export type PlaintextBlock = number[][]

export const preprocessPlaintext = (plaintext: string): PlaintextBlock[] => {
  /**
   * @param {string} plaintext - The plaintext to encrypt.
   * @returns {PlaintextBlock[]} Blocks of 128 bits representing the plaintext. Each block is a 4x4 column-major matrix.
  */

  const encoder = new TextEncoder()
  const byteArray = encoder.encode(plaintext) // Array where each item is an 8-bit representation of a character of the string
  const blockSize = 16 // 128 bits = 16 bytes

  // Loop through the byteArray and split it into 128-bit blocks
  const blocks: Uint8Array[] = []
  for (let i = 0;i < byteArray.length;i += blockSize) {
    const block = byteArray.slice(i, i + blockSize)

    if (block.length < blockSize) {
      // Pad the block with zeroes
      const paddedBlock = new Uint8Array(blockSize)
      paddedBlock.set(block)
      blocks.push(paddedBlock)
    } else {
      blocks.push(block)
    }
  }

  const plaintextBlocks: number[][][] = blocks.map(block => {
    // Block is a 128-bit array containing 16 8-bit integers.

    const matrix: number[][] = [
      [0, 0, 0, 0],
      [0, 0, 0, 0],
      [0, 0, 0, 0],
      [0, 0, 0, 0],
    ]

    // Fill the matrix in column-major order, i.e., top-to-bottom + left-to-right
    for (let i = 0;i < blockSize;i++) {
      const row = i % 4
      const col = Math.floor(i / 4)
      matrix[row][col] = block[i]
    }

    return matrix
  })

  return plaintextBlocks
}