refactor(auto-thumbnail): [PKG-AUTO-THUMB-03] type internal extraction contracts

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

@@ -0,0 +1,124 @@
+import type { ExtractionJob } from './types'
+import { cleanupAll } from './session'
+
+interface PendingFrame {
+  frame: number | null
+  timer: ReturnType<typeof setTimeout> | null
+  sought: boolean
+  presented: boolean
+  retries: number
+  sequence: number
+  started: boolean
+}
+
+export default function createFrameReader(job: ExtractionJob, video: HTMLVideoElement) {
+  const presentedFrames = typeof video.requestVideoFrameCallback === 'function'
+    && typeof video.cancelVideoFrameCallback === 'function'
+  let pending: PendingFrame | undefined
+
+  function clear() {
+    const previous = pending
+    pending = undefined
+    video.onloadeddata = null
+    video.onseeked = null
+    if (!previous)
+      return
+    const result = cleanupAll([
+      () => {
+        if (previous.timer !== null)
+          clearTimeout(previous.timer)
+      },
+      () => {
+        if (previous.frame !== null)
+          video.cancelVideoFrameCallback(previous.frame)
+      },
+    ])
+    if (result.failed)
+      throw result.failure
+  }
+  job.own(clear)
+
+  return (target: number, draw: () => void) => {
+    clear()
+    if (!job.active())
+      return
+    const current: PendingFrame = { frame: null, timer: null, sought: false, presented: !presentedFrames, retries: 0, sequence: 0, started: false }
+    pending = current
+    const active = () => job.active() && pending === current
+    const finish = job.guard(() => {
+      if (!active() || !current.sought || !current.presented)
+        return
+      clear()
+      if (job.active())
+        draw()
+    })
+    const requestFrame = () => {
+      if (!presentedFrames)
+        return
+      const sequence = ++current.sequence
+      current.presented = false
+      const previous = current.frame
+      current.frame = null
+      if (previous !== null)
+        video.cancelVideoFrameCallback(previous)
+      if (!active())
+        return
+      let delivered = false
+      const id = video.requestVideoFrameCallback(job.guard(() => {
+        if (!active() || sequence !== current.sequence || delivered)
+          return
+        delivered = true
+        current.frame = null
+        current.presented = true
+        finish()
+      }))
+      if (active() && sequence === current.sequence && !delivered)
+        current.frame = id
+      else
+        video.cancelVideoFrameCallback(id)
+    }
+    const seek = () => {
+      current.sought = false
+      requestFrame()
+      if (active())
+        video.currentTime = target
+    }
+    const begin = job.guard(() => {
+      if (!active() || current.started)
+        return
+      current.started = true
+      video.onloadeddata = null
+      video.onseeked = job.guard(() => {
+        if (!active() || video.seeking)
+          return
+        const time = video.currentTime
+        if (!active())
+          return
+        if (!Number.isFinite(time) || Math.abs(time - target) > 0.05) {
+          if (++current.retries > 3)
+            throw new Error('Auto-thumbnail seek did not reach the requested time')
+          seek()
+          return
+        }
+        current.sought = true
+        finish()
+      })
+      seek()
+    })
+    current.timer = setTimeout(job.guard(() => {
+      if (active())
+        throw new Error('Auto-thumbnail frame readiness timed out')
+    }), 30000)
+    if (!active()) {
+      clearTimeout(current.timer)
+      return
+    }
+    const ready = !presentedFrames || video.readyState >= 2
+    if (!active())
+      return
+    if (!ready)
+      video.onloadeddata = begin
+    else
+      begin()
+  }
+}