// Copyright 2017-2025 @polkadot/util authors & contributors
// SPDX-License-Identifier: Apache-2.0

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

/**
 * @name u8aToNumber
 * @summary Creates a number from a Uint8Array object.
 */
export function u8aToNumber (value: Uint8Array, { isLe = true, isNegative = false }: ToBnOptions = {}): number {
  // slice + reverse is expensive, however SCALE is LE by default so this is the path
  // we are most interested in (the BE is added for the sake of being comprehensive)
  if (!isLe) {
    value = value.slice().reverse();
  }

  const count = value.length;

  // When the value is a i{8, 16, 24, 32, 40, 40} values and the top-most bit
  // indicates a signed value, we use a two's complement conversion. If one of these
  // flags are not set, we just do a normal unsigned conversion (the same shortcut
  // applies in both the u8aTo{BigInt, Bn} conversions as well)
  if (isNegative && count && (value[count - 1] & 0x80)) {
    switch (count) {
      case 0:
        return 0;

      case 1:
        return (((value[0] ^ 0x0000_00ff) * -1) - 1);

      case 2:
        return ((((value[0] + (value[1] << 8)) ^ 0x0000_ffff) * -1) - 1);

      case 3:
        return ((((value[0] + (value[1] << 8) + (value[2] << 16)) ^ 0x00ff_ffff) * -1) - 1);

      case 4:
        // for the 3rd byte, we don't << 24 - since JS converts all bitwise operators to
        // 32-bit, in the case where the top-most bit is set this yields a negative value
        return ((((value[0] + (value[1] << 8) + (value[2] << 16) + (value[3] * 0x1_00_00_00)) ^ 0xffff_ffff) * -1) - 1);

      case 5:
        return (((((value[0] + (value[1] << 8) + (value[2] << 16) + (value[3] * 0x1_00_00_00)) ^ 0xffff_ffff) + ((value[4] ^ 0xff) * 0x1_00_00_00_00)) * -1) - 1);

      case 6:
        return (((((value[0] + (value[1] << 8) + (value[2] << 16) + (value[3] * 0x1_00_00_00)) ^ 0xffff_ffff) + (((value[4] + (value[5] << 8)) ^ 0x0000_ffff) * 0x1_00_00_00_00)) * -1) - 1);

      default:
        throw new Error('Value more than 48-bits cannot be reliably converted');
    }
  }

  switch (count) {
    case 0:
      return 0;

    case 1:
      return value[0];

    case 2:
      return value[0] + (value[1] << 8);

    case 3:
      return value[0] + (value[1] << 8) + (value[2] << 16);

    case 4:
      // for the 3rd byte, we don't << 24 - since JS converts all bitwise operators to
      // 32-bit, in the case where the top-most bit is set this yields a negative value
      return value[0] + (value[1] << 8) + (value[2] << 16) + (value[3] * 0x1_00_00_00);

    case 5:
      return value[0] + (value[1] << 8) + (value[2] << 16) + ((value[3] + (value[4] << 8)) * 0x1_00_00_00);

    case 6:
      return value[0] + (value[1] << 8) + (value[2] << 16) + ((value[3] + (value[4] << 8) + (value[5] << 16)) * 0x1_00_00_00);

    default:
      throw new Error('Value more than 48-bits cannot be reliably converted');
  }
}
