/**
 * Calculate day of year (1-365/366) using UTC date components.
 * Uses UTC to ensure consistent calculations regardless of local timezone.
 * @param date - Date to calculate day of year for
 * @returns Day of year (1 = Jan 1, 365/366 = Dec 31)
 */
export declare function getDayOfYear(date: Date): number;
/**
 * Get UTC offset in hours from ISO 8601 string with timezone
 * @example getUTCOffset("2025-11-01T09:00:00+09:00") -> 9
 * @example getUTCOffset("2025-11-01T09:00:00-05:00") -> -5
 * @example getUTCOffset("2025-11-01T09:00:00Z") -> 0
 */
export declare function getUTCOffset(isoDateTime: string): number;
/**
 * Get UTC midnight of the local date (accounting for timezone).
 * Returns midnight for the local date as ISO string, not the UTC date.
 * @param isoDateTime - ISO 8601 string with timezone
 * @returns UTC midnight (00:00:00) of the local date as ISO string
 */
export declare function getUTCMidnight(isoDateTime: string): string;
/**
 * Add minutes to an ISO 8601 datetime and return new ISO 8601 string
 * Preserves timezone from input
 * @param isoDateTime - Base ISO 8601 datetime string
 * @param minutes - Minutes to add (can be negative)
 * @param timezoneOffset - UTC offset in hours
 */
export declare function addMinutes(isoDateTime: string, minutes: number, timezoneOffset: number): string;
/**
 * Get local time of day in minutes (0-1440), accounting for timezone.
 * @param isoDateTime - ISO 8601 string with timezone
 * @returns Minutes since midnight (0-1440 range)
 */
export declare function getLocalTimeInMinutes(isoDateTime: string): number;