/*
 * mCaptcha is a PoW based DoS protection software.
 * This is the frontend web component of the mCaptcha system
 * Copyright © 2021 Aravinth Manivnanan <realaravinth@batsense.net>.
 *
 * Use of this source code is governed by Apache 2.0 or MIT license.
 * You shoud have received a copy of MIT and Apache 2.0 along with
 * this program. If not, see <https://spdx.org/licenses/MIT.html> for
 * MIT or <http://www.apache.org/licenses/LICENSE-2.0> for Apache.
 */

import { gen_pow } from "@mcaptcha/pow-wasm";
import * as p from "@mcaptcha/pow_sha256-polyfill";
import { WasmWork, PoWConfig, SubmitWork } from "./types";

/**
 * proove work
 * @param {PoWConfig} config - the proof-of-work configuration using which
 * work needs to be computed
 * */
const prove = async (config: PoWConfig): Promise<SubmitWork> => {
  const WASM = "wasm";
  const JS = "js";
  if (WasmSupported) {
    let proof: WasmWork = null;
    let res: SubmitWork = null;
    let time: number = null;

    const t0 = performance.now();
    const proofString = gen_pow(
      config.salt,
      config.string,
      config.difficulty_factor
    );
    const t1 = performance.now();
    time = t1 - t0;

    proof = JSON.parse(proofString);
    const worker_type = WASM;
    res = {
      result: proof.result,
      nonce: proof.nonce,
      worker_type,
      time,
    };
    return res;
  } else {
    console.log("WASM unsupported, expect delay during proof generation");

    let proof: WasmWork = null;
    let time: number = null;
    let res: SubmitWork = null;

    const t0 = performance.now();

    proof = await p.generate_work(
      config.salt,
      config.string,
      config.difficulty_factor
    );
    const t1 = performance.now();
    time = t1 - t0;

    const worker_type = JS;
    res = {
      result: proof.result,
      nonce: proof.nonce,
      worker_type,
      time,
    };

    return res;
  }
};

// credits: @jf-bastien on Stack Overflow
// https://stackoverflow.com/questions/47879864/how-can-i-check-if-a-browser-supports-webassembly
const WasmSupported = (() => {
  try {
    if (
      typeof WebAssembly === "object" &&
      typeof WebAssembly.instantiate === "function"
    ) {
      const module = new WebAssembly.Module(
        Uint8Array.of(0x0, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00)
      );
      if (module instanceof WebAssembly.Module)
        return new WebAssembly.Instance(module) instanceof WebAssembly.Instance;
    }
  } catch (e) {
    console.error(e);
  }
  return false;
})();

export default prove;