Method performDecode

src/Encoder/PolybiusSquare.js:168–238

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

(content)

   * @return {number[]|string|Uint8Array|Chain} Decoded content
   */
  performDecode (content) {
    const alphabet = this.getSettingValue('alphabet').getCodePoints()
    const separator = this.getSettingValue('separator').getCodePoints()
    const includeForeignChars = this.getSettingValue('includeForeignChars')

    const rows = this.getSettingValue('rows').getCodePoints()
    const columns = this.getSettingValue('columns').getCodePoints()

    // Ignore all separators inside the given content
    const input = ArrayUtil.replaceSlice(content.getCodePoints(), separator)

    const alphabetLength = alphabet.length
    const width = columns.length
    const inputLength = input.length
    const result = new Array(inputLength)

    let i = 0
    let j = 0
    let row, column, index

    while (i < inputLength) {
      // Find the next valid row character
      row = null
      while (row === null && i < inputLength) {
        index = rows.indexOf(input[i])
        if (index !== -1) {
          // Found row character
          row = index
        } else if (includeForeignChars) {
          // Include foreign character
          result[j++] = input[i]
        }
        i++
      }

      // Find the next valid column character
      column = null
      while (column === null && i < inputLength) {
        index = rows.indexOf(input[i])
        if (index !== -1) {
          // Found column character
          column = index
        } else if (includeForeignChars) {
          // Include foreign character
          result[j++] = input[i]
        }
        i++
      }

      if (row !== null && column !== null) {
        // Decode square coordinates
        index = row * width + column

        // Make sure the given square cell is defined by the alphabet
        if (index >= alphabetLength) {
          throw new InvalidInputError(
            `Polybius square cell at coordinates ${row},${column} are not ` +
            'defined by the alphabet.')