Initial commit: Fahrrad Verschleißteile Tracker

- Next.js SPA mit Bun Runtime
- Prisma mit SQLite Datenbank
- Vollständige CRUD-Operationen für Fahrräder, Verschleißteile und Wartungshistorie
- Warnsystem für bevorstehende Wartungen
- Statistik-Features (Gesamtkosten, durchschnittliche Lebensdauer)
- Zod-Validierung für alle API-Requests
- Umfassende Test-Suite (41 Tests)

lib/utils.ts

@@ -0,0 +1,85 @@
+import { WearPart, MaintenanceHistory } from '@prisma/client'
+
+export function calculateServiceStatus(
+  part: WearPart & { maintenanceHistory: MaintenanceHistory[] }
+): {
+  status: 'OK' | 'WARNING' | 'CRITICAL'
+  remainingKm: number
+  percentageUsed: number
+} {
+  const latestMaintenance = part.maintenanceHistory[0]
+  const currentMileage = latestMaintenance?.mileage ?? part.installMileage
+  const kmSinceInstall = currentMileage - part.installMileage
+  const remainingKm = part.serviceInterval - kmSinceInstall
+  const percentageUsed = (kmSinceInstall / part.serviceInterval) * 100
+
+  let status: 'OK' | 'WARNING' | 'CRITICAL' = 'OK'
+  if (percentageUsed >= 90) {
+    status = 'CRITICAL'
+  } else if (percentageUsed >= 75) {
+    status = 'WARNING'
+  }
+
+  return {
+    status,
+    remainingKm: Math.max(0, remainingKm),
+    percentageUsed: Math.min(100, percentageUsed),
+  }
+}
+
+export function calculateTotalCosts(
+  parts: (WearPart & { maintenanceHistory: MaintenanceHistory[] })[]
+): number {
+  return parts.reduce((total, part) => {
+    const partCost = part.cost ?? 0
+    const maintenanceCost = part.maintenanceHistory.reduce(
+      (sum, m) => sum + (m.cost ?? 0),
+      0
+    )
+    return total + partCost + maintenanceCost
+  }, 0)
+}
+
+export function calculateAverageLifespan(
+  parts: (WearPart & { maintenanceHistory: MaintenanceHistory[] })[]
+): number | null {
+  const replacedParts = parts.filter(
+    (p) => p.status === 'REPLACED' && p.maintenanceHistory.length > 0
+  )
+
+  if (replacedParts.length === 0) return null
+
+  const totalKm = replacedParts.reduce((sum, part) => {
+    const installHistory = part.maintenanceHistory.find(
+      (h) => h.action === 'INSTALL'
+    )
+    const replaceHistory = part.maintenanceHistory.find(
+      (h) => h.action === 'REPLACE'
+    )
+
+    if (installHistory && replaceHistory) {
+      return sum + (replaceHistory.mileage - installHistory.mileage)
+    }
+    return sum
+  }, 0)
+
+  return totalKm / replacedParts.length
+}
+
+export function formatDate(date: Date | string): string {
+  const d = typeof date === 'string' ? new Date(date) : date
+  return d.toLocaleDateString('de-DE', {
+    year: 'numeric',
+    month: '2-digit',
+    day: '2-digit',
+  })
+}
+
+export function formatCurrency(amount: number | null | undefined): string {
+  if (amount === null || amount === undefined) return '0,00 €'
+  return new Intl.NumberFormat('de-DE', {
+    style: 'currency',
+    currency: 'EUR',
+  }).format(amount)
+}
+