/**
 * Reminder scheduler — shared-timed-event 15-min reminder scan.
 *
 * Fires every minute via node-cron.  Each tick calls runReminderCheck() which:
 *   1. Queries shared (isShared=true) timed (allDay=false) events whose dtstartUtc
 *      falls in [now+14min, now+16min] — the ±1 min window around 15 min lead.
 *   2. Cross-joins with ALL push_subscriptions (shared reminder → every member).
 *   3. Deduplicates on (uid, minuteBucket) so a window-boundary double-tick never
 *      fires twice (D-06, RESEARCH Pitfall 5 / Open Question 3).
 *   4. Calls dispatchPush once per subscription per due event.
 *
 * Decisions enforced here:
 *   D-05  — isShared=true in the SQL WHERE (not in copy); personal events excluded.
 *   D-06  — fixed 15-min lead; no per-event customisation.
 *   D-07  — allDay=false in the SQL WHERE; all-day events are silently excluded.
 *   D-11  — every push goes through dispatchPush which always sends a visible notification.
 *   D-12  — in-memory Set; no Redis; single-process deployment.
 *   D-16  — empty shared-calendar set (Family calendar not yet created) produces zero
 *           sends and no crash (cross-join on empty table returns no rows).
 *
 * Threat mitigations:
 *   T-05-17 — D-05 enforced in QUERY (WHERE isShared=true), not in copy.
 *   T-05-18 — in-memory dedup Set keyed (uid, minuteBucket); per-event try/catch.
 *   T-05-19 — per-subscription try/catch; dispatchPush already swallows 410/404.
 */

import { schedule } from 'node-cron'
import { and, eq, gte, lte, sql } from 'drizzle-orm'
import { db } from '../db/client.js'
import { calendars, calendarEvents, pushSubscriptions } from '../db/schema.js'
import { dispatchPush } from '../lib/pushDispatcher.js'
import type { NotificationPayload } from '../lib/pushDispatcher.js'

// ── In-memory dedup (D-12: single-process, no Redis) ─────────────────────────
// Key: `${eventUid}:${minuteBucket}` where minuteBucket = floor(now ms / 60000).
// Prevents double-fire when the same event sits in the window across two consecutive ticks.
// Acceptable data loss on process restart for a two-person household.
const sentReminders = new Set<string>()

// ── Helpers ───────────────────────────────────────────────────────────────────

/**
 * Format a UTC Date as "YYYY-MM-DD" for calendar deep-link URLs.
 */
function yyyyMmDd(d: Date): string {
  const y = d.getUTCFullYear()
  const m = String(d.getUTCMonth() + 1).padStart(2, '0')
  const day = String(d.getUTCDate()).padStart(2, '0')
  return `${y}-${m}-${day}`
}

// ── Core scan ─────────────────────────────────────────────────────────────────

/**
 * Run one reminder scan cycle.
 *
 * Exported with an injectable `now` parameter so tests can control time without
 * needing the cron schedule to fire.  Production call passes no argument;
 * default = new Date() (current wall-clock time).
 */
export async function runReminderCheck(now = new Date()): Promise<void> {
  const minuteBucket = Math.floor(now.getTime() / 60000)
  const windowStart = new Date(now.getTime() + 14 * 60 * 1000)
  const windowEnd = new Date(now.getTime() + 16 * 60 * 1000)

  // Single query: events (isShared, timed, in window) cross-joined with ALL
  // push_subscriptions.  The cross-join (sql`1=1`) fans every matching event out
  // to every subscriber — shared reminder, every member notified (D-05, member-agnostic).
  //
  // With an empty push_subscriptions table (no subscribers yet) the INNER JOIN
  // on sql`1=1` returns no rows — zero sends, no crash (D-16 empty-calendar analogue).
  const rows = await db
    .select({
      uid: calendarEvents.uid,
      title: calendarEvents.title,
      dtstartUtc: calendarEvents.dtstartUtc,
      allDay: calendarEvents.allDay,
      isShared: calendars.isShared,
      subId: pushSubscriptions.id,
      subUserId: pushSubscriptions.userId,
      subEndpoint: pushSubscriptions.endpoint,
      subP256dh: pushSubscriptions.p256dh,
      subAuth: pushSubscriptions.auth,
    })
    .from(calendarEvents)
    .innerJoin(calendars, eq(calendarEvents.calendarId, calendars.id))
    .innerJoin(pushSubscriptions, sql`1=1`)
    .where(
      and(
        eq(calendars.isShared, true),       // D-05: shared calendar only (in QUERY, not copy)
        eq(calendarEvents.allDay, false),    // D-07: timed events only
        gte(calendarEvents.dtstartUtc, windowStart),
        lte(calendarEvents.dtstartUtc, windowEnd),
      ),
    )

