import type { SupabaseClient } from '@supabase/supabase-js'

export interface SupplierLedgerEntry {
  supplier_id: string
  supplier_name: string
  current: number
  days_1_30: number
  days_31_60: number
  days_61_90: number
  days_90_plus: number
  total_outstanding: number
}

export interface SupplierLedgerReport {
  entries: SupplierLedgerEntry[]
  total_outstanding: number
  total_current: number
  total_overdue: number
  unpaid_count: number
}

/**
 * Generate supplier ledger (leverantörsreskontra) with aging analysis
 */
export async function generateSupplierLedger(
  supabase: SupabaseClient,
  userId: string,
  asOfDate?: string
): Promise<SupplierLedgerReport> {
  const refDate = asOfDate ? new Date(asOfDate) : new Date()

  // Fetch all unpaid/partially_paid supplier invoices
  const { data: invoices, error } = await supabase
    .from('supplier_invoices')
    .select('*, supplier:suppliers(id, name)')
    .eq('user_id', userId)
    .in('status', ['registered', 'approved', 'partially_paid', 'overdue'])

  if (error || !invoices) {
    return {
      entries: [],
      total_outstanding: 0,
      total_current: 0,
      total_overdue: 0,
      unpaid_count: 0,
    }
  }

  // Group by supplier and calculate aging
  const bySupplier = new Map<string, SupplierLedgerEntry>()

  for (const inv of invoices) {
    const supplierId = inv.supplier_id
    const supplierName = inv.supplier?.name || 'Okänd leverantör'

    if (!bySupplier.has(supplierId)) {
      bySupplier.set(supplierId, {
        supplier_id: supplierId,
        supplier_name: supplierName,
        current: 0,
        days_1_30: 0,
        days_31_60: 0,
        days_61_90: 0,
        days_90_plus: 0,
        total_outstanding: 0,
      })
    }

    const entry = bySupplier.get(supplierId)!
    const dueDate = new Date(inv.due_date)
    const daysOverdue = Math.floor((refDate.getTime() - dueDate.getTime()) / (1000 * 60 * 60 * 24))
    const amount = inv.remaining_amount || 0

    if (daysOverdue <= 0) {
      entry.current += amount
    } else if (daysOverdue <= 30) {
      entry.days_1_30 += amount
    } else if (daysOverdue <= 60) {
      entry.days_31_60 += amount
    } else if (daysOverdue <= 90) {
      entry.days_61_90 += amount
    } else {
      entry.days_90_plus += amount
    }

    entry.total_outstanding += amount
  }

  const entries = Array.from(bySupplier.values())
    .sort((a, b) => b.total_outstanding - a.total_outstanding)

  const total_outstanding = entries.reduce((sum, e) => sum + e.total_outstanding, 0)
  const total_current = entries.reduce((sum, e) => sum + e.current, 0)
  const total_overdue = total_outstanding - total_current

  return {
    entries,
    total_outstanding: Math.round(total_outstanding * 100) / 100,
    total_current: Math.round(total_current * 100) / 100,
    total_overdue: Math.round(total_overdue * 100) / 100,
    unpaid_count: invoices.length,
  }
}