Julian Date Converter

def gregorian_to_jdn(year: int, month: int, day: int) -> float:
    """Convert Gregorian date to Julian Day Number (Meeus algorithm)."""
    if month <= 2:
        year -= 1
        month += 12
    A = year // 100
    B = 2 - A + A // 4
    return int(365.25 * (year + 4716)) + int(30.6001 * (month + 1)) + day + B - 1524.5

def jdn_to_gregorian(jdn: float) -> tuple[int, int, int]:
    """Convert Julian Day Number to Gregorian date (Meeus algorithm)."""
    jdn = jdn + 0.5
    Z = int(jdn)
    if Z < 2299161:
        A = Z
    else:
        alpha = int((Z - 1867216.25) / 36524.25)
        A = Z + 1 + alpha - alpha // 4
    B = A + 1524
    C = int((B - 122.1) / 365.25)
    D = int(365.25 * C)
    E = int((B - D) / 30.6001)
    day = B - D - int(30.6001 * E)
    month = E - 1 if E < 14 else E - 13
    year = C - 4716 if month > 2 else C - 4715
    return year, month, day

jdn = gregorian_to_jdn(2024, 3, 15)
print(f"2024-03-15 → JDN: {jdn}")
y, m, d = jdn_to_gregorian(jdn)
print(f"JDN {jdn} → {y}-{m:02d}-{d:02d}")