import { useEffect, useMemo, useState } from "react";
import { qk } from "../lib/queryKeys";
import { useTranslation } from "react-i18next";
import { useQueryClient } from "@tanstack/react-query";
import {
  DndContext,
  KeyboardSensor,
  PointerSensor,
  closestCenter,
  useSensor,
  useSensors,
  type DragEndEvent,
} from "@dnd-kit/core";
import {
  SortableContext,
  arrayMove,
  sortableKeyboardCoordinates,
  useSortable,
  verticalListSortingStrategy,
} from "@dnd-kit/sortable";
import { CSS } from "@dnd-kit/utilities";
import {
  ArrowLeft,
  ChevronDown,
  ChevronRight,
  GripVertical,
  ListTree,
  Pencil,
  Play,
  Rows3,
  Trash2,
  X,
} from "lucide-react";
import { api, HttpError, type PlexCard } from "../lib/api";
import { notifyActionError } from "../lib/actionErrors";
import { formatRuntime } from "../lib/format";
import { getAccountRaw, LS, setAccountRaw } from "../lib/storage";
import { useConfirm } from "./confirmContext";
import { Button } from "./ui/Button";
import { LoadingState, StateMessage } from "./ui/QueryState";
import ViewSwitcher, { type ViewOption } from "./ViewSwitcher";
import { FocusSafeButton } from "./ui/FocusSafeButton";
import { usePlexPlaylistEdits } from "./usePlexPlaylistEdits";

// A playlist's items, grouped for readability: movies stay standalone, while a run of episodes from the
// same show collapses into a season/show group so a whole series doesn't sprawl into an endless flat
// list. Reorder is drag & drop (a whole show-group moves as one block; episodes reorder within their
// show). Two layouts — Accordion (A) and Tree (C) — are a per-account preference. Rendered as a
// PlexBrowse subview; "Play all" opens the player with the whole ordered list as its queue.

type Layout = "accordion" | "tree";
type Season = { key: string; number: number | null; items: PlexCard[] };
type Block =
  | { kind: "movie"; id: string; item: PlexCard }
  | {
      kind: "show";
      id: string;
      showKey: string;
      title: string;
      items: PlexCard[];
      seasons: Season[];
    };

function buildSeasons(items: PlexCard[]): Season[] {
  const map = new Map<string, Season>();
  for (const it of items) {
    const num = it.season_number ?? null;
    const key = String(num ?? "?");
    let s = map.get(key);
    if (!s) {
      s = { key, number: num, items: [] };
      map.set(key, s);
    }
    s.items.push(it);
  }
  return [...map.values()];
}

// Turn the flat ordered list into blocks: contiguous episodes of one show group together (then split
// into seasons for display); everything else (movies) is its own block.
function buildBlocks(items: PlexCard[]): Block[] {
  const blocks: Block[] = [];
  for (const it of items) {
    if (it.type === "episode") {
      const showKey = it.show_id || it.show_title || "?";
      const last = blocks[blocks.length - 1];
      if (last && last.kind === "show" && last.showKey === showKey) {
        last.items.push(it);
      } else {
        blocks.push({
          kind: "show",
          id: `show:${showKey}`,
          showKey,
          title: it.show_title || it.title,
          items: [it],
          seasons: [],
        });
      }
    } else {
      blocks.push({ kind: "movie", id: it.id, item: it });
    }
  }
  for (const b of blocks) if (b.kind === "show") b.seasons = buildSeasons(b.items);
  return blocks;
}

const flatten = (blocks: Block[]): PlexCard[] =>
  blocks.flatMap((b) => (b.kind === "movie" ? [b.item] : b.items));

// Callbacks + shared state passed down to the module-scope block/row components.
type Ctx = {
  layout: Layout;
  busy: boolean;
  expandedShows: Set<string>;
  collapsedSeasons: Set<string>;
  toggleShow: (k: string) => void;
  toggleSeason: (k: string) => void;
  onPlay: (rk: string) => void;
  onRemove: (keys: string[]) => void;
};

function Poster({ src, className }: { src: string; className: string }) {
  return (
    <div
      className={`relative shrink-0 overflow-hidden rounded-sm border border-border bg-surface ${className}`}
    >
      <img src={src} alt="" loading="lazy" className="h-full w-full object-cover" />
    </div>
  );
}

