
#include <sys/types.h>
#include <ctype.h>
#include <stdlib.h>
#include "unescape_c_string.h"

#ifndef isoctal
# define isoctal(c)     ((c) >= '0' && (c) <= '7')
#endif
#ifndef digittoint
# define digittoint(c) (((c) >= '0' && (c) <= '9') ? (c) - '0' : tolower(c) - 'a' + 10)
#endif

typedef enum C_STRING_STATE {
        C_STRING_STATE_GROUND,
        C_STRING_STATE_START,
        C_STRING_STATE_OCTAL2,
        C_STRING_STATE_OCTAL3,
        C_STRING_STATE_HEX1,
        C_STRING_STATE_HEX2
} C_STRING_STATE;

int
unescape_c_string(char *cp, char c, int *astate, int flag)
{
    if (flag & C_STRING_FLAG_END) {
        switch (*astate) {
        case C_STRING_STATE_OCTAL2:
        case C_STRING_STATE_OCTAL3:
        case C_STRING_STATE_HEX1:
        case C_STRING_STATE_HEX2:
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;
        case C_STRING_STATE_GROUND:
            return C_STRING_RESULT_NOCHAR;
        default:
            return C_STRING_RESULT_SYNBAD;
        }
    }

    switch (*astate) {
    case C_STRING_STATE_GROUND:
        *cp = 0;
        if (c == '\\') {
            *astate = C_STRING_STATE_START;
            return C_STRING_RESULT_PENDING;
        }
        *cp = c;
        return C_STRING_RESULT_VALID;

    case C_STRING_STATE_START:
        *cp = 0;
        switch (c) {
        case '\\':
            *cp = c;
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;

        case '0': case '1': case '2': case '3':
        case '4': case '5': case '6': case '7':
            *cp = (c - '0');
            *astate = C_STRING_STATE_OCTAL2;
            return C_STRING_RESULT_PENDING;

        case 'x':
            *astate = C_STRING_STATE_HEX1;
            return C_STRING_RESULT_PENDING;

        case 'n':
            *cp = '\n';
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;
        case 'r':
            *cp = '\r';
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;
        case 'b':
            *cp = '\b';
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;
        case 'a':
            *cp = '\a';
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;
        case 'v':
            *cp = '\v';
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;
        case 't':
            *cp = '\t';
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;
        case 'f':
            *cp = '\f';
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;
        case 's':
            *cp = ' ';
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;
        case 'E':
            *cp = '\033';
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_VALID;

        case '\n':
        case '$':
            *astate = C_STRING_STATE_GROUND;
            return C_STRING_RESULT_NOCHAR;
        }
        *astate = C_STRING_STATE_GROUND;
        return C_STRING_RESULT_SYNBAD;

    case C_STRING_STATE_OCTAL2:
        if (isoctal((int) (unsigned char) c)) {
            *cp = (*cp << 3) + (c - '0');
            *astate = C_STRING_STATE_OCTAL3;
            return C_STRING_RESULT_PENDING;
        }
        *astate = C_STRING_STATE_GROUND;
        return C_STRING_RESULT_VALIDPUSH;

    case C_STRING_STATE_OCTAL3:
        *astate = C_STRING_STATE_GROUND;
        if (isoctal((int) (unsigned char) c)) {
            *cp = (*cp << 3) + (c - '0');
            return C_STRING_RESULT_VALID;
        }
        return C_STRING_RESULT_VALIDPUSH;

    case C_STRING_STATE_HEX1:
        if (isxdigit((int) (unsigned char) c)) {
            *cp = digittoint((int) (unsigned char) c);
            *astate = C_STRING_STATE_HEX2;
            return C_STRING_RESULT_PENDING;
        }
        *astate = C_STRING_STATE_GROUND;
        return C_STRING_RESULT_VALIDPUSH;

    case C_STRING_STATE_HEX2:
        *astate = C_STRING_STATE_GROUND;
        if (isxdigit((int) (unsigned char) c)) {
            *cp = (*cp << 4) + digittoint((int) (unsigned char) c);
            return C_STRING_RESULT_VALID;
        }
        return C_STRING_RESULT_VALIDPUSH;

    default:
        *astate = C_STRING_STATE_GROUND;
        return C_STRING_RESULT_SYNBAD;
    }
}

int
str_unescape_c_string(char *dst, const char *src)
{
    char c;
    char *start = dst;
    int state = 0;

    while ((c = *src++)) {
again:
        switch (unescape_c_string(dst, c, &state, 0)) {
        case C_STRING_RESULT_VALID:
            dst++;
            break;
        case C_STRING_RESULT_VALIDPUSH:
            dst++;
            goto again;
        case C_STRING_RESULT_PENDING:
        case C_STRING_RESULT_NOCHAR:
            break;
        default:
            *dst = 0;
            return -1;
        }
    }
    if (unescape_c_string(dst, c, &state, C_STRING_FLAG_END) == C_STRING_RESULT_VALID) {
        dst++;
    }
    *dst = 0;
    return dst - start;
}

ssize_t
strn_unescape_c_string(char *dst, const char *src, size_t sz)
{
    char c, p;
    char *start = dst, *end = dst + sz - 1;
    int state = 0;

    if (sz > 0) {
        *end = 0;
    }
    while ((c = *src++)) {
again:
        switch (unescape_c_string(&p, c, &state, 0)) {
        case C_STRING_RESULT_VALID:
            if (dst < end) {
                *dst = p;
            }
            dst++;
            break;
        case C_STRING_RESULT_VALIDPUSH:
            if (dst < end) {
                *dst = p;
            }
            dst++;
            goto again;
        case 0:
        case C_STRING_RESULT_NOCHAR:
            break;
        default:
            if (dst <= end) {
                *dst = 0;
            }
            return -1;
        }
    }
    if (unescape_c_string(&p, c, &state, C_STRING_FLAG_END) == C_STRING_RESULT_VALID) {
        if (dst < end) {
            *dst = p;
        }
        dst++;
    }
    if (dst <= end) {
        *dst = 0;
    }
    return dst - start;
}