document
  .querySelector("#button-generate")
  .addEventListener("click", generate, false);

async function generate() {
  const parentPrivateKeyRaw = await readFile(
    document.querySelector("#file-private-key")
  );
  if (!parentPrivateKeyRaw) {
    return;
  }
  const parentPrivateKey = await crypto.subtle.importKey(
    "jwk",
    JSON.parse(parentPrivateKeyRaw),
    {
      name: "ECDSA",
      namedCurve: "P-521"
    },
    true,
    ["sign"]
  );
  // https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/generateKey
  const keyPair = await crypto.subtle.generateKey(
    // https://developer.mozilla.org/en-US/docs/Web/API/EcKeyGenParams
    {
      name: "ECDSA",
      namedCurve: "P-521"
    },
    true,
    ["sign", "verify"]
  );

  // jwk == JSON Web Key
  const publicKey = await crypto.subtle.exportKey("jwk", keyPair.publicKey);
  const privateKey = await crypto.subtle.exportKey("jwk", keyPair.privateKey);
  const salt = createSalt();
  const publicKeySignature = arrayBufferToBase64(
    await crypto.subtle.sign(
      {
        name: "ECDSA",
        hash: { name: "SHA-512" }
      },
      parentPrivateKey,
      new TextEncoder().encode(salt + JSON.stringify(publicKey)).buffer
    )
  );

  setupDownload(
    document.querySelector("#download-public"),
    {
      publicKey,
      signature: salt + "." + publicKeySignature
    },
    "user-public-key-and-sig.json"
  );
  setupDownload(
    document.querySelector("#download-private"),
    privateKey,
    "user-private-key.json"
  );
  document.querySelector("#output").style.display = "";
}

function setupDownload(a, data, name) {
  if (a.href) {
    URL.revokeObjectURL(a.href);
  }
  a.download = decodeURI(name);
  const blob = new Blob([JSON.stringify(data)], { type: "text/json" });
  a.href = URL.createObjectURL(blob);
  a.type = "text/json";
}

async function readFile(file) {
  if (file.files.length === 0) {
    return;
  }
  return await new Promise((resolve, reject) => {
    const fileReader = new FileReader();
    fileReader.onload = (e) => {
      if (!e.target) {
        reject();
        return;
      }
      resolve(e.target.result);
    };
    fileReader.readAsText(file.files[0]);
  });
}
function createSalt() {
  const salt = new Uint8Array(4);
  crypto.getRandomValues(salt);
  return uint8ArrayToBase64(salt);
}
function uint8ArrayToBase64(data) {
  return btoa(String.fromCharCode.apply(null, [...data]));
}
function arrayBufferToBase64(data) {
  return uint8ArrayToBase64(new Uint8Array(data));
}
function base64ToArrayBuffer(str) {
  return Uint8Array.from(atob(str), (c) => c.charCodeAt(0));
}