"use client";

import Link from "next/link";
import { useMemo, useRef, useState, useSyncExternalStore } from "react";

import { ApiKeyBanner } from "@/components/ApiKeyBanner";
import { DeckCard } from "@/components/DeckCard";
import { FolderBar } from "@/components/FolderBar";
import { FolderIcon, UploadIcon } from "@/components/icons";
import { Button, EmptyState } from "@/components/ui";
import { folderStore, renameFolder } from "@/lib/folders";
import { ALL_FOLDERS, folderSelection, useSelectedFolder } from "@/lib/nav";
import { openSettings } from "@/lib/ui-events";
import { UNORGANIZED_ID, type Deck } from "@/lib/schemas";
import { deckStore, deleteFolder, importDeck, sortDecks, upsertDeck } from "@/lib/storage";
import { cn } from "@/lib/utils";

/**
 * Dashboard: page title, folder pills, then a spacious responsive grid of
 * deck cards grouped by folder.
 */
export function LibraryScreen() {
  const decks = useSyncExternalStore(deckStore.subscribe, deckStore.getSnapshot, deckStore.getServerSnapshot);
  const folders = useSyncExternalStore(
    folderStore.subscribe,
    folderStore.getSnapshot,
    folderStore.getServerSnapshot,
  );
  const selected = useSelectedFolder();
  const setSelected = folderSelection.set;
  const [message, setMessage] = useState<{ tone: "ok" | "error"; text: string } | null>(null);
  const [editingFolder, setEditingFolder] = useState<{ id: string; name: string } | null>(null);
  const [confirmDelete, setConfirmDelete] = useState<string | null>(null);
  const importRef = useRef<HTMLInputElement>(null);

  const sorted = useMemo(() => sortDecks(decks), [decks]);
  const folderList = useMemo(
    () => [...folders].sort((a, b) => a.name.localeCompare(b.name, undefined, { sensitivity: "base" })),
    [folders],
  );

  const counts = useMemo(() => {
    const map: Record<string, number> = {};
    for (const folder of folderList) map[folder.id] = 0;
    for (const deck of decks) {
      const key = deck.folderId && map[deck.folderId] !== undefined ? deck.folderId : UNORGANIZED_ID;
      map[key] = (map[key] ?? 0) + 1;
    }
    return map;
  }, [decks, folderList]);

  const groups = useMemo(() => {
    const unorganized: { id: string; name: string; decks: Deck[]; virtual: boolean } = {
      id: UNORGANIZED_ID,
      name: "Unorganized",
      decks: sorted.filter((deck) => !deck.folderId),
      virtual: true,
    };

    if (selected === UNORGANIZED_ID) return [unorganized];
    if (selected !== ALL_FOLDERS) {
      const folder = folderList.find((entry) => entry.id === selected);
      if (!folder) return [unorganized];
      return [
        { id: folder.id, name: folder.name, decks: sorted.filter((deck) => deck.folderId === folder.id), virtual: false },
      ];
    }

    const named = folderList.map((folder) => ({
      id: folder.id,
      name: folder.name,
      decks: sorted.filter((deck) => deck.folderId === folder.id),
      virtual: false,
    }));
    return [...named, unorganized];
  }, [folderList, selected, sorted]);

  const totalActivities = decks.reduce((sum, deck) => sum + deck.activities.length, 0);
  const bestEver = decks.reduce((best, deck) => Math.max(best, deck.bestScore ?? 0), 0);
  const played = decks.some((deck) => deck.attempts > 0);

  const handleImport = async (file: File | undefined) => {
    if (!file) return;
    try {
      const text = await file.text();
      const result = importDeck(text);
      if ("error" in result) setMessage({ tone: "error", text: result.error });
      else setMessage({ tone: "ok", text: `Imported “${result.deck.title}”.` });
    } catch {
      setMessage({ tone: "error", text: "Could not read that file." });
    }
  };

