"use client";

import { motion } from "framer-motion";
import Link from "next/link";
import { useRouter } from "next/navigation";
import { useCallback, useEffect, useMemo, useRef, useState, useSyncExternalStore } from "react";

import { ApiError, generateDeck, type GenerateProgress } from "@/lib/client-api";
import {
  DOCUMENT_ACCEPT_ATTR,
  KIND_LABELS,
  describeDocumentError,
  documentKindOf,
  documentsToText,
  extractDocument,
  isDocumentFile,
  type DocumentKind,
  type ExtractedDocument,
} from "@/lib/documents";
import {
  ACCEPTED_TYPES,
  MAX_IMAGES,
  describeFileError,
  formatBytes,
  imageFilesFromDataTransfer,
  isImageFile,
  prepareImage,
  type PreparedImage,
} from "@/lib/image";
import { createFolder, folderStore } from "@/lib/folders";
import { useI18n } from "@/lib/i18n";
import { UNORGANIZED_ID, type Difficulty } from "@/lib/schemas";
import { upsertDeck } from "@/lib/storage";
import { openSettings } from "@/lib/ui-events";
import { cn, uid } from "@/lib/utils";
import { CameraIcon, ChevronRightIcon, FolderIcon, IceCubeIcon, PlusIcon, SnowflakeIcon, SparklesIcon, SunIcon } from "@/components/icons";
import { Button, ProgressBar } from "@/components/ui";

type Phase = "idle" | "preparing" | "loading" | "error";

/** A document the user added, with its client-side extraction state. */
type DocItem = {
  id: string;
  name: string;
  kind: DocumentKind;
  status: "extracting" | "ready" | "error";
  progress?: string;
  extracted?: ExtractedDocument;
  error?: string;
};

const MAX_DOCUMENTS = 6;
/** Photos + rendered PDF pages + images embedded in documents. */
const MAX_IMAGES_TO_SEND = 12;
/** Cap for the merged text sent to the API. */
const MAX_TEXT_TO_SEND = 100_000;

function describeExtraction(
  document: ExtractedDocument,
  tr: (key: string, vars?: Record<string, string | number>) => string,
  pl: (n: number, base: string, vars?: Record<string, string | number>) => string,
): string {
  const parts = [
    pl(document.words, "upload.words", { n: document.words.toLocaleString() }),
    document.pages ? pl(document.pages, "upload.pages") : "",
    document.images.length ? pl(document.images.length, "upload.pageImages") : "",
    document.truncated ? tr("upload.truncated") : "",
  ];
  return parts.filter(Boolean).join(" · ");
}

const DIFFICULTIES: Array<{ value: Difficulty; labelKey: string; icon: React.ReactNode; blurbKey: string }> = [
  { value: "easy", labelKey: "upload.easy", icon: <SunIcon className="size-5" />, blurbKey: "upload.easyBlurb" },
  {
    value: "medium",
    labelKey: "upload.medium",
    icon: <SnowflakeIcon className="size-5" />,
    blurbKey: "upload.mediumBlurb",
  },
  { value: "hard", labelKey: "upload.hard", icon: <IceCubeIcon className="size-5" />, blurbKey: "upload.hardBlurb" },
];

const COUNT_OPTIONS = [8, 10, 12, 15];

const GENERATION_TIPS = ["upload.tip1", "upload.tip2", "upload.tip3", "upload.tip4"];

export function UploadScreen() {
  const router = useRouter();
  const { t, plural } = useI18n();
  const [images, setImages] = useState<PreparedImage[]>([]);
  const [documents, setDocuments] = useState<DocItem[]>([]);
  const [text, setText] = useState("");
  const [focus, setFocus] = useState("");
  const [difficulty, setDifficulty] = useState<Difficulty>("medium");
  const [folderId, setFolderId] = useState<string>(UNORGANIZED_ID);
  const [creatingFolder, setCreatingFolder] = useState(false);
  const [folderDraft, setFolderDraft] = useState("");
  const [count, setCount] = useState(10);
  const [phase, setPhase] = useState<Phase>("idle");
  const [error, setError] = useState<{ message: string; kind?: string } | null>(null);
  const [fileError, setFileError] = useState<string | null>(null);
  const [dragging, setDragging] = useState(false);
  const [progress, setProgress] = useState<GenerateProgress>({ stage: "vision", message: "" });