/** `title` names the row it moves: a screen reader heard the English word "reorder" on every
 *  row, with nothing to say which. */
function DragHandle({ title, ...props }: { title: string } & Record<string, unknown>) {
  const { t } = useTranslation();
  return (
    <button
      {...props}
      className="shrink-0 cursor-grab text-muted hover:text-fg active:cursor-grabbing"
      aria-label={t("plex.playlist.reorderItem", { title })}
    >
      <GripVertical className="h-4 w-4" />
    </button>
  );
}

function EpisodeRow({ ep, ctx, dense }: { ep: PlexCard; ctx: Ctx; dense: boolean }) {
  const { t } = useTranslation();
  const { attributes, listeners, setNodeRef, transform, transition, isDragging } = useSortable({
    id: ep.id,
    disabled: ctx.busy,
  });
  const style = {
    transform: CSS.Transform.toString(transform),
    transition,
    opacity: isDragging ? 0.6 : 1,
  };
  const inProgress = (ep.position_seconds ?? 0) > 0 && ep.status !== "watched";
  return (
    <div
      ref={setNodeRef}
      style={style}
      className={`flex items-center gap-2.5 rounded-lg ${dense ? "px-1.5 py-1" : "glass-card p-1.5"}`}
    >
      <DragHandle title={ep.title} {...attributes} {...listeners} />
      <span className="w-5 shrink-0 text-center text-2xs text-muted tabular-nums">
        {ep.episode_number}
      </span>
      <button
        onClick={() => ctx.onPlay(ep.id)}
        className="group flex min-w-0 flex-1 items-center gap-2.5 text-left"
      >
        <div
          className={`relative shrink-0 overflow-hidden rounded-sm border border-border bg-surface ${dense ? "aspect-video w-14" : "aspect-video w-20"}`}
        >
          <img src={ep.thumb} alt="" loading="lazy" className="h-full w-full object-cover" />
          {ep.status === "watched" && (
            <span className="absolute right-0.5 top-0.5 rounded-sm bg-black/70 px-1 text-[0.5625rem] text-white">
              ✓
            </span>
          )}
          {inProgress && <div className="absolute inset-x-0 bottom-0 h-0.5 bg-accent" />}
          <div className="absolute inset-0 grid place-items-center bg-black/40 opacity-0 transition group-hover:opacity-100">
            <Play className="h-4 w-4 text-white" fill="currentColor" />
          </div>
        </div>
        <div className="min-w-0 truncate text-[0.8125rem]">{ep.title}</div>
      </button>
      <FocusSafeButton
        onClick={() => ctx.onRemove([ep.id])}
        disabled={ctx.busy}
        className="shrink-0 rounded-sm p-1 text-muted hover:text-danger disabled:opacity-30"
        aria-label={t("plex.playlist.removeItem", { title: ep.title })}
      >
        <X className="h-4 w-4" />
      </FocusSafeButton>
    </div>
  );
}

function MovieRow({ item, ctx }: { item: PlexCard; ctx: Ctx }) {
  const { t } = useTranslation();
  const { attributes, listeners, setNodeRef, transform, transition, isDragging } = useSortable({
    id: item.id,
    disabled: ctx.busy,
  });
  const style = {
    transform: CSS.Transform.toString(transform),
    transition,
    opacity: isDragging ? 0.6 : 1,
  };
  const dense = ctx.layout === "tree";
  return (
    <div
      ref={setNodeRef}
      style={style}
      className="glass-card flex items-center gap-3 rounded-xl p-2"
    >
      <DragHandle title={item.title} {...attributes} {...listeners} />
      <button
        onClick={() => ctx.onPlay(item.id)}
        className="group flex min-w-0 flex-1 items-center gap-3 text-left"
      >
        <Poster src={item.thumb} className={dense ? "aspect-2/3 w-10" : "aspect-2/3 w-14"} />
        <div className="min-w-0">
          <div className="truncate text-sm font-medium">{item.title}</div>
          <div className="text-xs text-muted">{item.year}</div>
        </div>
        <div className="pointer-events-none ml-auto grid h-8 w-8 shrink-0 place-items-center rounded-full bg-accent/0 text-transparent transition group-hover:bg-accent/15 group-hover:text-accent">
          <Play className="h-4 w-4" fill="currentColor" />
        </div>
      </button>
      <FocusSafeButton
        onClick={() => ctx.onRemove([item.id])}
        disabled={ctx.busy}
        className="shrink-0 rounded-sm p-1 text-muted hover:text-danger disabled:opacity-30"
        aria-label={t("plex.playlist.removeItem", { title: item.title })}
      >
        <X className="h-4 w-4" />
      </FocusSafeButton>
    </div>
  );
}

