#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>

/* Read a file and return a buffer with the file contents */

unsigned char *readfile(const char *filename,int *len)
{
    int fd = open(filename,O_RDONLY);
    struct stat st;

    if(fd<0) err(1,filename);
    if(fstat(fd,&st)) err(1,"fstat");

    *len = st.st_size;
    unsigned char *buf = (unsigned char *)malloc(st.st_size);
    if(!buf) err(1,"malloc 1");
    if(read(fd,buf,st.st_size)<0) err(1,"read1");
    close(fd);
    return buf;
}


main(int argc, char **argv)
{
    if(argc!=3){
	fprintf(stderr,"usage: %s <key> <cipher>\n");
	exit(0);
    }
    int  len1;
    unsigned char *buf1 = readfile(argv[1],&len1);

    int  len2;
    unsigned char *buf2 = readfile(argv[2],&len2);

    int  len = len1<len2 ? len1 : len2;

    printf("Output (%d bytes):\n",len);

    int i;
    int bad=0;
    for(i=0;i<len;i++){
	unsigned char ch = buf1[i] ^ buf2[i];
	/* Print non-printing characters at '.' */
	if(ch>127){
	    ch='.';
	    bad++;
	}
	if(ch<32 && ch!=10){
	    ch='.';
	    bad++;
	}
	putchar(ch);
    }
    putchar('\n');
    if(bad>0){
	printf("%d non-printing characters are shown as periods.\n",bad);
    }

    printf("\n\nOutput in hex:\n");
    for(i=0;i<len;i++){
	unsigned char ch = buf1[i] ^ buf2[i];
	printf("%02x ",ch);
	if(i%20==19) putchar('\n');
    }
    putchar('\n');

    printf("\n\nMany people find octal easier than hex.\n");
    printf("\n\n");
    printf("Here is the output in octal:\n");
    for(i=0;i<len;i++){
	unsigned char ch = buf1[i] ^ buf2[i];
	printf("%03o ",ch);
	if(i%20==19) putchar('\n');
    }
    putchar('\n');

    printf("\n\n");
    printf("Here is how the results were obtained:\n");
    int row;
    const int npr=10;
    for(i=0;i<len;i+=npr){
	printf("Bytes %d .. %d\n",i,i+npr-1);
	for(row=0;row<4;row++){
	    switch(row){
	    case 0:printf("file %-14s",argv[1]);break;
	    case 1:printf("file %-14s",argv[2]);break;
	    case 2:printf("================== ");break;
	    case 3:printf("file1 XOR file2    ");break;
	    }
	    for(int j=i;j<i+npr;j++){
		switch(row){
		case 0:printf("%03o ",buf1[j]);break;
		case 1:printf("%03o ",buf2[j]);break;
		case 2:printf("====");break;
		case 3:printf("%03o ",buf1[j] ^ buf2[j]);break;
		}
	    }
	    putchar(' ');
	    for(int j=i;j<i+npr;j++){
		unsigned char ch=' ';
		switch(row){
		case 0:ch = buf1[j];break;
		case 1:ch = buf2[j];break;
		case 2:ch = ' ';break;
		case 3:ch = buf1[j] ^ buf2[j];break;
		}
		if((ch>=32 && ch<=127)){
		    putchar(ch);
		}
		else {
		    putchar('.');
		}
	    }
		
	    putchar('\n');
	}
	putchar('\n');
	putchar('\n');
    }
}