//----------------------------------------------------------------------
//  '22.02.13 bug fix
//----------------------------------------------------------------------
#include <stdio.h>
#include <string.h>

void encrypt( char*a, char*b, char* key) {
  char x[128];
  int i,j,k,m;
  k = 0;
  int n = strlen(key);
  for (i=0; b[i]!=0; i++) {
    x[i] = b[i]^key[k++];
    k %= n;
  }
  m = i;

  // 8bit -> 6bit
  // 8bit           0          1          2
  //        000000|00, 0000|0000, 00|000000
  // 6bit        0        1        2      3
  j = 0;
  for (i=0; i<m; j++) {
    switch (j%4) {
      case 0:
        a[j] = (x[i]&0xFC)>>2;
        break;
      case 1:
        a[j] = (x[i]&0x03)<<4 | (x[i+1]&0xF0)>>4; 
        i++;
        break;
      case 2:
        a[j] = (x[i]&0x0F)<<2 | (x[i+1]&0xC0)>>6; 
        i++;
        break;
      case 3:
        a[j] = x[i]&0x3F;
        i++; 
        break;
    }
  }

  // ascii文字に変換
  for (i=0; i<j; i++) {
    a[i] += (int)'#';
  }
  a[i] = 0;
  
}

void decrypt( char*a, char*b, char* key) {
  char x[128];
  int i,j,k,m;
  // ascii文字をbinaryに戻す
  for(i=0; b[i]!=0; i++) {
    x[i] = b[i] - (int)'#';
  }
  m = i - 1;

  // 6bit -> 8bit
  j = 0;
  for(i=0; j<m ; i++) {
    switch (i%3) {
      case 0:
        a[i] = (x[j]&0x3F)<<2 | (x[j+1]&0x30)>>4;
        j++;
        break;
      case 1:
        a[i] = (x[j]&0x0F)<<4 | (x[j+1]&0x3C)>>2; 
        j++;
        break;
      case 2:
        a[i] = (x[j]&0x03)<<6 | (x[j+1]&0x3F);
        j += 2;
        break;
    }
  }
  m = i;
  
  k = 0;
  int n = strlen(key);
  for (i=0; i<m; i++) {
    a[i] ^= key[k++];
    k %= n;
  }
  a[i]= 0;
}

int main(int argc, char *argv[]) {
  int i;
  if (argc!=3) {
    printf("Usage: encrypt.exe key_text file_name\n");
    return(0);
  }
  char* key  = argv[1];
  char* file = argv[2];
  char  cryptfile[128];
  strcpy(cryptfile,file);
  strcat(cryptfile,"_crypt.txt");

  FILE *fp = fopen(file,"r");
  if (!fp) {
    printf("input file open error. %s\n",file);
    return(-1);
  }

  FILE *cfp = fopen(cryptfile,"w");
  if (!cfp) {
    printf("output file open error. %s\n",cryptfile);
    return(-1);
  }

  char plain_text[128];
  char encrypted[256];
  char decrypted[256];

  for (i=0;i<3;i++) {
    fgets(plain_text,128,fp);
    strtok(plain_text,"\n\0");
    encrypt(encrypted,plain_text,key);
    fprintf(cfp,"%s\n",encrypted);
    printf("encrypted:%s\n",encrypted);

    decrypt(decrypted,encrypted,key);
    printf("decrypted:%s\n",decrypted);
  }
  while( fgets(plain_text,128,fp) ) {
    printf("plaintext:%s",plain_text);
    fprintf(cfp,"%s",plain_text);
  }
  
  fclose(cfp);
  fclose(fp);
  printf("\nencrypted file : %s\n",cryptfile);

}