accounted/lib/reports/vat-declaration.ts

import type { SupabaseClient } from '@supabase/supabase-js'
import type {
  VatDeclaration,
  VatDeclarationRutor,
  VatPeriodType,
} from '@/types'
import type { VatCheckAccountTotals } from './vat-declaration-checks'
import { fetchDynamicRuta05Accounts } from './vat-revenue-accounts'

/**
 * Calculate VAT declaration (Momsdeklaration) for a given period.
 *
 * Reads directly from the general ledger: sums posted journal entry lines
 * on 26xx (VAT) and 3xxx (revenue) accounts for the period. This makes the
 * momsdeklaration a pure projection from the double-entry bookkeeping ledger.
 *
 * The accounting method (accrual vs cash) is already reflected in when
 * journal entries were created by the entry generators, so no separate
 * filtering logic is needed here.
 */

/**
 * Account-to-ruta mapping for the Swedish momsdeklaration (SKV 4700).
 *
 * Pure ledger projection: every Ruta on the SKV 4700 form maps to one or more
 * BAS account balances aggregated over the period. The mapping below follows
 * the BAS 2026 chart and Skatteverket's published BAS-to-Ruta spec
 * (`.claude/skills/swedish-vat/references/vat-compliance-reference.md` §7).
 *
 * Output VAT (261x/262x/263x) → ruta 10/11/12 per rate (credit balance)
 *   Includes parent/summary accounts (2610/2620/2630) for users who post
 *   directly to the group account, and vilande accounts (2618/2628/2638)
 *   used by cash-method bookkeepers for invoices not yet paid.
 * Reverse charge output (2614/2624/2634) → ruta 30/31/32 (credit)
 * Import VAT (2615/2625/2635) → ruta 60/61/62 (credit)
 * Input VAT (2640-2649) → ruta 48 (debit), incl. parent 2640
 * Domestic taxable sales (3000-3003) → ruta 05 (credit)
 *   The company's OWN class 3 accounts marked with a moms-sats join ruta 05 on
 *   top of this fixed list: see fetchDynamicRuta05Accounts (#1261). This map
 *   only covers the accounts Accounted itself seeds.
 * Uttag (3401-3403) → ruta 06 (credit)
 * EU goods (3108) → ruta 35; EU services (3308) → ruta 39 (credit)
 * Export (3105/3305) → ruta 36/40; Exempt (3004/3100/3404/3994/3980) → ruta 42 (credit)
 * Reverse-charge purchase bases: read from the cost account the journal
 * entry posted to (debit balance), not from supplier classification:
 *   4515/4516/4517 (EU goods 25/12/6%) → ruta 20
 *   4535/4536/4537 (EU services 25/12/6%) → ruta 21
 *   4531/4532/4533 (non-EU services 25/12/6%) → ruta 22
 *   4415/4416/4417 (domestic goods reverse charge) → ruta 23
 *   4425/4426/4427 (domestic services reverse charge) → ruta 24
 *   4545/4546/4547 (import) → ruta 50
 */
export const ACCOUNT_RUTA: Record<string, { box: keyof VatDeclarationRutor; side: 'credit' | 'debit' }> = {
  // Output VAT 25% → ruta 10
  '2610': { box: 'ruta10', side: 'credit' },  // Utgående moms 25% (summary/parent)
  '2611': { box: 'ruta10', side: 'credit' },  // Försäljning inom Sverige
  '2612': { box: 'ruta10', side: 'credit' },  // Egna uttag
  '2613': { box: 'ruta10', side: 'credit' },  // Uthyrning (frivillig skattskyldighet)
  '2616': { box: 'ruta10', side: 'credit' },  // Vinstmarginalbeskattning
  '2618': { box: 'ruta10', side: 'credit' },  // Vilande utgående moms 25%
  // Output VAT 12% → ruta 11
  '2620': { box: 'ruta11', side: 'credit' },  // Utgående moms 12% (summary/parent)
  '2621': { box: 'ruta11', side: 'credit' },
  '2622': { box: 'ruta11', side: 'credit' },  // Egna uttag
  '2623': { box: 'ruta11', side: 'credit' },  // Uthyrning
  '2626': { box: 'ruta11', side: 'credit' },  // VMB
  '2628': { box: 'ruta11', side: 'credit' },  // Vilande utgående moms 12%
  // Output VAT 6% → ruta 12
  '2630': { box: 'ruta12', side: 'credit' },  // Utgående moms 6% (summary/parent)
  '2631': { box: 'ruta12', side: 'credit' },
  '2632': { box: 'ruta12', side: 'credit' },  // Egna uttag
