tefter/frontend/src/sync/engine.ts

import { writable, get } from 'svelte/store';
import type { PushResult, Revision, ServerNote, SyncState } from '../types';
import { notes, settings, cursor, setCursor, applyServerNotes, markPushed, replaceWithServer } from '../db/store';

export const syncState = writable<SyncState>('local');
export const lastSyncAt = writable<number | null>(null);
export const syncError = writable<string>('');

let editTimer: ReturnType<typeof setTimeout> | null = null;
let interval: ReturnType<typeof setInterval> | null = null;
let running = false;
let queued = false;

function configured(): boolean {
  const s = get(settings);
  return !!s.serverUrl;
}

function api(path: string, init: RequestInit = {}): Promise<Response> {
  const s = get(settings);
  const base = s.serverUrl.replace(/\/+$/, '');
  return fetch(base + path, {
    ...init,
    headers: {
      ...(init.headers || {}),
      Authorization: 'Bearer ' + s.token,
      'Content-Type': 'application/json',
    },
  });
}

async function pull(): Promise<void> {
  for (;;) {
    const since = get(cursor);
    const res = await api(`/api/v1/changes?since=${since}&limit=500`);
    if (!res.ok) throw new Error(`pull: HTTP ${res.status}`);
    const body: { notes: ServerNote[]; cursor: number; more: boolean } = await res.json();
    await applyServerNotes(body.notes);
    if (body.cursor > since) await setCursor(body.cursor);
    if (!body.more) break;
  }
}

async function push(): Promise<void> {
  const dirty = [...get(notes).values()].filter((n) => n.dirty);
  if (!dirty.length) return;
  const payload = dirty.map((n) => ({
    id: n.id,
    content: n.content,
    tags: n.tags,
    created_at: n.created_at,
    modified_at: n.modified_at,
    deleted: n.deleted,
    baseVersion: n.baseVersion,
  }));
  const res = await api('/api/v1/notes/batch', { method: 'POST', body: JSON.stringify({ notes: payload }) });
  if (!res.ok) throw new Error(`push: HTTP ${res.status}`);
  const body: { results: PushResult[] } = await res.json();
  const sentAt = new Map(dirty.map((n) => [n.id, n.modified_at]));
  for (const r of body.results) {
    if (r.status === 'accepted' && r.version) {
      await markPushed(r.id, sentAt.get(r.id) ?? 0, r.version);
    } else if (r.status === 'conflict' && r.serverNote) {
      await replaceWithServer(r.serverNote); // conflict copy arrives on next pull
    }
  }
}

/** Fetch a note's server-side revision history (newest first). */
export async function fetchHistory(id: string): Promise<Revision[]> {
  if (!configured()) throw new Error('no server configured');
  const res = await api(`/api/v1/notes/${encodeURIComponent(id)}/history`);
  if (!res.ok) throw new Error(`history: HTTP ${res.status}`);
  const body: { revisions: Revision[] } = await res.json();
  return body.revisions;
}

/** Pull-then-push; safe to interrupt at any point (SPEC §4). */
export async function syncNow(): Promise<void> {
  if (!configured()) {
    syncState.set('local');
    return;
  }
  if (running) {
    queued = true;
    return;
  }
  running = true;
  syncState.set('syncing');
  try {
    await pull();
    await push();
    await pull(); // pick up conflict copies + versions created by our own push
    syncState.set(navigator.onLine ? 'synced' : 'offline');
    lastSyncAt.set(Date.now());
    syncError.set('');
  } catch (e) {
    syncState.set(navigator.onLine ? 'error' : 'offline');
    syncError.set(e instanceof Error ? e.message : String(e));
  } finally {
    running = false;
    if (queued) {
      queued = false;
      void syncNow();
    }
  }
}

/** Debounced trigger: sync 3 s after the last edit (SPEC §4 client loop). */
export function notifyEdit(): void {
  if (!configured()) return;
  if (editTimer) clearTimeout(editTimer);
  editTimer = setTimeout(() => void syncNow(), 3000);
}

export function startSync(): void {
  window.addEventListener('online', () => void syncNow());
  window.addEventListener('offline', () => syncState.set('offline'));
  if (interval) clearInterval(interval);
  interval = setInterval(() => void syncNow(), 60_000);
  void syncNow();
}