import { useSyncExternalStore } from 'react';
import { AppState } from 'react-native';
import { isNewerVersion, type AppUpdateDTO } from '@musicshare/shared';
import Updater, { type InstallStatus } from '@/modules/updater';
import { api } from './api';
import { FOSS_BUILD } from './build';

/**
 * Self-updating for the APKs we publish (not F-Droid builds, which F-Droid updates, nor dev builds).
 *
 * When the app opens (at most every few hours) it asks the server for the newest release and, if
 * it's newer, downloads it in the background and checks its SHA-256. Then:
 *  - leaving the app tries a quiet install, once per version. Android 12+ allows that once this app has
 *    installed an update itself (and "install unknown apps" is allowed for it); the new version runs next
 *    time it's opened. On phones with Google Play, Play Protect may still ask to scan a new version.
 *  - otherwise the feed shows "Update ready", and tapping it opens Android's install screen.
 */
export const updaterAvailable = Updater !== null && !FOSS_BUILD && !__DEV__;

export type UpdateState =
  | { status: 'idle' | 'checking' | 'upToDate' }
  | { status: 'downloading'; update: AppUpdateDTO; progress: number }
  | { status: 'ready' | 'installing'; update: AppUpdateDTO; path: string }
  | { status: 'error'; message: string; update?: AppUpdateDTO };

const CHECK_EVERY_MS = 6 * 3600_000;

let state: UpdateState = { status: 'idle' };
let lastCheck = 0;
/** Versions we've already tried to install on the way out; after that, only when asked (no repeat prompts). */
const autoTried = new Set<string>();
const listeners = new Set<() => void>();

function set(next: UpdateState) {
  // Visible with `adb logcat -s ReactNativeJS`, for checking updates on a real phone.
  if (next.status !== state.status) console.log(`[updates] ${next.status}${'message' in next ? `: ${next.message}` : ''}`);
  state = next;
  listeners.forEach((l) => l());
}

export const currentVersion = () => Updater?.currentVersion() ?? null;

/** Look for an update and download it. `force` skips the every-few-hours limit (the Settings button). */
export async function checkForUpdate({ force = false } = {}): Promise<void> {
  if (!Updater || !updaterAvailable) return;
  if (['checking', 'downloading', 'installing'].includes(state.status)) return;
  if (state.status === 'ready') return; // already have it
  if (!force && Date.now() - lastCheck < CHECK_EVERY_MS) return;
  lastCheck = Date.now();

  set({ status: 'checking' });
  let update: AppUpdateDTO | null;
  try {
    update = await api.androidUpdate();
  } catch {
    set({ status: 'error', message: "Couldn't check for updates." });
    return;
  }
  if (!update || !isNewerVersion(update.version, Updater.currentVersion())) {
    Updater.clearDownloads(); // e.g. the update we downloaded has since been installed
    set({ status: 'upToDate' });
    return;
  }

  set({ status: 'downloading', update, progress: 0 });
  const progress = Updater.addListener('onProgress', ({ received, total }) => {
    if (state.status === 'downloading') set({ ...state, progress: total > 0 ? received / total : 0 });
  });
  try {
    const path = await Updater.download(update.apkUrl, update.sha256, `musicshare-${update.version}.apk`);
    set({ status: 'ready', update, path });
  } catch (err) {
    set({ status: 'error', message: err instanceof Error ? err.message : "Couldn't download the update.", update });
  } finally {
    progress.remove();
  }
}

/** Install the downloaded update. `interactive` shows Android's confirmation screen if it needs one. */
export async function installUpdate(interactive: boolean): Promise<void> {
  if (!Updater || state.status !== 'ready') return;
  const ready = state;
  set({ ...ready, status: 'installing' });
  try {
    await Updater.install(ready.path, interactive);
  } catch (err) {
    set({ status: 'error', message: err instanceof Error ? err.message : "Couldn't install the update.", update: ready.update });
    lastCheck = 0; // e.g. the download went missing: fetch it again next time
  }
}

function onInstallStatus(status: InstallStatus, message: string | null) {
  if (state.status !== 'installing') return;
  const { update, path } = state;
  switch (status) {
    case 'waiting':
      return; // Android's screen is up; its answer comes next
    case 'needs_user':
    case 'cancelled':
      return set({ status: 'ready', update, path });
    case 'installed':
      return set({ status: 'upToDate' });
    case 'failed':
      return set({ status: 'error', message: message ?? "Couldn't install the update.", update });
  }
}

let started = false;

/** Call once at startup: checks now, again when the app comes back, and tries a quiet install on the way out. */
export function startUpdater() {
  if (started || !Updater || !updaterAvailable) return;
  started = true;
  Updater.addListener('onInstallStatus', ({ status, message }) => onInstallStatus(status, message));
  AppState.addEventListener('change', (appState) => {
    if (appState === 'active') checkForUpdate().catch(() => {});
    else if (appState === 'background' && state.status === 'ready' && !autoTried.has(state.update.version)) {
      autoTried.add(state.update.version);
      installUpdate(false).catch(() => {});
    }
  });
  checkForUpdate().catch(() => {});
}

export function useUpdateState(): UpdateState {
  return useSyncExternalStore(
    (listener) => {
      listeners.add(listener);
      return () => listeners.delete(listener);
    },
    () => state,
  );
}