feat(vat-declaration): implement RC basis gap detection and correctio… (#466)

* feat(vat-declaration): implement RC basis gap detection and correction functionality

* fix(vat-declaration): improve error handling and validation for RC basis account selection

lib/reports/rc-basis-gaps.ts

@@ -0,0 +1,200 @@
+import type { SupabaseClient } from '@supabase/supabase-js'
+import { fetchAllRows } from '@/lib/supabase/fetch-all'
+import { calculatePeriodDates } from './vat-declaration'
+import type { VatPeriodType } from '@/types'
+
+/**
+ * Per-voucher detection of FK004: reverse-charge output VAT booked
+ * (2614/2624/2634) without a matching basbelopp pair on 44xx/45xx.
+ *
+ * Used by the momsdeklaration UI to give the user a concrete list of
+ * verifikationer to correct, rather than a generic "ruta 30-32 utan
+ * ruta 20-24" warning that doesn't tell them what to fix.
+ */
+
+const RC_OUTPUT_ACCOUNTS = ['2614', '2624', '2634'] as const
+type RcOutputAccount = typeof RC_OUTPUT_ACCOUNTS[number]
+
+const RC_BASIS_ACCOUNTS = new Set([
+  '4515', '4516', '4517', // EU goods 25/12/6%
+  '4531', '4532', '4533', // non-EU services 25/12/6%
+  '4535', '4536', '4537', // EU services 25/12/6%
+  '4415', '4416', '4417', // domestic goods RC
+  '4425', '4426', '4427', // domestic services RC
+])
+
+const RATE_BY_OUTPUT: Record<RcOutputAccount, number> = {
+  '2614': 0.25,
+  '2624': 0.12,
+  '2634': 0.06,
+}
+
+// Default to EU services (matches the booking-template default
+// reverse_charge_supplier_type = 'eu_business'). The user can pick a
+// different supplier type on the Korrigera form if needed.
+const DEFAULT_BASIS_BY_OUTPUT: Record<RcOutputAccount, string> = {
+  '2614': '4535',
+  '2624': '4536',
+  '2634': '4537',
+}
+
+export interface RcBasisGap {
+  entryId: string
+  voucherNumber: number
+  voucherSeries: string
+  entryDate: string
+  description: string
+  rcOutputAccount: RcOutputAccount
+  rcOutputAmount: number
+  expectedBasisAmount: number
+  suggestedBasisAccount: string
+  rate: number
+}
+
+interface RcLineRow {
+  journal_entry_id: string
+  account_number: string
+  debit_amount: number
+  credit_amount: number
+  // Supabase typings unpredictably model joined relations as either an object
+  // or an array depending on the FK; we accept both and normalize below.
+  journal_entries:
+    | {
+        id: string
+        voucher_number: number
+        voucher_series: string
+        entry_date: string
+        description: string
+      }
+    | {
+        id: string
+        voucher_number: number
+        voucher_series: string
+        entry_date: string
+        description: string
+      }[]
+}
+
+interface EntryFields {
+  id: string
+  voucher_number: number
+  voucher_series: string
+  entry_date: string
+  description: string
+}
+
+function pickEntry(row: RcLineRow): EntryFields | null {
+  const j = row.journal_entries
+  if (Array.isArray(j)) return j.length > 0 ? j[0] : null
+  return j ?? null
+}
+
+interface SiblingLineRow {
+  journal_entry_id: string
+  account_number: string
+  debit_amount: number
+  credit_amount: number
+}
+
+export async function findRcBasisGaps(
+  supabase: SupabaseClient,
+  companyId: string,
+  periodType: VatPeriodType,
+  year: number,
+  period: number,
+): Promise<RcBasisGap[]> {
+  const { start, end } = calculatePeriodDates(periodType, year, period)
+
+  const rcLines = (await fetchAllRows<unknown>(({ from, to }) =>
+    supabase
+      .from('journal_entry_lines')
+      .select(`
+        journal_entry_id,
+        account_number,
+        debit_amount,
+        credit_amount,
+        journal_entries!inner (
+          id, voucher_number, voucher_series, entry_date, description, status, company_id
+        )
+      `)
+      .in('account_number', RC_OUTPUT_ACCOUNTS as unknown as string[])
+      .eq('journal_entries.company_id', companyId)
+      .eq('journal_entries.status', 'posted')
+      .gte('journal_entries.entry_date', start)
+      .lte('journal_entries.entry_date', end)
+      .range(from, to),
+  )) as RcLineRow[]
+
+  if (rcLines.length === 0) return []
+
+  const entryIds = [...new Set(rcLines.map((l) => l.journal_entry_id))]
+
+  const siblingLines = await fetchAllRows<SiblingLineRow>(({ from, to }) =>
+    supabase
+      .from('journal_entry_lines')
+      .select('journal_entry_id, account_number, debit_amount, credit_amount')
+      .in('journal_entry_id', entryIds)
+      .range(from, to),
+  )
+
+  const basisByEntry = new Map<string, number>()
+  for (const line of siblingLines) {
+    if (RC_BASIS_ACCOUNTS.has(line.account_number)) {
+      const prev = basisByEntry.get(line.journal_entry_id) || 0
+      basisByEntry.set(
+        line.journal_entry_id,
+        prev + (Number(line.debit_amount) || 0) - (Number(line.credit_amount) || 0),
+      )
+    }
+  }
+
+  // Aggregate RC output per (entry, account) — a voucher may have multiple
+  // 2614 lines (rare) and we want to flag the total shortfall.
+  const aggregated = new Map<string, { row: RcLineRow; amount: number }>()
+  for (const line of rcLines) {
+    const key = `${line.journal_entry_id}:${line.account_number}`
+    const amount = (Number(line.credit_amount) || 0) - (Number(line.debit_amount) || 0)
+    const existing = aggregated.get(key)
+    if (existing) {
+      existing.amount += amount
+    } else {
+      aggregated.set(key, { row: line, amount })
+    }
+  }
+
+  const eps = 0.5
+  const gaps: RcBasisGap[] = []
+  for (const { row, amount } of aggregated.values()) {
+    if (amount <= eps) continue
+    const account = row.account_number as RcOutputAccount
+    const rate = RATE_BY_OUTPUT[account]
+    if (!rate) continue
+    const expectedBasis = Math.round((amount / rate) * 100) / 100
+    const actualBasis = basisByEntry.get(row.journal_entry_id) || 0
+    if (actualBasis + eps >= expectedBasis) continue
+
+    const entry = pickEntry(row)
+    if (!entry) continue
+    gaps.push({
+      entryId: row.journal_entry_id,
+      voucherNumber: entry.voucher_number,
+      voucherSeries: entry.voucher_series,
+      entryDate: entry.entry_date,
+      description: entry.description,
+      rcOutputAccount: account,
+      rcOutputAmount: amount,
+      expectedBasisAmount: expectedBasis,
+      suggestedBasisAccount: DEFAULT_BASIS_BY_OUTPUT[account],
+      rate,
+    })
+  }
+
+  gaps.sort((a, b) => {
+    if (a.voucherSeries !== b.voucherSeries) {
+      return a.voucherSeries.localeCompare(b.voucherSeries)
+    }
+    return a.voucherNumber - b.voucherNumber
+  })
+
+  return gaps
+}