  const folders = useSyncExternalStore(
    folderStore.subscribe,
    folderStore.getSnapshot,
    folderStore.getServerSnapshot,
  );
  const sortedFolders = useMemo(
    () => [...folders].sort((a, b) => a.name.localeCompare(b.name, undefined, { sensitivity: "base" })),
    [folders],
  );
  const targetFolder = folderId === UNORGANIZED_ID ? undefined : folderId;

  const fileInputRef = useRef<HTMLInputElement>(null);
  const cameraInputRef = useRef<HTMLInputElement>(null);
  const abortRef = useRef<AbortController | null>(null);
  /**
   * Mirrors of the current lists. React defers state updaters, so reading the
   * count from inside `setState` would silently skip work — always read these.
   */
  const imagesRef = useRef<PreparedImage[]>([]);
  const documentsRef = useRef<DocItem[]>([]);

  useEffect(() => {
    imagesRef.current = images;
  }, [images]);
  useEffect(() => {
    documentsRef.current = documents;
  }, [documents]);

  const addFiles = useCallback(async (files: File[]) => {
    if (files.length === 0) return;
    setFileError(null);
    setPhase("preparing");

    const problems: string[] = [];
    const imageFiles: File[] = [];
    const documentFiles: File[] = [];

    for (const file of files) {
      if (isImageFile(file)) {
        const problem = describeFileError(file);
        if (problem) problems.push(problem);
        else imageFiles.push(file);
      } else if (isDocumentFile(file)) {
        const problem = describeDocumentError(file);
        if (problem) problems.push(problem);
        else documentFiles.push(file);
      } else {
        problems.push(t("upload.unsupported", { name: file.name }));
      }
    }

    const documentRoom = Math.max(0, MAX_DOCUMENTS - documentsRef.current.length);
    const acceptedDocuments = documentFiles.slice(0, documentRoom);
    if (documentFiles.length > documentRoom) problems.push(t("upload.tooManyDocs", { n: MAX_DOCUMENTS }));

    // Documents are read asynchronously (pdf.js can take a while for scans).
    if (acceptedDocuments.length > 0) {
      for (const file of acceptedDocuments) {
        const kind = documentKindOf(file);
        if (!kind) continue;
        const item: DocItem = { id: uid("doc"), name: file.name, kind, status: "extracting" };
        documentsRef.current = [...documentsRef.current, item];
        setDocuments((current) => (current.some((entry) => entry.id === item.id) ? current : [...current, item]));

        const update = (patch: Partial<DocItem>) =>
          setDocuments((current) =>
            current.map((entry) => (entry.id === item.id ? { ...entry, ...patch } : entry)),
          );

        try {
          const extracted = await extractDocument(file, (progress) => update({ progress: progress.message }));
          update({ status: "ready", extracted, progress: undefined });
        } catch (error) {
          update({
            status: "error",
            error: error instanceof Error ? error.message : t("upload.couldNotReadDoc"),
          });
        }
      }
    }

    const photoRoom = Math.max(0, MAX_IMAGES - imagesRef.current.length);
    const acceptedImages = imageFiles.slice(0, photoRoom);
    if (imageFiles.length > photoRoom) problems.push(t("upload.tooManyPhotos", { n: MAX_IMAGES }));

    const prepared: PreparedImage[] = [];
    for (const file of acceptedImages) {
      try {
        prepared.push(await prepareImage(file));
      } catch {
        problems.push(t("upload.couldNotReadFile", { name: file.name }));
      }
    }
    if (prepared.length > 0) {
      imagesRef.current = [...imagesRef.current, ...prepared];
      setImages((current) => [...current, ...prepared]);
    }

    if (problems.length) setFileError(problems.slice(0, 3).join(" "));
    setPhase("idle");
  }, [t]);

