"use client";

/**
 * Deck library backed by localStorage. No accounts, no server state.
 * Exposes a tiny observable store so every screen stays in sync.
 */

import { t } from "./i18n";
import { deckSchema, UNORGANIZED_ID, type Activity, type Deck } from "./schemas";
import { createFolder, findFolderByName, getFolder, removeFolder } from "./folders";
import { markSyncDirty } from "./sync-state";
import { uid } from "./utils";

const STORAGE_KEY = "freezmo.decks.v1";
const EMPTY: Deck[] = [];

type Listener = () => void;

let decks: Deck[] | null = null;
let cached: Deck[] = EMPTY;
const listeners = new Set<Listener>();

function read(): Deck[] {
  if (typeof window === "undefined") return EMPTY;
  try {
    const raw = window.localStorage.getItem(STORAGE_KEY);
    if (!raw) return EMPTY;
    const parsed: unknown = JSON.parse(raw);
    if (!Array.isArray(parsed)) return EMPTY;
    const valid: Deck[] = [];
    for (const entry of parsed) {
      const result = deckSchema.safeParse(entry);
      if (result.success) valid.push(result.data);
      else console.warn("[freezmo] skipping invalid deck in storage", result.error.issues);
    }
    return valid;
  } catch (error) {
    console.warn("[freezmo] could not read the deck library", error);
    return EMPTY;
  }
}

function ensureLoaded(): void {
  if (decks !== null) return;
  decks = read();
  cached = decks;
}

function write(next: Deck[]): void {
  decks = next;
  cached = next;
  try {
    window.localStorage.setItem(STORAGE_KEY, JSON.stringify(next));
  } catch (error) {
    console.warn("[freezmo] could not save the deck library (storage full?)", error);
  }
  /* A deck change (add, edit, delete, import) with sync on pushes itself. */
  if (markSyncDirty()) void import("./sync-auto").then((module) => module.scheduleAutoSync());
  listeners.forEach((listener) => listener());
}

/** Used by backup import and sync: wholesale replacement of the library. */
export function replaceDecks(next: Deck[]): void {
  const valid: Deck[] = [];
  for (const entry of next) {
    const result = deckSchema.safeParse(entry);
    if (result.success) valid.push(result.data);
    else console.warn("[freezmo] skipping invalid deck in import", result.error.issues);
  }
  write(valid);
}

export const deckStore = {
  subscribe(listener: Listener): () => void {
    ensureLoaded();
    listeners.add(listener);
    // Another tab may have changed the library.
    const onStorage = (event: StorageEvent) => {
      if (event.key === STORAGE_KEY) {
        decks = null;
        ensureLoaded();
        listeners.forEach((l) => l());
      }
    };
    window.addEventListener("storage", onStorage);
    return () => {
      listeners.delete(listener);
      window.removeEventListener("storage", onStorage);
    };
  },
  getSnapshot(): Deck[] {
    ensureLoaded();
    return cached;
  },
  getServerSnapshot(): Deck[] {
    return EMPTY;
  },
};

/** Newest first. */
export function sortDecks(list: Deck[]): Deck[] {
  return [...list].sort((a, b) => b.updatedAt - a.updatedAt);
}

export function getDeck(id: string): Deck | undefined {
  return deckStore.getSnapshot().find((deck) => deck.id === id);
}

export function upsertDeck(deck: Deck): void {
  ensureLoaded();
  const current = deckStore.getSnapshot();
  const index = current.findIndex((entry) => entry.id === deck.id);
  const next = index === -1 ? [deck, ...current] : current.map((entry) => (entry.id === deck.id ? deck : entry));
  write(next);
}

export function renameDeck(id: string, title: string): void {
  ensureLoaded();
  write(deckStore.getSnapshot().map((deck) => (deck.id === id ? { ...deck, title, updatedAt: Date.now() } : deck)));
}

export function deleteDeck(id: string): void {
  ensureLoaded();
  write(deckStore.getSnapshot().filter((deck) => deck.id !== id));
}

/**
 * Removes the stored notes text from a deck (the deck and its activities stay).
 * Used by "Delete notes text" — the notes live in the deck record because
 * Regenerate needs them; chat reads them from here too.
 */
export function deleteNotesText(id: string): void {
  ensureLoaded();
  write(
    deckStore.getSnapshot().map((deck) =>
      deck.id === id ? { ...deck, sourceText: "", updatedAt: Date.now() } : deck,
    ),
  );
}

export function recordAttempt(
  id: string,
  result: { scorePercent: number; correct: number; total: number },
): void {
  ensureLoaded();
  write(
    deckStore.getSnapshot().map((deck) =>
      deck.id === id
        ? {
            ...deck,
            attempts: deck.attempts + 1,
            bestScore: Math.max(deck.bestScore ?? 0, Math.round(result.scorePercent)),
            updatedAt: Date.now(),
          }
        : deck,
    ),
  );
}

