mailadmin/backend/src/services/billing.ts

import { pool } from '../db.js';

const PRICE_PER_INBOX_USD = 5;

export interface BillingEvent {
  id: number;
  occurred_at: string;
  domain: string;
  email: string;
  action: 'created' | 'deleted';
  actor_email: string | null;
  notes: string | null;
}

export interface MonthlyDomainBilling {
  domain: string;
  year: number;
  month: number;       // 1-12
  ym: string;          // 'YYYY-MM'
  inbox_count: number;
  amount_usd: number;
  inbox_emails: string[];
}

/**
 * Record a billing event. Called from the create/delete mailbox routes.
 * Failures are logged but never thrown — billing must not block the
 * actual mailbox operation that just succeeded.
 */
export async function recordBillingEvent(
  action: 'created' | 'deleted',
  domain: string,
  email: string,
  actorEmail: string | null,
  notes?: string,
): Promise<void> {
  try {
    await pool.query(
      `INSERT INTO mailbox_billing_events (domain, email, action, actor_email, notes)
       VALUES ($1, $2, $3, $4, $5)`,
      [domain.toLowerCase(), email.toLowerCase(), action, actorEmail, notes ?? null],
    );
  } catch (err) {
    console.warn('[billing] failed to record event:', err);
  }
}

/**
 * Get raw events for a domain (or all domains) within a time range.
 */
export async function listBillingEvents(opts: {
  domain?: string;
  fromIso?: string;
  toIso?: string;
  limit?: number;
}): Promise<BillingEvent[]> {
  const params: unknown[] = [];
  const where: string[] = [];

  if (opts.domain) {
    params.push(opts.domain.toLowerCase());
    where.push(`domain = $${params.length}`);
  }
  if (opts.fromIso) {
    params.push(opts.fromIso);
    where.push(`occurred_at >= $${params.length}`);
  }
  if (opts.toIso) {
    params.push(opts.toIso);
    where.push(`occurred_at < $${params.length}`);
  }

  const limit = Math.min(Math.max(opts.limit ?? 500, 1), 5000);

  const sql = `
    SELECT id, occurred_at, domain, email, action, actor_email, notes
    FROM mailbox_billing_events
    ${where.length ? 'WHERE ' + where.join(' AND ') : ''}
    ORDER BY occurred_at DESC, id DESC
    LIMIT ${limit}
  `;

  const result = await pool.query(sql, params);
  return result.rows;
}

/**
 * Compute monthly billing aggregation across all months that contain
 * at least one mailbox in the given domain.
 *
 * Rule: a mailbox is billable in a month if it existed at any point
 * during that month — i.e. it was created on or before the last day
 * of the month, AND (still active OR was deleted on or after the
 * first day of that same month).
 *
 * In other words: every month between the create and the delete
 * (inclusive on both ends) counts. If still active, every month
 * since creation up to and including the current month counts.
 */
export async function computeMonthlyBilling(opts: {
  domain?: string;
}): Promise<MonthlyDomainBilling[]> {
  // Pull events. We need the full history, but for performance we
  // could later add an "earliest month" cutoff. With <100k events
  // this is well under 100ms.
  const rows = await listBillingEvents({ domain: opts.domain, limit: 5000 });

  // Group events per (domain, email) so we can pair create/delete
  // and reconstruct lifespans.
  const byMailbox = new Map<string, BillingEvent[]>();
  for (const ev of rows) {
    const key = `${ev.domain}\u0000${ev.email}`;
    if (!byMailbox.has(key)) byMailbox.set(key, []);
    byMailbox.get(key)!.push(ev);
  }

  const now = new Date();

  // For each domain+email, walk through events sorted ascending and
  // build a list of (createdAt, deletedAt|null) intervals. A mailbox
  // can be re-created after deletion, so multiple intervals per
  // (domain, email) are possible.
  type Interval = { domain: string; email: string; from: Date; to: Date | null };
  const intervals: Interval[] = [];

  for (const [key, evs] of byMailbox) {
    const [domain, email] = key.split('\u0000');
    const sorted = [...evs].sort((a, b) =>
      new Date(a.occurred_at).getTime() - new Date(b.occurred_at).getTime()
    );

    let openCreatedAt: Date | null = null;

    for (const ev of sorted) {
      if (ev.action === 'created') {
        // If we already had an open interval (no matching delete), we
        // close it implicitly on the new create. This shouldn't happen
        // in practice but guards against malformed data.
        if (openCreatedAt) {
          intervals.push({ domain, email, from: openCreatedAt, to: new Date(ev.occurred_at) });
        }
        openCreatedAt = new Date(ev.occurred_at);
      } else if (ev.action === 'deleted' && openCreatedAt) {
        intervals.push({ domain, email, from: openCreatedAt, to: new Date(ev.occurred_at) });
        openCreatedAt = null;
      }
      // delete without prior create is ignored (defensive).
    }

    if (openCreatedAt) {
      // Still active: open-ended interval up to "now".
      intervals.push({ domain, email, from: openCreatedAt, to: null });
    }
  }

  // Now bucket each interval into the months it covers.
  // Per (domain, ym) we keep a Set of emails to dedupe and to expose
  // the actual list in the UI.
  type Bucket = { domain: string; ym: string; year: number; month: number; emails: Set<string> };
  const buckets = new Map<string, Bucket>();

  const ensureBucket = (domain: string, year: number, month: number): Bucket => {
    const ym = `${year}-${String(month).padStart(2, '0')}`;
    const key = `${domain}\u0000${ym}`;
    let b = buckets.get(key);
    if (!b) {
      b = { domain, ym, year, month, emails: new Set() };
      buckets.set(key, b);
    }
    return b;
  };

  for (const iv of intervals) {
    const fromY = iv.from.getUTCFullYear();
    const fromM = iv.from.getUTCMonth() + 1;
    const end = iv.to ?? now;
    const toY = end.getUTCFullYear();
    const toM = end.getUTCMonth() + 1;

    let y = fromY;
    let m = fromM;
    while (y < toY || (y === toY && m <= toM)) {
      ensureBucket(iv.domain, y, m).emails.add(iv.email);
      m++;
      if (m > 12) { m = 1; y++; }
    }
  }

  const result: MonthlyDomainBilling[] = [...buckets.values()].map((b) => ({
    domain: b.domain,
    year: b.year,
    month: b.month,
    ym: b.ym,
    inbox_count: b.emails.size,
    amount_usd: b.emails.size * PRICE_PER_INBOX_USD,
    inbox_emails: [...b.emails].sort(),
  }));

  // Newest months first, then domain name.
  result.sort((a, b) => {
    if (a.ym !== b.ym) return a.ym < b.ym ? 1 : -1;
    return a.domain.localeCompare(b.domain);
  });

  return result;
}

export const PRICE_PER_INBOX = PRICE_PER_INBOX_USD;