  // Clipboard paste (Ctrl/⌘ + V) of screenshots or copied photos.
  useEffect(() => {
    const onPaste = (event: ClipboardEvent) => {
      if (phase === "loading") return;
      const target = event.target as HTMLElement | null;
      const isTextField = target && /^(INPUT|TEXTAREA)$/.test(target.tagName);
      const files = imageFilesFromDataTransfer(event.clipboardData);
      if (files.length > 0) {
        event.preventDefault();
        void addFiles(files);
        return;
      }
      if (!isTextField) {
        const pasted = event.clipboardData?.getData("text/plain")?.trim();
        if (pasted && pasted.length > 40) {
          event.preventDefault();
          setText((current) => (current ? `${current}\n${pasted}` : pasted));
        }
      }
    };
    window.addEventListener("paste", onPaste);
    return () => window.removeEventListener("paste", onPaste);
  }, [addFiles, phase]);

  const removeImage = (id: string) => {
    imagesRef.current = imagesRef.current.filter((image) => image.id !== id);
    setImages((current) => current.filter((image) => image.id !== id));
  };
  const removeDocument = (id: string) => {
    documentsRef.current = documentsRef.current.filter((entry) => entry.id !== id);
    setDocuments((current) => current.filter((entry) => entry.id !== id));
  };

  const readyDocuments = documents.filter((entry) => entry.status === "ready" && entry.extracted);
  const documentsBusy = documents.some((entry) => entry.status === "extracting");
  const documentImages = readyDocuments.flatMap((entry) => entry.extracted!.images);
  const documentText = documentsToText(readyDocuments.map((entry) => entry.extracted!));

  const totalBytes = images.reduce((sum, image) => sum + image.bytes, 0);
  const hasContent =
    images.length > 0 || documentImages.length > 0 || text.trim().length > 0 || documentText.trim().length > 0;
  const canGenerate = hasContent && !documentsBusy && phase !== "preparing";
  const imagesToSend = [...images.map((image) => image.dataUrl), ...documentImages.map((image) => image.dataUrl)].slice(
    0,
    MAX_IMAGES_TO_SEND,
  );
  const imagesSkipped =
    images.length + documentImages.length - imagesToSend.length;

  const generate = async () => {
    if (!canGenerate) return;
    setError(null);
    setPhase("loading");
    setProgress({
      stage: imagesToSend.length ? "vision" : "generation",
      message: imagesToSend.length ? t("upload.vision1") : t("upload.gen1"),
    });

    const controller = new AbortController();
    abortRef.current = controller;

    const mergedText = [text.trim(), documentText.trim()].filter(Boolean).join("\n\n").slice(0, MAX_TEXT_TO_SEND);

    try {
      const { deck } = await generateDeck(
        {
          images: imagesToSend.length ? imagesToSend : undefined,
          text: mergedText || undefined,
          focus: focus.trim() || undefined,
          difficulty,
          count,
        },
        { onProgress: setProgress, signal: controller.signal },
      );

      const now = Date.now();
      const stored = {
        ...deck,
        id: uid("deck"),
        folderId: targetFolder,
        createdAt: now,
        updatedAt: now,
        attempts: 0,
      };
      upsertDeck(stored);
      router.push(`/deck/${stored.id}`);
    } catch (generateError) {
      setError({
        message:
          generateError instanceof ApiError
            ? generateError.message
            : t("upload.genericError"),
        kind: generateError instanceof ApiError ? generateError.kind : undefined,
      });
      setPhase("error");
    } finally {
      abortRef.current = null;
    }
  };

  if (phase === "loading") {
    return <LoadingState progress={progress} onCancel={() => abortRef.current?.abort()} />;
  }

  return (
    <div className="relative">
      <div className="relative space-y-5">
        <section className="space-y-2">
          <h1 className="flex flex-wrap items-center gap-x-3 gap-y-1 text-[28px] font-semibold leading-tight tracking-[-0.02em] text-[var(--text)] text-balance sm:text-[32px]">
            <SnowflakeIcon className="size-8 shrink-0 text-frost-500 dark:text-frost-200" />
            <span>{t("upload.title")}</span>
          </h1>
          <p className="max-w-xl text-[15px] text-frost-600 dark:text-frost-300">
            {t("upload.intro")}
          </p>
        </section>

