/* keylength.c 

 * This program attempts to guess the key length based on repetitions  *
 * that are some number of characters apart.  The program will only    *
 * work for alphabetic characters.                                     */

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

#define MAX_LETTERS 26
#define MAX_OCCUR 256
#define THRESH 0

int main (argc, argv)
     int argc;
     char *argv[];
{
  int doubleL [MAX_LETTERS][MAX_LETTERS][MAX_OCCUR] = {0};
  int keysize [MAX_OCCUR] = {0};
  int prev, curr;
  int count = 0, totalReps = 0;
  int i = 0, j = 0, k = 0;
  int temp;

  if ((curr = tolower(getchar())) == EOF){
    fprintf(stderr, "No input given\n");
    return 1;
  }
  while (curr < (int)'a' || curr > (int)'z'){
    if ((curr = tolower(getchar())) == EOF){
      fprintf(stderr, "No input or invalid input\n");
      return 1;
    }
  }
  
  prev = curr;
  count++;

  while ((curr = tolower(getchar())) != EOF){
    if (curr >= (int)'a' && curr <= (int)'z'){
      doubleL[prev - (int)'a'][curr - (int)'a'][0]++;
      temp = doubleL[prev-(int)'a'][curr-(int)'a'][0];
      if (temp < MAX_OCCUR)
	doubleL[prev - (int)'a'][curr - (int)'a'][temp] = count;
      prev = curr;
      count++;
    }
  }

  while (i < MAX_LETTERS){
    while (j < MAX_LETTERS){
      while (k < doubleL[i][j][0] && doubleL[i][j][0] > 1){
	totalReps += doubleL[i][j][0]-1;
	fprintf(stdout, "\nThe characters %c%c occured at positions : ", (char)(i+(int)'a'), (char)(j+(int)'a'));
	while (k < doubleL[i][j][0]){
	  if (k == 0)
	    fprintf(stdout, "%d, ", doubleL[i][j][1]);
	  else{
	    temp = doubleL[i][j][k+1] - doubleL[i][j][k];
	    fprintf(stdout, "%d(%d), ", doubleL[i][j][k+1], 
		    temp);
	    if (temp < MAX_OCCUR)
	      keysize[temp]++;
	  }
	  k++;
	}
	k++;
      }
      k = 0;
      j++;
    }
    j = 0;
    i++;
  }

  fprintf(stdout, "\n\n");

  fprintf(stdout, "-------------------------------------------------------\n");
  fprintf(stdout, "Keysize statistics\n");
  temp = 0;
  for (i = 0; i < MAX_OCCUR; i++){
    if (keysize[i] > keysize[temp])
      temp = i;
    if (keysize[i] > THRESH)
      fprintf(stdout, "Keysize = %d     with frequency %d/%d\n", i, keysize[i], totalReps);
  }
  fprintf(stdout, "\n\n*****************************************************************\n");
  fprintf(stdout, "Highest frequency = %d(%0.3f)    with first occurance at %d\n", keysize[temp], (double)keysize[temp]/totalReps, temp);
  fprintf(stdout, "*****************************************************************\n\n");
  return 0;
}