refactor(auto-thumbnail): [PKG-AUTO-THUMB-10] own JPEG encoding cancellation and deadlines

packages/artplayer-plugin-auto-thumbnail/src/encoding.ts

@@ -0,0 +1,41 @@
+import type { ExtractionJob } from './types'
+
+interface PendingEncoding {
+  timer: ReturnType<typeof setTimeout> | null
+}
+
+export default function createEncoder(job: ExtractionJob, canvas: HTMLCanvasElement) {
+  let pending: PendingEncoding | undefined
+  function clear() {
+    const previous = pending
+    pending = undefined
+    if (previous && previous.timer !== null)
+      clearTimeout(previous.timer)
+  }
+  job.own(clear)
+
+  return (publish: (blob: Blob | null) => void) => {
+    if (!job.active())
+      return
+    if (pending)
+      throw new Error('Auto-thumbnail encoding is already pending')
+    const current: PendingEncoding = { timer: null }
+    pending = current
+    const active = () => job.active() && pending === current
+    current.timer = setTimeout(job.guard(() => {
+      if (active())
+        throw new Error('Auto-thumbnail encoding timed out')
+    }), 30000)
+    if (!active()) {
+      clearTimeout(current.timer)
+      return
+    }
+    canvas.toBlob(job.guard((blob) => {
+      if (!active())
+        return
+      clear()
+      if (job.active())
+        publish(blob)
+    }), 'image/jpeg')
+  }
+}