Add Waveform component

frontend/src/App.tsx

@@ -1,24 +1,13 @@
 import React from 'react';
-import logo from './logo.svg';
 import './App.css';
+import { Waveform } from './Waveform';
+
+const audioContext = new AudioContext();
 
 function App() {
   return (
     <div className="App">
-      <header className="App-header">
-        <img src={logo} className="App-logo" alt="logo" />
-        <p>
-          Edit <code>src/App.tsx</code> and save to reload.
-        </p>
-        <a
-          className="App-link"
-          href="https://reactjs.org"
-          target="_blank"
-          rel="noopener noreferrer"
-        >
-          Learn React
-        </a>
-      </header>
+      <Waveform audioContext={audioContext}/>
     </div>
   );
 }

frontend/src/Waveform.tsx

@@ -0,0 +1,61 @@
+import { useEffect, useState, useRef } from "react";
+
+type WaveformProps = {
+  audioContext: AudioContext;
+};
+
+export const Waveform: React.FC<WaveformProps> = ({ audioContext }: WaveformProps) => {
+  const [audioData, setAudioData] = useState<AudioBuffer | null>(null);
+  const canvasRef = useRef<HTMLCanvasElement>(null);
+
+  // load audio data on page load:
+  useEffect(() => {
+    (async function() {
+      console.log("fetching audio data...");
+
+      const videoID = "s_oJYdRlrv0";
+
+      const resp = await fetch(`http://localhost:8888/api/audio?video_id=${videoID}`)
+      console.log("resp =", resp)
+
+      const body = await resp.arrayBuffer();
+      console.log("body =", body)
+
+      const data = await audioContext.decodeAudioData(body);
+
+      console.log("decodedAudio =", data, "len =", data.length);
+      setAudioData(data);
+    })();
+  }, [audioContext]);
+
+  // render waveform to canvas when audioData is updated:
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (canvas == null) {
+      console.error("no canvas ref available");
+      return
+    }
+
+    const ctx = canvas.getContext("2d");
+    if (ctx == null) {
+      console.error("no 2d context available");
+      return;
+    }
+
+    ctx.fillStyle = 'black';
+    ctx.fillRect(0, 0, canvas.width, canvas.height);
+
+    if (audioData == null) {
+      return;
+    }
+
+    console.log("rendering audio")
+  }, [audioData]);
+
+  // render component:
+
+  console.log("rendering, audioData =", audioData);
+
+  const canvasProps = {width: "100%", height: "500px"};
+  return <canvas ref={canvasRef} style={canvasProps}></canvas>
+}