feat: add caching for backend objects

app/composables/useAppCache.ts

@@ -0,0 +1,74 @@
+import { weekMonday } from '~/utils/toronto'
+
+const TTL_MS = 24 * 60 * 60 * 1000
+
+interface CacheEntry<T> {
+  data: T
+  ts: number
+}
+
+function storageKey(key: string) {
+  return `cache:${key}`
+}
+
+export function useAppCache() {
+  function set<T>(key: string, data: T): void {
+    try {
+      localStorage.setItem(storageKey(key), JSON.stringify({ data, ts: Date.now() } satisfies CacheEntry<T>))
+    } catch { /* quota exceeded or unavailable */ }
+  }
+
+  /** Returns data only if fresh (< 24 h). Returns null if stale or absent. */
+  function get<T>(key: string): T | null {
+    try {
+      const raw = localStorage.getItem(storageKey(key))
+      if (!raw) return null
+      const entry = JSON.parse(raw) as CacheEntry<T>
+      if (Date.now() - entry.ts > TTL_MS) return null
+      return entry.data
+    } catch { return null }
+  }
+
+  /** Returns data regardless of age — for offline fallback when cache is stale. */
+  function peek<T>(key: string): T | null {
+    try {
+      const raw = localStorage.getItem(storageKey(key))
+      if (!raw) return null
+      return (JSON.parse(raw) as CacheEntry<T>).data
+    } catch { return null }
+  }
+
+  /** Returns age in ms, or null if absent. */
+  function age(key: string): number | null {
+    try {
+      const raw = localStorage.getItem(storageKey(key))
+      if (!raw) return null
+      return Date.now() - (JSON.parse(raw) as CacheEntry<unknown>).ts
+    } catch { return null }
+  }
+
+  function invalidate(key: string): void {
+    localStorage.removeItem(storageKey(key))
+  }
+
+  /** Removes all cache entries whose key starts with prefix. */
+  function invalidatePrefix(prefix: string): void {
+    const full = storageKey(prefix)
+    const toRemove: string[] = []
+    for (let i = 0; i < localStorage.length; i++) {
+      const k = localStorage.key(i)
+      if (k?.startsWith(full)) toRemove.push(k)
+    }
+    toRemove.forEach(k => localStorage.removeItem(k))
+  }
+
+  /**
+   * Cache key for schedule data (intervals or slots) for the ISO week containing
+   * the given UTC ISO timestamp. Desktop and mobile both key to week-Monday.
+   */
+  function weekKey(utcIso: string): string {
+    return weekMonday(utcIso.slice(0, 10))
+  }
+
+  return { set, get, peek, age, invalidate, invalidatePrefix, weekKey }
+}

app/composables/useBookingDraft.ts

@@ -0,0 +1,26 @@
+import type { Database } from '~/types/supabase'
+
+type Boat = Database['public']['Tables']['boats']['Row']
+
+export interface BookingDraft {
+  boat: Boat
+  startTime: string
+  endTime: string
+}
+
+const _draft = ref<BookingDraft | null>(null)
+
+export function useBookingDraft() {
+  function set(boat: Boat, startTime: string, endTime: string): void {
+    _draft.value = { boat, startTime, endTime }
+  }
+
+  /** Reads and clears the draft — call once in the destination page. */
+  function take(): BookingDraft | null {
+    const val = _draft.value
+    _draft.value = null
+    return val
+  }
+
+  return { set, take }
+}

app/composables/useOfflineStatus.ts

@@ -0,0 +1,10 @@
+const _isOnline = ref(typeof navigator !== 'undefined' ? navigator.onLine : true)
+
+if (import.meta.client) {
+  window.addEventListener('online',  () => { _isOnline.value = true })
+  window.addEventListener('offline', () => { _isOnline.value = false })
+}
+
+export function useOfflineStatus() {
+  return { isOnline: readonly(_isOnline) }
+}