Solution to solve feature request for new GetPreviousOccurence() meth…

…ods. atifaziz#64

NCrontab.Tests/CrontabScheduleTests.cs

@@ -408,6 +408,14 @@ public void GetNextOccurrences_NextOccurrenceInvalidTime_ShouldStopAtLastValidTi
             Assert.AreEqual(new DateTime(9988, 2, 29), occurrences.Last());
         }
 
+        [Test]
+        public void GetPrevOccurrences_PrevOccurrenceInvalidTime_ShouldStopAtLastValidTime()
+        {
+            var schedule = CrontabSchedule.Parse("0 0 29 Feb Mon");
+            var occurrences = schedule.GetPrevOccurrences(new DateTime(20, 1, 1), DateTime.MinValue);
+            Assert.AreEqual(new DateTime(16, 2, 29), occurrences.Last());
+        }
+
         // Instead of using strings and parsing as date,
         // consider NUnit's TestCaseData:
         // https://github.com/nunit/docs/wiki/TestCaseData
@@ -426,6 +434,24 @@ public void GetNextOccurrence(string expression, string startDate, string endDat
             Assert.AreEqual(expected, occurrence);
         }
 
+        // Instead of using strings and parsing as date,
+        // consider NUnit's TestCaseData:
+        // https://github.com/nunit/docs/wiki/TestCaseData
+
+        [TestCase("0 0 29 Feb Mon", "2017-12-31", "2017-01-01", "2017-01-01")]
+        [TestCase("0 0 29 Feb Mon", "9009-12-31", "9000-01-01", "9008-02-29")]
+        public void GetPrevOccurrence(string expression, string startDate, string endDate, string expectedValue)
+        {
+            var schedule = CrontabSchedule.Parse(expression);
+            var start = Time(startDate);
+            var end = Time(endDate);
+            var expected = Time(expectedValue);
+
+            var occurrence = schedule.GetPrevOccurrence(start, end);
+
+            Assert.AreEqual(expected, occurrence);
+        }
+
 
         static void CronCall(string startTimeString, string cronExpression, string nextTimeString, ParseOptions options)
         {

NCrontab/CrontabField.cs

@@ -117,6 +117,11 @@ public static CrontabField DaysOfWeek(string expression) =>
 
         public int GetFirst() => _minValueSet < int.MaxValue ? _minValueSet : -1;
 
+        /// <summary>
+        /// Gets the last value of the field or -1.
+        /// </summary>
+        public int GetLast() => _maxValueSet >= 0 ? _maxValueSet : -1;
+
         /// <summary>
         /// Gets the next value of the field that occurs after the given
         /// start value or -1 if there is no next value available.
@@ -139,6 +144,23 @@ public int Next(int start)
             return -1;
         }
 
+        public int Prev(int start)
+        {
+            if (start > _maxValueSet)
+                return _maxValueSet;
+
+            var startIndex = ValueToIndex(start);
+            var lastIndex = ValueToIndex(_minValueSet);
+
+            for (var i = startIndex; i >= lastIndex; i--)
+            {
+                if (_bits[i])
+                    return IndexToValue(i);
+            }
+
+            return -1;
+        }
+
         int IndexToValue(int index) => index + _impl.MinValue;
         int ValueToIndex(int value) => value - _impl.MinValue;
 

NCrontab/CrontabSchedule.cs

@@ -185,13 +185,27 @@ public IEnumerable<DateTime> GetNextOccurrences(DateTime baseTime, DateTime endT
             }
         }
 
+        public IEnumerable<DateTime> GetPrevOccurrences(DateTime baseTime, DateTime startTime)
+        {
+            for (var occurrence = TryGetPrevOccurrence(baseTime, startTime);
+                 occurrence != null && occurrence > startTime;
+                 occurrence = TryGetPrevOccurrence(occurrence.Value, startTime))
+            {
+                yield return occurrence.Value;
+            }
+        }
+
         /// <summary>
         /// Gets the next occurrence of this schedule starting with a base time.
         /// </summary>
 
         public DateTime GetNextOccurrence(DateTime baseTime) =>
             GetNextOccurrence(baseTime, DateTime.MaxValue);
 
+
+        public DateTime GetPrevOccurrence(DateTime baseTime) =>
+            GetPrevOccurrence(baseTime, DateTime.MinValue);
+
         /// <summary>
         /// Gets the next occurrence of this schedule starting with a base
         /// time and up to an end time limit.
@@ -210,6 +224,9 @@ public DateTime GetNextOccurrence(DateTime baseTime) =>
         public DateTime GetNextOccurrence(DateTime baseTime, DateTime endTime) =>
             TryGetNextOccurrence(baseTime, endTime) ?? endTime;
 