        {/* The other thing you can bring here: an assignment. */}
        <Link
          href="/homework"
          className="card card-hover flex items-center gap-3 p-4 text-left"
        >
          <span
            aria-hidden
            className="grid size-10 shrink-0 place-items-center rounded-xl bg-[var(--surface-sunken)] text-[var(--text-muted)]"
          >
            <SparklesIcon className="size-5" />
          </span>
          <span className="min-w-0 flex-1">
            <span className="block text-[14px] font-semibold text-[var(--text)]">{t("homework.entry")}</span>
            <span className="block text-[12.5px] text-[var(--text-subtle)]">{t("homework.nav")} →</span>
          </span>
          <ChevronRightIcon className="size-4 shrink-0 text-[var(--text-subtle)]" />
        </Link>


        {error ? (
          <div
            role="alert"
            className="animate-rise rounded-3xl border-2 border-rose-300 bg-rose-50/95 p-4 text-sm text-rose-900 dark:border-rose-400/40 dark:bg-rose-400/10 dark:text-rose-100"
          >
            <p className="font-bold">
              {error.kind === "needs_key"
                ? t("upload.errNeedsKey")
                : error.kind === "rate_limited"
                  ? t("upload.errRate")
                  : error.kind === "auth"
                    ? t("upload.errAuth")
                    : t("upload.errFailed")}
            </p>
            <p className="mt-1">{error.message}</p>
            <div className="mt-3 flex flex-wrap gap-2">
              {error.kind === "needs_key" || error.kind === "auth" ? (
                <Button size="sm" onClick={openSettings}>
                  {t("upload.openSettings")}
                </Button>
              ) : null}
              <Button size="sm" variant={error.kind === "needs_key" || error.kind === "auth" ? "secondary" : "primary"} onClick={() => void generate()}>
                {t("common.retry")}
              </Button>
            </div>
          </div>
        ) : null}

        {/* ---------------------------------------------------------- */}
        <section
          aria-label={t("upload.addPhotosAria")}
          onDragOver={(event) => {
            event.preventDefault();
            setDragging(true);
          }}
          onDragLeave={() => setDragging(false)}
          onDrop={(event) => {
            event.preventDefault();
            setDragging(false);
            void addFiles(imageFilesFromDataTransfer(event.dataTransfer));
          }}
          className={cn(
            "card relative overflow-hidden p-4 transition-all sm:p-5",
            dragging && "border-frost-400 bg-frost-50 ring-4 ring-frost-200 dark:bg-frost-500/10 dark:ring-frost-500/30",
          )}
        >
          <div className="flex flex-wrap items-center justify-between gap-3">
            <div>
              <h2 className="text-[15px] font-semibold tracking-[-0.01em] text-[var(--text)]">{t("upload.step1")}</h2>
              <p className="text-[12.5px] text-[var(--text-subtle)]">
                {t("upload.step1Help", { images: MAX_IMAGES, documents: MAX_DOCUMENTS })}
              </p>
            </div>
            <div className="flex flex-wrap gap-2">
              <Button variant="secondary" size="sm" onClick={() => fileInputRef.current?.click()}>
                <FolderIcon className="size-4" /> {t("upload.chooseFiles")}
              </Button>
              <Button variant="secondary" size="sm" onClick={() => cameraInputRef.current?.click()}>
                <CameraIcon className="size-4" /> {t("upload.camera")}
              </Button>
            </div>
          </div>

          <input
            ref={fileInputRef}
            type="file"
            accept={`${ACCEPTED_TYPES.join(",")},${DOCUMENT_ACCEPT_ATTR}`}
            multiple
            className="sr-only"
            onChange={(event) => {
              void addFiles(Array.from(event.target.files ?? []));
              event.target.value = "";
            }}
          />
          <input
            ref={cameraInputRef}
            type="file"
            accept="image/*"
            capture="environment"
            className="sr-only"
            onChange={(event) => {
              void addFiles(Array.from(event.target.files ?? []));
              event.target.value = "";
            }}
          />

