export async function genArrayBufferFromFileReference(fileReference) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = function(e) {
      resolve(e.target.result);
    };
    reader.onerror = function(e) {
      reject(e);
    };

    reader.readAsArrayBuffer(fileReference);
  });
}

export async function genArrayBufferFromUrl(url) {
  return new Promise((resolve, reject) => {
    const oReq = new XMLHttpRequest();
    oReq.open("GET", url, true);
    oReq.responseType = "arraybuffer";

    oReq.onload = () => {
      const arrayBuffer = oReq.response; // Note: not oReq.responseText
      resolve(arrayBuffer);
    };
    oReq.onerror = reject;

    oReq.send(null);
  });
}

export async function promptForFileReferences(accept) {
  return new Promise(resolve => {
    // Does this represent a memory leak somehow?
    // Can this fail? Do we ever reject?
    const fileInput = document.createElement("input");
    if (accept) fileInput.setAttribute("accept", accept);
    fileInput.type = "file";
    fileInput.multiple = true;
    // Not entirely sure why this is needed, since the input
    // was just created, but somehow this helps prevent change
    // events from getting swallowed.
    // https://stackoverflow.com/a/12102992/1263117
    fileInput.value = null;
    fileInput.addEventListener("change", e => {
      resolve(e.target.files);
    });
    fileInput.click();
  });
}