+        public DateTime GetPrevOccurrence(DateTime baseTime, DateTime startTime) =>
+            TryGetPrevOccurrence(baseTime, startTime) ?? startTime;
+
         DateTime? TryGetNextOccurrence(DateTime baseTime, DateTime endTime)
         {
             const int nil = -1;
@@ -377,6 +394,183 @@ public DateTime GetNextOccurrence(DateTime baseTime, DateTime endTime) =>
             return TryGetNextOccurrence(new DateTime(year, month, day, 23, 59, 59, 0, baseTime.Kind), endTime);
         }
 
+
+        DateTime? TryGetPrevOccurrence(DateTime baseTime, DateTime startTime)
+        {
+            const int nil = -1;
+
+            var baseYear = baseTime.Year;
+            var baseMonth = baseTime.Month;
+            var baseDay = baseTime.Day;
+            var baseHour = baseTime.Hour;
+            var baseMinute = baseTime.Minute;
+            var baseSecond = baseTime.Second;
+
+            var startYear = startTime.Year;
+            var startMonth = startTime.Month;
+            var startDay = startTime.Day;
+
+            var year = baseYear;
+            var month = baseMonth;
+            var day = baseDay;
+            var hour = baseHour;
+            var minute = baseMinute;
+            var second = baseSecond - 1;
+
+            //
+            // Second
+            //
+
+            var seconds = _seconds ?? SecondZero;
+            second = seconds.Prev(second);
+
+            if (second == nil)
+            {
+                second = seconds.GetLast();
+                minute--;
+            }
+
+            //
+            // Minute
+            //
+
+            minute = _minutes.Prev(minute);
+
+            if (minute == nil)
+            {
+                second = seconds.GetLast();
+                minute = _minutes.GetLast();
+                hour--;
+            }
+            else if (minute < baseMinute)
+            {
+                second = seconds.GetLast();
+            }
+
+            //
+            // Hour
+            //
+
+            hour = _hours.Prev(hour);
+
+            // this variable for trick
+            // to keep day when it adjusted day 31 for
+            // "short" months
+            bool adjusting = false;
+
+            RetryDayMonth:
+
+            if (hour == nil)
+            {
+                minute = _minutes.GetLast();
+                hour = _hours.GetLast();
+                day--;
+            }
+            else if (hour > baseHour)
+            {
+                second = seconds.GetLast();
+                minute = _minutes.GetLast();
+            }
+
+            //
+            // Day
+            //
+
+
+
+            day = _days.Prev(day);
+
+
+            if (day == nil)
+            {
+                second = seconds.GetLast();
+                minute = _minutes.GetLast();
+                hour = _hours.GetLast();
+                day = _days.GetLast();
+                month--;
+            }
+            else if (day < baseDay)
+            {
+                second = seconds.GetLast();
+                minute = _minutes.GetLast();
+                hour = _hours.GetLast();
+            }
+
+            //
+            // Month
+            //
+
+            month = _months.Prev(month);
+
+            if (month == nil)
+            {
+                second = seconds.GetLast();
+                minute = _minutes.GetLast();
+                hour = _hours.GetLast();
+                day = _days.GetLast();
+                month = _months.GetLast();
+                year--;
+            }
+            else if (month < baseMonth)
+            {
+                second = seconds.GetLast();
+                minute = _minutes.GetLast();
+                hour = _hours.GetLast();
+                if (!adjusting)
+                    day = _days.GetLast();
+            }
+
+            //
+            // Stop processing when year is too large for the datetime or calendar
+            // object. Otherwise we would get an exception.
+            //
+
+            if (year < Calendar.MinSupportedDateTime.Year)
+                return null;
+
+            //
+            // The day field in a cron expression spans the entire range of days
+            // in a month, which is from 1 to 31. However, the number of days in
+            // a month tend to be variable depending on the month (and the year
+            // in case of February). So a check is needed here to see if the
+            // date is a border case. If the day happens to be beyond 28
+            // (meaning that we're dealing with the suspicious range of 29-31)
+            // and the date part has changed then we need to determine whether
+            // the day still makes sense for the given year and month. If the
+            // day is beyond the last possible value, then the day/month part
+            // for the schedule is re-evaluated. So an expression like "0 0
+            // 15,31 * *" will yield the following sequence starting on midnight
+            // of Jan 1, 2000:
+            //
+            //  Jan 15, Jan 31, Feb 15, Mar 15, Apr 15, Apr 31, ...
+            //
+
+            var dateChanged = day != baseDay || month != baseMonth || year != baseYear;
+
+            if (day > 28 && dateChanged && day > Calendar.GetDaysInMonth(year, month))
+            {
+                if (year <= startYear && month <= startMonth && day <= startDay)
+                    return startTime;
+
+                hour = nil;
+                adjusting = true;
+                goto RetryDayMonth;
+            }
+
+            var prevTime = new DateTime(year, month, day, hour, minute, second, 0, baseTime.Kind);
+
+            if (prevTime <= startTime)
+                return startTime;
+
+            //
+            // Day of week
+            //
+
+            if (_daysOfWeek.Contains((int)prevTime.DayOfWeek))
+                return prevTime;
+
+            return TryGetPrevOccurrence(new DateTime(year, month, day, 0, 0, 0, 0, baseTime.Kind), startTime);
+        }
         /// <summary>
         /// Returns a string in crontab expression (expanded) that represents
         /// this schedule.

