            </Card>
          )}

          {/* Bottom navigation */}
          <ChapterNav
            prev={prev}
            next={next}
            sections={sections}
            activeKey={activeKey}
            onSelect={handleSelect}
            drawerTitle={title}
          />
        </main>
      </div>
    </>
  );
}