import wasmUrl from '../../../codecs/rotate/rotate.wasm';
import { RotateOptions, RotateModuleInstance } from './processor-meta';

// We are loading a 500B module here. Loading the code to feature-detect
// `instantiateStreaming` probably takes longer to load than the time we save by
// using `instantiateStreaming` in the first place. So let’s just use
// `ArrayBuffer`s here.
const instancePromise = fetch(wasmUrl)
  .then(r => r.arrayBuffer())
  .then(buf => WebAssembly.instantiate(buf));

export async function rotate(
  data: ImageData,
  opts: RotateOptions,
): Promise<ImageData> {
  const { instance } = (await instancePromise) as {
    instance: RotateModuleInstance;
  };

  // Number of wasm memory pages (á 64KiB) needed to store the image twice.
  const bytesPerImage = data.width * data.height * 4;
  const numPagesNeeded = Math.ceil((bytesPerImage * 2 + 8) / (64 * 1024));
  // Only count full pages, just to be safe.
  const numPagesAvailable = Math.floor(
    instance.exports.memory.buffer.byteLength / (64 * 1024),
  );
  const additionalPagesToAllocate = numPagesNeeded - numPagesAvailable;

  if (additionalPagesToAllocate > 0) {
    instance.exports.memory.grow(additionalPagesToAllocate);
  }
  const view = new Uint8ClampedArray(instance.exports.memory.buffer);
  view.set(data.data, 8);

  instance.exports.rotate(data.width, data.height, opts.rotate);

  const flipDimensions = opts.rotate % 180 !== 0;
  return new ImageData(
    view.slice(bytesPerImage + 8, bytesPerImage * 2 + 8),
    flipDimensions ? data.height : data.width,
    flipDimensions ? data.width : data.height,
  );
}