/**
 * Todoist background sync scheduler (Issue #22).
 *
 * Periodically fetches Todoist tasks for every user with an active token so
 * that signals are fresh before the next /recommend call. The on-demand fetch
 * in TodoistSignalSource remains as the freshness-critical fallback — if a user
 * hits /recommend and the cache is stale, it re-fetches inline.
 *
 * Interval: TODOIST_SYNC_INTERVAL_MS (default 15 min).
 */

import { db } from '../db/index.js';
import { integrationTokens } from '../db/schema.js';
import { eq } from 'drizzle-orm';
import { todoistSource } from './todoist.js';
import { logger } from '../logger.js';

const DEFAULT_INTERVAL_MS = 15 * 60 * 1000;

export function startTodoistSyncScheduler(intervalMs = DEFAULT_INTERVAL_MS): NodeJS.Timeout {
  async function syncAll(): Promise<void> {
    let users: { userId: string }[] = [];
    try {
      users = await db
        .select({ userId: integrationTokens.userId })
        .from(integrationTokens)
        .where(eq(integrationTokens.tokenStatus, 'active'));
    } catch (err: any) {
      logger.error({ err }, 'scheduler: failed to query users');
      return;
    }

    if (!users.length) return;

    const results = await Promise.allSettled(
      users.map((u) => todoistSource.fetchSignals(u.userId)),
    );

    let ok = 0;
    let failed = 0;
    for (const r of results) {
      if (r.status === 'fulfilled') ok++;
      else { failed++; logger.error({ err: r.reason }, 'scheduler: sync error'); }
    }

    logger.info({ ok, failed, total: users.length }, 'scheduler: todoist sync');
  }

  // Run once shortly after startup, then on interval
  const delay = setTimeout(() => {
    syncAll();
    setInterval(syncAll, intervalMs);
  }, 10_000);

  return delay;
}