mod part_2 {
    pub fn calibrate(text: &str) -> u32 {
        let mut calibration_value = 0;
        for lines in text.split('\n') {
            calibration_value = calibration_value + decrypt_value(lines);
        }
        calibration_value
   }

    fn decrypt_value(line: &str) -> u32 {
        let mut digits = (0, 0);
        let (mut lower_index, mut upper_index) = (0, 1);

        while upper_index <= line.len() {
            let region = &line[lower_index .. upper_index];
            let update = regional_digit(region);
            if update == 0 { upper_index = upper_index + 1; continue; } // update = 0 means no digit at current region

            if digits.0 > 0 { digits.1 = update; } else { digits.0 = update; }
            lower_index = upper_index - 1;
            upper_index = upper_index + 1;
        }

        if digits.1 > 0 { digits.0*10 + digits.1 } else { digits.0*10 + digits.0 }
    }

    fn regional_digit(region: &str) -> u32 {
        let last_character = region.chars().last().unwrap();
        let mut update = 0;
        if last_character.is_digit(10) {
            update = last_character.to_digit(10).unwrap();
        }
        if region.contains("one") {
            update = 1;
        }
        if region.contains("two") {
            update = 2;
        }
        if region.contains("three") {
            update = 3;
        }
        if region.contains("four") {
            update = 4;
        }
        if region.contains("five") {
            update = 5;
        }
        if region.contains("six") {
            update = 6;
        }
        if region.contains("seven") {
            update = 7;
        }
        if region.contains("eight") {
            update = 8;
        }
        if region.contains("nine") {
            update = 9;
        }
        update
    }
}