parse pattern string

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdint.h>
#include <stdbool.h>
#include <stddef.h>

#define TENS(x)  (((char) x - 0x30) * 10)
#define UNITS(x) ((char) x - 0x30)

#define ID_FOUND_MARK 255

/* The pattern string tell us what elements on the array units should we mark.
 *
 * The comma separator are used to mark single units, the dash separator are used
 * for 'ranges' with the former number being the lower bound of the range and
 * the latter number being the upper bound of the range.
 *
 * Numbers found on the pattern string will be marked with the 255 number.
 *
 * Assumptions made:
 * - The former number on the range is smaller then the former number.
 * - There is no spaces on the string.
 * - There is no ranges with double dash, e.g. 1-5-7.
 * - All numbers are 1 or 2 digits.
 */
void parse_units(char *pattern, uint8_t *units, size_t units_size)
{
    char *parser_cursor = NULL;
    size_t parser_cursor_pos = 0;
    size_t parser_step = 1;

    printf("\r\nPattern %s\r\n\r\n", pattern);

    // Begin the parsing
    for (parser_cursor = pattern; parser_cursor_pos < strlen(pattern); parser_cursor += parser_step) {

        bool is_comma_separator = false;
        bool is_dash_separator = false;
        bool is_last_number = false;

        // Does the parser_cursor points to a digit character?
        if (isdigit(*parser_cursor)) {
            char *next_comma = NULL;
            char *next_dash = NULL;

            // Found the closest separator (comma, dash o NULL):
            next_comma = strchr(parser_cursor, ',');
            next_dash = strchr(parser_cursor, '-');

            if ((NULL != next_comma) && (NULL != next_dash)) {
                if (next_comma < next_dash) {
                    is_comma_separator = true;
                } else {
                    is_dash_separator = true;
                }
            } else if ((NULL == next_comma) && (NULL != next_dash)) {
                is_dash_separator = true;
            } else if ((NULL != next_comma) && (NULL == next_dash)) {
                is_comma_separator = true;
            } else {
                // No more comas nor dashes, so we reached
                // the last number on the pattern
                is_last_number = true;
            }

            if (is_comma_separator) {
                uint8_t num = 0;
                ptrdiff_t num_digits = 0;

                num_digits = next_comma - parser_cursor;

                if (num_digits == 1) {
                    num = UNITS(*parser_cursor);
                } else if (num_digits == 2) {
                    num = TENS(*parser_cursor) + UNITS(*(parser_cursor + 1));
                }

                printf("number found: %d\r\n", num);

                // Mark the number found
                if (num < units_size) {
                    units[num] = ID_FOUND_MARK;
                }
                // this will place the cursor right after the comma
                parser_step = (size_t) num_digits + 1;

            } else if (is_dash_separator) {
                // If a dash is being found then we need to parse the first
                // and second numbers.
                printf("Range found\r\n");

                uint8_t first_number = 0;
                ptrdiff_t first_num_digits = 0;

                ptrdiff_t second_num_digits = 0;
                uint8_t second_num = 0;
                char *second_comma = NULL;
                char *next_separator = NULL;

                // first number
                first_num_digits = next_dash - parser_cursor;

                if (first_num_digits == 1) {
                    first_number = UNITS(*parser_cursor);
                } else if (first_num_digits == 2) {
                    first_number = TENS(*parser_cursor) + UNITS(*(parser_cursor + 1));
                }

                printf("\tfirst_number: %d\r\n", first_number);

                // Move the parser_cursor after the dash separator
                parser_cursor = next_dash + 1;
                parser_cursor_pos += (size_t) first_num_digits + 1;

                // ASSUMPTION:
                // When we found a dash separator the next separator can only be:
                // - comma
                // - NULL (end of the pattern string)
                second_comma = strchr(parser_cursor, ',');
                next_separator = pattern + strlen(pattern);

                // If a comma was found then next_separator will point to it.
                if (second_comma != NULL) {
                    next_separator = second_comma;
                }

                second_num_digits = next_separator - parser_cursor;

                if (second_num_digits == 1) {
                    second_num = UNITS(*parser_cursor);
                } else if (second_num_digits == 2) {
                    second_num = TENS(*parser_cursor) + UNITS(*(parser_cursor + 1));
                }

                printf("\tsecond_number: %d\r\n", second_num);

                // Mark the numbers found
                // TODO:
                // If the second_num is bigger than units_size should we
                // truncate marking the numbers up to the last element of the
                // units array?
                if (first_number < units_size || second_num < units_size) {
                    for (size_t idx = first_number; idx <= second_num; idx++) {
                        units[idx] = ID_FOUND_MARK;
                    }
                }

                // this will place the cursor right after the comma
                parser_step = (size_t) second_num_digits + 1;
            } else if (is_last_number) {
                size_t num_size = 0;
                uint8_t num = 0;

                // Get the amount of the remaining digits
                num_size = strlen(parser_cursor);

                if (num_size == 1) {
                    num = UNITS(*parser_cursor);
                } else if (num_size == 2) {
                    num = TENS(*parser_cursor) + UNITS(*(parser_cursor + 1));
                }

                printf("last number: %d\r\n", num);

                // Mark the number found
                if (num < units_size) {
                    units[num] = ID_FOUND_MARK;
                }
                parser_step = num_size;
            }

        } else {
            // The parser cursor was not pointing to a number character so we
            // just move the pointer to the next character.
            parser_step = 1;
        }

        // Keep the parser_cursor_pos up to date
        parser_cursor_pos += parser_step;
    }

    printf("parsing done\r\n");
}

int main(void)
{
    uint8_t objects[40] = {0};
    parse_units("1-3,4,5,6,8,9,10,12-14", objects, sizeof(objects));
    memset(objects, 0, sizeof(objects));
    parse_units("4-10,26", objects, sizeof(objects));

    return 0;
}