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#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#define ALPHA "ABCDEFGHIJKLMNOPQRSTUVXYZ"

void playfair_table(char key[], char table[5][5])
{
    int r = 0;
    int s = 0;
    int count;

    for (size_t j = 0; j < strlen(key); j++)
    {
        table[r][s] = key[j];
        s++;
        if (s == 5)
        {
            s = 0;
            r++;
        }
    }
    for (size_t i = 0; i < 26; i++)
    {
        count = 0;
        for (size_t j = 0; j < strlen(key); j++)
            if (ALPHA[i] == key[j])
                count++;
        if (count == 1)
            continue;
        else
        {
            table[r][s] = ALPHA[i];
            s++;
            if (s == 5)
            {
                s = 0;
                r++;
            }
        }
    }
}

void find_pos(char table[5][5], char posc, int pos[])
{
    for (size_t i = 0; i < 5; i++)
    {
        for (size_t j = 0; j < 5; j++)
        {
            if (posc == table[i][j])
            {
                pos[0] = i;
                pos[1] = j;
            }
        }
    }
}

void sipher(char table[5][5], char encrypt[], int pos1[], int pos2[])
{
    if (pos1[0] == pos2[0])
    {
        if (pos1[1] == 4)
            encrypt[0] = table[pos1[0]][0];
        else
            encrypt[0] = table[pos1[0]][pos1[1] + 1];
        if (pos2[1] == 4)
            encrypt[1] = table[pos2[0]][0];
        else
            encrypt[1] = table[pos2[0]][pos2[1] + 1];
    }
    else if (pos1[1] == pos2[1])
    {
        if (pos1[0] == 4)
            encrypt[0] = table[0][pos1[1]];
        else
            encrypt[0] = table[pos1[0] + 1][pos1[1]];
        if (pos2[0] == 4)
            encrypt[1] = table[0][pos2[1]];
        else
            encrypt[1] = table[pos2[0] + 1][pos2[1]];
    }
    else
    {
        encrypt[0] = table[pos1[0]][pos2[1]];
        encrypt[1] = table[pos2[0]][pos1[1]];
    }
}

char *playfair_encrypt(const char *key, const char *text)
{
    if (key == NULL || text == NULL || text[0] == '\0' || key[0] == '\0')
        return NULL;

    // PREMENNE
    char chan_text[strlen(text) + 50];
    char chan_key[strlen(key) + 50];
    size_t text_in = 0;
    size_t key_in = 0;
    int count;
    char table[5][5];
    int pos_a[2];
    int pos_b[2];
    char encrypt[2];

    // uprava textu
    for (size_t i = 0; i < strlen(text); i++, text_in++)
    {
        if (isalpha(text[i]) == 0)
            if (text[i] != ' ')
                return NULL;
        if (text[i] == ' ')
        {
            text_in--;
            continue;
        }
        chan_text[text_in] = toupper(text[i]);
        if (chan_text[text_in] == 'W')
            chan_text[text_in] = 'V';
        if ((chan_text[text_in] == chan_text[text_in - 1]) && chan_text[text_in] != 'X')
        {
            chan_text[text_in] = 'X';
            text_in++;
            chan_text[text_in] = chan_text[text_in - 2];
        }
    }
    if (text_in % 2 != 0)
    {
        chan_text[text_in] = 'X';
        text_in++;
    }
    chan_text[text_in] = '\0';

    //uprava key
    for (size_t i = 0; i < strlen(key); i++, key_in++)
    {
        count = 0;
        if (isalpha(key[i]) == 0)
            if (key[i] != ' ')
                return NULL;
        if (key[i] == ' ')
        {
            key_in--;
            continue;
        }
        if (i > 1)
            for (size_t j = i - 1; j > 0; j--)
                if (key[i] == key[j])
                    count++;
        if (count == 1)
        {
            key_in--;
            continue;
        }
        chan_key[key_in] = toupper(key[i]);
        if (chan_key[key_in] == 'W')
            chan_key[key_in] = 'V';
    }
    chan_key[key_in] = '\0';

    //vygenerovanie tabulky s klucovym slovom
    playfair_table(chan_key, table);

    // magic
    int fin_len = strlen(chan_text) + strlen(chan_text) / 2;
    char *playfair = calloc(fin_len, sizeof(char));
    for (size_t i = 0, j = 0; i < strlen(chan_text); i++, j++)
    {
        find_pos(table, chan_text[i], pos_a);
        i++;
        find_pos(table, chan_text[i], pos_b);
        sipher(table, encrypt, pos_a, pos_b);
        playfair[j] = encrypt[0];
        j++;
        playfair[j] = encrypt[1];
        j++;
        if (j != fin_len)
            playfair[j] = ' ';
    }
    playfair[fin_len] = '\0';
    return playfair;
}