  '2633': { box: 'ruta12', side: 'credit' },  // Uthyrning
  '2636': { box: 'ruta12', side: 'credit' },  // VMB
  '2638': { box: 'ruta12', side: 'credit' },  // Vilande utgående moms 6%
  // Reverse charge output VAT → ruta 30/31/32
  '2614': { box: 'ruta30', side: 'credit' },
  '2624': { box: 'ruta31', side: 'credit' },
  '2634': { box: 'ruta32', side: 'credit' },
  // Input VAT → ruta 48
  '2640': { box: 'ruta48', side: 'debit' },   // Ingående moms (summary/parent)
  '2641': { box: 'ruta48', side: 'debit' },   // Debiterad ingående moms
  '2642': { box: 'ruta48', side: 'debit' },   // Frivillig skattskyldighet
  '2645': { box: 'ruta48', side: 'debit' },   // Förvärv utlandet (EU/non-EU RC)
  '2646': { box: 'ruta48', side: 'debit' },   // Uthyrning
  '2647': { box: 'ruta48', side: 'debit' },   // Omvänd skattskyldighet i Sverige
  '2649': { box: 'ruta48', side: 'debit' },   // Blandad verksamhet
  // Import VAT (since 2015, via momsdeklaration) → ruta 60/61/62
  '2615': { box: 'ruta60', side: 'credit' },  // Import 25%
  '2625': { box: 'ruta61', side: 'credit' },  // Import 12%
  '2635': { box: 'ruta62', side: 'credit' },  // Import 6%
  // Revenue: domestic taxable sales → ruta 05
  '3000': { box: 'ruta05', side: 'credit' },  // Försäljning inom Sverige (summary/parent)
  '3001': { box: 'ruta05', side: 'credit' },
  '3002': { box: 'ruta05', side: 'credit' },
  '3003': { box: 'ruta05', side: 'credit' },
  // Revenue: momspliktiga uttag → ruta 06
  '3401': { box: 'ruta06', side: 'credit' },
  '3402': { box: 'ruta06', side: 'credit' },
  '3403': { box: 'ruta06', side: 'credit' },
  // Revenue: EU goods/services → ruta 35/39
  '3108': { box: 'ruta35', side: 'credit' },  // Varuförsäljning till EU
  '3308': { box: 'ruta39', side: 'credit' },  // Tjänsteförsäljning till EU
  // Revenue: export/other → ruta 36/40/42
  '3105': { box: 'ruta36', side: 'credit' },  // Varuförsäljning export
  '3305': { box: 'ruta40', side: 'credit' },  // Tjänsteförsäljning export
  '3004': { box: 'ruta42', side: 'credit' },  // Momsfri försäljning (AB)
  '3100': { box: 'ruta42', side: 'credit' },  // Momsfria intäkter (EF)
  '3404': { box: 'ruta42', side: 'credit' },  // Momsfria uttag
  '3980': { box: 'ruta42', side: 'credit' },  // Erhållna offentliga stöd m.m.
  '3994': { box: 'ruta42', side: 'credit' },  // Övriga rörelseintäkter momsfria
  // Reverse-charge purchase bases (debit on cost accounts) → ruta 20-24, 50
  '4515': { box: 'ruta20', side: 'debit' },   // Inköp varor EU 25%
  '4516': { box: 'ruta20', side: 'debit' },   // Inköp varor EU 12%
  '4517': { box: 'ruta20', side: 'debit' },   // Inköp varor EU 6%
  '4535': { box: 'ruta21', side: 'debit' },   // Inköp tjänster EU 25%
  '4536': { box: 'ruta21', side: 'debit' },   // Inköp tjänster EU 12%
  '4537': { box: 'ruta21', side: 'debit' },   // Inköp tjänster EU 6%
  '4531': { box: 'ruta22', side: 'debit' },   // Inköp tjänster utanför EU 25%
  '4532': { box: 'ruta22', side: 'debit' },   // Inköp tjänster utanför EU 12%
  '4533': { box: 'ruta22', side: 'debit' },   // Inköp tjänster utanför EU 6%
  '4415': { box: 'ruta23', side: 'debit' },   // Inköp varor SE reverse charge 25%
  '4416': { box: 'ruta23', side: 'debit' },   // Inköp varor SE reverse charge 12%
  '4417': { box: 'ruta23', side: 'debit' },   // Inköp varor SE reverse charge 6%
  '4425': { box: 'ruta24', side: 'debit' },   // Inköp tjänster SE reverse charge 25%
  '4426': { box: 'ruta24', side: 'debit' },   // Inköp tjänster SE reverse charge 12%
  '4427': { box: 'ruta24', side: 'debit' },   // Inköp tjänster SE reverse charge 6%
  '4545': { box: 'ruta50', side: 'debit' },   // Beskattningsunderlag import 25%
  '4546': { box: 'ruta50', side: 'debit' },   // Beskattningsunderlag import 12%
  '4547': { box: 'ruta50', side: 'debit' },   // Beskattningsunderlag import 6%
}

