/*
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * Jordan K. Hubbard
 * 29 August 1998
 *
 *	$Id: interp_backslash.c,v 1.2 1998/09/03 06:14:41 jkh Exp $
 *
 * Routine for doing backslash elimination.
 */

#include <stand.h>
#include <string.h>

#define DIGIT(x) (isdigit(x) ? (x) - '0' : islower(x) ? (x) + 10 - 'a' : (x) + 10 - 'A')

/*
 * backslash: Return malloc'd copy of str with all standard "backslash
 * processing" done on it.  Original can be free'd if desired.
 */
char *
backslash(char *str)
{
    /*
     * Remove backslashes from the strings. Turn \040 etc. into a single
     * character (we allow eight bit values). Currently NUL is not
     * allowed.
     *
     * Turn "\n" and "\t" into '\n' and '\t' characters. Etc.
     *
     */
    char *new_str;
    int seenbs = 0;
    int i = 0;

    if ((new_str = strdup(str)) == NULL)
	return NULL;

    while (*str) {
	if (seenbs) {
	    seenbs = 0;
	    switch (*str) {
	    case '\\':
		new_str[i++] = '\\';
		str++;
		break;

	    /* preserve backslashed quotes */
	    case '\'':
	    case '"':
		new_str[i++] = '\\';
		new_str[i++] = *str++;
		break;

	    case 'b':
		new_str[i++] = '\b';
		str++;
		break;

	    case 'f':
		new_str[i++] = '\f';
		str++;
		break;

	    case 'r':
		new_str[i++] = '\r';
		str++;
		break;

	    case 'n':
		new_str[i++] = '\n';
		str++;
		break;

	    case 's':
		new_str[i++] = ' ';
		str++;
		break;

	    case 't':
		new_str[i++] = '\t';
		str++;
		break;

	    case 'v':
		new_str[i++] = '\13';
		str++;
		break;

	    case 'z':
		str++;
		break;

	    case '0': case '1': case '2': case '3': case '4':
	    case '5': case '6': case '7': case '8': case '9': {
		char val;

		/* Three digit octal constant? */
		if (*str >= '0' && *str <= '3' && 
		    *(str + 1) >= '0' && *(str + 1) <= '7' &&
		    *(str + 2) >= '0' && *(str + 2) <= '7') {

		    val = (DIGIT(*str) << 6) + (DIGIT(*(str + 1)) << 3) + 
			DIGIT(*(str + 2));

		    /* Allow null value if user really wants to shoot
                       at feet, but beware! */
		    new_str[i++] = val;
		    str += 3;
		    break;
		}

		/* One or two digit hex constant?
		 * If two are there they will both be taken.
		 * Use \z to split them up if this is not wanted.
		 */
		if (*str == '0' &&
		    (*(str + 1) == 'x' || *(str + 1) == 'X') &&
		    isxdigit(*(str + 2))) {
		    val = DIGIT(*(str + 2));
		    if (isxdigit(*(str + 3))) {
			val = (val << 4) + DIGIT(*(str + 3));
			str += 4;
		    }
		    else
			str += 3;
		    /* Yep, allow null value here too */
		    new_str[i++] = val;
		    break;
		}
	    }
	    break;

	    default:
		new_str[i++] = *str++;
		break;
	    }
	}
        else {
            if (*str == '\\') {
                seenbs = 1;
                str++;
            }
	    else
		new_str[i++] = *str++;
        }
    }

    if (seenbs) {
        /*
         * The final character was a '\'. Put it in as a single backslash.
         */
	new_str[i++] = '\\';
    }
    new_str[i] = '\0';
    return new_str;
}
