Method performDecode

src/Encoder/NihilistCipher.js:132–173

* Performs decode on given content. * @protected * @param {Chain} content * @return {number[]|string|Uint8Array|Chain} Decoded content

(content)

   * @return {number[]|string|Uint8Array|Chain} Decoded content
   */
  async performDecode (content) {
    const key = this.getSettingValue('key')
    const separator = this.getSettingValue('separator')
    const values = content.getString().split(separator)

    const contentLength = values.length
    const keyLength = key.getLength()

    const keyPolybius = await this._polybiusSquare.encode(key)

    let value, plaintextValue, keyIndex, keyValue
    let plaintextPolybius = ''

    for (let i = 0; i < contentLength; i++) {
      // Read next value
      value = parseInt(values[i])
      if (isNaN(value)) {
        throw new InvalidInputError(
          `Block at index ${i + 1} is not a number.`)
      }

      // Compose key number
      keyIndex = MathUtil.mod(i, keyLength) * 2
      keyValue = parseInt(
        keyPolybius.getCharAt(keyIndex) +
        keyPolybius.getCharAt(keyIndex + 1)
      )

      // Compute plaintext number
      plaintextValue = value - keyValue
      if (!plaintextValue.toString().match(/^[1-5]{2}$/)) {
        throw new InvalidInputError(
          `Block at index ${i + 1} results in invalid ` +
          `Polybius square coordinates '${plaintextValue}'.`)
      }

      plaintextPolybius += plaintextValue.toString()
    }

    // Unwrap Polybius square encoded content
    return this._polybiusSquare.decode(plaintextPolybius)
  }

  /**
   * Triggered when a setting field has changed.