const VAT_ACCOUNTS = Object.keys(ACCOUNT_RUTA)

/**
 * 26xx output VAT accounts feeding rutor 10/11/12, 30/31/32 and 60/61/62.
 * Derived from ACCOUNT_RUTA so the KPI vatLiability widget can never drift
 * from the momsdeklaration (ruta 49) calculation.
 */
export const VAT_OUTPUT_ACCOUNTS = Object.entries(ACCOUNT_RUTA)
  .filter(([account, mapping]) => account.startsWith('26') && mapping.side === 'credit')
  .map(([account]) => account)

/** Input VAT accounts feeding ruta 48 (2640-2649 series). */
export const VAT_INPUT_ACCOUNTS = Object.entries(ACCOUNT_RUTA)
  .filter(([, mapping]) => mapping.box === 'ruta48')
  .map(([account]) => account)

/**
 * The reverse-charge INPUT VAT accounts the momsdeklaration completeness check
 * compares rutor 30-32 against: 2645 (beräknad ingående moms på förvärv från
 * utlandet, EU and non-EU) and 2647 (ingående moms, omvänd betalningsskyldighet
 * i Sverige). The other five ruta 48 accounts are not reverse charge and stay
 * out, 2649 (blandad verksamhet) above all: counting it would reintroduce the
 * aggregation the sharpened check exists to remove.
 *
 * Mirrors RC_INPUT_ACCOUNTS in ./vat-declaration-checks, which keeps its copy
 * private. The two lists are pinned together behaviourally in
 * __tests__/vat-declaration.test.ts: it feeds the projected pair and a full
 * totals map carrying a balance on every OTHER ruta 48 account to
 * runVatDeclarationChecks and asserts identical findings, so widening the list
 * on one side without the other fails there.
 */
export const RC_INPUT_VAT_ACCOUNTS = ['2645', '2647'] as const

