import { getBASReference } from './bas-reference'

export type AccountType =
  | 'asset'
  | 'liability'
  | 'equity'
  | 'revenue'
  | 'expense'
  | 'untaxed_reserves'

export type NormalBalance = 'debit' | 'credit'

export interface ClassifiedAccount {
  account_type: AccountType
  normal_balance: NormalBalance
}

/**
 * Map a 4-digit BAS account number to its account_type and normal_balance.
 *
 * Strategy:
 *   1. If the number is in BAS_REFERENCE, return that authoritative entry.
 *   2. Otherwise fall back to a group-based heuristic aligned with BAS 2026.
 *
 * Class-8 groups are subtle: 80/81/82/83/87/88 are intäkter (revenue), 84/89 are
 * kostnader (expense). The legacy heuristic defaulted everything not in 83/84 to
 * expense, which silently misclassified dividends, capital gains, and
 * bokslutsdispositioner.
 */
export function classifyAccount(accountNumber: string): ClassifiedAccount {
  const ref = getBASReference(accountNumber)
  if (ref) {
    return { account_type: ref.account_type, normal_balance: ref.normal_balance }
  }

  const cls = parseInt(accountNumber[0], 10)
  const group = parseInt(accountNumber.substring(0, 2), 10)

  switch (cls) {
    case 1:
      return { account_type: 'asset', normal_balance: 'debit' }
    case 2:
      if (group === 20) return { account_type: 'equity', normal_balance: 'credit' }
      if (group === 21) return { account_type: 'untaxed_reserves', normal_balance: 'credit' }
      return { account_type: 'liability', normal_balance: 'credit' }
    case 3:
      return { account_type: 'revenue', normal_balance: 'credit' }
    case 4:
    case 5:
    case 6:
    case 7:
      return { account_type: 'expense', normal_balance: 'debit' }
    case 8:
      if (group >= 80 && group <= 83) return { account_type: 'revenue', normal_balance: 'credit' }
      if (group === 84) return { account_type: 'expense', normal_balance: 'debit' }
      if (group === 85) return { account_type: 'revenue', normal_balance: 'credit' }
      if (group === 86) return { account_type: 'expense', normal_balance: 'debit' }
      if (group === 87 || group === 88) return { account_type: 'revenue', normal_balance: 'credit' }
      if (group === 89) return { account_type: 'expense', normal_balance: 'debit' }
      return { account_type: 'expense', normal_balance: 'debit' }
    default:
      return { account_type: 'expense', normal_balance: 'debit' }
  }
}