// Copyright 2017-2022 @polkadot/util authors & contributors
// SPDX-License-Identifier: Apache-2.0

type HexString = `0x${string}`;

const U8 = new Array<string>(256);
const U16 = new Array<string>(256 * 256);

for (let n = 0; n < 256; n++) {
  U8[n] = n.toString(16).padStart(2, '0');
}

for (let i = 0; i < 256; i++) {
  const s = i << 8;

  for (let j = 0; j < 256; j++) {
    U16[s | j] = U8[i] + U8[j];
  }
}

/** @internal */
function hex(value: Uint8Array, result: HexString): HexString {
  const mod = value.length % 2 | 0;
  const length = (value.length - mod) | 0;

  for (let i = 0; i < length; i += 2) {
    // @ts-ignore
    result += U16[(value[i] << 8) | value[i + 1]];
  }

  if (mod) {
    // @ts-ignore
    result += U8[value[length] | 0];
  }

  return result;
}

/**
 * @name u8aToHex
 * @summary Creates a hex string from a Uint8Array object.
 * @description
 * `UInt8Array` input values return the actual hex string. `null` or `undefined` values returns an `0x` string.
 * @example
 * <BR>
 *
 * ```javascript
 * import { u8aToHex } from '@polkadot/util';
 *
 * u8aToHex(new Uint8Array([0x68, 0x65, 0x6c, 0x6c, 0xf])); // 0x68656c0f
 * ```
 */
export function u8aToHex(value?: Uint8Array | null, bitLength = -1, isPrefixed = true): HexString {
  // this is not 100% correct sinmce we support isPrefixed = false....
  const empty = isPrefixed ? '0x' : ('' as HexString);

  if (!value || !value.length) {
    return empty;
  } else if (bitLength > 0) {
    const length = Math.ceil(bitLength / 8);

    if (value.length > length) {
      return `${hex(value.subarray(0, length / 2), empty)}…${hex(
        value.subarray(value.length - length / 2),
        '' as HexString
      )}`;
    }
  }

  return hex(value, empty);
}