  // Group flat (event, subscription) rows by event uid so we can:
  //   a) dedup per event (not per (event, sub) pair), and
  //   b) fan out to ALL subscriptions for a deduped event in one pass.
  type SubRow = { id: number; userId: number; endpoint: string; p256dh: string; auth: string }
  const byUid = new Map<
    string,
    { uid: string; title: string | null; dtstartUtc: Date; subs: SubRow[] }
  >()

  for (const row of rows) {
    if (!byUid.has(row.uid)) {
      byUid.set(row.uid, {
        uid: row.uid,
        title: row.title ?? null,
        // dtstartUtc is guaranteed non-null by the allDay=false + gte/lte WHERE
        dtstartUtc: row.dtstartUtc as Date,
        subs: [],
      })
    }
    // subId is undefined when cross-join produces no subscriptions row (empty table)
    if (row.subId != null) {
      byUid.get(row.uid)!.subs.push({
        id: row.subId,
        userId: row.subUserId!,
        endpoint: row.subEndpoint,
        p256dh: row.subP256dh,
        auth: row.subAuth,
      })
    }
  }

  // Dedup and dispatch
  for (const [uid, event] of byUid) {
    try {
      const key = `${uid}:${minuteBucket}`
      if (sentReminders.has(key)) continue

      const dateStr = yyyyMmDd(event.dtstartUtc)
      const notification: NotificationPayload = {
        // Null-safe title fallback (D-02 / NOTIF-01): title column may be NULL on rows
        // created before the Plan 05-07 sync update.  Use the uid rather than "undefined".
        title: event.title ?? uid,
        body: 'Starts in 15 min',
        tag: `reminder-${uid}`,
        navigate: `/calendar?date=${dateStr}&event=${uid}`,
      }

      // Fan out to every subscriber (member-count-agnostic)
      for (const sub of event.subs) {
        try {
          await dispatchPush(sub, notification)
        } catch (err) {
          // Per-subscription error isolation (T-05-19): one bad sub never aborts the cycle.
          // dispatchPush itself never throws (it resolves after logging), so this outer
          // catch is a belt-and-suspenders guard for unexpected errors.
          console.error(
            `[broker/reminderScheduler] Error dispatching reminder to sub id=${sub.id} for event uid=${uid}:`,
            err instanceof Error ? err.message : String(err),
          )
        }
      }

      // WR-01: mark sent AFTER all dispatches have been attempted. Pre-marking before
      // dispatch prevents retry in the same bucket when dispatchPush throws — at-least-once
      // delivery requires not pre-marking the key.
      sentReminders.add(key)
    } catch (err) {
      // Per-event error isolation (T-05-18): one bad event never aborts remaining events.
      console.error(
        `[broker/reminderScheduler] Error processing event uid=${uid}:`,
        err instanceof Error ? err.message : String(err),
      )
    }
  }

  // CR-01: Prune stale entries from sentReminders to prevent unbounded growth.
  // Entries for the previous minute bucket and older are no longer needed — the
  // dedup window is (uid, minuteBucket), and the current minute has now been
  // processed. Keep only the current bucket; discard everything older.
  const staleBucket = minuteBucket - 1
  for (const key of sentReminders) {
    const colonIdx = key.lastIndexOf(':')
    if (colonIdx !== -1 && Number(key.slice(colonIdx + 1)) < staleBucket) {
      sentReminders.delete(key)
    }
  }
}

// ── Scheduler ─────────────────────────────────────────────────────────────────

/**
 * Start the 1-minute reminder scan schedule.
 * Call once from index.ts's isMainModule() guard — NOT at import time
 * (keeps the cron out of the test process; mirrors startBrokerPoller pattern).
 */
export function startReminderScheduler(): void {
  schedule('* * * * *', () => {
    runReminderCheck().catch((err: unknown) => {
      console.error('[broker/reminderScheduler] Unhandled runReminderCheck error:', err)
    })
  })
}