function ShowGroup({ block, ctx }: { block: Extract<Block, { kind: "show" }>; ctx: Ctx }) {
  const { t } = useTranslation();
  const { attributes, listeners, setNodeRef, transform, transition, isDragging } = useSortable({
    id: block.id,
    disabled: ctx.busy,
  });
  const style = {
    transform: CSS.Transform.toString(transform),
    transition,
    opacity: isDragging ? 0.6 : 1,
  };
  const open = ctx.expandedShows.has(block.showKey);
  const dense = ctx.layout === "tree";
  const seasonLabel = (s: Season) =>
    s.number != null
      ? t("plex.playlist.season", { n: s.number })
      : t("plex.playlist.seasonUnknown");

  return (
    <div ref={setNodeRef} style={style} className="glass-card overflow-hidden rounded-xl">
      {/* Group header — drag moves the whole show; chevron collapses; X removes the whole show. */}
      <div className="flex items-center gap-2.5 p-2">
        <DragHandle title={block.title} {...attributes} {...listeners} />
        <button
          onClick={() => ctx.toggleShow(block.showKey)}
          className="grid h-6 w-6 shrink-0 place-items-center rounded-sm text-muted hover:text-fg"
          aria-expanded={open}
          aria-label={block.title}
        >
          {open ? <ChevronDown className="h-4 w-4" /> : <ChevronRight className="h-4 w-4" />}
        </button>
        {!dense && (
          // A second, pointer-only target for the same toggle (its images are decorative): out of
          // the tab order, so the keyboard does not stop on a button with no name.
          <button
            onClick={() => ctx.toggleShow(block.showKey)}
            className="flex shrink-0"
            tabIndex={-1}
            aria-hidden
          >
            {block.items.slice(0, 3).map((ep, i) => (
              <img
                key={ep.id}
                src={ep.thumb}
                alt=""
                loading="lazy"
                className="aspect-2/3 w-8 rounded-sm border-2 border-surface object-cover"
                style={{ marginLeft: i ? -14 : 0 }}
              />
            ))}
          </button>
        )}
        <button onClick={() => ctx.toggleShow(block.showKey)} className="min-w-0 flex-1 text-left">
          <div className="truncate text-sm font-semibold">{block.title}</div>
          <div className="text-2xs text-muted">
            {t("plex.playlist.episodes", { count: block.items.length })}
          </div>
        </button>
        <FocusSafeButton
          onClick={() => ctx.onRemove(block.items.map((i) => i.id))}
          disabled={ctx.busy}
          title={t("plex.playlist.removeShow")}
          className="shrink-0 rounded-sm p-1 text-muted hover:text-danger disabled:opacity-30"
        >
          <X className="h-4 w-4" />
        </FocusSafeButton>
      </div>

      {open && (
        <div className={`border-t border-border/50 ${dense ? "px-2 pb-1.5 pt-1" : "px-2 pb-2"}`}>
          <SortableContext
            items={block.items.map((i) => i.id)}
            strategy={verticalListSortingStrategy}
          >
            {block.seasons.map((s) => {
              const sKey = `${block.showKey}:${s.key}`;
              const sOpen = !dense || !ctx.collapsedSeasons.has(sKey);
              return (
                <div key={s.key} className={dense ? "" : "mt-1.5 first:mt-0.5"}>
                  <div className="flex items-center gap-1.5 py-1 pl-1">
                    {dense && (
                      <button
                        onClick={() => ctx.toggleSeason(sKey)}
                        className="grid h-5 w-5 shrink-0 place-items-center rounded-sm text-muted hover:text-fg"
                        aria-expanded={sOpen}
                      >
                        {sOpen ? (
                          <ChevronDown className="h-3.5 w-3.5" />
                        ) : (
                          <ChevronRight className="h-3.5 w-3.5" />
                        )}
                      </button>
                    )}
                    <span className="text-2xs font-medium uppercase tracking-wide text-muted">
                      {seasonLabel(s)} · {s.items.length}
                    </span>
                    <FocusSafeButton
                      onClick={() => ctx.onRemove(s.items.map((i) => i.id))}
                      disabled={ctx.busy}
                      title={t("plex.playlist.removeSeason")}
                      className="ml-1 rounded-sm p-0.5 text-muted hover:text-danger disabled:opacity-30"
                    >
                      <X className="h-3.5 w-3.5" />
                    </FocusSafeButton>
                  </div>
                  {sOpen && (
                    <div
                      className={
                        dense ? "ml-2 space-y-0.5 border-l border-border/50 pl-1.5" : "space-y-1"
                      }
                    >
                      {s.items.map((ep) => (
                        <EpisodeRow key={ep.id} ep={ep} ctx={ctx} dense={dense} />
                      ))}
                    </div>
                  )}
                </div>
              );
            })}
          </SortableContext>
        </div>
      )}
    </div>
  );
}

