Ajout de Promotion et de Commande fonctionnel

src/context/OrdersContext.jsx

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+import {
+  createContext,
+  useCallback,
+  useContext,
+  useEffect,
+  useMemo,
+  useState,
+} from 'react'
+
+const STORAGE_KEY = 'librairie-orders'
+
+function loadOrders() {
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY)
+    if (raw === null) return []
+    const parsed = JSON.parse(raw)
+    return Array.isArray(parsed) ? parsed : []
+  } catch {
+    return []
+  }
+}
+
+function saveOrders(orders) {
+  localStorage.setItem(STORAGE_KEY, JSON.stringify(orders))
+}
+
+function round2(n) {
+  return Math.round((Number(n) + Number.EPSILON) * 100) / 100
+}
+
+function calcSubtotal(items) {
+  return round2(
+    items.reduce((sum, it) => sum + Number(it.unitPrice) * Number(it.qty), 0),
+  )
+}
+
+function calcDiscount({ subtotal, promotion }) {
+  if (!promotion) return 0
+  if (promotion.type === 'percent') {
+    const pct = Number(promotion.value)
+    if (!Number.isFinite(pct) || pct <= 0) return 0
+    return round2((subtotal * pct) / 100)
+  }
+  return 0
+}
+
+const OrdersContext = createContext(null)
+
+export function OrdersProvider({ children }) {
+  const [orders, setOrders] = useState(loadOrders)
+
+  useEffect(() => {
+    saveOrders(orders)
+  }, [orders])
+
+  /**
+   * Équivalent local d’un POST /api/orders.
+   * orderDraft: { items: [{ bookId, title, unitPrice, qty }], promotion?: { code, type, value } }
+   */
+  const createOrder = useCallback((orderDraft) => {
+    const items = Array.isArray(orderDraft?.items) ? orderDraft.items : []
+    const cleaned = items
+      .map((it) => ({
+        bookId: String(it.bookId),
+        title: String(it.title || ''),
+        unitPrice: Number(it.unitPrice),
+        qty: Math.max(0, Math.trunc(Number(it.qty) || 0)),
+      }))
+      .filter((it) => it.bookId && it.qty > 0 && Number.isFinite(it.unitPrice))
+
+    if (cleaned.length === 0) {
+      throw new Error('Aucun article dans la commande')
+    }
+
+    const subtotal = calcSubtotal(cleaned)
+    const promotion = orderDraft?.promotion
+      ? {
+          code: String(orderDraft.promotion.code || ''),
+          type: String(orderDraft.promotion.type || 'percent'),
+          value: Number(orderDraft.promotion.value),
+        }
+      : null
+    const discount = calcDiscount({ subtotal, promotion })
+    const total = round2(Math.max(0, subtotal - discount))
+
+    const order = {
+      id: crypto.randomUUID(),
+      createdAt: new Date().toISOString(),
+      items: cleaned,
+      promotion: promotion && promotion.code ? promotion : null,
+      subtotal,
+      discount,
+      total,
+    }
+
+    setOrders((prev) => [order, ...prev])
+    return order
+  }, [])
+
+  const value = useMemo(() => ({ orders, createOrder }), [orders, createOrder])
+
+  return <OrdersContext.Provider value={value}>{children}</OrdersContext.Provider>
+}
+
+// eslint-disable-next-line react-refresh/only-export-components
+export function useOrders() {
+  const ctx = useContext(OrdersContext)
+  if (!ctx) {
+    throw new Error('useOrders doit être utilisé dans un OrdersProvider')
+  }
+  return ctx
+}
+