#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>

#define BUFF_SIZE 32


// Vérification que la clé est bien composée de lettres majuscules uniquement
bool check_key(char* key) {
  for (size_t i=0; i < strlen(key); i++) {
    if ('A' > key[i] || key[i] > 'Z')
      return false;
  }
  return true;
}

// Chiffre/ Déchiffre uniquement les lettres, incrémente k_uses si la clé est utilisée
char enc(char in, char k, int action, int* k_uses) {
  if ('a' <= in && in <= 'z')
    in += 'A'-'a';

  if ('A' > in || in > 'Z')
    return in;

  (*k_uses)++;
  return ((in - 'A' + (action * (k-'A')) +('Z'-'A'+1))%('Z'-'A'+1))+'A';
}

int vigenere(char* src, char* key, int action) {
  FILE* fp = fopen(src, "r");

  char buffer[BUFF_SIZE];

  int k_uses = 0;
  int klength = strlen(key);
  while (fgets(buffer, klength, fp)) {
    for (int i=0; i < BUFF_SIZE; i++) {
      if (buffer[i] == '\0') {
        printf("%s", buffer);
        break;
      }
      buffer[i] = enc(buffer[i], key[k_uses%klength], action, &k_uses);
    }
  }

  fclose(fp);

  return 0;
}


int main(int argc, char* argv[]) {
  char* src = NULL;
  char* key = NULL;
  int action = 0;

  for (int i=1; i < argc; i++) {
    if (!strcmp(argv[i], "-e")) {
      action = 1;
      src = argv[i+1];
      i++;
    } else if (!strcmp(argv[i], "-d")) {
      action = -1;
      src = argv[i+1];
      i++;
    } else if (!strcmp(argv[i], "-k")) {
      key = argv[i+1];
      i++;
    } else {
      printf("Unknown option %s\n", argv[i]);
    }
  }

  if (!src || !key || !action) {
    printf("Usage: %s -[e|d] <file> -k <key>\n", argv[0]);
    return 1;
  }

  if (!check_key(key)) {
    printf("Clé de chiffrement invalide. Utilisez seulement des lettres majuscules.\n");
    return 1;
  }

  return vigenere(src, key, action);
}