/**
 * Settings persistence.
 *
 * Settings live at `/.sys/config.json` on the WebDAV server. The bundled
 * `config.json` is used as the initial value while the file is being
 * fetched, and as a fallback if the server is unreachable.
 *
 * The `useSettings()` hook returns the same `(config, setConfig)` shape
 * the page components already use, but every change is also persisted
 * to the WebDAV server after a short debounce.
 */

import { useCallback, useEffect, useRef, useState } from 'react';
import bundledConfig from '../imports/config.json';
import {
  createFolder,
  getFileContents,
  putFileContents,
  stat,
} from './webdav';

/** The canonical paths on the WebDAV server. */
export const SETTINGS_PATH = '/.sys/config.json';
export const DEVICES_PATH  = '/.sys/devices.json';
const SETTINGS_DIR = '/.sys';
const SD_SYS_DIR   = '/sd/.sys';

/**
 * How long to wait after the last change before writing to disk.
 *
 * The debounce timer is reset on every change, so this is effectively
 * "the number of milliseconds the user must be idle before the change
 * is committed". Bump this up to give the user more time to make
 * multiple related edits; lower it to write changes more eagerly.
 */
export const SAVE_IDLE_MS = 3000;

/** How long the "Saved" indicator lingers before fading out. */
const SAVED_INDICATOR_MS = 1500;

export type SettingsConfig = Record<string, any>;

/** Try primary path first, fall back to secondary. Returns null if both fail. */
async function getTextWithFallback(primary: string, fallback: string): Promise<string | null> {
  try { return await getFileContents(primary).then(b => b.text()); } catch { /* try fallback */ }
  try { return await getFileContents(fallback).then(b => b.text()); } catch { /* both failed */ }
  return null;
}

/** Read both config files from the WebDAV server and merge them. Returns null on failure. */
export async function readSettings(): Promise<SettingsConfig | null> {
  try {
    // Mirror firmware priority: /sd/.sys/ first, fall back to /.sys/
    const [configText, devicesText] = await Promise.all([
      getTextWithFallback('/sd' + SETTINGS_PATH, SETTINGS_PATH),
      getTextWithFallback('/sd' + DEVICES_PATH,  DEVICES_PATH),
    ]);
    if (!configText) return null;
    const config = JSON.parse(configText);
    if (!config || typeof config !== 'object') return null;
    if (devicesText) {
      const devices = JSON.parse(devicesText);
      if (devices && typeof devices === 'object') {
        // One-level deep merge: devices.json keys are merged into matching
        // top-level objects in config (e.g. devices.iec.devices → config.iec.devices).
        for (const [k, v] of Object.entries(devices)) {
          if (config[k] && typeof config[k] === 'object' && !Array.isArray(config[k]) &&
              v          && typeof v          === 'object' && !Array.isArray(v)) {
            config[k] = { ...config[k], ...(v as object) };
          } else {
            config[k] = v;
          }
        }
      }
    }
    return config as SettingsConfig;
  } catch {
    return null;
  }
}

/**
 * Persist the settings object to the WebDAV server, creating the
 * containing `/.sys/` directory if needed. Pretty-prints with 2-space
 * indentation so the file is diff-friendly.
 */
export async function writeSettings(config: SettingsConfig): Promise<void> {
  try { await createFolder(SETTINGS_DIR, true); } catch { /* exists */ }

  const { iec, ...mainConfig } = config;
  const { devices: iecDevices, ...iecBusConfig } = (iec ?? {}) as any;
  const configJson  = JSON.stringify({ ...mainConfig, iec: iecBusConfig }, null, 2) + '\n';
  const devicesJson = JSON.stringify({ iec: { devices: iecDevices } },     null, 2) + '\n';

  await Promise.all([
    putFileContents(SETTINGS_PATH, configJson),
    putFileContents(DEVICES_PATH,  devicesJson),
  ]);

  // Mirror to /sd/.sys/ if the SD card is mounted.
  try {
    const sdStat = await stat('/sd');
    if (sdStat) {
      try { await createFolder(SD_SYS_DIR, true); } catch { /* exists */ }
      await Promise.all([
        putFileContents(SD_SYS_DIR + '/config.json',  configJson),
        putFileContents(SD_SYS_DIR + '/devices.json', devicesJson),
      ]);
    }
  } catch { /* /sd unreachable — skip mirror */ }
}

export type SaveStatus =
  | 'idle'        // nothing to do
  | 'loading'     // initial fetch from server
  | 'unsaved'     // one or more changes pending; waiting for the idle timer
  | 'saving'      // a write is currently in flight
  | 'saved'       // last write succeeded (fades back to 'idle' shortly)
  | 'error';      // last write failed; will retry on the next change

export interface UseSettingsResult {
  config: SettingsConfig;
  setConfig: (next: SettingsConfig | ((prev: SettingsConfig) => SettingsConfig)) => void;
  /** Whether the initial load from the server has completed. */
  loaded: boolean;
  /** Current save status (see {@link SaveStatus}). */
  saveStatus: SaveStatus;
  /** Number of pending (uncommitted) changes since the last successful save. */
  pendingCount: number;
  /** Force a re-fetch from the server and replace local state. */
  reload: () => Promise<void>;
  /** Flush any pending changes immediately, ignoring the idle timer. */
  flushNow: () => Promise<void>;
}