/**
 * Calculate period start and end dates
 */
export function calculatePeriodDates(
  periodType: VatPeriodType,
  year: number,
  period: number
): { start: string; end: string } {
  let startMonth: number
  let endMonth: number

  switch (periodType) {
    case 'monthly':
      // period is 1-12
      startMonth = period
      endMonth = period
      break
    case 'quarterly':
      // period is 1-4
      startMonth = (period - 1) * 3 + 1
      endMonth = period * 3
      break
    case 'yearly':
      // period is 1
      startMonth = 1
      endMonth = 12
      break
    default:
      startMonth = 1
      endMonth = 12
  }

  const startDate = new Date(year, startMonth - 1, 1)
  const endDate = new Date(year, endMonth, 0) // Last day of end month

  return {
    start: formatDate(startDate),
    end: formatDate(endDate),
  }
}

/**
 * Format date as YYYY-MM-DD
 */
function formatDate(date: Date): string {
  const y = date.getFullYear()
  const m = String(date.getMonth() + 1).padStart(2, '0')
  const d = String(date.getDate()).padStart(2, '0')
  return `${y}-${m}-${d}`
}

/**
 * Round to 2 decimal places
 */
function round(value: number): number {
  return Math.round(value * 100) / 100
}

/**
 * Resolve the start/end dates for a VAT period.
 *
 * Monthly and quarterly VAT periods are always calendar months/quarters
 * (kalendermånad / kalenderkvartal per SFL 26 kap), so they use the plain
 * calendar calculation.
 *
 * Annual VAT (helårsmoms), however, is reported per *räkenskapsår* (the
 * beskattningsår), not per calendar year (SFL 26 kap 10-11 §§). A räkenskapsår
 * can be extended or shortened (up to 18 months for a first/changed year per
 * BFL 3 kap 3 §), so a calendar Jan-Dec span would silently drop part of an
 * extended year (e.g. a first year 2025-07-03 → 2026-12-31). When the caller
 * supplies the fiscal period we therefore use its actual bounds. If the period
 * can't be resolved we fall back to the calendar span so behaviour degrades
 * gracefully instead of erroring.
 */
export async function resolvePeriodDates(
  supabase: SupabaseClient,
  companyId: string,
  periodType: VatPeriodType,
  year: number,
  period: number,
  fiscalPeriodId?: string
): Promise<{ start: string; end: string }> {
  if (periodType === 'yearly') {
    if (fiscalPeriodId) {
      const { data: fp } = await supabase
        .from('fiscal_periods')
        .select('period_start, period_end')
        .eq('id', fiscalPeriodId)
        .eq('company_id', companyId)
        .maybeSingle()
      if (fp?.period_start && fp?.period_end) {
        return { start: fp.period_start, end: fp.period_end }
      }
    } else {
      // No explicit fiscal period: resolve the räkenskapsår ending in `year`
      // instead of assuming a calendar FY. Helårsmoms is filed per
      // räkenskapsår (SFL 26 kap 10-11 §§), so for a broken fiscal year the
      // calendar-year assumption would put both the redovisningsperiod and
      // the figures on the wrong period. For calendar-FY companies this
      // resolves to Jan-Dec of `year`, identical to the arithmetic fallback.
      const { data: fp } = await supabase
        .from('fiscal_periods')
        .select('period_start, period_end')
        .eq('company_id', companyId)
        .gte('period_end', `${year}-01-01`)
        .lte('period_end', `${year}-12-31`)
        .order('period_end', { ascending: false })
        .limit(1)
        .maybeSingle()
      if (fp?.period_start && fp?.period_end) {
        return { start: fp.period_start, end: fp.period_end }
      }
    }
  }
  return calculatePeriodDates(periodType, year, period)
}

/**
 * Accounts a momsredovisning settles the period's net against: 2650
 * (Redovisningskonto för moms, att betala) and 1650 (Momsfordran, att återfå).
 * Mirrors VAT_SETTLEMENT_ACCOUNT/VAT_REFUND_ACCOUNT in vat-settlement.ts,
 * which imports from this module and therefore cannot be imported here.
 */
export const VAT_SETTLEMENT_NET_ACCOUNTS = ['2650', '1650']