export default function PlexPlaylistView({
  playlistId,
  onBack,
  onPlay,
}: {
  playlistId: number;
  onBack: () => void;
  onPlay: (itemRk: string, queue: string[]) => void;
}) {
  const { t } = useTranslation();
  const qc = useQueryClient();
  const confirm = useConfirm();
  const [renaming, setRenaming] = useState(false);
  const [name, setName] = useState("");
  const [layout, setLayout] = useState<Layout>(() =>
    getAccountRaw(LS.plexPlaylistLayout) === "tree" ? "tree" : "accordion",
  );
  useEffect(() => {
    setAccountRaw(LS.plexPlaylistLayout, layout);
  }, [layout]);
  // Show groups start collapsed (compact headers) so a long series doesn't force endless scrolling;
  // seasons start expanded once their show is opened. Both are just local view state.
  const [expandedShows, setExpandedShows] = useState<Set<string>>(new Set());
  const [collapsedSeasons, setCollapsedSeasons] = useState<Set<string>>(new Set());

  // The query, the optimistic copy and the two writes that edit it (reorder, remove) live in
  // `usePlexPlaylistEdits`, where their failure paths can be driven directly: the drag that reaches
  // `commit` cannot be, since dnd-kit's sensors do not activate under jsdom.
  const { q, items, busy, invalidate, commit, onRemove } = usePlexPlaylistEdits(playlistId);
  const blocks = useMemo(() => buildBlocks(items), [items]);
  const order = useMemo(() => items.map((i) => i.id), [items]);
  // Total playtime of the whole playlist, mirroring the YouTube playlist header (E9 12D): items with
  // an unknown duration count as 0, and the runtime is dropped from the meta line when nothing sums.
  const totalSeconds = useMemo(
    () => items.reduce((acc, it) => acc + (it.duration_seconds ?? 0), 0),
    [items],
  );

  async function rename() {
    const title = name.trim();
    if (!title) return;
    try {
      await api.plexRenamePlaylist(playlistId, title);
    } catch (e) {
      notifyActionError(e, t("plex.playlist.renameFailed")); // the field stays open to try again
      return;
    }
    setRenaming(false);
    invalidate();
  }
  async function del() {
    if (
      !(await confirm({
        message: t("plex.playlist.deleteConfirm", { title: q.data?.title }),
        danger: true,
      }))
    )
      return;
    try {
      await api.plexDeletePlaylist(playlistId);
    } catch (e) {
      // Gone already (deleted on another device): what was asked for is true — leave the dead page.
      // Anything else is a real failure, and the page stays.
      if (!(e instanceof HttpError && e.status === 404)) {
        notifyActionError(e, t("plex.playlist.deleteFailed"));
        return;
      }
    }
    qc.invalidateQueries({ queryKey: qk.plexPlaylists() });
    onBack();
  }

  const toggleShow = (k: string) =>
    setExpandedShows((s) => {
      const n = new Set(s);
      n.has(k) ? n.delete(k) : n.add(k);
      return n;
    });
  const toggleSeason = (k: string) =>
    setCollapsedSeasons((s) => {
      const n = new Set(s);
      n.has(k) ? n.delete(k) : n.add(k);
      return n;
    });

  const sensors = useSensors(
    useSensor(PointerSensor, { activationConstraint: { distance: 4 } }),
    useSensor(KeyboardSensor, { coordinateGetter: sortableKeyboardCoordinates }),
  );

  function onDragEnd(e: DragEndEvent) {
    const { active, over } = e;
    if (!over || active.id === over.id) return;
    const aId = String(active.id);
    const oId = String(over.id);
    const blockIds = new Set(blocks.map((b) => b.id));
    if (blockIds.has(aId)) {
      // Moving a whole block (movie or show). Resolve the drop target to a block.
      let oBlockId = oId;
      if (!blockIds.has(oId)) {
        const b = blocks.find((bl) => bl.kind === "show" && bl.items.some((it) => it.id === oId));
        if (!b) return;
        oBlockId = b.id;
      }
      const from = blocks.findIndex((b) => b.id === aId);
      const to = blocks.findIndex((b) => b.id === oBlockId);
      if (from < 0 || to < 0) return;
      commit(flatten(arrayMove(blocks, from, to)));
    } else {
      // Moving an episode — only within its own show block.
      const b = blocks.find((bl) => bl.kind === "show" && bl.items.some((it) => it.id === aId));
      if (!b || b.kind !== "show" || !b.items.some((it) => it.id === oId)) return;
      const from = b.items.findIndex((it) => it.id === aId);
      const to = b.items.findIndex((it) => it.id === oId);
      commit(
        flatten(
          blocks.map((bl) =>
            bl.id === b.id ? { ...bl, items: arrayMove(b.items, from, to) } : bl,
          ),
        ),
      );
    }
  }

