/* Run only on a local teaching page at http://127.0.0.1 or http://localhost.
   Own canvas + oscillator input, no microphone, no remote fetch, no real voice.
   Decoding support is browser/format dependent; this does not promise all video formats.
   The output is decoded/re-encoded PCM16 WAV, not a lossless copy of compressed bytes. */
function requireTeachingOrigin() {
  if (!['127.0.0.1','localhost'].includes(location.hostname)) throw new Error('Use a dedicated local teaching page');
}
async function teachingBytesHash(bytes) {
  return Array.from(new Uint8Array(await crypto.subtle.digest('SHA-256',bytes)),x=>x.toString(16).padStart(2,'0')).join('');
}
function teachingPcm16Wav(buffer) {
  const channels=buffer.numberOfChannels,frames=buffer.length;
  if (![1,2].includes(channels)) throw new Error('This example supports only mono/stereo');
  const bytes=new ArrayBuffer(44+frames*channels*2),d=new DataView(bytes);
  const text=(offset,s)=>{for(let i=0;i<s.length;i++)d.setUint8(offset+i,s.charCodeAt(i))};
  text(0,'RIFF');d.setUint32(4,bytes.byteLength-8,true);text(8,'WAVE');text(12,'fmt ');
  d.setUint32(16,16,true);d.setUint16(20,1,true);d.setUint16(22,channels,true);
  d.setUint32(24,buffer.sampleRate,true);d.setUint32(28,buffer.sampleRate*channels*2,true);
  d.setUint16(32,channels*2,true);d.setUint16(34,16,true);text(36,'data');d.setUint32(40,frames*channels*2,true);
  const data=Array.from({length:channels},(_,c)=>buffer.getChannelData(c));let pos=44;
  for(let n=0;n<frames;n++)for(let c=0;c<channels;c++){
    const v=Math.max(-1,Math.min(1,data[c][n]));d.setInt16(pos,Math.round(v<0?v*32768:v*32767),true);pos+=2;
  }
  return new Blob([bytes],{type:'audio/wav'});
}
async function decodeTeachingVideoBlob(blob) {
  requireTeachingOrigin();
  if (!(blob instanceof Blob)||blob.size===0||blob.size>8*1024*1024) throw new Error('Nonempty Blob up to 8 MiB required; actual bytes='+blob?.size);
  const input=await blob.arrayBuffer(),inputSha256=await teachingBytesHash(input);
  const decoder=new OfflineAudioContext(1,1,16000);
  const decoded=await decoder.decodeAudioData(input.slice(0));
  const wavBlob=teachingPcm16Wav(decoded),wav=await wavBlob.arrayBuffer(),d=new DataView(wav);
  if (d.getUint32(4,true)+8!==wav.byteLength||d.getUint32(40,true)!==decoded.length*decoded.numberOfChannels*2)throw new Error('WAV byte contract mismatch');
  let squares=0,peak=0;
  for(let i=44;i<wav.byteLength;i+=2){const x=d.getInt16(i,true)/32768;squares+=x*x;peak=Math.max(peak,Math.abs(x))}
  return {wavBlob,report:{inputMimeLabel:blob.type,inputBytes:blob.size,inputSha256,decodedRateHz:decoded.sampleRate,decodedChannels:decoded.numberOfChannels,decodedFrames:decoded.length,decodedSeconds:decoded.duration,wavBytes:wav.byteLength,wavSha256:await teachingBytesHash(wav),wavRms:squares?Math.sqrt(squares/((wav.byteLength-44)/2)):0,wavPeak:peak,compressedAudioBytesCopiedWithoutDecoding:false,originalBlobModified:false}};
}
async function teachingVideoAudioExtractDemo() {
  requireTeachingOrigin();const mime='video/webm;codecs=vp8,opus';
  if (!MediaRecorder.isTypeSupported(mime)) throw new Error('This fixture format is not supported here');
  const canvas=document.createElement('canvas');canvas.width=160;canvas.height=90;
  document.body.appendChild(canvas);
  const ctx=canvas.getContext('2d');ctx.fillStyle='#4290C6';ctx.fillRect(0,0,160,90);
  const visual=canvas.captureStream(10),audio=new AudioContext({sampleRate:48000});
