accounted/lib/bookkeeping/settlement-account.ts

import type { SupabaseClient } from '@supabase/supabase-js'
import type { Logger } from '@/lib/logger'
import { BookkeepingDatabaseError } from '@/lib/bookkeeping/errors'

const FALLBACK_ACCOUNT = '1930'

/**
 * Resolve the BAS ledger account a transaction actually settles from/to.
 *
 * Never fall back to a company-wide "last used" setting (e.g.
 * last_supplier_payment_account, written by the manual mark-paid
 * private-funds flow): those reflect unrelated flows with no relationship
 * to which bank account a specific transaction is linked to.
 * cash_account_id -> cash_accounts.ledger_account is the only source of
 * truth for a real transaction's settlement account.
 */
export async function resolveSettlementAccount(
  supabase: SupabaseClient,
  companyId: string,
  cashAccountId: string | null,
  log: Logger,
): Promise<string> {
  if (!cashAccountId) return FALLBACK_ACCOUNT

  const { data, error } = await supabase
    .from('cash_accounts')
    .select('ledger_account')
    .eq('id', cashAccountId)
    .eq('company_id', companyId)
    .maybeSingle()

  if (error) {
    // An EXPLICIT cash_account_id exists: it almost certainly resolves to a
    // non-1930 account, so silently degrading to 1930 on a transient lookup
    // failure risks the exact class of misbooking this helper exists to
    // prevent, just triggered by infra flakiness instead of a stale setting.
    // Fail the request instead: the caller can retry, whereas a wrongly
    // booked verifikat needs a storno to correct (BFL 5 kap).
    throw new BookkeepingDatabaseError('resolve_settlement_account', error.message)
  }

  // A transaction with a cash_account_id that resolves to no row, or a row
  // with no ledger_account, is a data-integrity gap (not a normal "no cash
  // account linked" case): the fallback fires silently otherwise, masking a
  // bad cash_accounts row behind a plausible-looking 1930 verifikat.
  if (!data?.ledger_account) {
    log.warn('settlement-account lookup returned no ledger_account; defaulting to 1930', {
      cashAccountId,
    })
    return FALLBACK_ACCOUNT
  }

  return data.ledger_account as string
}