// Photo backup: this phone's photos sent to `<folder>/<account>-photos` of the
// destination every backup shares (sync-destination.js), once a day, on an
// unmetered network (docs/MESHBAY_DESIGN.md §9.12).
//
// The phone (platform.photoSync) lists the photos, keeps the ledger of what was
// sent and hands each photo's bytes over; this module decides when a run is
// due and does the sending, because the transport and the group key are here.
// Loaded only where the bridge offers it — the Android application — so no
// browser and no desktop pays for it.
//
// Additive by construction: nothing here deletes, renames or replaces anything
// on the node. `test_photo_sync.py` reads this file for the operations that
// would, and refuses them.

import { ConnectionPool } from './connection-pool.js';
import * as platform from './platform.js';
import { t } from './i18n.js';
import { setSyncContext, checkDestination } from './sync-destination.js';

const DAY_MS = 24 * 3600 * 1000;
// A run cut short by something passing — the node offline, the network gone —
// is tried again at the next chance, but not more often than this: every
// return to the foreground would otherwise be a connection attempt.
const RETRY_MS = 15 * 60 * 1000;
// A slot the node keeps queued this long means it is busy with others; the
// backup can wait for tomorrow's run, they cannot.
const LEASE_WAIT_MS = 10 * 60 * 1000;

// Refusals that will hold at the next run too. Said once (a notification, from
// the phone) and retried a day later, never at every opening.
const LASTING = {
  disk_full: 'photosync.fail_disk_full',
  root_read_only: 'photosync.fail_read_only',
  no_writable_root: 'photosync.fail_read_only',
  no_such_root: 'photosync.fail_no_folder',
  no_such_directory: 'photosync.fail_no_folder',
  root_unavailable: 'photosync.fail_unavailable',
  not_a_member: 'photosync.fail_not_member',
  not_private: 'photosync.fail_not_private',
  permission: 'photosync.fail_permission',
};

// ── A runner, for photos here and for chosen folders (drive-sync.js) ────────

/**
 * One backup's scheduling and sending: what is due, when, on which network,
 * a file at a time under a slot, the ledger kept by the phone (`sync`, its
 * bridge object). `configured(status)` says whether the person turned it on;
 * `progress` is the notification line's key; `failures` holds the refusals
 * that will hold tomorrow too, and `say(code)` the words for one.
 */
export function createBackup({
  name, sync, configured, progress, failures, say,
}) {
  let state = { phase: 'idle', done: 0, total: 0 };
  const listeners = new Set();
  let ctx = null;          // { hub, hubFetch, getUser, getBundleKey }
  let running = null;
  let timer = 0;
  let lastAttempt = 0;
  let unmeteredNow = null;

  // ── What the settings section shows ───────────────────────────────────────

  function setState(patch) {
    state = { ...state, ...patch };
    for (const fn of [...listeners]) {
      try { fn(state); } catch (e) { console.error(`[MeshBay] ${name} backup listener threw:`, e); }
    }
  }

  function subscribe(fn) {
    listeners.add(fn);
    fn(state);
    return () => listeners.delete(fn);
  }

  // ── When it runs ──────────────────────────────────────────────────────────

  /** True when `status` says a scheduled run should go now. */
  function isDue(status, now = Date.now()) {
    if (!status || !configured(status) || !status.destination) return false;
    // A lasting refusal waits a day, like a finished run; anything else is
    // decided by the last run that finished.
    if (status.failure && status.failureAt && now - status.failureAt < DAY_MS) return false;
    const last = status.lastCompleted;
    return last == null || now - last >= DAY_MS || now < last;
  }