  const removeFolderEverywhere = (folderId: string) => {
    deleteFolder(folderId);
    setConfirmDelete(null);
    setSelected(ALL_FOLDERS);
    setMessage({ tone: "ok", text: "Folder deleted — its decks moved to Unorganized." });
  };

  const isEmpty = sorted.length === 0 && folderList.length === 0;

  return (
    <div className="relative">
      {/* page header ---------------------------------------------------- */}
      <section className="mb-6 space-y-5">
        <div className="flex flex-wrap items-end justify-between gap-4">
          <div>
            <h1 className="text-[24px] font-medium leading-tight tracking-[-0.01em] text-[var(--text)] sm:text-[26px]">
              Your icebox
            </h1>
            <p className="mt-1.5 text-[13.5px] text-[var(--text-subtle)]">
              Decks frozen from your notes, saved in this browser.
            </p>
          </div>

          <div className="flex flex-wrap items-center gap-2">
            <Button variant="secondary" size="md" onClick={() => importRef.current?.click()}>
              <UploadIcon className="size-4" />
              Import JSON
            </Button>
            <input
              ref={importRef}
              type="file"
              accept="application/json,.json"
              className="sr-only"
              onChange={(event) => {
                void handleImport(event.target.files?.[0]);
                event.target.value = "";
              }}
            />
          </div>
        </div>

        {/* Secondary stats folded into the header as quiet text on desktop,
            where the sidebar already shows per-folder counts. */}
        {decks.length > 0 ? (
          <p className="text-[13px] text-[var(--text-subtle)] lg:hidden">
            {decks.length} {decks.length === 1 ? "deck" : "decks"}
            <span aria-hidden> · </span>
            {folderList.length} {folderList.length === 1 ? "folder" : "folders"}
            <span aria-hidden> · </span>
            {totalActivities} activities
            {played ? (
              <>
                <span aria-hidden> · </span>
                best {bestEver}%
              </>
            ) : null}
          </p>
        ) : null}

        {/* Mobile folder switcher; the sidebar covers desktop. */}
        <FolderBar className="lg:hidden"
          folders={folderList}
          counts={counts}
          selected={selected}
          onSelect={(id) => {
            setSelected(id);
            setConfirmDelete(null);
          }}
          onCreated={(id) => {
            setSelected(id);
            setMessage({
              tone: "ok",
              text: "Folder created — decks you freeze while it's selected land here.",
            });
          }}
        />

        <ApiKeyBanner />

        {message ? (
          <p
            role="status"
            className={cn(
              "flex items-center gap-2 rounded-xl border border-[var(--hairline)] bg-[var(--surface)] px-3.5 py-2.5 text-[13px] font-medium",
              message.tone === "ok" ? "text-emerald-700 dark:text-emerald-300" : "text-rose-700 dark:text-rose-300",
            )}
          >
            {message.text}
          </p>
        ) : null}
      </section>

      {/* deck grid ------------------------------------------------------ */}
      {isEmpty ? (
        <EmptyState
          title="No decks yet"
          action={
            <Link href="/create" className="btn-primary h-10 px-4 text-sm">
              Make your first deck
            </Link>
          }
        >
          Freeze a page of notes into a feed of flashcards and quizzes.
          <span className="mt-3 block text-[12.5px] text-[var(--text-subtle)]">
            Using your own Ollama models —{" "}
            <button
              type="button"
              onClick={openSettings}
              className="font-medium text-[var(--text-muted)] underline underline-offset-2 hover:text-[var(--text)]"
            >
              check the connection in Settings
            </button>
            .
          </span>
        </EmptyState>
      ) : (
        <div className="space-y-8">
          {groups.map((group) => {
            const isEditing = editingFolder?.id === group.id;
            return (
              <section key={group.id} aria-label={group.name}>
                {/* group header -------------------------------------- */}
                <div className="mb-4 flex items-center gap-2">
                  <FolderIcon className="size-4 shrink-0 text-[var(--text-subtle)]" />

