accounted/app/api/salary/runs/[id]/preview/route.ts

import { NextResponse } from 'next/server'
import { ensureInitialized } from '@/lib/init'
import { withRouteContext } from '@/lib/api/with-route-context'
import { SALARY_ACCOUNTS, getLineItemAccount } from '@/lib/salary/account-mapping'
import { roundOre } from '@/lib/money'
import type { CreateJournalEntryLineInput } from '@/types'

ensureInitialized()

/**
 * Preview the journal entries that would be created when booking this salary run.
 * Shows exact BAS accounts and amounts: this is a key differentiator.
 */
export const GET = withRouteContext<{ params: Promise<{ id: string }> }>(
  'salary.run.preview',
  async (_request, ctx, { params }) => {
    const { id } = await params
    const { supabase, companyId } = ctx

    const { data: run, error: runError } = await supabase
      .from('salary_runs')
      .select('*')
      .eq('id', id)
      .eq('company_id', companyId)
      .single()

    if (runError || !run) {
      return NextResponse.json({ error: 'Lönekörning hittades inte' }, { status: 404 })
    }

    // Load employees with line items
    const { data: employees } = await supabase
      .from('salary_run_employees')
      .select('*, employee:employees(employment_type), line_items:salary_line_items(*)')
      .eq('salary_run_id', id)

    if (!employees || employees.length === 0) {
      return NextResponse.json({ error: 'Inga beräknade resultat: kör beräkning först' }, { status: 400 })
    }

    const periodLabel = `${run.period_year}-${String(run.period_month).padStart(2, '0')}`
    const desc = `Lön ${periodLabel}`

    // Build salary entry preview
    const salaryLines: CreateJournalEntryLineInput[] = []
    const expenseByAccount = new Map<string, number>()
    // Net deductions book as settlement lines on their mapped liability or
    // receivable account, mirroring createSalaryEntry; they must not merge
    // into the 7xxx expense buckets.
    const netDeductionByAccount = new Map<string, number>()

    for (const sre of employees) {
      for (const li of sre.line_items || []) {
        if (li.is_net_deduction) {
          const account = li.account_number || getLineItemAccount(li.item_type, sre.employee?.employment_type || 'employee')
          netDeductionByAccount.set(account, (netDeductionByAccount.get(account) || 0) + li.amount)
          continue
        }
        if (li.is_gross_deduction) continue
        const account = li.account_number || getLineItemAccount(li.item_type, sre.employee?.employment_type || 'employee')
        expenseByAccount.set(account, (expenseByAccount.get(account) || 0) + li.amount)
      }
    }

    for (const [account, amount] of expenseByAccount) {
      if (amount === 0) continue
      salaryLines.push({
        account_number: account,
        debit_amount: amount > 0 ? Math.round(amount * 100) / 100 : 0,
        credit_amount: amount < 0 ? Math.round(Math.abs(amount) * 100) / 100 : 0,
        line_description: `${desc}`,
      })
    }

    for (const [account, amount] of netDeductionByAccount) {
      const rounded = roundOre(Math.abs(amount))
      if (rounded === 0) continue
      salaryLines.push({
        account_number: account,
        debit_amount: amount > 0 ? rounded : 0,
        credit_amount: amount < 0 ? rounded : 0,
        line_description: `${desc}`,
      })
    }

    const totalTax = employees.reduce((sum, e) => sum + e.tax_withheld, 0)
    if (totalTax > 0) {
      salaryLines.push({
        account_number: SALARY_ACCOUNTS.TAX_WITHHELD,
        debit_amount: 0,
        credit_amount: Math.round(totalTax * 100) / 100,
        line_description: `${desc}: Personalskatt`,
      })
    }

    const totalNet = employees.reduce((sum, e) => sum + e.net_salary, 0)
    if (totalNet > 0) {
      salaryLines.push({
        account_number: SALARY_ACCOUNTS.BANK,
        debit_amount: 0,
        credit_amount: Math.round(totalNet * 100) / 100,
        line_description: `${desc}: Nettolön`,
      })
    }