/** A momsredovisning entry detected by shape rather than source_type. */
export interface VatSettlementShapedEntry {
  id: string
  status: string
  entry_date: string
  source_type: string | null
  voucher_series: string | null
  voucher_number: number | null
}

export interface VatAccountTotals {
  totals: Map<string, { debit: number; credit: number }>
  /**
   * Untagged momsredovisning entries found in the period (manual vouchers,
   * SIE-imported settlements, stornos of a settlement). Already excluded
   * from `totals`; surfaced so the settlement proposal can warn and gate.
   */
  settlementShapedEntries: VatSettlementShapedEntry[]
  /**
   * Posted/reversed entry counts per source_type for the whole period,
   * INCLUDING tagged vat_settlement entries (they never match the
   * invoice/transaction buckets, and the metadata scan always counted them).
   * Comes back in the same RPC round trip so the declaration metadata no
   * longer needs its own paginated entry scan.
   */
  sourceTypeCounts: Record<string, number>
}

/** Wire shape of the get_vat_declaration_totals RPC jsonb payload. */
interface VatTotalsRpcPayload {
  totals: Array<{ account_number: string; debit: number; credit: number }>
  settlement_shaped_entries: VatSettlementShapedEntry[]
  source_type_counts: Record<string, number>
}

/**
 * Fetch and aggregate debit/credit totals per VAT-relevant account
 * (ACCOUNT_RUTA) for a period. Shared by the declaration calculation and the
 * settlement proposal (lib/reports/vat-settlement.ts) so the two can never
 * disagree on which ledger lines count.
 *
 * Momsredovisning entries are excluded. They are bookkeeping about the
 * declaration, not VAT-bearing business activity; including them would zero
 * out the rutor the moment the settlement is booked, turning the report, its
 * exports, and a later Skatteverket submission into an empty declaration
 * (#984). Two detection paths:
 *
 *   - tagged: source_type 'vat_settlement' (the app's own settlement flow),
 *     filtered in the query;
 *   - shaped: an entry with at least one line on a declaration account
 *     (ACCOUNT_RUTA) and at least one on 2650/1650. This catches settlements
 *     booked before the tagged flow existed, manual vouchers, SIE-imported
 *     settlements, and storno reversals of a settlement (source_type
 *     'storno', which would otherwise re-inflate the rutor after annullera).
 *
 * Opening-balance entries are exempt from the shape rule: 26xx balances
 * carried in by a migrating company are unsettled VAT that belongs in the
 * next declaration, even when the same entry carries a 2650/1650 balance.
 */
export async function fetchVatAccountTotals(
  supabase: SupabaseClient,
  companyId: string,
  start: string,
  end: string,
  dynamicRuta05Accounts: string[] = []
): Promise<VatAccountTotals> {
  // Aggregation, settlement-shape detection, and source_type counts all
  // happen in one SQL pass (get_vat_declaration_totals). The previous
  // implementation paged every entry + line for the period through PostgREST
  // and reduced in JS: dozens of round trips for a busy quarter. The account
  // lists are parameters so ACCOUNT_RUTA stays the single source of truth.
  //
  // The company's own ruta 05 accounts join p_accounts (they must be summed)
  // but deliberately NOT p_ruta_accounts. That second list is the settlement
  // SHAPE detector: an entry with a line on it plus a line on 2650/1650 is
  // classified a momsredovisning and dropped from the totals entirely. A plain
  // sale booked 1930 / 3013 / 2650 (a company clearing moms straight off the
  // revenue voucher) would then vanish from its own declaration. The fixed
  // ACCOUNT_RUTA list is what defines settlement shape; user accounts widen
  // what is measured, never what counts as a momsredovisning.
  const { data, error } = await supabase.rpc('get_vat_declaration_totals', {
    p_company_id: companyId,
    p_start: start,
    p_end: end,
    p_accounts: [...VAT_ACCOUNTS, ...VAT_SETTLEMENT_NET_ACCOUNTS, ...dynamicRuta05Accounts],
    p_ruta_accounts: VAT_ACCOUNTS,
    p_net_accounts: VAT_SETTLEMENT_NET_ACCOUNTS,
  })
  if (error) {
    throw new Error(`get_vat_declaration_totals failed: ${error.message}`)
  }

  const payload = (data ?? {}) as Partial<VatTotalsRpcPayload>
  const totals = new Map<string, { debit: number; credit: number }>()
  for (const row of payload.totals ?? []) {
    totals.set(row.account_number, {
      debit: Number(row.debit) || 0,
      credit: Number(row.credit) || 0,
    })
  }

  return {
    totals,
    settlementShapedEntries: payload.settlement_shaped_entries ?? [],
    sourceTypeCounts: payload.source_type_counts ?? {},
  }
}

