"use client";

/**
 * Full-data backup: one JSON file with decks, folders, homework, progress and
 * safe settings — **never the API key**. Import validates with zod, shows a
 * preview of what will be added or replaced, and offers merge or replace.
 *
 * The same payload shape is what encrypted sync uploads (minus settings), so
 * the two features share this file's validation.
 */

import { z } from "zod";

import { applyTheme } from "./theme";
import { chatHistoryStore, ensureChatsHydrated, replaceChats } from "./chat-store";
import { replaceFolders, folderStore } from "./folders";
import { homeworkStore, replaceHomework } from "./homework";
import { ensureLearningHydrated, learningStore, replaceLearning } from "./history";
import { setLocale, t } from "./i18n";
import { folderSchema, deckSchema, homeworkRecordSchema, answerRecordSchema, srsRecordSchema, chatConversationSchema } from "./schemas";
import { saveSettings, settingsStore } from "./settings";
import { deckStore, replaceDecks } from "./storage";

export const BACKUP_VERSION = 1;

const settingsSchema = z.object({
  haptics: z.boolean().optional(),
  locale: z.enum(["en", "cs"]).optional(),
  theme: z.enum(["light", "dark"]).optional(),
  dailyGoal: z.number().int().min(1).max(500).optional(),
});

export const backupDataSchema = z.object({
  decks: z.array(deckSchema).max(2000),
  folders: z.array(folderSchema).max(500),
  homework: z.array(homeworkRecordSchema).max(2000),
  /** Answer log and SRS schedule (IndexedDB). Optional for old backups. */
  history: z.array(answerRecordSchema).max(20_000).optional(),
  srs: z.array(srsRecordSchema).max(50_000).optional(),
  /** Chat conversations (IndexedDB). Optional for old backups. */
  chats: z.array(chatConversationSchema).max(100).optional(),
});

export const backupSchema = z.object({
  app: z.literal("freezmo"),
  kind: z.literal("backup"),
  version: z.literal(1),
  exportedAt: z.string(),
  data: backupDataSchema.extend({ settings: settingsSchema.optional() }),
});

export type BackupFile = z.infer<typeof backupSchema>;

/* ------------------------------------------------------------------ */
/* Building and downloading                                            */
/* ------------------------------------------------------------------ */

export async function buildBackup(): Promise<BackupFile> {
  await ensureLearningHydrated();
  await ensureChatsHydrated();
  return {
    app: "freezmo",
    kind: "backup",
    version: BACKUP_VERSION,
    exportedAt: new Date().toISOString(),
    data: {
      decks: deckStore.getSnapshot(),
      folders: folderStore.getSnapshot(),
      homework: homeworkStore.getSnapshot(),
      history: learningStore.getAnswersSnapshot(),
      srs: learningStore.getSrsSnapshot(),
      chats: chatHistoryStore.getSnapshot(),
      settings: {
        haptics: settingsStore.getSnapshot().haptics,
        dailyGoal: settingsStore.getSnapshot().dailyGoal,
        locale: (window.localStorage.getItem("freezmo.locale.v1") as "en" | "cs" | null) ?? undefined,
        theme: (window.localStorage.getItem("freezmo.theme") as "light" | "dark" | null) ?? undefined,
      },
    },
  };
}

export async function downloadBackup(): Promise<BackupFile> {
  const backup = await buildBackup();
  const blob = new Blob([JSON.stringify(backup, null, 2)], { type: "application/json" });
  const url = URL.createObjectURL(blob);
  const anchor = document.createElement("a");
  anchor.href = url;
  anchor.download = `freezmo-backup-${new Date().toISOString().slice(0, 10)}.json`;
  document.body.appendChild(anchor);
  anchor.click();
  anchor.remove();
  URL.revokeObjectURL(url);
  markBackedUp(backup.data.decks.length);
  return backup;
}

/* ------------------------------------------------------------------ */
/* Parsing, previewing, applying                                       */
/* ------------------------------------------------------------------ */

export function parseBackup(raw: string): { backup: BackupFile } | { error: string } {
  let parsed: unknown;
  try {
    parsed = JSON.parse(raw);
  } catch {
    return { error: t("import.notJson") };
  }
  const result = backupSchema.safeParse(parsed);
  if (!result.success) return { error: t("import.notBackup") };
  return { backup: result.data };
}

export type ImportCounts = { added: number; replaced: number };

function countMerge<T extends { id: string }>(current: T[], incoming: T[]): ImportCounts {
  const ids = new Set(current.map((item) => item.id));
  let added = 0;
  let replaced = 0;
  for (const item of incoming) {
    if (ids.has(item.id)) replaced += 1;
    else added += 1;
  }
  return { added, replaced };
}

function mergeById<T extends { id: string }>(current: T[], incoming: T[]): T[] {
  const positions = new Map(current.map((item, index) => [item.id, index]));
  const merged = [...current];
  for (const item of incoming) {
    const at = positions.get(item.id);
    if (at === undefined) {
      positions.set(item.id, merged.length);
      merged.push(item);
    } else {
      merged[at] = item;
    }
  }
  return merged;
}

export type ImportPreview = {
  decks: ImportCounts;
  folders: ImportCounts;
  homework: ImportCounts;
  chats: ImportCounts;
};

export function previewImport(backup: BackupFile): ImportPreview {
  return {
    decks: countMerge(deckStore.getSnapshot(), backup.data.decks),
    folders: countMerge(folderStore.getSnapshot(), backup.data.folders),
    homework: countMerge(homeworkStore.getSnapshot(), backup.data.homework),
    chats: countMerge(chatHistoryStore.getSnapshot(), backup.data.chats ?? []),
  };
}

