105 lines
2.5 KiB
Python
105 lines
2.5 KiB
Python
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# -*- coding: utf-8 -*-
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# This file is part of convertdate.
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# http://github.com/fitnr/convertdate
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# Licensed under the MIT license:
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# http://opensource.org/licenses/MIT
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# Copyright (c) 2016, fitnr <fitnr@fakeisthenewreal>
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from math import trunc
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from .utils import jwday, monthcalendarhelper
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from .gregorian import to_jd as gregorian_to_jd, from_jd as gregorian_from_jd
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J0000 = 1721424.5 # Julian date of Gregorian epoch: 0000-01-01
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J1970 = 2440587.5 # Julian date at Unix epoch: 1970-01-01
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JMJD = 2400000.5 # Epoch of Modified Julian Date system
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JULIAN_EPOCH = 1721423.5
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J2000 = 2451545.0 # Julian day of J2000 epoch
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JULIANCENTURY = 36525.0 # Days in Julian century
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HAVE_30_DAYS = (4, 6, 9, 11)
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HAVE_31_DAYS = (1, 3, 5, 7, 8, 10, 12)
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def leap(year):
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if year % 4 and year > 0:
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return 0
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else:
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return 3
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def month_length(year, month):
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if month == 2:
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daysinmonth = 29 if leap(year) else 28
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else:
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daysinmonth = 30 if month in HAVE_30_DAYS else 31
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return daysinmonth
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def legal_date(year, month, day):
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'''Check if this is a legal date in the Julian calendar'''
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daysinmonth = month_length(year, month)
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if not (0 < day <= daysinmonth):
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raise ValueError("Month {} doesn't have a day {}".format(month, day))
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return True
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def from_jd(jd):
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'''Calculate Julian calendar date from Julian day'''
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jd += 0.5
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z = trunc(jd)
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a = z
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b = a + 1524
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c = trunc((b - 122.1) / 365.25)
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d = trunc(365.25 * c)
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e = trunc((b - d) / 30.6001)
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if trunc(e < 14):
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month = e - 1
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else:
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month = e - 13
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if trunc(month > 2):
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year = c - 4716
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else:
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year = c - 4715
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day = b - d - trunc(30.6001 * e)
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return (year, month, day)
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def to_jd(year, month, day):
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'''Convert to Julian day using astronomical years (0 = 1 BC, -1 = 2 BC)'''
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legal_date(year, month, day)
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# Algorithm as given in Meeus, Astronomical Algorithms, Chapter 7, page 61
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if month <= 2:
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year -= 1
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month += 12
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return (trunc((365.25 * (year + 4716))) + trunc((30.6001 * (month + 1))) + day) - 1524.5
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def from_gregorian(year, month, day):
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return from_jd(gregorian_to_jd(year, month, day))
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def to_gregorian(year, month, day):
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return gregorian_from_jd(to_jd(year, month, day))
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def monthcalendar(year, month):
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start_weekday = jwday(to_jd(year, month, 1))
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monthlen = month_length(year, month)
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return monthcalendarhelper(start_weekday, monthlen)
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