/**
 * Map aggregated per-account totals to the momsdeklaration boxes, including
 * the recomputed ruta 49 net (FK009). Pure projection over ACCOUNT_RUTA plus
 * the company's own ruta 05 accounts (fetchDynamicRuta05Accounts).
 *
 * `dynamicRuta05Accounts` is optional so callers that only need the 26xx boxes
 * keep working untouched: ruta 05 is a beskattningsunderlag, not moms, so it
 * never reaches ruta 49 and the settlement proposal nets the same either way.
 */
export function rutorFromTotals(
  totals: Map<string, { debit: number; credit: number }>,
  dynamicRuta05Accounts: string[] = []
): VatDeclarationRutor {
  const rutor: VatDeclarationRutor = {
    ruta05: 0, ruta06: 0, ruta07: 0, ruta08: 0,
    ruta10: 0, ruta11: 0, ruta12: 0,
    ruta20: 0, ruta21: 0, ruta22: 0, ruta23: 0, ruta24: 0,
    ruta30: 0, ruta31: 0, ruta32: 0,
    ruta35: 0, ruta36: 0, ruta37: 0, ruta38: 0,
    ruta39: 0, ruta40: 0, ruta41: 0, ruta42: 0,
    ruta48: 0, ruta49: 0,
    ruta50: 0, ruta60: 0, ruta61: 0, ruta62: 0,
  }

  for (const [account, mapping] of Object.entries(ACCOUNT_RUTA)) {
    const t = totals.get(account)
    if (!t) continue
    const balance = mapping.side === 'credit'
      ? t.credit - t.debit
      : t.debit - t.credit
    rutor[mapping.box] = round(rutor[mapping.box] + balance)
  }

  // The company's own momspliktiga intäktskonton. Always credit-side: these are
  // revenue accounts by construction (account_class 3).
  for (const account of dynamicRuta05Accounts) {
    const t = totals.get(account)
    if (!t) continue
    rutor.ruta05 = round(rutor.ruta05 + (t.credit - t.debit))
  }

  // FK009: summaMoms = (10 + 11 + 12 + 30 + 31 + 32 + 60 + 61 + 62) - 48
  rutor.ruta49 = round(
    rutor.ruta10 + rutor.ruta11 + rutor.ruta12 +
    rutor.ruta30 + rutor.ruta31 + rutor.ruta32 +
    rutor.ruta60 + rutor.ruta61 + rutor.ruta62 -
    rutor.ruta48
  )

  return rutor
}

/**
 * Project the reverse-charge input pair (2645/2647) out of a full totals map,
 * for `VatDeclaration.rcInputAccountTotals`.
 *
 * Both keys are always present, zeros included, so the wire shape is stable and
 * an absent field keeps meaning "this producer does not carry the pair" rather
 * than "no reverse charge in the period".
 */
function rcInputTotals(
  totals: Map<string, { debit: number; credit: number }>
): Record<string, { debit: number; credit: number }> {
  const pair: Record<string, { debit: number; credit: number }> = {}
  for (const account of RC_INPUT_VAT_ACCOUNTS) {
    const t = totals.get(account)
    pair[account] = { debit: round(t?.debit ?? 0), credit: round(t?.credit ?? 0) }
  }
  return pair
}

/**
 * Rebuild the per-account totals map `runVatDeclarationChecks` takes as its
 * optional second argument, from a declaration that may have arrived as JSON
 * over HTTP.
 *
 * Returns undefined when the pair is absent, which makes the check fall back to
 * its weaker ruta 48 comparison. That is deliberate: an empty map would read as
 * "0 kr beräknad ingående moms" and turn a correct declaration into a warning.
 */
export function rcInputTotalsFromDeclaration(
  declaration: Pick<VatDeclaration, 'rcInputAccountTotals'>
): VatCheckAccountTotals | undefined {
  const pair = declaration.rcInputAccountTotals
  return pair ? new Map(Object.entries(pair)) : undefined
}

