Compare DateTime against current system time?

Question

I'm trying to make a C# method to fulfill this user story.

These are the 2 acceptance criteria

• Start time must be at least one hour later than the current system time.
• End time must be at last one hour after start time.

Both of the start and end time must be DateTime values, so I can parse it with the TryParse method.

Here's what I have in my code so far:

`

private DateTime datetime;
public DateTime datetimeStart { get; set; }
public DateTime datetimeEnd { get; set; }

while (true) {
    Util.GetInput("Delivery window start (dd/mm/yyyy hh:mm)");
    string userInput = ReadLine();
    
    if(DateTime.TryParse(userInput, out datetime))
    {
        if (datetime.TimeOfDay.Hours - DateTime.Now.TimeOfDay.Hours >= 1) {
            datetimeStart = datetime;
        }
        break;
    }
    else
    {
        WriteLine("\tDelivery window start must be at least one hour in the future.");
    }
}

while (true) {
    Util.GetInput("Delivery window end (dd/mm/yyyy hh:mm)");
    string userInput = ReadLine();
    
    if(DateTime.TryParse(userInput, out datetime))
    {
        if (datetime.TimeOfDay.Hours - datetimeStart.TimeOfDay.Hours >= 1) {
            datetimeEnd = datetime;
        }
        break;
    }
    else
    {
        WriteLine("\tDelivery window end must be at least one hour later than the start.");
    }
}

`

I'm not fully sure how the DateTime type works yet, but later on, I'd need to get an output string with this format: "The pickup window for your order will be 04:00 on 30/10/2022 and 20:00 on 30/10/2022", and just replace the data in the string with values from datetimeStart and datetimeEnd

Answer 1

DateTime provides all the tools to write your conditions in straightforward code:

one hour later than / after checkTime

is just

checkTime.AddHours(1)

and

someTime must be at least one hour later than / after checkTime

becomes

someTime >= checkTime.AddHours(1)

So your code may look something like this:

...........................
    if (datetime >= DateTime.Now.AddHours(1)) {
        datetimeStart = datetime;
    }
...........................
    if (datetime >= datetimeStart.AddHours(1)) {
        datetimeEnd = datetime;
    }
...........................

Answer 2

A general rule of thumb is that any internal time keeping should be done in UTC, but when presenting in a UI (form or console) that you may show in local time.

Another rule is that when comparing DateTime objects that they should have the same Kind.

Perhaps add something like:

DateTime earliestStartTime = DateTime.UtcNow.AddHours(1);

Later if you have a variable named startTime you want to make sure that it is greater than or equal to earliestStartTime. Once you have startTime set, you can then have:

DateTime earliestEndTime = startTime.AddHours(1);

and likewise compare endTime to earliestStartTime for validity.

When presenting times to the user, you can use the .ToLocalTime() method.