feat: add ensureFiscalPeriod function and related tests for fiscal period validation (#264)

lib/import/__tests__/sie-import.test.ts

@@ -1,5 +1,11 @@
 import { describe, it, expect } from 'vitest'
-import { generateImportPreview, validateIBBalance, isBalanceSheetAccount } from '../sie-import'
+import {
+  generateImportPreview,
+  validateIBBalance,
+  isBalanceSheetAccount,
+  ensureFiscalPeriod,
+} from '../sie-import'
+import { createQueuedMockSupabase } from '@/tests/helpers'
 import type { ParsedSIEFile, AccountMapping } from '../types'
 
 // --- Helpers ---
@@ -312,6 +318,83 @@ describe('validateIBBalance', () => {
   })
 })
 
+describe('ensureFiscalPeriod validation', () => {
+  // Mirrors the `enforce_period_start_day` DB trigger so users get an
+  // actionable Swedish error instead of a raw Postgres message.
+  type Supabase = Parameters<typeof ensureFiscalPeriod>[0]
+
+  it('rejects mid-month start when another period exists for the company', async () => {
+    const { supabase, enqueueMany } = createQueuedMockSupabase()
+    enqueueMany([
+      { data: null, error: null }, // containing check — no match
+      { data: [], error: null },   // overlapping check — none
+      { data: null, error: null, count: 1 }, // count existing — 1 period already
+    ])
+
+    await expect(
+      ensureFiscalPeriod(
+        supabase as unknown as Supabase,
+        'company-id',
+        '2026-04-16',
+        '2026-12-31',
+      ),
+    ).rejects.toThrow(/endast företagets första räkenskapsår får börja mitt i månaden/)
+  })
+
+  it('rejects end date that is not the last day of the month', async () => {
+    const { supabase, enqueueMany } = createQueuedMockSupabase()
+    enqueueMany([
+      { data: null, error: null },
+      { data: [], error: null },
+      { data: null, error: null, count: 0 }, // first fiscal period
+    ])
+
+    await expect(
+      ensureFiscalPeriod(
+        supabase as unknown as Supabase,
+        'company-id',
+        '2026-01-01',
+        '2026-12-30', // not the last day of December
+      ),
+    ).rejects.toThrow(/måste sluta på månadens sista dag/)
+  })
+
+  it('allows mid-month start for the company first fiscal period', async () => {
+    const { supabase, enqueueMany } = createQueuedMockSupabase()
+    enqueueMany([
+      { data: null, error: null },
+      { data: [], error: null },
+      { data: null, error: null, count: 0 }, // no existing periods
+      { data: { id: 'new-period-id' }, error: null }, // insert result
+    ])
+
+    const id = await ensureFiscalPeriod(
+      supabase as unknown as Supabase,
+      'company-id',
+      '2026-04-16',
+      '2026-12-31',
+    )
+
+    expect(id).toBe('new-period-id')
+  })
+
+  it('reuses an existing period that contains the range (no validation needed)', async () => {
+    const { supabase, enqueueMany } = createQueuedMockSupabase()
+    enqueueMany([
+      { data: { id: 'existing-period-id' }, error: null }, // containing match
+    ])
+
+    const id = await ensureFiscalPeriod(
+      supabase as unknown as Supabase,
+      'company-id',
+      '2026-04-16',
+      '2026-12-31',
+    )
+
+    expect(id).toBe('existing-period-id')
+  })
+})
+
 describe('isBalanceSheetAccount', () => {
   it('returns true for class 1 (assets)', () => {
     expect(isBalanceSheetAccount('1510')).toBe(true)

lib/import/sie-import.ts

@@ -22,6 +22,7 @@ import { calculateFileHash } from './sie-parser'
 import { getBASReference } from '@/lib/bookkeeping/bas-reference'
 import { computeSRUCode } from '@/lib/bookkeeping/bas-data/sru-mapping'
 import { populateTemplatesFromSieVouchers } from '@/lib/bookkeeping/counterparty-templates'
+import { parseDateParts } from '@/lib/bookkeeping/validate-period-duration'
 
 /**
  * Format a date to ISO date string (YYYY-MM-DD)
@@ -211,8 +212,11 @@ async function cleanupStaleImportRecords(
 /**
  * Create a fiscal period if one doesn't exist for the date range.
  * Dates are ISO strings "YYYY-MM-DD" to avoid timezone issues.
+ *
+ * Exported for unit testing of the pre-validation that mirrors the
+ * `enforce_period_start_day` DB trigger.
  */
-async function ensureFiscalPeriod(
+export async function ensureFiscalPeriod(
   supabase: SupabaseClient,
   companyId: string,
   startDate: string,
@@ -246,9 +250,38 @@ async function ensureFiscalPeriod(
     return overlapping[0].id
   }
 
+  // Pre-validate against the DB-side enforce_period_start_day trigger so the
+  // user gets an actionable Swedish error instead of a raw Postgres message.
+  // Only the company's FIRST fiscal period may start mid-month (BFL 3 kap.);
+  // any subsequent period must start on day 1. The trigger queries the same
+  // table, so "another period exists" == the overlap check above missed it,
+  // i.e. this would be a non-contiguous second period.
+  const { count: existingCount } = await supabase
+    .from('fiscal_periods')
+    .select('id', { count: 'exact', head: true })
+    .eq('company_id', companyId)
+
+  const startParts = parseDateParts(startDate)
+  const endParts = parseDateParts(endDate)
+
+  if ((existingCount ?? 0) > 0 && startParts.day !== 1) {
+    throw new Error(
+      `SIE-filens räkenskapsår börjar ${startDate} — endast företagets första räkenskapsår får börja mitt i månaden. Efterföljande räkenskapsår måste börja den 1:a i en månad (BFL 3 kap.). Kontrollera datumen i #RAR-raden eller importera filen innan du skapar fler perioder.`
+    )
+  }
+
+  // Matches the fiscal_period_end_last_of_month CHECK constraint on prod;
+  // surface it as a clean message instead of a DB error.
+  const lastDayOfEndMonth = new Date(endParts.year, endParts.month, 0).getDate()
+  if (endParts.day !== lastDayOfEndMonth) {
+    throw new Error(
+      `SIE-filens räkenskapsår slutar ${endDate} — räkenskapsår måste sluta på månadens sista dag (BFL 3 kap.). Kontrollera datumen i #RAR-raden.`
+    )
+  }
+
   // Create new fiscal period
-  const startYear = parseInt(startDate.substring(0, 4), 10)
-  const endYear = parseInt(endDate.substring(0, 4), 10)
+  const startYear = startParts.year
+  const endYear = endParts.year
   const name = startYear === endYear
     ? `Räkenskapsår ${startYear}`
     : `Räkenskapsår ${startYear}/${endYear}`
@@ -1175,7 +1208,7 @@ async function finalizeImportRecord(
   // Archive the SIE file to Supabase Storage (BFL 7 kap 1-2§ retention)
   if (result.success) {
     const storagePath = `${companyId}/${importId}.se`
-    const fileBlob = new Blob([fileContent], { type: 'text/plain; charset=cp437' })
+    const fileBlob = new Blob([fileContent], { type: 'text/plain' })
     const { error: uploadError } = await supabase.storage
       .from('sie-files')
       .upload(storagePath, fileBlob, { upsert: false })