/**
 * Calculate VAT declaration from the general ledger.
 *
 * Sums posted journal entry lines on the BAS accounts in ACCOUNT_RUTA per the
 * SKV 4700 form mapping. Pure ledger projection: no supplier classification
 * or other side-channel signals.
 *
 *   - ruta 49 = (10 + 11 + 12 + 30 + 31 + 32 + 60 + 61 + 62) - 48
 *
 * INVARIANT: the company's accounting method (faktureringsmetoden vs
 * kontantmetoden) needs no parameter here and must not become one. The method
 * is already baked into journal entry TIMING: kontantmetod companies post
 * VAT-bearing entries at payment date, faktureringsmetod companies at invoice
 * date, so summing posted lines per period is correct for both. A method
 * parameter existed until 2026-07-23 and was silently ignored; it was removed
 * so no future code path can branch on a value that callers hard-code.
 */
export async function calculateVatDeclaration(
  supabase: SupabaseClient,
  companyId: string,
  periodType: VatPeriodType,
  year: number,
  period: number,
  options: { fiscalPeriodId?: string } = {}
): Promise<VatDeclaration> {
  // For yearly VAT this resolves to the räkenskapsår bounds (when a fiscal
  // period is supplied), not the calendar year: see resolvePeriodDates.
  const { start, end } = await resolvePeriodDates(
    supabase, companyId, periodType, year, period, options.fiscalPeriodId
  )

  // Which of the company's OWN class 3 accounts count as momspliktig
  // försäljning. Resolved from their "Standard moms" rather than a fixed BAS
  // list, because Accounted seeds no varugrupp accounts: every 3011/3013-style
  // konto is user-added and would otherwise never be fetched at all (#1261).
  const dynamicRuta05 = await fetchDynamicRuta05Accounts(supabase, companyId)

  // Fetch and aggregate posted VAT-account activity for the period. The same
  // RPC round trip carries the per-source_type entry counts for the metadata.
  const { totals, sourceTypeCounts } = await fetchVatAccountTotals(
    supabase, companyId, start, end, dynamicRuta05.accounts
  )

  // Map account balances to momsdeklaration boxes
  const rutor = rutorFromTotals(totals, dynamicRuta05.accounts)

  // Compute per-rate base amounts from individual revenue accounts. The
  // company's own accounts carry their rate on the konto itself, so they land
  // in the same three buckets: without that, a 3013 company would show a
  // ruta 05 base that none of base25/12/6 accounts for.
  //
  // These three are REPORTING metadata (breakdown.invoices), not check inputs:
  // vat-declaration-checks.ts derives its expected base from the output-VAT
  // rutor (ruta10/0.25 + ruta11/0.12 + ruta12/0.06) and never reads base25/12/6.
  // So an incomplete split understates nothing that gets filed; it only makes
  // the breakdown fail to add up to ruta 05.
  const revenueByRate = {
    base25: 0,  // 3001
    base12: 0,  // 3002
    base6: 0,   // 3003
  }
  const RATE_BUCKET = { 0.25: 'base25', 0.12: 'base12', 0.06: 'base6' } as const
  for (const [account, rate] of [['3001', 'base25'], ['3002', 'base12'], ['3003', 'base6']] as const) {
    const t = totals.get(account)
    if (t) revenueByRate[rate] = round(t.credit - t.debit)
  }
  for (const [account, rate] of dynamicRuta05.rateByAccount) {
    const t = totals.get(account)
    if (!t) continue
    const bucket = RATE_BUCKET[rate as keyof typeof RATE_BUCKET]
    if (!bucket) continue
    revenueByRate[bucket] = round(revenueByRate[bucket] + (t.credit - t.debit))
  }
  // Accounts the static map ALREADY sums into ruta 05 (3000, the 30xx
  // gruppkonto) but whose rate only exists as the konto's "Standard moms".
  // Rate-only on purpose: their balance is in ruta 05 either way, so adding
  // them to dynamicRuta05.accounts would double the filed figure.
  for (const [account, rate] of dynamicRuta05.staticRateByAccount) {
    const t = totals.get(account)
    if (!t) continue
    const bucket = RATE_BUCKET[rate as keyof typeof RATE_BUCKET]
    if (!bucket) continue
    revenueByRate[bucket] = round(revenueByRate[bucket] + (t.credit - t.debit))
  }

