import type { SupabaseClient } from '@supabase/supabase-js'
import { generateTrialBalance } from './trial-balance'
import type { BalanceSheetReport, BalanceSheetSection, TrialBalanceRow } from '@/types'

/**
 * Generate Balance Sheet (Balansräkning)
 *
 * Filters to class 1-2 accounts:
 * - Tillgångar (1xxx): Assets
 * - Eget kapital och skulder (2xxx): Equity and liabilities
 */
export async function generateBalanceSheet(
  supabase: SupabaseClient,
  userId: string,
  fiscalPeriodId: string
): Promise<BalanceSheetReport> {
  const { rows } = await generateTrialBalance(supabase, userId, fiscalPeriodId)

  // Filter to balance sheet accounts (class 1-2)
  const balanceRows = rows.filter(
    (r) => r.account_class >= 1 && r.account_class <= 2
  )

  // Asset sections (class 1)
  const assetSections = buildBalanceSections(
    balanceRows.filter((r) => r.account_class === 1),
    {
      '10': 'Immateriella anläggningstillgångar',
      '11': 'Byggnader och mark',
      '12': 'Maskiner och inventarier',
      '13': 'Finansiella anläggningstillgångar',
      '14': 'Lager och pågående arbeten',
      '15': 'Kundfordringar',
      '16': 'Övriga kortfristiga fordringar',
      '17': 'Förutbetalda kostnader och upplupna intäkter',
      '18': 'Kortfristiga placeringar',
      '19': 'Kassa och bank',
    },
    'debit' // Assets have debit normal balance
  )

  // Equity and liability sections (class 2)
  const equityLiabilitySections = buildBalanceSections(
    balanceRows.filter((r) => r.account_class === 2),
    {
      '20': 'Eget kapital',
      '21': 'Obeskattade reserver',
      '22': 'Avsättningar',
      '23': 'Långfristiga skulder',
      '24': 'Kortfristiga skulder',
      '25': 'Skatteskulder',
      '26': 'Moms och punktskatter',
      '27': 'Personalens skatter och avgifter',
      '28': 'Övriga kortfristiga skulder',
      '29': 'Upplupna kostnader och förutbetalda intäkter',
    },
    'credit' // Equity/liabilities have credit normal balance
  )

  // Calculate period result from income/expense accounts (class 3-8)
  // Before year-end closing, this result lives on class 3-8 accounts and must
  // be included in equity for the balance sheet to balance.
  const incomeExpenseRows = rows.filter(
    (r) => r.account_class >= 3 && r.account_class <= 8
  )
  const periodResult = Math.round(
    incomeExpenseRows.reduce(
      (sum, r) => sum + (r.closing_credit - r.closing_debit),
      0
    ) * 100
  ) / 100

  // Add period result as a synthetic section under equity if non-zero
  if (Math.abs(periodResult) > 0.005) {
    equityLiabilitySections.push({
      title: 'Årets resultat',
      rows: [
        {
          account_number: '',
          account_name: 'Beräknat resultat',
          amount: periodResult,
        },
      ],
      subtotal: periodResult,
    })
  }

  const totalAssets = assetSections.reduce((sum, s) => sum + s.subtotal, 0)
  const totalEquityLiabilities = equityLiabilitySections.reduce((sum, s) => sum + s.subtotal, 0)

  return {
    asset_sections: assetSections.filter((s) => s.rows.length > 0),
    total_assets: Math.round(totalAssets * 100) / 100,
    equity_liability_sections: equityLiabilitySections.filter((s) => s.rows.length > 0),
    total_equity_liabilities: Math.round(totalEquityLiabilities * 100) / 100,
    period: { start: '', end: '' },
  }
}

function buildBalanceSections(
  rows: TrialBalanceRow[],
  groupLabels: Record<string, string>,
  normalBalance: 'debit' | 'credit'
): BalanceSheetSection[] {
  const sections: BalanceSheetSection[] = []

  for (const [groupCode, title] of Object.entries(groupLabels)) {
    const groupRows = rows.filter((r) => r.account_number.startsWith(groupCode))
    if (groupRows.length === 0) continue

    const sectionRows = groupRows.map((r) => {
      const amount =
        normalBalance === 'debit'
          ? r.closing_debit - r.closing_credit
          : r.closing_credit - r.closing_debit

      return {
        account_number: r.account_number,
        account_name: r.account_name,
        amount: Math.round(amount * 100) / 100,
      }
    })

    const subtotal = sectionRows.reduce((sum, r) => sum + r.amount, 0)

    sections.push({
      title,
      rows: sectionRows.filter((r) => Math.abs(r.amount) > 0.005),
      subtotal: Math.round(subtotal * 100) / 100,
    })
  }

  return sections
}