  const destination=audio.createMediaStreamDestination(),osc=audio.createOscillator(),gain=audio.createGain();
  gain.gain.value=.1;osc.frequency.value=440;osc.connect(gain).connect(destination);
  const silentSink=audio.createGain();silentSink.gain.value=0;gain.connect(silentSink).connect(audio.destination);
  const mixed=new MediaStream([...visual.getVideoTracks(),...destination.stream.getAudioTracks()]);
  const recorder=new MediaRecorder(mixed,{mimeType:mime});const chunks=[];
  const diagnostics={events:[],requestedMime:mime};window.teachingCaptureDiagnostics=diagnostics;
  recorder.ondataavailable=e=>{diagnostics.events.push({kind:'data',bytes:e.data.size});if(e.data.size)chunks.push(e.data)};
  let timer;
  try {
    await audio.resume();diagnostics.audioState=audio.state;diagnostics.trackStates=mixed.getTracks().map(t=>({kind:t.kind,readyState:t.readyState,muted:t.muted}));osc.start();
    const stopped=new Promise((resolve,reject)=>{recorder.onstop=resolve;recorder.onerror=e=>reject(new Error(e.error?.message||'recording failed'))});
    recorder.start(100);let frame=0;
    timer=setInterval(()=>{ctx.fillStyle=frame++%2?'#A39BDB':'#4290C6';ctx.fillRect(0,0,160,90)},100);
    await new Promise(resolve=>setTimeout(resolve,1200));recorder.stop();await stopped;
    diagnostics.recorderState=recorder.state;diagnostics.chunks=chunks.length;
    const videoBlob=new Blob(chunks,{type:recorder.mimeType});diagnostics.videoBytes=videoBlob.size;
    const video=document.createElement('video'),url=URL.createObjectURL(videoBlob);video.muted=true;video.preload='metadata';
    let videoMetadata;
    try {
      await new Promise((resolve,reject)=>{const timeout=setTimeout(()=>reject(new Error('encoded video metadata timeout')),5000);video.onloadedmetadata=()=>{clearTimeout(timeout);resolve()};video.onerror=()=>{clearTimeout(timeout);reject(new Error('encoded video metadata failed'))};video.src=url;video.load()});
      videoMetadata={width:video.videoWidth,height:video.videoHeight,containerDurationSeconds:Number.isFinite(video.duration)?video.duration:null,unknownDurationIsNotZero:true,playbackPerformed:false};
    } finally {video.removeAttribute('src');video.load();URL.revokeObjectURL(url)}
    const result=await decodeTeachingVideoBlob(videoBlob);result.report.encodedVideoMetadata=videoMetadata;
    result.report.fixture={kind:'own alternating-color canvas plus 440-Hz oscillator',recordedVideoTracks:mixed.getVideoTracks().length,recordedAudioTracks:mixed.getAudioTracks().length,requestedRecordingMilliseconds:1200,recordingMime:recorder.mimeType,actualCapturedDurationNotGuaranteedByTimer:true,microphoneUsed:false,zeroGainSpeakerSinkConnected:true,audibleSignalSentToSpeakers:false,realSpeech:false};
    let invalidRejected=false;
    try{await decodeTeachingVideoBlob(new Blob([new Uint8Array([1,2,3,4])],{type:'video/webm'}))}catch(e){invalidRejected=true}
    result.report.invalidFourByteContainerRejected=invalidRejected;
    return result;
  } finally {
    clearInterval(timer);if(recorder.state!=='inactive')recorder.stop();
    osc.stop();mixed.getTracks().forEach(t=>t.stop());visual.getTracks().forEach(t=>t.stop());await audio.close();canvas.remove();
  }
}
// Explicit local use from a real button click:
// button.onclick=async()=>{ window.localVideoAudioResult=await teachingVideoAudioExtractDemo(); console.log(window.localVideoAudioResult.report); };
// localVideoAudioResult.wavBlob contains the generated WAV; this script never auto-uploads or auto-downloads it.