// Fill the environment with js functions we want to expose to the wasm module.
// since we compile with -Wl,--allow-undefined, the linked does not complain
// about undefined symbols. So we use make_environment to resolve from env below
// and fail at runtime if a symbol is not found.
function make_environment(...envs) {
  return new Proxy(envs, {
    get(_target, prop, _receiver) {
      for (let env of envs) {
        if (env.hasOwnProperty(prop)) {
          return env[prop];
        }
      }
      return (...args) => {
        throw "NOT IMPLEMENTED: " + prop + " " + args + "";
      }
    }
  });
}

async function init() {
  const WIDTH = 800;
  const HEIGHT = 600;
  const { instance } = await WebAssembly.instantiateStreaming(fetch("./main.wasm"), {
    env: make_environment({})
  });
  const canvas = document.getElementById("canvas");
  const ctx = canvas.getContext("2d");
  canvas.width = WIDTH;
  canvas.height = HEIGHT;

  // Fill the gradient before the first frame is displayed.
  instance.exports.init();

  const ptr = instance.exports.get_buffer_ptr();
  const len = instance.exports.get_buffer_len();
  const image = new ImageData(
    new Uint8ClampedArray(
      instance.exports.memory.buffer,
      ptr,
      len * 4,
    ),
    WIDTH,
  );

  let previousTimestamp;
  const render = (timestamp) => {
    const dt = previousTimestamp === undefined
      ? 0
      : Math.min((timestamp - previousTimestamp) / 1000, 0.05);
    previousTimestamp = timestamp;
    instance.exports.render_frame(dt);
    ctx.putImageData(image, 0, 0);
    window.requestAnimationFrame(render);
  };

  window.requestAnimationFrame(render);
}
init();