/** Move a deck into a folder (pass undefined/UNORGANIZED_ID for "Unorganized"). */
export function moveDeck(id: string, folderId: string | undefined): void {
  ensureLoaded();
  const target = !folderId || folderId === UNORGANIZED_ID ? undefined : folderId;
  write(
    deckStore.getSnapshot().map((deck) =>
      deck.id === id ? { ...deck, folderId: target, updatedAt: Date.now() } : deck,
    ),
  );
}

/** Used when a folder is deleted: every deck inside goes back to Unorganized. */
export function unfileDecks(folderId: string): void {
  ensureLoaded();
  write(
    deckStore.getSnapshot().map((deck) =>
      deck.folderId === folderId ? { ...deck, folderId: undefined, updatedAt: Date.now() } : deck,
    ),
  );
}

/** Deletes a folder for good — its decks always survive in "Unorganized". */
export function deleteFolder(folderId: string): void {
  unfileDecks(folderId);
  removeFolder(folderId);
}

export function countDecksInFolder(folderId: string): number {
  ensureLoaded();
  if (folderId === UNORGANIZED_ID) return deckStore.getSnapshot().filter((deck) => !deck.folderId).length;
  return deckStore.getSnapshot().filter((deck) => deck.folderId === folderId).length;
}

export function appendActivities(id: string, activities: Activity[], title?: string): void {
  ensureLoaded();
  write(
    deckStore.getSnapshot().map((deck) =>
      deck.id === id
        ? {
            ...deck,
            title: title ?? deck.title,
            activities: [...deck.activities, ...activities],
            updatedAt: Date.now(),
          }
        : deck,
    ),
  );
}

/* ------------------------------------------------------------------ */
/* Import / export                                                     */
/* ------------------------------------------------------------------ */

export type ExportBundle = {
  app: "freezmo";
  version: 1;
  exportedAt: string;
  /** Folder name travels with the deck so imports land in the right place. */
  folder?: string | null;
  deck: Deck;
};

export function exportDeck(deck: Deck): string {
  const bundle: ExportBundle = {
    app: "freezmo",
    version: 1,
    exportedAt: new Date().toISOString(),
    folder: folderNameOf(deck),
    deck,
  };
  return JSON.stringify(bundle, null, 2);
}

function folderNameOf(deck: Deck): string | null {
  if (!deck.folderId) return null;
  return getFolder(deck.folderId)?.name ?? null;
}

export function downloadDeck(deck: Deck): void {
  const blob = new Blob([exportDeck(deck)], { type: "application/json" });
  const url = URL.createObjectURL(blob);
  const anchor = document.createElement("a");
  anchor.href = url;
  anchor.download = `${deck.title.replace(/[^a-z0-9]+/gi, "-").toLowerCase() || "freezmo-deck"}.json`;
  document.body.appendChild(anchor);
  anchor.click();
  anchor.remove();
  URL.revokeObjectURL(url);
}

/** Accepts a Freezmo export bundle or a bare deck object. */
export function importDeck(raw: string): { deck: Deck } | { error: string } {
  let parsed: unknown;
  try {
    parsed = JSON.parse(raw);
  } catch {
    return { error: t("import.notJson") };
  }

  const bundle = parsed && typeof parsed === "object" && "deck" in parsed ? (parsed as { folder?: unknown }) : null;
  const candidate = bundle ? (parsed as { deck: unknown }).deck : parsed;

  const result = deckSchema.safeParse(candidate);
  if (!result.success) {
    return { error: t("import.notDeck") };
  }

  // Recreate the exported folder (or reuse an existing one with the same name).
  let folderId: string | undefined;
  const folderName = typeof bundle?.folder === "string" ? bundle.folder.trim() : "";
  if (folderName) {
    const existing = findFolderByName(folderName);
    if (existing) {
      folderId = existing.id;
    } else {
      const created = createFolder(folderName);
      folderId = "folder" in created ? created.folder.id : undefined;
    }
  }

  const now = Date.now();
  const deck: Deck = {
    ...result.data,
    folderId,
    id: uid("deck"),
    createdAt: now,
    updatedAt: now,
    attempts: 0,
    bestScore: undefined,
  };
  upsertDeck(deck);
  return { deck };
}