polkadot-js/common

// Copyright 2017-2024 @polkadot/util authors & contributors
// SPDX-License-Identifier: Apache-2.0

import type { HexString } from '../types.js';

import { hexAddPrefix } from './addPrefix.js';
import { hexStripPrefix } from './stripPrefix.js';

/**
 * @name hexFixLength
 * @summary Shifts a hex string to a specific bitLength
 * @description
 * Returns a `0x` prefixed string with the specified number of bits contained in the return value. (If bitLength is -1, length checking is not done). Values with more bits are trimmed to the specified length. Input values with less bits are returned as-is by default. When `withPadding` is set, shorter values are padded with `0`.
 * @example
 * <BR>
 *
 * ```javascript
 * import { hexFixLength } from '@polkadot/util';
 *
 * console.log('fixed', hexFixLength('0x12', 16)); // => 0x12
 * console.log('fixed', hexFixLength('0x12', 16, true)); // => 0x0012
 * console.log('fixed', hexFixLength('0x0012', 8)); // => 0x12
 * ```
 */
export function hexFixLength (value: string, bitLength = -1, withPadding = false): HexString {
  const strLength = Math.ceil(bitLength / 4);
  const hexLength = strLength + 2;

  return hexAddPrefix(
    (bitLength === -1 || value.length === hexLength || (!withPadding && value.length < hexLength))
      ? hexStripPrefix(value)
      : (value.length > hexLength)
        ? hexStripPrefix(value).slice(-1 * strLength)
        : `${'0'.repeat(strLength)}${hexStripPrefix(value)}`.slice(-1 * strLength)
  );
}