Is Leap year a threat?

DateTime sampleDate = new DateTime(2019, 1, 1);
DateTime nextSampleDate = date.AddYears(1); //the next date will be 2020 Jan 1

DateTime sampleDate = new DateTime(2019, 1, 1);
DateTime nextSampleDate = date.AddYears(1); //the next date will be 2020 Jan 1

DateTime sampleDate = new DateTime(2019, 1, 1);
DateTime nextSampleDate = date.AddYears(1); //the next date will be 2020 Jan 1

DateTime sampleDate = new DateTime(2019, 1, 1);
DateTime nextSampleDate = date.AddYears(1); //the next date will be 2020 Jan 1

We have an algorithm that generates data for present day of next year. This algorithm is executed daily which ensures the availability of data for the forthcoming year.
But here the leap year became an edge case and put a hole in our algorithm.

Unfortunately, 2020 is a leap year and the data generation was skipped for the 29th of February. We didn't realize it until the day came. On February 29th of 2020, there was no data in the database. As we handled the case when there is no data, there were no crashes reported.

One way we could have solved the issue was by using
AddDays(365) instead of AddYears(1). After evaluating the outcomes of this implementation, we observed the generation of anti-pattern dates.

There were fewer concerns about the performance since it is executing once in a day. So we decided to generate for both days if there is a possibility of skipping the leap day.

public async Task GenerateData()
{
    //Get current utc date
    DateTime currentDate = DateTime.UtcNow;
    DateTime nextYearDate = currentDate.AddYears(1);
    
    //Generate data for the current date
    await GenerateData(nextYearDate);

    //check if there is any upcoming leap day
    if (nextYearDate.Day == 28 && nextYearDate.Month == 2
    && DateTime.IsLeapYear(nextYearDate.Year))
    {
        await GenerateData(nextYearDate.AddDays(1));
    }
}

public async Task GenerateData(DateTime date)
{
    /* 
    code for generating data for the given date    
    */

public async Task GenerateData()
{
    //Get current utc date
    DateTime currentDate = DateTime.UtcNow;
    DateTime nextYearDate = currentDate.AddYears(1);
    
    //Generate data for the current date
    await GenerateData(nextYearDate);

    //check if there is any upcoming leap day
    if (nextYearDate.Day == 28 && nextYearDate.Month == 2
    && DateTime.IsLeapYear(nextYearDate.Year))
    {
        await GenerateData(nextYearDate.AddDays(1));
    }
}

public async Task GenerateData(DateTime date)
{
    /* 
    code for generating data for the given date    
    */

public async Task GenerateData()
{
    //Get current utc date
    DateTime currentDate = DateTime.UtcNow;
    DateTime nextYearDate = currentDate.AddYears(1);
    
    //Generate data for the current date
    await GenerateData(nextYearDate);

    //check if there is any upcoming leap day
    if (nextYearDate.Day == 28 && nextYearDate.Month == 2
    && DateTime.IsLeapYear(nextYearDate.Year))
    {
        await GenerateData(nextYearDate.AddDays(1));
    }
}

public async Task GenerateData(DateTime date)
{
    /* 
    code for generating data for the given date    
    */

public async Task GenerateData()
{
    //Get current utc date
    DateTime currentDate = DateTime.UtcNow;
    DateTime nextYearDate = currentDate.AddYears(1);
    
    //Generate data for the current date
    await GenerateData(nextYearDate);

    //check if there is any upcoming leap day
    if (nextYearDate.Day == 28 && nextYearDate.Month == 2
    && DateTime.IsLeapYear(nextYearDate.Year))
    {
        await GenerateData(nextYearDate.AddDays(1));
    }
}

public async Task GenerateData(DateTime date)
{
    /* 
    code for generating data for the given date    
    */

The output of this updated algorithm shows that the data of the leap day gets generated at the right time.

RecurringJob.AddOrUpdate<IGenerationService>("IGenerationService-GenerateData",
gs => gs.GenerateData(), Cron.Daily);     //Generate data for the day

RecurringJob.AddOrUpdate<IGenerationService>("IGenerationService-GenerateData",
gs => gs.GenerateData(), Cron.Daily);     //Generate data for the day

RecurringJob.AddOrUpdate<IGenerationService>("IGenerationService-GenerateData",
gs => gs.GenerateData(), Cron.Daily);     //Generate data for the day

RecurringJob.AddOrUpdate<IGenerationService>("IGenerationService-GenerateData",
gs => gs.GenerateData(), Cron.Daily);     //Generate data for the day

There exists a significant amount of leap year issues reported around the world. Even though the problem we encountered may seem small, the impact it can create was almost huge. We were able to identify the issue at an early stage and was able to release a Hotfix. Mistakes can happen to anyone. We grow when we learn from our mistakes, and sharing it will help others grow along.