          {images.length === 0 ? (
            <button
              type="button"
              onClick={() => fileInputRef.current?.click()}
              className="mt-4 flex w-full flex-col items-center gap-2 rounded-2xl border-2 border-dashed border-white/70 bg-white/40 px-4 py-10 text-center backdrop-blur-xl transition hover:border-accent-300 hover:bg-white/65 dark:border-white/15 dark:bg-white/[0.05] dark:hover:bg-white/[0.09]"
            >
              <span aria-hidden className="animate-float text-frost-500 dark:text-frost-200">
                <SnowflakeIcon className="size-12" />
              </span>
              <span className="text-[14px] font-medium text-[var(--text)]">
                {t("upload.dropHere")}
              </span>
              <span className="text-[12.5px] text-[var(--text-subtle)]">
                {t("upload.formats")}
              </span>
            </button>
          ) : (
            <ul className="mt-4 grid grid-cols-3 gap-2 sm:grid-cols-4">
              {images.map((image) => (
                <li key={image.id} className="group relative overflow-hidden rounded-2xl border border-frost-200 dark:border-white/15">
                  {/* eslint-disable-next-line @next/next/no-img-element */}
                  <img
                    src={image.dataUrl}
                    alt={image.name}
                    className="aspect-square w-full object-cover"
                  />
                  <button
                    type="button"
                    onClick={() => removeImage(image.id)}
                    aria-label={t("upload.remove", { name: image.name })}
                    className="absolute right-1 top-1 grid size-7 place-items-center rounded-full bg-frost-950/70 text-xs font-bold text-white transition hover:bg-rose-600"
                  >
                    ✕
                  </button>
                  <span className="absolute inset-x-0 bottom-0 bg-frost-950/60 px-2 py-1 text-[10px] font-semibold text-white">
                    {formatBytes(image.bytes)}
                  </span>
                </li>
              ))}
              {images.length < MAX_IMAGES ? (
                <li>
                  <button
                    type="button"
                    onClick={() => fileInputRef.current?.click()}
                    className="grid aspect-square w-full place-items-center rounded-2xl border-2 border-dashed border-white/70 text-2xl text-accent-500 backdrop-blur-xl transition hover:border-accent-300 hover:bg-white/60 dark:border-white/15 dark:text-accent-200"
                    aria-label={t("upload.addMorePhotos")}
                  >
                    +
                  </button>
                </li>
              ) : null}
            </ul>
          )}

          {documents.length > 0 ? (
            <ul className="mt-3 space-y-2">
              {documents.map((entry) => (
                <li
                  key={entry.id}
                  className="flex items-start gap-3 rounded-2xl border border-white/60 bg-white/50 p-3 backdrop-blur-xl dark:border-white/12 dark:bg-white/[0.06]"
                >
                  <span className="grid size-10 shrink-0 place-items-center rounded-xl bg-frost-100 text-[10px] font-extrabold uppercase tracking-wide text-frost-700 dark:bg-white/10 dark:text-frost-100">
                    {KIND_LABELS[entry.kind]}
                  </span>
                  <div className="min-w-0 flex-1">
                    <p className="truncate text-sm font-semibold text-[var(--text)]" title={entry.name}>
                      {entry.name}
                    </p>
                    {entry.status === "extracting" ? (
                      <p className="text-xs font-medium text-frost-700 dark:text-frost-200">
                        {entry.progress ?? t("upload.reading")}
                      </p>
                    ) : null}
                    {entry.status === "error" ? (
                      <p className="text-xs font-medium text-rose-600 dark:text-rose-300">{entry.error}</p>
                    ) : null}
                    {entry.status === "ready" && entry.extracted ? (
                      <>
                        <p className="text-[12.5px] text-[var(--text-subtle)]">
                          {describeExtraction(entry.extracted, t, plural)}
                        </p>
                        {entry.extracted.words === 0 && entry.extracted.images.length === 0 ? (
                          <p className="text-xs font-medium text-amber-700 dark:text-amber-300">
                            {t("upload.noReadable")}
                          </p>
                        ) : null}
                        {entry.extracted.warnings.map((warning) => (
                          <p key={warning} className="text-[12.5px] text-[var(--text-subtle)]">
                            ⓘ {warning}
                          </p>
                        ))}
                      </>
                    ) : null}
                  </div>
                  <button
                    type="button"
                    onClick={() => removeDocument(entry.id)}
                    aria-label={t("upload.remove", { name: entry.name })}
                    className="grid size-7 shrink-0 place-items-center rounded-full bg-frost-950/10 text-xs font-bold text-frost-900 transition hover:bg-rose-500 hover:text-white dark:bg-white/10 dark:text-frost-50"
                  >
                    ✕
                  </button>
                </li>
              ))}
            </ul>
          ) : null}