NCrontab/ICrontabField.cs

@@ -24,6 +24,8 @@ public interface ICrontabField
     {
         int GetFirst();
         int Next(int start);
+        int GetLast();
+        int Prev(int start);
         bool Contains(int value);
     }
 }

NCrontab/PublicAPI/net35/PublicAPI.Shipped.txt

@@ -9,7 +9,9 @@ NCrontab.CrontabField.Contains(int value) -> bool
 NCrontab.CrontabField.Format(System.IO.TextWriter! writer) -> void
 NCrontab.CrontabField.Format(System.IO.TextWriter! writer, bool noNames) -> void
 NCrontab.CrontabField.GetFirst() -> int
+NCrontab.CrontabField.GetLast() -> int
 NCrontab.CrontabField.Next(int start) -> int
+NCrontab.CrontabField.Prev(int start) -> int
 NCrontab.CrontabField.ToString(string? format) -> string!
 NCrontab.CrontabFieldKind
 NCrontab.CrontabFieldKind.Day = 3 -> NCrontab.CrontabFieldKind
@@ -22,6 +24,9 @@ NCrontab.CrontabSchedule
 NCrontab.CrontabSchedule.GetNextOccurrence(System.DateTime baseTime) -> System.DateTime
 NCrontab.CrontabSchedule.GetNextOccurrence(System.DateTime baseTime, System.DateTime endTime) -> System.DateTime
 NCrontab.CrontabSchedule.GetNextOccurrences(System.DateTime baseTime, System.DateTime endTime) -> System.Collections.Generic.IEnumerable<System.DateTime>!
+NCrontab.CrontabSchedule.GetPrevOccurrence(System.DateTime baseTime) -> System.DateTime
+NCrontab.CrontabSchedule.GetPrevOccurrence(System.DateTime baseTime, System.DateTime startTime) -> System.DateTime
+NCrontab.CrontabSchedule.GetPrevOccurrences(System.DateTime baseTime, System.DateTime startTime) -> System.Collections.Generic.IEnumerable<System.DateTime>!
 NCrontab.CrontabSchedule.ParseOptions
 NCrontab.CrontabSchedule.ParseOptions.IncludingSeconds.get -> bool
 NCrontab.CrontabSchedule.ParseOptions.IncludingSeconds.set -> void
@@ -30,7 +35,9 @@ NCrontab.ExceptionProvider
 NCrontab.ICrontabField
 NCrontab.ICrontabField.Contains(int value) -> bool
 NCrontab.ICrontabField.GetFirst() -> int
+NCrontab.ICrontabField.GetLast() -> int
 NCrontab.ICrontabField.Next(int start) -> int
+NCrontab.ICrontabField.Prev(int start) -> int
 override NCrontab.CrontabField.ToString() -> string!
 override NCrontab.CrontabSchedule.ToString() -> string!
 static NCrontab.CrontabField.Days(string! expression) -> NCrontab.CrontabField!