/** Applies a backup; the API key is never touched (it is not in the file). */
export async function applyImport(
  backup: BackupFile,
  mode: "merge" | "replace",
): Promise<{ decks: number; homework: number }> {
  const data = backup.data;
  const decks =
    mode === "replace" ? data.decks : mergeById(deckStore.getSnapshot(), data.decks);
  const folders =
    mode === "replace" ? data.folders : mergeById(folderStore.getSnapshot(), data.folders);
  const homework =
    mode === "replace" ? data.homework : mergeById(homeworkStore.getSnapshot(), data.homework);

  // Folders first so imported decks can point at them. Importing is a real
  // local change, so it also marks sync dirty (via the stores' write()).
  replaceFolders(folders);
  replaceDecks(decks);
  replaceHomework(homework);

  // Answer log + schedule: merge by id (answers) and by key (schedules).
  await ensureLearningHydrated();
  const incomingAnswers = data.history ?? [];
  const incomingSrs = data.srs ?? [];
  if (incomingAnswers.length > 0 || incomingSrs.length > 0) {
    const currentAnswers = learningStore.getAnswersSnapshot();
    const currentSrs = learningStore.getSrsSnapshot();
    const answers =
      mode === "replace" ? incomingAnswers : mergeById(currentAnswers, incomingAnswers);
    const srsByKey = new Map(currentSrs.map((entry) => [entry.key, entry]));
    for (const entry of incomingSrs) {
      const current = srsByKey.get(entry.key);
      if (!current || current.lastAt < entry.lastAt) srsByKey.set(entry.key, entry);
    }
    await replaceLearning(answers, [...srsByKey.values()]);
  }

  // Chat conversations: merge by id (newest wins) or replace wholesale.
  await ensureChatsHydrated();
  const incomingChats = data.chats ?? [];
  if (incomingChats.length > 0) {
    replaceChats(mode === "replace" ? incomingChats : mergeById(chatHistoryStore.getSnapshot(), incomingChats));
  }

  const settings = data.settings;
  if (settings) {
    if (typeof settings.haptics === "boolean") saveSettings({ haptics: settings.haptics });
    if (typeof settings.dailyGoal === "number") saveSettings({ dailyGoal: settings.dailyGoal });
    if (settings.locale) setLocale(settings.locale);
    if (settings.theme) applyTheme(settings.theme);
  }

  return { decks: decks.length, homework: homework.length };
}

/* ------------------------------------------------------------------ */
/* Backup nudge                                                        */
/* ------------------------------------------------------------------ */

const BACKUP_STATE_KEY = "freezmo.backup.v1";
const NUDGE_DAYS = 14;
const NUDGE_DECKS = 5;

type BackupState = {
  lastBackupAt: number | null;
  decksAtLastBackup: number;
  snoozedUntil: number | null;
};

const EMPTY_STATE: BackupState = { lastBackupAt: null, decksAtLastBackup: 0, snoozedUntil: null };

function readBackupState(): BackupState {
  try {
    const raw = window.localStorage.getItem(BACKUP_STATE_KEY);
    if (!raw) return EMPTY_STATE;
    const parsed = JSON.parse(raw) as Partial<BackupState>;
    return {
      lastBackupAt: typeof parsed.lastBackupAt === "number" ? parsed.lastBackupAt : null,
      decksAtLastBackup: typeof parsed.decksAtLastBackup === "number" ? parsed.decksAtLastBackup : 0,
      snoozedUntil: typeof parsed.snoozedUntil === "number" ? parsed.snoozedUntil : null,
    };
  } catch {
    return EMPTY_STATE;
  }
}

function writeBackupState(next: BackupState): void {
  try {
    window.localStorage.setItem(BACKUP_STATE_KEY, JSON.stringify(next));
  } catch {
    /* private mode */
  }
}

export function markBackedUp(deckCount: number): void {
  writeBackupState({ lastBackupAt: Date.now(), decksAtLastBackup: deckCount, snoozedUntil: null });
}

export function snoozeBackupNudge(): void {
  const state = readBackupState();
  writeBackupState({ ...state, snoozedUntil: Date.now() + NUDGE_DAYS * 86_400_000 });
}

export function backupNudgeDue(deckCount: number): boolean {
  if (deckCount < 2) return false;
  const state = readBackupState();
  if (state.snoozedUntil && state.snoozedUntil > Date.now()) return false;
  if (state.lastBackupAt === null) return deckCount >= NUDGE_DECKS;
  if (Date.now() - state.lastBackupAt > NUDGE_DAYS * 86_400_000) return true;
  return deckCount >= state.decksAtLastBackup + NUDGE_DECKS;
}

export function lastBackupAt(): number | null {
  return readBackupState().lastBackupAt;
}

/* ------------------------------------------------------------------ */
/* Storage persistence                                                 */
/* ------------------------------------------------------------------ */

export type PersistenceState = "persistent" | "best-effort" | "unsupported";

export async function getStoragePersistence(): Promise<PersistenceState> {
  try {
    if (!navigator.storage?.persisted) return "unsupported";
    return (await navigator.storage.persisted()) ? "persistent" : "best-effort";
  } catch {
    return "unsupported";
  }
}

export async function requestStoragePersistence(): Promise<boolean> {
  try {
    if (!navigator.storage?.persist) return false;
    return await navigator.storage.persist();
  } catch {
    return false;
  }
}