          {images.length > 0 || documents.length > 0 ? (
            <p className="mt-2 text-[12.5px] text-[var(--text-subtle)]">
              {images.length > 0
                ? plural(images.length, "upload.photoSummary", { size: formatBytes(totalBytes) })
                : ""}
              {images.length > 0 && documents.length > 0 ? " · " : ""}
              {documents.length > 0
                ? `${plural(documents.length, "upload.docSummary")}${
                    documentImages.length
                      ? ` (${plural(documentImages.length, "upload.docImages")})`
                      : ""
                  }`
                : ""}
              {imagesSkipped > 0
                ? ` · ${plural(imagesSkipped, "upload.skipImages", { max: MAX_IMAGES_TO_SEND })}`
                : ""}
            </p>
          ) : null}

          {phase === "preparing" ? (
            <p className="mt-2 text-[12.5px] font-medium text-[var(--text-muted)]">{t("upload.compressing")}</p>
          ) : null}
          {fileError ? (
            <p role="alert" className="mt-2 text-xs font-semibold text-rose-600 dark:text-rose-300">
              {fileError}
            </p>
          ) : null}
        </section>

        {/* ---------------------------------------------------------- */}
        <section className="card space-y-4 p-4 sm:p-5">
          <div>
            <h2 className="text-[15px] font-semibold tracking-[-0.01em] text-[var(--text)]">{t("upload.step2")}</h2>
            <p className="text-[12.5px] text-[var(--text-subtle)]">
              {t("upload.step2Help")}
            </p>
          </div>

          <div className="space-y-1.5">
            <label htmlFor="notes-text" className="text-[11px] font-semibold uppercase tracking-wide text-[var(--text-subtle)]">
              {t("upload.pastedNotes")}
            </label>
            <textarea
              id="notes-text"
              value={text}
              onChange={(event) => setText(event.target.value)}
              rows={4}
              placeholder={t("upload.pastedPlaceholder")}
              className="w-full resize-y rounded-2xl border border-white/60 bg-white/55 px-4 py-3 text-sm text-frost-950 outline-none backdrop-blur-xl transition placeholder:text-frost-400 focus:border-accent-400 dark:border-white/12 dark:bg-white/[0.07] dark:text-frost-50"
            />
          </div>

          <div className="space-y-1.5">
            <label htmlFor="focus" className="text-[11px] font-semibold uppercase tracking-wide text-[var(--text-subtle)]">
              {t("upload.topicHint")}
            </label>
            <input
              id="focus"
              value={focus}
              onChange={(event) => setFocus(event.target.value)}
              placeholder={t("upload.topicPlaceholder")}
              className="w-full rounded-2xl border border-white/60 bg-white/55 px-4 py-3 text-sm text-frost-950 outline-none backdrop-blur-xl transition placeholder:text-frost-400 focus:border-accent-400 dark:border-white/12 dark:bg-white/[0.07] dark:text-frost-50"
            />
          </div>
        </section>

        {/* ---------------------------------------------------------- */}
        <section className="card space-y-4 p-4 sm:p-5">
          <h2 className="text-[15px] font-semibold tracking-[-0.01em] text-[var(--text)]">{t("upload.step3")}</h2>