NCrontab/PublicAPI/netstandard1.0/PublicAPI.Shipped.txt

@@ -8,7 +8,9 @@ NCrontab.CrontabField.Contains(int value) -> bool
 NCrontab.CrontabField.Format(System.IO.TextWriter! writer) -> void
 NCrontab.CrontabField.Format(System.IO.TextWriter! writer, bool noNames) -> void
 NCrontab.CrontabField.GetFirst() -> int
+NCrontab.CrontabField.GetLast() -> int
 NCrontab.CrontabField.Next(int start) -> int
+NCrontab.CrontabField.Prev(int start) -> int
 NCrontab.CrontabField.ToString(string? format) -> string!
 NCrontab.CrontabFieldKind
 NCrontab.CrontabFieldKind.Day = 3 -> NCrontab.CrontabFieldKind
@@ -21,6 +23,9 @@ NCrontab.CrontabSchedule
 NCrontab.CrontabSchedule.GetNextOccurrence(System.DateTime baseTime) -> System.DateTime
 NCrontab.CrontabSchedule.GetNextOccurrence(System.DateTime baseTime, System.DateTime endTime) -> System.DateTime
 NCrontab.CrontabSchedule.GetNextOccurrences(System.DateTime baseTime, System.DateTime endTime) -> System.Collections.Generic.IEnumerable<System.DateTime>!
+NCrontab.CrontabSchedule.GetPrevOccurrence(System.DateTime baseTime) -> System.DateTime
+NCrontab.CrontabSchedule.GetPrevOccurrence(System.DateTime baseTime, System.DateTime startTime) -> System.DateTime
+NCrontab.CrontabSchedule.GetPrevOccurrences(System.DateTime baseTime, System.DateTime startTime) -> System.Collections.Generic.IEnumerable<System.DateTime>!
 NCrontab.CrontabSchedule.ParseOptions
 NCrontab.CrontabSchedule.ParseOptions.IncludingSeconds.get -> bool
 NCrontab.CrontabSchedule.ParseOptions.IncludingSeconds.set -> void
@@ -29,7 +34,9 @@ NCrontab.ExceptionProvider
 NCrontab.ICrontabField
 NCrontab.ICrontabField.Contains(int value) -> bool
 NCrontab.ICrontabField.GetFirst() -> int
+NCrontab.ICrontabField.GetLast() -> int
 NCrontab.ICrontabField.Next(int start) -> int
+NCrontab.ICrontabField.Prev(int start) -> int
 override NCrontab.CrontabField.ToString() -> string!
 override NCrontab.CrontabSchedule.ToString() -> string!
 static NCrontab.CrontabField.Days(string! expression) -> NCrontab.CrontabField!

NCrontab/PublicAPI/netstandard2.0/PublicAPI.Shipped.txt

@@ -8,7 +8,9 @@ NCrontab.CrontabField.Contains(int value) -> bool
 NCrontab.CrontabField.Format(System.IO.TextWriter! writer) -> void
 NCrontab.CrontabField.Format(System.IO.TextWriter! writer, bool noNames) -> void
 NCrontab.CrontabField.GetFirst() -> int
+NCrontab.CrontabField.GetLast() -> int
 NCrontab.CrontabField.Next(int start) -> int
+NCrontab.CrontabField.Prev(int start) -> int
 NCrontab.CrontabField.ToString(string? format) -> string!
 NCrontab.CrontabFieldKind
 NCrontab.CrontabFieldKind.Day = 3 -> NCrontab.CrontabFieldKind
@@ -21,6 +23,9 @@ NCrontab.CrontabSchedule
 NCrontab.CrontabSchedule.GetNextOccurrence(System.DateTime baseTime) -> System.DateTime
 NCrontab.CrontabSchedule.GetNextOccurrence(System.DateTime baseTime, System.DateTime endTime) -> System.DateTime
 NCrontab.CrontabSchedule.GetNextOccurrences(System.DateTime baseTime, System.DateTime endTime) -> System.Collections.Generic.IEnumerable<System.DateTime>!
+NCrontab.CrontabSchedule.GetPrevOccurrence(System.DateTime baseTime) -> System.DateTime
+NCrontab.CrontabSchedule.GetPrevOccurrence(System.DateTime baseTime, System.DateTime startTime) -> System.DateTime
+NCrontab.CrontabSchedule.GetPrevOccurrences(System.DateTime baseTime, System.DateTime startTime) -> System.Collections.Generic.IEnumerable<System.DateTime>!
 NCrontab.CrontabSchedule.ParseOptions
 NCrontab.CrontabSchedule.ParseOptions.IncludingSeconds.get -> bool
 NCrontab.CrontabSchedule.ParseOptions.IncludingSeconds.set -> void
@@ -29,7 +34,9 @@ NCrontab.ExceptionProvider
 NCrontab.ICrontabField
 NCrontab.ICrontabField.Contains(int value) -> bool
 NCrontab.ICrontabField.GetFirst() -> int
+NCrontab.ICrontabField.GetLast() -> int
 NCrontab.ICrontabField.Next(int start) -> int
+NCrontab.ICrontabField.Prev(int start) -> int
 override NCrontab.CrontabField.ToString() -> string!
 override NCrontab.CrontabSchedule.ToString() -> string!
 static NCrontab.CrontabField.Days(string! expression) -> NCrontab.CrontabField!