fix(import): actionable hint when a bank CSV lands in the opening-balance importer (#953)

* fix(import): hint when a bank statement is uploaded as opening balances

Uploading a bank statement CSV to the opening-balance importer produced
the generic 'Inga konton med belopp hittades' error with no clue that
the file belongs in the bank-transactions importer (#918, users got
stuck together with #915).

When the opening-balance parse yields zero account rows, the parser now
runs the registered bank-file format detectors over the CSV content
(the generic CSV fallback never auto-detects, so any match is a real
bank format) and reports the matched format name as
detected_bank_format on the parse result. The upload step then shows an
actionable Swedish error naming the bank plus a button that routes to
the bank-transactions importer (/import?mode=bank).

Closes #918

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(import): use the standard bank-import CTA wording (CodeRabbit)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/import/opening-balance/__tests__/parser.test.ts

@@ -255,3 +255,68 @@ describe('parseOpeningBalanceFile', () => {
     expect(result.total_credit).toBe(40000)
   })
 })
+
+describe('bank statement detection (issue #918)', () => {
+  const toBuffer = (csv: string): ArrayBuffer =>
+    new TextEncoder().encode(csv).buffer as ArrayBuffer
+
+  it('flags a Swedbank bank statement CSV that yields no account rows', async () => {
+    const { parseOpeningBalanceFile } = await import('../parser')
+
+    const csv = [
+      'Radnr,Clnr,Kontonr,Produkt,Valuta,Bokfdag,Transdag,Valutadag,Referens,Text,Belopp,Saldo',
+      '1,8385-9,9350000000,Företagskonto,SEK,2026-05-02,2026-05-02,2026-05-02,Hyra maj,Bg-bet. via internet,-12000.00,54321.00',
+      '2,8385-9,9350000000,Företagskonto,SEK,2026-05-03,2026-05-03,2026-05-03,Kundbetalning,Insättning,25000.00,79321.00',
+    ].join('\n')
+
+    const result = parseOpeningBalanceFile(toBuffer(csv), 'kontoutdrag.csv')
+
+    expect(result.rows.length).toBe(0)
+    expect(result.detected_bank_format).toBe('Swedbank')
+  })
+
+  it('flags an SEB bank statement CSV that yields no account rows', async () => {
+    const { parseOpeningBalanceFile } = await import('../parser')
+
+    const csv = [
+      'Bokföringsdatum;Valutadatum;Verifikationsnummer;Text;Belopp;Saldo',
+      '2026-05-02;2026-05-02;5501234567;Hyra maj;-12000,00;54321,00',
+      '2026-05-03;2026-05-03;5501234568;Kundbetalning;25000,00;79321,00',
+    ].join('\n')
+
+    const result = parseOpeningBalanceFile(toBuffer(csv), 'export.csv')
+
+    expect(result.rows.length).toBe(0)
+    expect(result.detected_bank_format).toBe('SEB')
+  })
+
+  it('does not flag a CSV that yields no rows but matches no bank format', async () => {
+    const { parseOpeningBalanceFile } = await import('../parser')
+
+    const csv = [
+      'Namn,Stad,Antal',
+      'Alfa,Göteborg,3',
+      'Beta,Malmö,7',
+    ].join('\n')
+
+    const result = parseOpeningBalanceFile(toBuffer(csv), 'annat.csv')
+
+    expect(result.rows.length).toBe(0)
+    expect(result.detected_bank_format).toBeNull()
+  })
+
+  it('does not flag a valid opening balance file', async () => {
+    const { parseOpeningBalanceFile } = await import('../parser')
+
+    const csv = [
+      'Kontonr,Kontonamn,Debet,Kredit',
+      '1930,Företagskonto,50000,0',
+      '2099,Årets resultat,0,50000',
+    ].join('\n')
+
+    const result = parseOpeningBalanceFile(toBuffer(csv), 'ib.csv')
+
+    expect(result.rows.length).toBe(2)
+    expect(result.detected_bank_format).toBeNull()
+  })
+})

lib/import/opening-balance/parser.ts

@@ -1,6 +1,8 @@
 import * as XLSX from 'xlsx'
 import { detectColumns } from './column-detector'
 import { getBASReference } from '@/lib/bookkeeping/bas-reference'
+import { detectFileFormat } from '../bank-file/parser'
+import { decodeFileContent } from '../shared/encoding'
 import { readWorkbookFromBuffer } from '../shared/workbook-reader'
 import type {
   DetectedColumns,
@@ -31,6 +33,25 @@ export function parseAmount(value: unknown): number {
   return Math.round(num * 100) / 100
 }
 
+/**
+ * When an opening-balance parse yields no rows, check whether the uploaded
+ * file is actually a bank statement (issue #918: users upload bank CSV
+ * exports here and only get a generic "no accounts found" error). Only CSV
+ * files can match: the bank-file detectors operate on decoded text, and the
+ * generic CSV fallback never auto-detects, so any match is a real bank format.
+ */
+function detectBankStatementFormat(buffer: ArrayBuffer, filename: string): string | null {
+  const ext = filename.toLowerCase().split('.').pop() ?? ''
+  if (ext !== 'csv') return null
+  try {
+    const content = decodeFileContent(buffer)
+    return detectFileFormat(content, filename)?.name ?? null
+  } catch {
+    // Detection is a best-effort hint: never let it break the parse result
+    return null
+  }
+}
+
 /**
  * Parse an opening balance file (Excel or CSV) and return structured rows
  * with validation and BAS account matching.
@@ -87,6 +108,7 @@ export function parseOpeningBalanceFile(
       total_credit: 0,
       is_balanced: true,
       warnings: ['Filen innehåller för få rader.'],
+      detected_bank_format: detectBankStatementFormat(buffer, filename),
     }
   }
 
@@ -242,5 +264,7 @@ export function parseOpeningBalanceFile(
     total_credit: totalCredit,
     is_balanced: isBalanced,
     warnings,
+    detected_bank_format:
+      mergedRows.length === 0 ? detectBankStatementFormat(buffer, filename) : null,
   }
 }

lib/import/opening-balance/types.ts

@@ -44,6 +44,12 @@ export interface OpeningBalanceParseResult {
   total_credit: number
   is_balanced: boolean
   warnings: string[]
+  /**
+   * Bank-file format name (e.g. "Swedbank") when the file produced no account
+   * rows but matches a known bank statement format: the user most likely
+   * uploaded a bank statement to the wrong importer. Null otherwise.
+   */
+  detected_bank_format: string | null
 }
 
 /** Input for executing the opening balance import */