import * as mod from "node:crypto";
import { atob } from "node:buffer";

/// Copy pasted from Mozilla
function str2ab(str: string) {
  const buf = new ArrayBuffer(str.length);
  const bufView = new Uint8Array(buf);
  for (let i = 0, strLen = str.length; i < strLen; i++) {
    bufView[i] = str.charCodeAt(i);
  }
  return buf;
}

export async function signatureVerifierV1(
  msgData: ArrayBuffer,
  signature: ArrayBuffer,
  Ku: mod.webcrypto.CryptoKey,
) {
  // UGLY: Assuming ECDSA P-256

  return await mod.subtle.verify(
    {
      name: "ECDSA",
      hash: "SHA-256",
    },
    Ku,
    signature,
    msgData,
  );
}

export async function pem2_P256key(filePath: string) {
  const publicKeyBytes = await Deno.readFile(filePath);
  const pemKey = new TextDecoder().decode(publicKeyBytes);

  // fetch the part of the PEM string between header and footer
  const pemHeader = "-----BEGIN PUBLIC KEY-----";
  const pemFooter = "-----END PUBLIC KEY-----";
  const pemContents = pemKey.substring(
    pemHeader.length,
    pemKey.length - pemFooter.length - 1,
  );
  // base64 decode the string to get the binary data
  // convert from a binary string to an ArrayBuffer
  const a = atob(pemContents);
  const binaryDer = str2ab(a);

  // UGLY: Assuming P-256
  return mod.subtle.importKey(
    "spki",
    binaryDer,
    {
      name: "ECDSA",
      namedCurve: "P-256",
    },
    true,
    ["verify"],
  );
}