"use client";

/**
 * Folder library, stored next to the decks in localStorage.
 *
 * Folders are pure organisation: deleting one never deletes decks, it just
 * moves them back to "Unorganized". The virtual folder `UNORGANIZED_ID` is
 * never persisted — it is simply every deck with no `folderId`.
 */

import { t } from "./i18n";
import { folderSchema, UNORGANIZED_ID, type Folder } from "./schemas";
import { uid } from "./utils";

const STORAGE_KEY = "freezmo.folders.v1";
const EMPTY: Folder[] = [];

type Listener = () => void;

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

function read(): Folder[] {
  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: Folder[] = [];
    for (const entry of parsed) {
      const result = folderSchema.safeParse(entry);
      if (result.success) valid.push(result.data);
      else console.warn("[freezmo] skipping invalid folder", result.error.issues);
    }
    return valid;
  } catch (error) {
    console.warn("[freezmo] could not read folders", error);
    return EMPTY;
  }
}

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

function write(next: Folder[]): void {
  folders = next;
  cached = next;
  try {
    window.localStorage.setItem(STORAGE_KEY, JSON.stringify(next));
  } catch (error) {
    console.warn("[freezmo] could not save folders", error);
  }
  listeners.forEach((listener) => listener());
}

export const folderStore = {
  subscribe(listener: Listener): () => void {
    ensureLoaded();
    listeners.add(listener);
    const onStorage = (event: StorageEvent) => {
      if (event.key === STORAGE_KEY) {
        folders = null;
        ensureLoaded();
        listeners.forEach((l) => l());
      }
    };
    window.addEventListener("storage", onStorage);
    return () => {
      listeners.delete(listener);
      window.removeEventListener("storage", onStorage);
    };
  },
  getSnapshot(): Folder[] {
    ensureLoaded();
    return cached;
  },
  getServerSnapshot(): Folder[] {
    return EMPTY;
  },
};

/* ------------------------------------------------------------------ */
/* Queries                                                             */
/* ------------------------------------------------------------------ */

export function listFolders(): Folder[] {
  return [...folderStore.getSnapshot()].sort((a, b) =>
    a.name.localeCompare(b.name, undefined, { sensitivity: "base" }),
  );
}

export function getFolder(id: string | undefined): Folder | undefined {
  if (!id || id === UNORGANIZED_ID) return undefined;
  return folderStore.getSnapshot().find((folder) => folder.id === id);
}

export function folderName(id: string | undefined): string {
  if (!id || id === UNORGANIZED_ID) return t("common.unorganized");
  return getFolder(id)?.name ?? t("common.unorganized");
}

export function findFolderByName(name: string): Folder | undefined {
  const wanted = name.trim().toLowerCase();
  return folderStore.getSnapshot().find((folder) => folder.name.trim().toLowerCase() === wanted);
}

/** Case-insensitive uniqueness; returns the existing folder when it matches. */
export function createFolder(name: string): { folder: Folder } | { error: string } {
  const trimmed = name.trim().replace(/\s+/g, " ");
  if (!trimmed) return { error: t("folder.nameRequired") };
  if (trimmed.length > 60) return { error: t("folder.nameTooLong") };

  const existing = findFolderByName(trimmed);
  if (existing) return { folder: existing };

  const folder: Folder = { id: uid("fold"), name: trimmed, createdAt: Date.now() };
  ensureLoaded();
  write([...folderStore.getSnapshot(), folder]);
  return { folder };
}

export function renameFolder(id: string, name: string): { ok: true } | { error: string } {
  const trimmed = name.trim().replace(/\s+/g, " ");
  if (!trimmed) return { error: t("folder.nameRequired") };
  const clash = folderStore
    .getSnapshot()
    .find((folder) => folder.id !== id && folder.name.trim().toLowerCase() === trimmed.toLowerCase());
  if (clash) return { error: t("folder.nameTaken") };

  ensureLoaded();
  write(folderStore.getSnapshot().map((folder) => (folder.id === id ? { ...folder, name: trimmed } : folder)));
  return { ok: true };
}

/** Removes the folder. Decks inside it are handed back to the caller to re-home. */
export function removeFolder(id: string): void {
  ensureLoaded();
  write(folderStore.getSnapshot().filter((folder) => folder.id !== id));
}

/** Deleting a folder must never delete decks: callers pair this with unfileDecks(). */
export function hasFolder(id: string): boolean {
  return Boolean(getFolder(id));
}

export function emptyFolder(): void {
  ensureLoaded();
  write([]);
}