test(multiple-subtitles): checkpoint native seek diagnostics [PKG-MULTI-SUB-05]

test/browser/source-seek-diagnostics.js

@@ -0,0 +1,27 @@
+export async function installSeekDiagnostics(page, properties = true) {
+  await page.evaluate((properties) => {
+    const art = window.art
+    const video = art.video
+    window.sourceSeekTrace = []
+    const state = () => ({ clock: performance.now(), time: video.currentTime, duration: video.duration, seeking: video.seeking, paused: video.paused, rate: video.playbackRate, readyState: video.readyState, source: video.currentSrc, active: Array.from(art.template.$track.track.activeCues || [], cue => cue.text) })
+    const record = (event, detail) => window.sourceSeekTrace.push({ event, detail, ...state() })
+    for (const property of properties ? ['currentTime', 'playbackRate'] : []) {
+      const descriptor = Object.getOwnPropertyDescriptor(HTMLMediaElement.prototype, property)
+      Object.defineProperty(video, property, {
+        configurable: true,
+        get() { return descriptor.get.call(this) },
+        set(value) {
+          record(`before:${property}`, { value, stack: new Error('Native media property write').stack })
+          descriptor.set.call(this, value)
+          record(`after:${property}`, { value })
+        },
+      })
+    }
+    for (const event of ['loadstart', 'loadedmetadata', 'loadeddata', 'canplay', 'seeking', 'seeked', 'emptied', 'pause', 'ratechange', 'timeupdate'])
+      video.addEventListener(event, () => record(`native:${event}`))
+    for (const event of ['restart', 'seek', 'fullscreen'])
+      art.on(event, (...values) => record(`art:${event}`, values))
+    window.recordSourceSeek = record
+    record('installed')
+  }, properties)
+}