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/*
 * xorimage.c - partially based on OpenWrt's addpattern.c
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <stdint.h>
#include <unistd.h>
#include <sys/stat.h>

static char default_pattern[] = "12345678";
static int is_hex_pattern;


int xor_data(uint8_t *data, size_t len, const uint8_t *pattern, int p_len, int p_off)
{
        int offset = p_off;
        while (len--) {
                *data ^= pattern[offset];
                data++;
                offset = (offset + 1) % p_len;
        }
        return offset;
}


void usage(void) __attribute__ (( __noreturn__ ));

void usage(void)
{
        fprintf(stderr, "Usage: xorimage [-i infile] [-o outfile] [-p <pattern>] [-x]\n");
        exit(EXIT_FAILURE);
}


int main(int argc, char **argv)
{
        char buf[1024]; /* keep this at 1k or adjust garbage calc below */
        FILE *in = stdin;
        FILE *out = stdout;
        char *ifn = NULL;
        char *ofn = NULL;
        const char *pattern = default_pattern;
        char hex_pattern[128];
        unsigned int hex_buf;
        int c;
        int v0, v1, v2;
        size_t n;
        int p_len, p_off = 0;

        while ((c = getopt(argc, argv, "i:o:p:xh")) != -1) {
                switch (c) {
                        case 'i':
                                ifn = optarg;
                                break;
                        case 'o':
                                ofn = optarg;
                                break;
                        case 'p':
                                pattern = optarg;
                                break;
                        case 'x':
                                is_hex_pattern = true;
                                break;
                        case 'h':
                        default:
                                usage();
                }
        }

        if (optind != argc || optind == 1) {
                fprintf(stderr, "illegal arg \"%s\"\n", argv[optind]);
                usage();
        }

        if (ifn && !(in = fopen(ifn, "r"))) {
                fprintf(stderr, "can not open \"%s\" for reading\n", ifn);
                usage();
        }

        if (ofn && !(out = fopen(ofn, "w"))) {
                fprintf(stderr, "can not open \"%s\" for writing\n", ofn);
                usage();
        }

        p_len = strlen(pattern);

        if (p_len == 0) {
                fprintf(stderr, "pattern cannot be empty\n");
                usage();
        }

        if (is_hex_pattern) {
                int i;

                if ((p_len / 2) > sizeof(hex_pattern)) {
                        fprintf(stderr, "provided hex pattern is too long\n");
                        usage();
                }

                if (p_len % 2 != 0) {
                        fprintf(stderr, "the number of characters (hex) is incorrect\n");
                        usage();
                }

                for (i = 0; i < (p_len / 2); i++) {
                        if (sscanf(pattern + (i * 2), "%2x", &hex_buf) < 0) {
                                fprintf(stderr, "invalid hex digit around %d\n", i * 2);
                                usage();
                        }
                        hex_pattern[i] = (char)hex_buf;
                }
        }

        while ((n = fread(buf, 1, sizeof(buf), in)) > 0) {
                if (n < sizeof(buf)) {
                        if (ferror(in)) {
                        FREAD_ERROR:
                                fprintf(stderr, "fread error\n");
                                return EXIT_FAILURE;
                        }
                }

                if (is_hex_pattern) {
                        p_off = xor_data(buf, n, hex_pattern, (p_len / 2),
                                         p_off);
                } else {
                        p_off = xor_data(buf, n, pattern, p_len, p_off);
                }

                if (!fwrite(buf, n, 1, out)) {
                FWRITE_ERROR:
                        fprintf(stderr, "fwrite error\n");
                        return EXIT_FAILURE;
                }
        }

        if (ferror(in)) {
                goto FREAD_ERROR;
        }

        if (fflush(out)) {
                goto FWRITE_ERROR;
        }

        fclose(in);
        fclose(out);

        return EXIT_SUCCESS;
}