  const ctx: Ctx = {
    layout,
    busy,
    expandedShows,
    collapsedSeasons,
    toggleShow,
    toggleSeason,
    onPlay: (rk) => onPlay(rk, order),
    onRemove,
  };

  const layoutOptions: ViewOption<Layout>[] = [
    { id: "accordion", label: t("plex.playlist.layoutAccordion"), icon: Rows3 },
    { id: "tree", label: t("plex.playlist.layoutTree"), icon: ListTree },
  ];

  return (
    <div className="mx-auto w-[90%] max-w-275 p-4">
      <Button variant="glass" size="xs" className="mb-4" onClick={onBack}>
        <ArrowLeft className="h-4 w-4" />
        {t("plex.backToLibrary")}
      </Button>

      <div className="glass rounded-2xl p-4 sm:p-6">
        <div className="mb-4 flex flex-wrap items-center gap-3">
          <div className="min-w-0 flex-1">
            {renaming ? (
              <input
                autoFocus
                value={name}
                onChange={(e) => setName(e.target.value)}
                onKeyDown={(e) => e.key === "Enter" && rename()}
                onBlur={rename}
                className="glass-card w-full rounded-lg px-3 py-1.5 text-lg font-bold focus:outline-hidden focus:ring-2 focus:ring-accent/40"
              />
            ) : (
              <h1 className="truncate text-2xl font-bold">{q.data?.title ?? " "}</h1>
            )}
            {items.length > 0 && (
              <div className="mt-0.5 text-sm text-muted">
                {t("plex.browse.items", { count: items.length })}
                {totalSeconds > 0 && ` · ${formatRuntime(totalSeconds)}`}
              </div>
            )}
          </div>
          {/* Layout preference: Accordion or Tree — the shared list-view switcher. */}
          <ViewSwitcher
            value={layout}
            options={layoutOptions}
            onChange={setLayout}
            label={t("plex.playlist.layoutLabel")}
          />
          <button
            onClick={() => {
              setName(q.data?.title ?? "");
              setRenaming(true);
            }}
            title={t("plex.playlist.rename")}
            className="glass-card glass-hover rounded-lg p-2 text-sm hover:text-accent"
          >
            <Pencil className="h-4 w-4" />
          </button>
          {items.length > 0 && (
            <button
              onClick={() => onPlay(order[0]!, order)}
              className="inline-flex items-center gap-2 rounded-xl bg-accent px-4 py-2 font-medium text-white hover:opacity-90"
            >
              <Play className="h-5 w-5 fill-current" />
              {t("plex.playlist.playAll")}
            </button>
          )}
          <button
            onClick={del}
            title={t("plex.playlist.delete")}
            className="glass-card glass-hover rounded-lg p-2 text-sm hover:text-danger"
          >
            <Trash2 className="h-4 w-4" />
          </button>
        </div>

        {q.isError && !q.data ? (
          <StateMessage tone="error" onRetry={() => q.refetch()}>
            {t("common.loadError")}
          </StateMessage>
        ) : q.isLoading ? (
          <LoadingState label={t("plex.loading")} />
        ) : items.length === 0 ? (
          <p className="py-6 text-center text-sm text-muted">{t("plex.playlist.empty")}</p>
        ) : (
          <DndContext sensors={sensors} collisionDetection={closestCenter} onDragEnd={onDragEnd}>
            <SortableContext items={blocks.map((b) => b.id)} strategy={verticalListSortingStrategy}>
              <div className="space-y-1.5">
                {blocks.map((b) =>
                  b.kind === "movie" ? (
                    <MovieRow key={b.id} item={b.item} ctx={ctx} />
                  ) : (
                    <ShowGroup key={b.id} block={b} ctx={ctx} />
                  ),
                )}
              </div>
            </SortableContext>
          </DndContext>
        )}
      </div>
    </div>
  );
}