                  {isEditing && editingFolder ? (
                    <span className="flex flex-1 items-center gap-2">
                      <input
                        autoFocus
                        value={editingFolder.name}
                        onChange={(event) => setEditingFolder({ ...editingFolder, name: event.target.value })}
                        onKeyDown={(event) => {
                          event.stopPropagation();
                          if (event.key === "Enter") {
                            const result = renameFolder(editingFolder.id, editingFolder.name);
                            if ("error" in result) setMessage({ tone: "error", text: result.error });
                            else setEditingFolder(null);
                          }
                          if (event.key === "Escape") setEditingFolder(null);
                        }}
                        aria-label="Folder name"
                        maxLength={60}
                        className="min-w-32 max-w-xs flex-1 rounded-lg border border-[var(--hairline)] bg-[var(--surface-strong)] px-2.5 py-1.5 text-[15px] font-semibold text-[var(--text)] outline-none focus:border-accent-400"
                      />
                      <Button
                        size="sm"
                        onClick={() => {
                          const result = renameFolder(editingFolder.id, editingFolder.name);
                          if ("error" in result) setMessage({ tone: "error", text: result.error });
                          else setEditingFolder(null);
                        }}
                      >
                        Save
                      </Button>
                    </span>
                  ) : (
                    <button
                      type="button"
                      onClick={() => setSelected(group.virtual ? UNORGANIZED_ID : group.id)}
                      className="truncate text-[15px] font-semibold tracking-[-0.01em] text-[var(--text)]"
                    >
                      {group.name}
                      <span className="ml-2 text-[13px] font-normal tabular-nums text-[var(--text-subtle)]">
                        {group.decks.length}
                      </span>
                    </button>
                  )}

                  {!group.virtual && !isEditing ? (
                    <div className="flex items-center gap-0.5">
                      <button
                        type="button"
                        onClick={() => setEditingFolder({ id: group.id, name: group.name })}
                        className="rounded-lg px-2 py-1 text-[12.5px] font-medium text-[var(--text-subtle)] transition hover:bg-[var(--hover)] hover:text-[var(--text)]"
                      >
                        Rename
                      </button>
                      {confirmDelete === group.id ? (
                        <>
                          <Button size="sm" variant="danger" onClick={() => removeFolderEverywhere(group.id)}>
                            Delete
                          </Button>
                          <Button size="sm" variant="ghost" onClick={() => setConfirmDelete(null)}>
                            Cancel
                          </Button>
                        </>
                      ) : (
                        <button
                          type="button"
                          onClick={() => setConfirmDelete(group.id)}
                          className="rounded-lg px-2 py-1 text-[12.5px] font-medium text-[var(--text-subtle)] transition hover:bg-[var(--hover)] hover:text-rose-600 dark:hover:text-rose-300"
                        >
                          Delete
                        </button>
                      )}
                    </div>
                  ) : null}
                </div>

                {confirmDelete === group.id ? (
                  <p className="mb-3 text-[12.5px] text-[var(--text-muted)]">
                    The {group.decks.length} deck{group.decks.length === 1 ? "" : "s"} inside will move to
                    Unorganized — nothing is deleted.
                  </p>
                ) : null}

                {group.decks.length === 0 ? (
                  <div className="rounded-2xl border border-dashed border-[var(--hairline)] px-5 py-8 text-center text-[13px] text-[var(--text-subtle)]">
                    {group.virtual
                      ? "Nothing unfiled right now."
                      : "Empty folder — freeze a deck into it or move one over from Unorganized."}
                  </div>
                ) : (
                  <ul className="grid list-none grid-cols-[repeat(auto-fill,minmax(280px,1fr))] gap-4">
                    {group.decks.map((deck) => (
                      <DeckCard
                        key={deck.id}
                        deck={deck}
                        onMove={(folderId) => {
                          upsertDeck({ ...deck, folderId });
                          setMessage({
                            tone: "ok",
                            text: folderId ? "Deck moved." : "Deck moved to Unorganized.",
                          });
                        }}
                      />
                    ))}
                  </ul>
                )}
              </section>
            );
          })}
        </div>
      )}


    </div>
  );
}