          <div className="space-y-2">
            <span className="text-[11px] font-semibold uppercase tracking-wide text-[var(--text-subtle)]">
              {t("upload.freezeInto")}
            </span>
            <div className="flex flex-wrap items-center gap-2">
              {[{ id: UNORGANIZED_ID, name: t("common.unorganized") }, ...sortedFolders].map((folder) => {
                const active = folderId === folder.id;
                return (
                  <button
                    key={folder.id}
                    type="button"
                    aria-pressed={active}
                    onClick={() => setFolderId(folder.id)}
                    className={cn(
                      "inline-flex items-center gap-1.5 rounded-full border px-3.5 py-1.5 text-[13px] font-medium transition",
                      active
                        ? "border-accent-500 bg-accent-50 text-accent-800 dark:bg-accent-500/20 dark:text-accent-100"
                        : "border-[var(--hairline)] text-frost-600 hover:text-frost-900 dark:text-frost-300 dark:hover:text-white",
                    )}
                  >
                    <FolderIcon className="size-4" />
                    {folder.name}
                  </button>
                );
              })}
              {creatingFolder ? (
                <span className="inline-flex items-center gap-1">
                  <input
                    autoFocus
                    value={folderDraft}
                    onChange={(event) => setFolderDraft(event.target.value)}
                    onKeyDown={(event) => {
                      event.stopPropagation();
                      if (event.key === "Escape") {
                        setCreatingFolder(false);
                        setFolderDraft("");
                      }
                      if (event.key === "Enter") {
                        const created = createFolder(folderDraft);
                        if ("folder" in created) {
                          setFolderId(created.folder.id);
                          setFolderDraft("");
                          setCreatingFolder(false);
                        } else {
                          setFileError(created.error);
                        }
                      }
                    }}
                    aria-label={t("common.newFolderName")}
                    placeholder={t("upload.folderPlaceholder")}
                    maxLength={60}
                    className="w-32 rounded-xl border border-[var(--hairline)] bg-[var(--surface-strong)] px-3 py-1.5 text-sm outline-none"
                  />
                  <Button
                    size="sm"
                    onClick={() => {
                      const created = createFolder(folderDraft);
                      if ("folder" in created) {
                        setFolderId(created.folder.id);
                        setFolderDraft("");
                        setCreatingFolder(false);
                      } else {
                        setFileError(created.error);
                      }
                    }}
                  >
                    {t("common.add")}
                  </Button>
                </span>
              ) : (
                <button
                  type="button"
                  onClick={() => setCreatingFolder(true)}
                  className="inline-flex items-center gap-1.5 rounded-xl border border-dashed border-[var(--hairline)] px-3 py-1.5 text-sm font-semibold text-frost-500 transition-colors hover:text-accent-700 dark:text-frost-400 dark:hover:text-accent-200"
                >
                  <PlusIcon className="size-4" /> {t("common.newFolder")}
                </button>
              )}
            </div>
          </div>

          <div role="radiogroup" aria-label={t("upload.difficultyAria")} className="grid grid-cols-3 gap-2">
            {DIFFICULTIES.map((option) => {
              const selected = difficulty === option.value;
              return (
                <button
                  key={option.value}
                  type="button"
                  role="radio"
                  aria-checked={selected}
                  onClick={() => setDifficulty(option.value)}
                  className={cn(
                    "flex flex-col items-center gap-1 rounded-2xl border px-2 py-3 text-center backdrop-blur-xl transition-colors",
                    selected
                      ? "border-accent-400 bg-accent-50/80 shadow-lift dark:bg-accent-500/20"
                      : "border-white/60 bg-white/45 backdrop-blur-xl hover:bg-white/70 dark:border-white/12 dark:bg-white/[0.05]",
                  )}
                >
                  <span aria-hidden className="text-frost-600 dark:text-frost-200">
                    {option.icon}
                  </span>
                  <span className="text-sm font-bold text-[var(--text)]">{t(option.labelKey)}</span>
                  <span className="hidden text-[11px] text-frost-500 sm:block dark:text-frost-400">{t(option.blurbKey)}</span>
                </button>
              );
            })}
          </div>

