feat(autosave): add autosave controller and status component

src/lib/admin/autoSave.ts

@@ -0,0 +1,107 @@
+export type AutoSaveStatus = 'idle' | 'saving' | 'saved' | 'error' | 'offline'
+
+interface CreateAutoSaveControllerOptions<TPayload, TResponse = unknown> {
+  debounceMs?: number
+  getPayload: () => TPayload | null | undefined
+  save: (payload: TPayload, ctx: { signal: AbortSignal }) => Promise<TResponse>
+  onSaved?: (res: TResponse) => void
+}
+
+export function createAutoSaveController<TPayload, TResponse = unknown>(
+  opts: CreateAutoSaveControllerOptions<TPayload, TResponse>
+) {
+  const debounceMs = opts.debounceMs ?? 2000
+  let timer: ReturnType<typeof setTimeout> | null = null
+  let controller: AbortController | null = null
+  let lastSentHash: string | null = null
+
+  let _status: AutoSaveStatus = 'idle'
+  let _lastError: string | null = null
+  const statusSubs = new Set<(v: AutoSaveStatus) => void>()
+  const errorSubs = new Set<(v: string | null) => void>()
+
+  function setStatus(next: AutoSaveStatus) {
+    _status = next
+    statusSubs.forEach((fn) => fn(_status))
+  }
+
+  function schedule() {
+    if (timer) clearTimeout(timer)
+    timer = setTimeout(() => void run(), debounceMs)
+  }
+
+  async function run() {
+    if (timer) {
+      clearTimeout(timer)
+      timer = null
+    }
+
+    const payload = opts.getPayload()
+    if (!payload) return
+
+    const hash = safeHash(payload)
+    if (lastSentHash && hash === lastSentHash) return
+
+    if (controller) controller.abort()
+    controller = new AbortController()
+
+    setStatus('saving')
+    _lastError = null
+    try {
+      const res = await opts.save(payload, { signal: controller.signal })
+      lastSentHash = hash
+      setStatus('saved')
+      if (opts.onSaved) opts.onSaved(res)
+    } catch (e: any) {
+      if (e?.name === 'AbortError') {
+        // Newer save superseded this one
+        return
+      }
+      if (typeof navigator !== 'undefined' && navigator.onLine === false) {
+        setStatus('offline')
+      } else {
+        setStatus('error')
+      }
+      _lastError = e?.message || 'Auto-save failed'
+      errorSubs.forEach((fn) => fn(_lastError))
+    }
+  }
+
+  function flush() {
+    return run()
+  }
+
+  function destroy() {
+    if (timer) clearTimeout(timer)
+    if (controller) controller.abort()
+  }
+
+  return {
+    status: {
+      subscribe(run: (v: AutoSaveStatus) => void) {
+        run(_status)
+        statusSubs.add(run)
+        return () => statusSubs.delete(run)
+      }
+    },
+    lastError: {
+      subscribe(run: (v: string | null) => void) {
+        run(_lastError)
+        errorSubs.add(run)
+        return () => errorSubs.delete(run)
+      }
+    },
+    schedule,
+    flush,
+    destroy
+  }
+}
+
+function safeHash(obj: unknown): string {
+  try {
+    return JSON.stringify(obj)
+  } catch {
+    // Fallback for circular structures; not expected for form payloads
+    return String(obj)
+  }
+}

src/lib/components/admin/AutoSaveStatus.svelte

@@ -0,0 +1,75 @@
+<script lang="ts">
+  import type { AutoSaveStatus } from '$lib/admin/autoSave'
+
+  interface Props {
+    statusStore: { subscribe: (run: (v: AutoSaveStatus) => void) => () => void }
+    errorStore?: { subscribe: (run: (v: string | null) => void) => () => void }
+    compact?: boolean
+  }
+
+  let { statusStore, errorStore, compact = true }: Props = $props()
+  let status = $state<AutoSaveStatus>('idle')
+  let errorText = $state<string | null>(null)
+
+  $effect(() => {
+    const unsub = statusStore.subscribe((v) => (status = v))
+    let unsubErr: (() => void) | null = null
+    if (errorStore) unsubErr = errorStore.subscribe((v) => (errorText = v))
+    return () => {
+      unsub()
+      if (unsubErr) unsubErr()
+    }
+  })
+
+  const label = $derived(() => {
+    switch (status) {
+      case 'saving':
+        return 'Saving…'
+      case 'saved':
+        return 'All changes saved'
+      case 'offline':
+        return 'Offline'
+      case 'error':
+        return errorText ? `Error — ${errorText}` : 'Save failed'
+      case 'idle':
+      default:
+        return ''
+    }
+  })
+</script>
+
+{#if label}
+  <div class="autosave-status" class:compact>
+    {#if status === 'saving'}
+      <span class="spinner" aria-hidden="true"></span>
+    {/if}
+    <span class="text">{label}</span>
+  </div>
+{/if}
+
+<style lang="scss">
+  .autosave-status {
+    display: inline-flex;
+    align-items: center;
+    gap: 6px;
+    color: $gray-40;
+    font-size: 0.875rem;
+
+    &.compact {
+      font-size: 0.75rem;
+    }
+  }
+
+  .spinner {
+    width: 12px;
+    height: 12px;
+    border: 2px solid $gray-80;
+    border-top-color: $gray-40;
+    border-radius: 50%;
+    animation: spin 0.9s linear infinite;
+  }
+
+  @keyframes spin {
+    to { transform: rotate(360deg); }
+  }
+</style>