Western Church Holy Days Code

Source Code (last updated: 21-May-2008)

#region Copyright (c) 2008 Larry D. Hunt
/******************************************************************************
' 
' License: MIT License (also called the X11 License)
' 
' Copyright (c) 2008 Larry D. Hunt
' 
' Permission is hereby granted, free of charge, to any person obtaining a copy
' of this software and associated documentation files (the "Software"), to deal
' in the Software without restriction, including without limitation the rights
' to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
' copies of the Software, and to permit persons to whom the Software is
' furnished to do so, subject to the following conditions:
' 
' The above copyright notice and this permission notice shall be included in
' all copies or substantial portions of the Software.
' 
' THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
' IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
' FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
' AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
' LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
' OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
' THE SOFTWARE.
' 
'*****************************************************************************/
#endregion

using System;
using System.Collections.Generic;
using System.Text;
using SpaceLib.Tools;

namespace SpaceLib.Algorithms
{
    // Western Church Holy Days Algorithms.
    // Reference: Astronomical Algorithms (2nd edition) by Jean Meeus, ISBN: 0-943396-61-1; Chapter 8.
    public class WesternChurchHolyDays
    {
        #region Properties

        private DateTime _ashWednesday;
        public DateTime AshWednesday
        {
            get
            {
                return _ashWednesday;
            }
            set
            {
                _ashWednesday = value;
            }
        }

        private DateTime _easter;
        public DateTime Easter
        {
            get
            {
                return _easter;
            }
            set
            {
                _easter = value;
            }
        }

        private DateTime _goodFriday;
        public DateTime GoodFriday
        {
            get
            {
                return _goodFriday;
            }
            set
            {
                _goodFriday = value;
            }
        }

        private DateTime _pentecost;
        public DateTime Pentecost
        {
            get
            {
                return _pentecost;
            }
            set
            {
                _pentecost = value;
            }
        }

        private int _year;
        public int Year
        {
            get
            {
                return _year;
            }
            set
            {
                _year = value;
                CalculateHolyDays(_year);
            }
        }

        #endregion

        public WesternChurchHolyDays(int year)
        {
            CalculateHolyDays(year);
        }

        private void CalculateHolyDays(int year)
        {
            JulianDay julianDay = new JulianDay(year, 1, 1);
            if (julianDay.IsGregorianDateRange())
            {
                CalculateGregorianEaster(year);
            }
            else
            {
                CalculateJulianEaster(year);
            }

            CalculateOtherHolyDays();
        }

        private void CalculateGregorianEaster(int x)
        {
            // Note; use one character variable names to match equation in Meeus book.
            _year = x;
            int a;
            Math.DivRem(x, 19, out a);
            int c;
            int b = Math.DivRem(x, 100, out c);
            int e;
            int d = Math.DivRem(b, 4, out e);
            int f = (b + 8) / 25;
            int g = (b - f  + 1) / 3;
            int h;
            Math.DivRem(((19 * a) + b - d - g + 15), 30, out h);
            int k;
            int i = Math.DivRem(c, 4, out k);
            int l;
            Math.DivRem((32 + (2 * e) + (2 * i) - h - k), 7, out l);
            int m = (a + (11 * h) + (22 * l)) / 451;
            int p;
            int n = Math.DivRem((h + l - (7 * m) + 114), 31, out p);

            _easter = new DateTime(x, n, p + 1);
        }

        private void CalculateJulianEaster(int x)
        {
            // Note; use one character variable names to match equation in Meeus book.
            _year = x;
            int a;
            Math.DivRem(x, 4, out a);
            int b;
            Math.DivRem(x, 7, out b);
            int c;
            Math.DivRem(x, 19, out c);
            int d;
            Math.DivRem(((19 * c) + 15), 30, out d);
            int e;
            Math.DivRem(((2 * a) + (4 * b) - d + 34), 7, out e);
            int g;
            int f = Math.DivRem((d + e + 114), 31, out g);

            _easter = new DateTime(x, f, g + 1);
        }

        private void CalculateOtherHolyDays()
        {
            _goodFriday = _easter.AddDays(-2);
            _ashWednesday = _easter.AddDays(-46);
            _pentecost = _easter.AddDays(49);
        }
    }
}

Unit Test Code (last updated: 21-May-2008)

    [TestFixture]
    public class WesternChurchHolyDaysTest
    {
        [Test]
        public void s001_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(1991);
            Assert.AreEqual(new DateTime(1991, 3, 31), holidays.Easter , "Easter date not correct.");
        }

        [Test]
        public void s002_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(1992);
            Assert.AreEqual(new DateTime(1992, 4, 19), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s003_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(1993);
            Assert.AreEqual(new DateTime(1993, 4, 11), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s004_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(1954);
            Assert.AreEqual(new DateTime(1954, 4, 18), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s005_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(2000);
            Assert.AreEqual(new DateTime(2000, 4, 23), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s006_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(1818);
            Assert.AreEqual(new DateTime(1818, 3, 22), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s010_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(179);
            Assert.AreEqual(new DateTime(179, 4, 12), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s011_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(711);
            Assert.AreEqual(new DateTime(711, 4, 12), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s012_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(1243);
            Assert.AreEqual(new DateTime(1243, 4, 12), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s013_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(1991);
            Assert.AreEqual(new DateTime(1991, 3, 31), holidays.Easter, "Easter date not correct.");

            holidays.Year = 1992;
            Assert.AreEqual(new DateTime(1992, 4, 19), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s020_AshWednesday()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(2008);
            Assert.AreEqual(new DateTime(2008, 2, 6), holidays.AshWednesday, "Ash Wednesday date not correct.");
        }

        [Test]
        public void s021_GoodFriday()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(2008);
            Assert.AreEqual(new DateTime(2008, 3, 21), holidays.GoodFriday, "Good Friday date not correct.");
        }
        [Test]
        public void s022_Easter()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(2008);
            Assert.AreEqual(new DateTime(2008, 3, 23), holidays.Easter, "Easter date not correct.");
        }

        [Test]
        public void s023_Pentecost()
        {
            WesternChurchHolyDays holidays = new WesternChurchHolyDays(2008);
            Assert.AreEqual(new DateTime(2008, 5, 11), holidays.Pentecost, "Pentecost date not correct.");
        }
    }