          <div className="flex flex-wrap items-center gap-2">
            <span className="text-[11px] font-semibold uppercase tracking-wide text-[var(--text-subtle)]">
              {t("upload.activities")}
            </span>
            {COUNT_OPTIONS.map((option) => (
              <button
                key={option}
                type="button"
                aria-pressed={count === option}
                onClick={() => setCount(option)}
                className={cn(
                  "min-w-12 rounded-xl border-2 px-3 py-1.5 text-sm font-bold transition",
                  count === option
                    ? "grad-ice border-transparent text-[#06111f]"
                    : "border-[var(--hairline)] text-[var(--text-muted)] hover:bg-[var(--hover)]",
                )}
              >
                {option}
              </button>
            ))}
          </div>
        </section>

        <div className="sticky bottom-[calc(env(safe-area-inset-bottom,0px)+4.6rem)] z-20 -mx-4 border-t border-[var(--hairline)] bg-white/65 px-4 py-3 backdrop-blur-2xl dark:bg-[color-mix(in_oklab,var(--surface)_70%,transparent)] sm:bottom-0 sm:mx-0 sm:rounded-[1.35rem] sm:border sm:px-5">
          <div className="flex flex-wrap items-center justify-between gap-3">
            <p className="text-[12.5px] text-[var(--text-subtle)]">
              {documentsBusy
                ? t("upload.readingDocs")
                : hasContent
                  ? t("upload.ready")
                  : t("upload.addToStart")}
            </p>
            <div className="flex flex-wrap gap-2">
              <Button size="lg" onClick={() => void generate()} disabled={!canGenerate}>
                <SnowflakeIcon className="size-5" /> {t("upload.freezeDeck")}
              </Button>
            </div>
          </div>
        </div>
      </div>
    </div>
  );
}

/* ------------------------------------------------------------------ */
/* Loading state                                                       */
/* ------------------------------------------------------------------ */

const STAGE_STEPS: Array<{ stage: GenerateProgress["stage"]; keys: string[] }> = [
  { stage: "vision", keys: ["upload.vision1", "upload.vision2", "upload.vision3"] },
  { stage: "generation", keys: ["upload.gen1", "upload.gen2", "upload.gen3"] },
];

function LoadingState({ progress, onCancel }: { progress: GenerateProgress; onCancel: () => void }) {
  const { t } = useI18n();
  const [tick, setTick] = useState(0);
  const [tip, setTip] = useState(0);

  useEffect(() => {
    const timer = window.setInterval(() => setTick((value) => value + 1), 3200);
    return () => window.clearInterval(timer);
  }, []);

  useEffect(() => {
    setTip(Math.floor(Math.random() * GENERATION_TIPS.length));
  }, []);

  const activeIndex = progress.stage === "vision" ? 0 : 1;
  const keys = STAGE_STEPS[activeIndex].keys;
  const message = progress.message && tick === 0 ? progress.message : t(keys[tick % keys.length]);

  return (
    <div className="relative flex min-h-[70dvh] flex-col items-center justify-center gap-6 text-center">
      <motion.div
        aria-hidden
        animate={{ rotate: [0, 8, -8, 0], scale: [1, 1.08, 1] }}
        transition={{ duration: 3.2, repeat: Infinity, ease: "easeInOut" }}
        className="relative grid size-28 place-items-center rounded-[1.75rem] bg-accent-600 text-white shadow-lift"
      >
        <SnowflakeIcon className="size-16" />
      </motion.div>

      <div className="relative w-full max-w-md space-y-3">
        <p className="text-xl font-extrabold text-[var(--text)]" aria-live="polite">
          {message}
        </p>
        <ProgressBar value={activeIndex + 1} max={2} label={t("upload.generationProgress")} />
        <ol className="space-y-1 text-left text-[14.5px] leading-relaxed text-[var(--text-muted)]">
          {STAGE_STEPS.map((step, index) => (
            <li key={step.stage} className="flex items-center gap-2">
              <span aria-hidden>
                {index < activeIndex ? "✅" : index === activeIndex ? "🌀" : "⬜"}
              </span>
              {t(step.keys[0])}
            </li>
          ))}
        </ol>
        <p className="pt-2 text-[12.5px] text-[var(--text-subtle)]">{t(GENERATION_TIPS[tip])}</p>
        <Button variant="ghost" size="sm" onClick={onCancel}>
          {t("upload.cancel")}
        </Button>
      </div>
    </div>
  );
}