/**
 * React hook that loads settings from the WebDAV server on mount and
 * auto-saves them on every change (debounced).
 *
 * Behavior:
 *  - State is initialised with the bundled `config.json` so the UI
 *    renders immediately, even before the server is contacted.
 *  - On mount, an async fetch replaces state with the server's copy.
 *  - On every `setConfig`, a debounced write fires `SAVE_DEBOUNCE_MS`
 *    after the most recent change.
 *  - On `beforeunload`, any pending change is flushed synchronously
 *    (best-effort: `sendBeacon` cannot be used with WebDAV, so the page
 *    may be allowed to close only if the user agrees via the browser's
 *    default "Leave site?" dialog).
 */
export function useSettings(): UseSettingsResult {
  const [config, setConfigState] = useState<SettingsConfig>(bundledConfig as SettingsConfig);
  const [loaded, setLoaded] = useState(false);
  const [saveStatus, setSaveStatus] = useState<SaveStatus>('loading');
  const [pendingCount, setPendingCount] = useState(0);

  // Refs so the debounced writer always sees the latest values without
  // needing to re-subscribe on every render.
  const configRef = useRef<SettingsConfig>(config);
  const loadedRef = useRef<boolean>(false);
  const timerRef = useRef<number | null>(null);
  const dirtyRef = useRef<boolean>(false);
  const pendingRef = useRef<number>(0);
  const savedTimerRef = useRef<number | null>(null);

  const load = useCallback(async () => {
    setSaveStatus('loading');
    const fromServer = await readSettings();
    if (fromServer) {
      configRef.current = fromServer;
      setConfigState(fromServer);
    }
    loadedRef.current = true;
    setLoaded(true);
    setSaveStatus('idle');
  }, []);

  useEffect(() => {
    void load();
  }, [load]);

  const flushNow = useCallback(async () => {
    if (timerRef.current !== null) {
      window.clearTimeout(timerRef.current);
      timerRef.current = null;
    }
    if (savedTimerRef.current !== null) {
      window.clearTimeout(savedTimerRef.current);
      savedTimerRef.current = null;
    }
    if (!dirtyRef.current) return;
    dirtyRef.current = false;
    const pending = pendingRef.current;
    pendingRef.current = 0;
    setPendingCount(0);
    setSaveStatus('saving');
    try {
      await writeSettings(configRef.current);
      setSaveStatus('saved');
      // Drop the "saved" badge after a short delay so it doesn't linger.
      savedTimerRef.current = window.setTimeout(() => {
        setSaveStatus((s) => (s === 'saved' ? 'idle' : s));
      }, SAVED_INDICATOR_MS);
    } catch (e) {
      // Roll back: the change is still pending.
      dirtyRef.current = true;
      pendingRef.current = pending;
      setPendingCount(pending);
      setSaveStatus('error');
      // Re-throw so the caller can handle it if they want.
      throw e;
    }
  }, []);

  // Flush on tab close (best effort; most browsers will block until the
  // fetch completes if it can).
  useEffect(() => {
    const onBeforeUnload = (e: BeforeUnloadEvent) => {
      if (!dirtyRef.current) return;
      // Modern browsers: `fetch` with `keepalive: true` continues even
      // after the page is being unloaded. We don't await it.
      try {
        const { iec, ...mainConfig } = configRef.current;
        const { devices: iecDevices, ...iecBusConfig } = (iec ?? {}) as any;
        void fetch(absoluteUrl(SETTINGS_PATH), {
          method: 'PUT',
          body: JSON.stringify({ ...mainConfig, iec: iecBusConfig }, null, 2) + '\n',
          headers: { 'Content-Type': 'application/json' },
          keepalive: true,
        });
        void fetch(absoluteUrl(DEVICES_PATH), {
          method: 'PUT',
          body: JSON.stringify({ iec: { devices: iecDevices } }, null, 2) + '\n',
          headers: { 'Content-Type': 'application/json' },
          keepalive: true,
        });
      } catch {
        /* ignore */
      }
      e.preventDefault();
      e.returnValue = '';
    };
    window.addEventListener('beforeunload', onBeforeUnload);
    return () => window.removeEventListener('beforeunload', onBeforeUnload);
  }, []);

  const setConfig = useCallback(
    (next: SettingsConfig | ((prev: SettingsConfig) => SettingsConfig)) => {
      const value = typeof next === 'function'
        ? (next as (p: SettingsConfig) => SettingsConfig)(configRef.current)
        : next;
      configRef.current = value;
      setConfigState(value);
      dirtyRef.current = true;
      pendingRef.current += 1;
      setPendingCount(pendingRef.current);
      setSaveStatus('unsaved');
      if (timerRef.current !== null) {
        window.clearTimeout(timerRef.current);
      }
      // Reset the idle timer: save `SAVE_IDLE_MS` after the most recent
      // change. Every additional change resets the timer again.
      timerRef.current = window.setTimeout(() => {
        void flushNow();
      }, SAVE_IDLE_MS);
    },
    [flushNow],
  );

  return {
    config,
    setConfig,
    loaded,
    saveStatus,
    pendingCount,
    reload: load,
    flushNow,
  };
}

function absoluteUrl(path: string): string {
  return `${window.location.protocol}//${window.location.hostname}${
    window.location.port ? ':' + window.location.port : ''
  }${path}`;
}