  /**
   * Checked at start, on coming back to the foreground, when the network turns
   * unmetered, and once the next run falls due. Nothing polls.
   */
  function start(context) {
    if (!sync.available || ctx) return;
    ctx = context;
    setSyncContext(context);
    document.addEventListener('visibilitychange', onVisible);
    window.addEventListener('meshbay-network', onNetwork);
    runNow();
  }

  function stop() {
    if (!ctx) return;
    ctx = null;
    clearTimeout(timer);
    document.removeEventListener('visibilitychange', onVisible);
    window.removeEventListener('meshbay-network', onNetwork);
  }

  function onVisible() {
    if (document.visibilityState === 'visible') runNow();
  }

  function onNetwork(e) {
    unmeteredNow = !!(e.detail && e.detail.unmetered);
    if (unmeteredNow) runNow();
  }

  function scheduleNext(status) {
    clearTimeout(timer);
    if (!ctx || !status || !configured(status) || !status.destination) return;
    const base = Math.max(status.lastCompleted || 0, status.failure ? (status.failureAt || 0) : 0);
    const wait = base + DAY_MS - Date.now();
    // A page left open past midnight runs on time; the cap keeps a timer from
    // being parked for days on a clock that may move.
    if (wait > 0) timer = setTimeout(runNow, Math.min(wait, DAY_MS));
  }

  /**
   * A run, if one is due. `force` is "Back up now": due or not. `metered` is the
   * person's yes to sending over mobile data, asked by the caller.
   */
  function runNow({ force = false, metered = false } = {}) {
    if (!ctx) return Promise.resolve();
    if (running) return running;
    running = (async () => {
      let status = null;
      try {
        status = await sync.status();
        await run(status, force, metered);
        status = await sync.status();
      } catch (e) {
        console.warn(`[MeshBay] ${name} backup:`, e.message);
        setState({ phase: 'interrupted', detail: e.message });
      } finally {
        running = null;
        scheduleNext(status);
      }
    })();
    return running;
  }

  async function run(status, force, metered) {
    const dest = status.destination;
    const user = ctx && ctx.getUser();
    if (!configured(status) || !dest) { setState({ phase: 'off' }); return; }
    if (!user || dest.account !== user.username) { setState({ phase: 'other_account' }); return; }
    if (status.permission === 'denied') { await lasting('permission'); return; }
    if (!force && !isDue(status)) {
      setState({ phase: status.failure ? 'failed' : 'up_to_date', reason: status.failure || '' });
      return;
    }
    unmeteredNow = status.unmetered;
    if (!status.unmetered && !metered) { setState({ phase: 'waiting_wifi' }); return; }
    if (!force && Date.now() - lastAttempt < RETRY_MS) return;
    lastAttempt = Date.now();

    // Before anything is read: still this account's own group, and nobody else's.
    setState({ phase: 'connecting', done: 0, total: 0 });
    const refused = await checkDestination(dest, user);
    if (refused === 'offline') { setState({ phase: 'offline' }); return; }
    if (refused) { await lasting(refused); return; }

    const { items, manifest } = await sync.plan();
    if (!items.length && !manifest) {
      await sync.completed();
      setState({ phase: 'up_to_date', done: 0, total: 0 });
      return;
    }

    setState({ phase: 'connecting', done: 0, total: items.length });
    const pool = new ConnectionPool(ctx.hub);
    let conn;
    try {
      const bundleKey = await ctx.getBundleKey();
      conn = await pool.connect(dest.groupId, user.token, bundleKey, user.username, user.userId);
    } catch (e) {
      pool.closeAll();
      if (e.reason === 'not_a_member') { await lasting('not_a_member'); return; }
      setState({ phase: 'offline' });
      return;
    }

    try {
      await send(conn.transport, dest, items, metered);
    } finally {
      sync.keepAlive(false).catch(() => {});
      pool.closeAll();
    }
  }

  async function send(transport, dest, items, metered) {
    const index = await transport.fetchIndex();
    const problem = destinationProblem(dest.folder, index);
    if (problem) { await lasting(problem); return; }

    // What is already in each folder, by name and size: after a reinstall the
    // ledger is empty, and a photo already there is recorded, not sent again.
    const present = new Map();
    for (const e of index.entries || []) {
      if (!present.has(e.path)) present.set(e.path, new Map());
      present.get(e.path).set(e.name, e.size);
    }
    const dirs = new Set(index.dirs || []);
    for (const r of index.roots || []) dirs.add(r.name);

    let done = 0;
    const report = () => {
      setState({ phase: 'sending', done, total: items.length });
      return t(progress, { done, total: items.length });
    };
    await sync.keepAlive(true, report());

    for (const item of items) {
      // Off Wi-Fi mid-run: stop after the file in flight. The node keeps the
      // partial upload, and the next unmetered moment carries on.
      if (!metered && unmeteredNow === false) { setState({ phase: 'waiting_wifi' }); return; }
      if (!ctx) return;

