const VALID_TIME_REGEX = /[\u4e0a\u4e0b\uc624]?[\u5348\ud6c4\uc804]?[0-9]{1,2}.?.?.?[0-9]{0,2}\s?[AaPp\u03C0\u03BC]?\.?\s?[Mm\u03BC]?/;
const AM_REGEX = /[Aa\u4e0a\u03C0\uc624]\.?\s?[Mm\u5348\ud6c4\u03BC\uc804]/;
const PM_REGEX = /[Pp\u4e0b\uc624\u03BC]\.?\s?[Mm\u5348\ud6c4\u03BC]/;
const NUMBER_REGEX = /[0-9]{1,2}/g;
const TWELVE_HOURS = 12;
const SIXTY_MINUTES = 60;
const DEFAULT_PARSED_TIME = { hours: 0, minutes: 0 };
const VALID_NUMBER_COUNT = 2;

/**
 * Check that the input string is in a valid time format
 * @param input - input string to test
 * @returns
 */
export const isValidTime = (input?: string): boolean => {
    return !!input && VALID_TIME_REGEX.test(input);
};

/**
 * Parse an input string and convert it into an object containing numerical hours and minutes.
 * @param input - input string to be converted
 * @param isRequired - whether the input is required
 * @returns
 */
export const parseTimeFromString = (input?: string, isRequired?: boolean): { hours: number; minutes: number } => {
    // Return the default time (midnight) if the input is empty, but not required
    if (!input && !isRequired) return DEFAULT_PARSED_TIME;

    // Throw an error if the input is empty and required, or if the input fails the initial regex
    if (!input || !isValidTime(input)) {
        throw new SyntaxError();
    }

    // Throw an error if the input contains more than four numbers
    const timeArray = input.match(NUMBER_REGEX);
    if (!timeArray || !timeArray.length) return DEFAULT_PARSED_TIME;
    if (timeArray.length > VALID_NUMBER_COUNT) {
        throw new SyntaxError();
    }

    // If there are three numbers total, the regex match will split them
    // unevenly, loading two numbers for the hours value and one for the
    // minutes value. For instance, "305" would be split into ["30", "5"].
    // This should be ["3", "05"] instead, so we will move the second
    // number in the hours value to the beginning of the minutes value.
    const hasAMNotation = AM_REGEX.test(input);
    const hasPMNotation = PM_REGEX.test(input);
    let [hours, minutes] = timeArray;
    if (hours && minutes && hours.length === 2 && minutes.length === 1) {
        minutes = hours[1] + minutes;
        hours = hours[0];
    }

    // Convert the minutes value into an integer
    const numericMinutes = minutes ? parseInt(minutes, 10) : 0;

    // Set the hours to "0" if the input translates to midnight
    // Convert the hours to 24-hour format if this is a PM time
    let numericHours = parseInt(hours, 10);
    if (hasAMNotation && numericHours === TWELVE_HOURS) {
        numericHours = 0;
    } else if (hasPMNotation && numericHours < TWELVE_HOURS) {
        numericHours += TWELVE_HOURS;
    }

    // Throw an error if the hours or minutes are out of range
    if (numericHours > TWELVE_HOURS * 2 || numericMinutes >= SIXTY_MINUTES) {
        throw new SyntaxError();
    }

    return {
        hours: numericHours,
        minutes: numericMinutes,
    };
};