#!/bin/bash
. matrix.sh
. mods.sh
. translator.sh

function hill_decrypt {
	local input=( $@ )
	key=($(letters_to_numbers $1))
	ciphertext=($(letters_to_numbers $2))

	if [ $((${#ciphertext[@]}%2)) -ne 0 ]; then
		echo "ERROR: Cipher text length must be even number!!"
		return
	fi

	det=$(getdet ${key[@]})
	det=$(mod $det 26)
	det=$(frac_mod $det 26)

	#~ echo "frac mod determinant is" $det

	inverse=( \
	$(mod $((${key[3]} * $det)) 26) \
	$(mod $((-${key[1]} * $det)) 26) \
	$(mod $((-${key[2]} * $det)) 26) \
	$(mod $((${key[0]} * $det)) 26) \
	)

	#~ echo "inverse of the key is" ${inverse[@]}

	plaintext=($(multiply ${inverse[@]} ${ciphertext[@]}))

	#~ echo "Decrypted numbers: "${plaintext[@]}

	echo $(numbers_to_letters ${plaintext[@]})
}

# Hill Cipher Encrypt
# Appends "X" to the end of the input if the input is odd-numbered
function hill_encrypt {
	KEY=$1
	PLAINTEXT=$2

	if (( ${#PLAINTEXT} % 2 ))
	then
		PLAINTEXT+=X
	fi

	K=($(letters_to_numbers "$KEY"))
	P=($(letters_to_numbers "$PLAINTEXT"))

	E=($(multiply ${K[@]} ${P[@]}))
	echo $(numbers_to_letters ${E[@]})
}