      const there = present.get(item.dir);
      const known = there && [item.name, item.alsoKnownAs]
        .find((n) => n && there.get(n) === item.size);
      if (known) {
        await sync.sent(item.token, item.dir, known);
      } else {
        try {
          await makeDirs(transport, dest.folder, item.dir, dirs);
          const ack = await upload(transport, item, sync.file);
          await sync.sent(item.token, ack.dir || item.dir, ack.stored_as || item.name);
        } catch (e) {
          if (e.code && failures[e.code]) { await lasting(e.code); return; }
          throw e;
        }
      }
      done += 1;
      await sync.keepAlive(true, report());
    }
    if (!await sendManifest(transport, dest, dirs)) return;
    await sync.completed();
    setState({ phase: 'up_to_date', done, total: items.length });
  }

  // What the phone knew of what was sent (its path and album, its dates and
  // hash), for a restore or a merge later: one file per run that sent
  // anything, beside the files, kept by the phone until the node has it.
  // False when a lasting refusal stopped it, which is then said.
  async function sendManifest(transport, dest, dirs) {
    const { item } = await sync.manifest();
    if (!item) return true;
    try {
      await makeDirs(transport, dest.folder, item.dir, dirs);
      await upload(transport, item, sync.file);
    } catch (e) {
      if (e.code && failures[e.code]) { await lasting(e.code); return false; }
      throw e;
    }
    await sync.manifestSent(item.token);
    return true;
  }

  async function lasting(code) {
    setState({ phase: 'failed', reason: code });
    await sync.failed(code, say(code)).catch(() => {});
  }

  return { start, stop, run: runNow, subscribe, isDue };
}

const photos = createBackup({
  name: 'photo',
  sync: platform.photoSync,
  configured: (status) => Boolean(status.config),
  progress: 'photosync.notif_progress',
  failures: LASTING,
  say: (code) => t(LASTING[code] || 'photosync.fail_other'),
});

export const startPhotoSync = (context) => photos.start(context);
export const stopPhotoSync = () => photos.stop();
export const runPhotoSync = (opts) => photos.run(opts);
export const subscribe = (fn) => photos.subscribe(fn);
export const isDue = (status, now) => photos.isDue(status, now);

/**
 * One photo, under a slot the node granted: the backup queues like anyone.
 * `file` is how its bytes come from the phone; contacts and messages pass theirs.
 */
export async function upload(transport, item, file = platform.photoSync.file) {
  const lease = transport.openTransfer({ kind: 'upload', bytes: item.size });
  try {
    let timeout;
    await Promise.race([
      lease.acquire(),
      new Promise((_, reject) => {
        timeout = setTimeout(() => reject(new Error('The node is busy')), LEASE_WAIT_MS);
      }),
    ]).finally(() => clearTimeout(timeout));
    const bytes = await file(item.token, item.name, item.size);
    return await transport.uploadFile(bytes, {
      dir: item.dir, root: item.dir.split('/')[0], tr: lease.tr,
    });
  } finally {
    lease.release();
  }
}

/** `<folder>/<account>-photos/YYYY/YYYY-MM`, one level at a time; a level that exists is fine. */
export async function makeDirs(transport, folder, dir, dirs) {
  let at = folder;
  for (const name of dir.slice(folder.length + 1).split('/').filter(Boolean)) {
    const next = `${at}/${name}`;
    if (!dirs.has(next)) {
      try {
        await transport.createDirectory(at, name);
      } catch (e) {
        // Somebody else's backup made it a moment ago: what was wanted.
        if (!/already exists/i.test(e.message || '')) throw e;
      }
      dirs.add(next);
    }
    at = next;
  }
}

/** A reason the chosen folder cannot take photos now, or null. */
export function destinationProblem(folder, index) {
  const root = (index.roots || []).find((r) => r.name === folder.split('/')[0]);
  if (!root) return 'no_such_root';
  if (!root.writable) return 'root_read_only';
  if (root.available === false) return 'root_unavailable';
  if (folder !== root.name && !(index.dirs || []).includes(folder)) return 'no_such_directory';
  return null;
}