#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define NUM_OF_LETTERS 'Z' - 'A'

struct Stats {
  int white_characters;
  int letter_counter[NUM_OF_LETTERS];
};

struct Stats statistic;

int main(int argc, char* argv[]) {

  FILE* inputFile = fopen(argv[1], "r+");
  FILE* tmpFile = fopen("tmp.txt", "w");
  FILE* outputFile = fopen("output.txt", "w+");

  char signToChange;
  char readSign;
  char userSign;

  printf("Enter sign to change: "); scanf("%c", &signToChange);
  getchar();
  printf("\nEnter sign you want to replace with: "); scanf("%c", &userSign);

  while ((readSign = getc(inputFile)) != EOF) {
    if (toupper(readSign) == toupper(signToChange)) {
      fwrite(&userSign, 1, 1, tmpFile);
    }
    else {
      fwrite(&readSign, 1, 1, tmpFile);
    }

    if (toupper(readSign) >= 'A' && toupper(readSign) <= 'Z')
      statistic.letter_counter[toupper(readSign) - 'A']++;
    else if (readSign == ' ' || readSign == '\t' || readSign == 'n')
      statistic.white_characters++;
  }

  char rarestLetter = 0 + 'A';
  int min = statistic.letter_counter[0];
  for (int i = 0; i < NUM_OF_LETTERS; ++i) {
    if (statistic.letter_counter[i] < min && statistic.letter_counter[i] != 0) {
      min = statistic.letter_counter[i];
      rarestLetter = i + 'A';
    }
  }
  fclose(tmpFile);
  tmpFile = fopen("tmp.txt", "r");
  while ((readSign = getc(tmpFile)) != EOF) {
    if (toupper(readSign) == toupper(rarestLetter)) {
      fprintf(outputFile, "VIRUS");
    }
    else {
      fwrite(&readSign, 1, 1, outputFile);
    }
  }

  for (int i = 0; i < NUM_OF_LETTERS; ++i) {
    printf("%c - %d\n", i + 'A', statistic.letter_counter[i]);
  }

  fclose(inputFile);
  fclose(tmpFile);
  fclose(outputFile);
  remove("tmp.txt");
  return 0;
}