  // Entry counts by source type for metadata: aggregated by the RPC in the
  // same round trip as the totals (SQL GROUP BY, so a busy VAT period can
  // never truncate the counts).
  const invoiceSources = new Set([
    'invoice_created', 'invoice_paid', 'invoice_cash_payment', 'credit_note',
  ])
  let invoiceCount = 0
  let transactionCount = 0
  for (const [sourceType, n] of Object.entries(sourceTypeCounts)) {
    if (invoiceSources.has(sourceType)) invoiceCount += n
    else if (sourceType === 'bank_transaction') transactionCount += n
  }

  return {
    period: { type: periodType, year, period, start, end },
    rutor,
    // The 2645/2647 pair travels with the declaration so an HTTP caller can run
    // the sharp RC_INPUT_VAT_MISMATCH comparison instead of the ruta 48
    // fallback: see VatDeclaration.rcInputAccountTotals.
    rcInputAccountTotals: rcInputTotals(totals),
    invoiceCount,
    transactionCount,
    breakdown: {
      invoices: {
        ruta05: rutor.ruta05,
        ruta06: rutor.ruta06,
        ruta07: rutor.ruta07,
        ruta10: rutor.ruta10,
        ruta11: rutor.ruta11,
        ruta12: rutor.ruta12,
        ruta39: rutor.ruta39,
        ruta40: rutor.ruta40,
        base25: revenueByRate.base25,
        base12: revenueByRate.base12,
        base6: revenueByRate.base6,
      },
      transactions: { ruta48: rutor.ruta48 },
      receipts: { ruta48: 0 },
      reverseCharge: {
        ruta20: rutor.ruta20,
        ruta21: rutor.ruta21,
        ruta22: rutor.ruta22,
        ruta23: rutor.ruta23,
        ruta24: rutor.ruta24,
        ruta30: rutor.ruta30,
        ruta31: rutor.ruta31,
        ruta32: rutor.ruta32,
      },
    },
  }
}

/**
 * Get a summary of the VAT declaration for display
 */
export function getVatDeclarationSummary(declaration: VatDeclaration): {
  totalOutputVat: number
  totalInputVat: number
  vatToPay: number
  isRefund: boolean
} {
  const totalOutputVat = round(
    declaration.rutor.ruta10 +
    declaration.rutor.ruta11 +
    declaration.rutor.ruta12 +
    declaration.rutor.ruta30 +
    declaration.rutor.ruta31 +
    declaration.rutor.ruta32 +
    declaration.rutor.ruta60 +
    declaration.rutor.ruta61 +
    declaration.rutor.ruta62
  )

  const totalInputVat = declaration.rutor.ruta48
  const vatToPay = declaration.rutor.ruta49

  return {
    totalOutputVat,
    totalInputVat,
    vatToPay,
    isRefund: vatToPay < 0,
  }
}

/**
 * Format period label for display
 */
export function formatPeriodLabel(
  periodType: VatPeriodType,
  year: number,
  period: number
): string {
  switch (periodType) {
    case 'monthly':
      const monthNames = [
        'Januari', 'Februari', 'Mars', 'April', 'Maj', 'Juni',
        'Juli', 'Augusti', 'September', 'Oktober', 'November', 'December'
      ]
      return `${monthNames[period - 1]} ${year}`
    case 'quarterly':
      return `Kvartal ${period} ${year}`
    case 'yearly':
      return `Helår ${year}`
    default:
      return `${year}`
  }
}