feat(frontend): add mealPlan Pinia store with immutable slot updates

frontend/src/stores/mealPlan.ts

@@ -0,0 +1,135 @@
+// frontend/src/stores/mealPlan.ts
+/**
+ * Meal Plan Store
+ *
+ * Manages the active week plan, shopping list, and prep session.
+ * Uses immutable update patterns — never mutates store state in place.
+ */
+import { defineStore } from 'pinia'
+import { ref, computed } from 'vue'
+import {
+  mealPlanAPI,
+  type MealPlan,
+  type MealPlanSlot,
+  type ShoppingList,
+  type PrepSession,
+  type PrepTask,
+} from '../services/api'
+
+export const useMealPlanStore = defineStore('mealPlan', () => {
+  const plans = ref<MealPlan[]>([])
+  const activePlan = ref<MealPlan | null>(null)
+  const shoppingList = ref<ShoppingList | null>(null)
+  const prepSession = ref<PrepSession | null>(null)
+  const loading = ref(false)
+  const shoppingListLoading = ref(false)
+  const prepLoading = ref(false)
+
+  const slots = computed<MealPlanSlot[]>(() => activePlan.value?.slots ?? [])
+
+  function getSlot(dayOfWeek: number, mealType: string): MealPlanSlot | undefined {
+    return slots.value.find(s => s.day_of_week === dayOfWeek && s.meal_type === mealType)
+  }
+
+  async function loadPlans() {
+    loading.value = true
+    try {
+      plans.value = await mealPlanAPI.list()
+    } finally {
+      loading.value = false
+    }
+  }
+
+  async function createPlan(weekStart: string, mealTypes: string[]): Promise<MealPlan> {
+    const plan = await mealPlanAPI.create(weekStart, mealTypes)
+    plans.value = [plan, ...plans.value]
+    activePlan.value = plan
+    shoppingList.value = null
+    prepSession.value = null
+    return plan
+  }
+
+  async function setActivePlan(planId: number) {
+    loading.value = true
+    try {
+      activePlan.value = await mealPlanAPI.get(planId)
+      shoppingList.value = null
+      prepSession.value = null
+    } finally {
+      loading.value = false
+    }
+  }
+
+  async function upsertSlot(dayOfWeek: number, mealType: string, data: { recipe_id?: number | null; servings?: number; custom_label?: string | null }): Promise<void> {
+    if (!activePlan.value) return
+    const slot = await mealPlanAPI.upsertSlot(activePlan.value.id, dayOfWeek, mealType, data)
+    const current = activePlan.value
+    const idx = current.slots.findIndex(
+      s => s.day_of_week === dayOfWeek && s.meal_type === mealType
+    )
+    activePlan.value = {
+      ...current,
+      slots: idx >= 0
+        ? [...current.slots.slice(0, idx), slot, ...current.slots.slice(idx + 1)]
+        : [...current.slots, slot],
+    }
+    shoppingList.value = null
+    prepSession.value = null
+  }
+
+  async function clearSlot(dayOfWeek: number, mealType: string): Promise<void> {
+    if (!activePlan.value) return
+    const slot = getSlot(dayOfWeek, mealType)
+    if (!slot) return
+    await mealPlanAPI.deleteSlot(activePlan.value.id, slot.id)
+    activePlan.value = {
+      ...activePlan.value,
+      slots: activePlan.value.slots.filter(s => s.id !== slot.id),
+    }
+    shoppingList.value = null
+    prepSession.value = null
+  }
+
+  async function loadShoppingList(): Promise<void> {
+    if (!activePlan.value) return
+    shoppingListLoading.value = true
+    try {
+      shoppingList.value = await mealPlanAPI.getShoppingList(activePlan.value.id)
+    } finally {
+      shoppingListLoading.value = false
+    }
+  }
+
+  async function loadPrepSession(): Promise<void> {
+    if (!activePlan.value) return
+    prepLoading.value = true
+    try {
+      prepSession.value = await mealPlanAPI.getPrepSession(activePlan.value.id)
+    } finally {
+      prepLoading.value = false
+    }
+  }
+
+  async function updatePrepTask(taskId: number, data: Partial<Pick<PrepTask, 'duration_minutes' | 'sequence_order' | 'notes' | 'equipment'>>): Promise<void> {
+    if (!activePlan.value || !prepSession.value) return
+    const updated = await mealPlanAPI.updatePrepTask(activePlan.value.id, taskId, data)
+    const idx = prepSession.value.tasks.findIndex(t => t.id === taskId)
+    if (idx >= 0) {
+      prepSession.value = {
+        ...prepSession.value,
+        tasks: [
+          ...prepSession.value.tasks.slice(0, idx),
+          updated,
+          ...prepSession.value.tasks.slice(idx + 1),
+        ],
+      }
+    }
+  }
+
+  return {
+    plans, activePlan, shoppingList, prepSession,
+    loading, shoppingListLoading, prepLoading, slots,
+    getSlot, loadPlans, createPlan, setActivePlan,
+    upsertSlot, clearSlot, loadShoppingList, loadPrepSession, updatePrepTask,
+  }
+})