accounting-frontend/src/utils/accounting.ts

import type {
  Account,
  AccountType,
  Invoice,
  InvoiceLine,
  Payslip,
  Voucher,
} from '../types'

export interface LineTotals {
  gross: number
  discount: number
  taxable: number
  tax: number
  net: number
}

/** Computes the monetary breakdown of a single invoice line. */
export function lineTotals(line: InvoiceLine): LineTotals {
  const gross = line.quantity * line.unitPrice
  const discount = Math.min(line.discount, gross)
  const taxable = gross - discount
  const tax = (taxable * line.taxRate) / 100
  return { gross, discount, taxable, tax, net: taxable + tax }
}

export interface InvoiceTotals {
  gross: number
  discount: number
  taxable: number
  tax: number
  net: number
}

/** Aggregates all line totals of an invoice. */
export function invoiceTotals(invoice: Invoice): InvoiceTotals {
  return invoice.lines.reduce<InvoiceTotals>(
    (acc, line) => {
      const t = lineTotals(line)
      return {
        gross: acc.gross + t.gross,
        discount: acc.discount + t.discount,
        taxable: acc.taxable + t.taxable,
        tax: acc.tax + t.tax,
        net: acc.net + t.net,
      }
    },
    { gross: 0, discount: 0, taxable: 0, tax: 0, net: 0 },
  )
}

export interface VoucherBalance {
  debit: number
  credit: number
  balanced: boolean
}

/** Sums debit/credit of a voucher and reports whether it balances. */
export function voucherBalance(voucher: Voucher): VoucherBalance {
  const debit = voucher.lines.reduce((sum, l) => sum + l.debit, 0)
  const credit = voucher.lines.reduce((sum, l) => sum + l.credit, 0)
  return { debit, credit, balanced: Math.abs(debit - credit) < 0.001 && debit > 0 }
}

export interface AccountBalance {
  account: Account
  debit: number
  credit: number
  balance: number
}

const isDebitNature = (type: AccountType): boolean =>
  type === 'asset' || type === 'expense'

/**
 * Builds a trial balance from posted vouchers and account opening balances.
 * Only leaf (non-group) accounts carry balances.
 */
export function trialBalance(
  accounts: Account[],
  vouchers: Voucher[],
): AccountBalance[] {
  const totals = new Map<string, { debit: number; credit: number }>()

  for (const account of accounts) {
    if (account.isGroup) continue
    const opening = account.openingBalance || 0
    totals.set(account.id, {
      debit: isDebitNature(account.type) ? Math.max(opening, 0) : Math.max(-opening, 0),
      credit: isDebitNature(account.type) ? Math.max(-opening, 0) : Math.max(opening, 0),
    })
  }

  for (const voucher of vouchers) {
    if (voucher.status !== 'posted') continue
    for (const line of voucher.lines) {
      const entry = totals.get(line.accountId)
      if (!entry) continue
      entry.debit += line.debit
      entry.credit += line.credit
    }
  }

  return accounts
    .filter((account) => !account.isGroup)
    .map((account) => {
      const entry = totals.get(account.id) ?? { debit: 0, credit: 0 }
      const net = entry.debit - entry.credit
      const balance = isDebitNature(account.type) ? net : -net
      return { account, debit: entry.debit, credit: entry.credit, balance }
    })
}

export interface LedgerRow {
  voucherId: string
  voucherNumber: number
  date: string
  description: string
  debit: number
  credit: number
  running: number
}

/** Produces the running general-ledger movements for a single account. */
export function accountLedger(
  accountId: string,
  account: Account | undefined,
  vouchers: Voucher[],
): LedgerRow[] {
  let running = account?.openingBalance ?? 0
  const rows: LedgerRow[] = []

  const sorted = [...vouchers]
    .filter((v) => v.status === 'posted')
    .sort((a, b) => a.date.localeCompare(b.date) || a.number - b.number)

  // Debit-nature accounts (asset, expense) increase with debits.
  // Credit-nature accounts (liability, equity, income) increase with credits.
  const debitNature = account ? isDebitNature(account.type) : true

  for (const voucher of sorted) {
    for (const line of voucher.lines) {
      if (line.accountId !== accountId) continue
      running += debitNature ? line.debit - line.credit : line.credit - line.debit
      rows.push({
        voucherId: voucher.id,
        voucherNumber: voucher.number,
        date: voucher.date,
        description: line.description || voucher.description,
        debit: line.debit,
        credit: line.credit,
        running,
      })
    }
  }

  return rows
}

export interface IncomeStatement {
  income: number
  expense: number
  profit: number
}

export function incomeStatement(balances: AccountBalance[]): IncomeStatement {
  const income = balances
    .filter((b) => b.account.type === 'income')
    .reduce((sum, b) => sum + b.balance, 0)
  const expense = balances
    .filter((b) => b.account.type === 'expense')
    .reduce((sum, b) => sum + b.balance, 0)
  return { income, expense, profit: income - expense }
}

export interface BalanceSheet {
  assets: number
  liabilities: number
  equity: number
  retainedEarnings: number
}

export function balanceSheet(balances: AccountBalance[]): BalanceSheet {
  const sumByType = (type: AccountType): number =>
    balances
      .filter((b) => b.account.type === type)
      .reduce((sum, b) => sum + b.balance, 0)

  const income = sumByType('income')
  const expense = sumByType('expense')

  return {
    assets: sumByType('asset'),
    liabilities: sumByType('liability'),
    equity: sumByType('equity'),
    retainedEarnings: income - expense,
  }
}

/** Net pay of a payslip: earnings minus all deductions. */
export function payslipNet(payslip: Payslip): number {
  return (
    payslip.baseSalary +
    payslip.overtime +
    payslip.bonus -
    payslip.deductions -
    payslip.insurance -
    payslip.tax
  )
}