    // Build avgifter entry preview: skipped for a nollkörning (0 avgifter),
    // mirroring the vacation/pension guards below. The bookkeeping engine never
    // posts an all-zero 7510/2731 voucher (see book/route.ts nollkörning path),
    // so previewing one would falsely imply a verifikat that is never created.
    const totalAvgifter = employees.reduce((sum, e) => sum + e.avgifter_amount, 0)
    const roundedAvgifter = Math.round(totalAvgifter * 100) / 100
    const avgifterLines: CreateJournalEntryLineInput[] = roundedAvgifter !== 0
      ? [
          {
            account_number: SALARY_ACCOUNTS.AVGIFTER_EXPENSE,
            debit_amount: roundedAvgifter,
            credit_amount: 0,
            line_description: `${desc}: Arbetsgivaravgifter`,
          },
          {
            account_number: SALARY_ACCOUNTS.AVGIFTER_LIABILITY,
            debit_amount: 0,
            credit_amount: roundedAvgifter,
            line_description: `${desc}: Arbetsgivaravgifter`,
          },
        ]
      : []

    // Build vacation entry preview
    const totalVacation = employees.reduce((sum, e) => sum + e.vacation_accrual, 0)
    const totalVacationAvgifter = employees.reduce((sum, e) => sum + e.vacation_accrual_avgifter, 0)
    const vacationLines: CreateJournalEntryLineInput[] = []
    if (totalVacation > 0) {
      vacationLines.push(
        {
          account_number: SALARY_ACCOUNTS.VACATION_ACCRUAL_EXPENSE,
          debit_amount: Math.round(totalVacation * 100) / 100,
          credit_amount: 0,
          line_description: `${desc}: Semesteravsättning`,
        },
        {
          account_number: SALARY_ACCOUNTS.VACATION_ACCRUAL_LIABILITY,
          debit_amount: 0,
          credit_amount: Math.round(totalVacation * 100) / 100,
          line_description: `${desc}: Semesteravsättning`,
        }
      )
    }
    if (totalVacationAvgifter > 0) {
      vacationLines.push(
        {
          account_number: SALARY_ACCOUNTS.VACATION_AVGIFTER_EXPENSE,
          debit_amount: Math.round(totalVacationAvgifter * 100) / 100,
          credit_amount: 0,
          line_description: `${desc}: Sociala avgifter semester`,
        },
        {
          account_number: SALARY_ACCOUNTS.VACATION_AVGIFTER_LIABILITY,
          debit_amount: 0,
          credit_amount: Math.round(totalVacationAvgifter * 100) / 100,
          line_description: `${desc}: Sociala avgifter semester`,
        }
      )
    }

    // Build pension entry preview (löneväxling, per deductions-lonevaxling.md)
    // This would be populated from salary_line_items with type 'gross_deduction_pension'
    // For now, pension preview is shown when pension line items exist
    const pensionLineItems = employees.flatMap(e =>
      ((e.line_items || []) as Array<Record<string, unknown>>)
        .filter(li => li.item_type === 'gross_deduction_pension')
    )
    const pensionLines: CreateJournalEntryLineInput[] = []
    if (pensionLineItems.length > 0) {
      const totalPensionDeduction = Math.abs(pensionLineItems.reduce((s, li) => s + ((li.amount as number) || 0), 0))
      const pensionContribution = Math.round(totalPensionDeduction * 1.058 * 100) / 100
      const slp = Math.round(pensionContribution * 0.2426 * 100) / 100
      if (pensionContribution > 0) {
        pensionLines.push(
          { account_number: '7410', debit_amount: pensionContribution, credit_amount: 0, line_description: `${desc}: Pensionsförsäkringspremier` },
          { account_number: '2740', debit_amount: 0, credit_amount: pensionContribution, line_description: `${desc}: Pensionsförsäkringspremier` },
        )
        if (slp > 0) {
          pensionLines.push(
            { account_number: '7533', debit_amount: slp, credit_amount: 0, line_description: `${desc}: Särskild löneskatt 24,26%` },
            { account_number: '2514', debit_amount: 0, credit_amount: slp, line_description: `${desc}: Särskild löneskatt 24,26%` },
          )
        }
      }
    }

    return NextResponse.json({
      data: {
        // Each entry is null when it has no lines: a nollkörning posts nothing,
        // so the salary and avgifter entries fall away just like vacation/pension
        // already do, and the UI can simply skip the null ones.
        salaryEntry: salaryLines.length > 0 ? {
          description: desc,
          lines: salaryLines,
        } : null,
        avgifterEntry: avgifterLines.length > 0 ? {
          description: `${desc}: Arbetsgivaravgifter`,
          lines: avgifterLines,
        } : null,
        vacationEntry: vacationLines.length > 0 ? {
          description: `${desc}: Semesteravsättning`,
          lines: vacationLines,
        } : null,
        pensionEntry: pensionLines.length > 0 ? {
          description: `${desc}: Pensionsavsättning`,
          lines: pensionLines,
        } : null,
      },
    })
  },
)