module Collapstring

static VALUE collapstring_collapse(VALUE self, VALUE src)
{
        VALUE dst = rb_obj_clone(src);
        assert(dst);
        collapstring_collapse_bang(self, dst);
        return dst;
}

static VALUE collapstring_collapse_bang(VALUE self, VALUE src)
{
        Check_Type(src, T_STRING);

        char *str = RSTRING_PTR(src);
        const size_t len = RSTRING_LEN(src);

        size_t dst_idx = 0, src_idx = 0;
        collapse_state state = C_S_OUT;

        for (; src_idx < len; src_idx++) {
                const char cur = str[src_idx];
                switch (cur) {
                case '\"':
                        switch (state) {
                        case C_S_OUT:
                                str[dst_idx++] = cur;
                                state = C_S_IN_DOUBLE;
                                break;
                        case C_S_OUT_BACKSLASH:
                        case C_S_IN_DOUBLE:
                                str[dst_idx++] = cur;
                                state = C_S_OUT;
                                break;
                        case C_S_IN_DOUBLE_BACKSLASH:
                                state = C_S_IN_DOUBLE;
                                /* fallthrough */
                        case C_S_IN_SINGLE:
                                break;
                        case C_S_IN_SINGLE_BACKSLASH:
                                state = C_S_IN_SINGLE;
                                break;
                        }
                        break;
                case '\'':
                        switch (state) {
                        case C_S_OUT:
                                str[dst_idx++] = cur;
                                state = C_S_IN_SINGLE;
                                break;
                        case C_S_OUT_BACKSLASH:
                        case C_S_IN_SINGLE:
                                str[dst_idx++] = cur;
                                state = C_S_OUT;
                                break;
                        case C_S_IN_SINGLE_BACKSLASH:
                                state = C_S_IN_SINGLE;
                                break;
                        case C_S_IN_DOUBLE_BACKSLASH:
                                state = C_S_IN_DOUBLE;
                                /* fallthrough */
                        case C_S_IN_DOUBLE:
                                break;
                        }
                        break;
                case '\\':
                        switch (state) {
                        case C_S_IN_SINGLE:
                                state = C_S_IN_SINGLE_BACKSLASH;
                                break;
                        case C_S_IN_SINGLE_BACKSLASH:
                                state = C_S_IN_SINGLE;
                                break;
                        case C_S_IN_DOUBLE:
                                state = C_S_IN_DOUBLE_BACKSLASH;
                                break;
                        case C_S_IN_DOUBLE_BACKSLASH:
                                state = C_S_IN_DOUBLE;
                                break;
                        case C_S_OUT:
                                str[dst_idx++] = cur;
                                state = C_S_OUT_BACKSLASH;
                                break;
                        case C_S_OUT_BACKSLASH:
                                str[dst_idx++] = cur;
                                state = C_S_OUT;
                                break;
                        }
                        break;
                default:
                        switch (state) {
                        case C_S_IN_SINGLE_BACKSLASH:
                                state = C_S_IN_SINGLE;
                                break;
                        case C_S_IN_DOUBLE_BACKSLASH:
                                state = C_S_IN_DOUBLE;
                                break;
                        case C_S_OUT:
                                str[dst_idx++] = cur;
                                break;
                        case C_S_OUT_BACKSLASH:
                                str[dst_idx++] = cur;
                                state = C_S_OUT;
                                break;
                        case C_S_IN_SINGLE:
                        case C_S_IN_DOUBLE:
                                break;
                        }
                }
        }

        return rb_str_resize(src, dst_idx);
}

static VALUE collapstring_fuzz(VALUE self, VALUE length)
{
        static char *chars = "\'\"\\ ";
        Check_Type(length, T_FIXNUM);
        int i, l = NUM2INT(length);
        VALUE res = rb_str_new(NULL, 0);
        assert(res);
        for (i = 0; i < l; i++) {
                res = rb_str_cat(res, chars + rand() % 4, 1);
        }
        return res;
}