Format A TimeSpan With Years

Question

I have a class with 2 date properties: FirstDay and LastDay. LastDay is nullable. I would like to generate a string in the format of "x year(s) y day(s)". If the total years are less than 1, I would like to omit the year section. If the total days are less than 1, I would like to omit the day section. If either years or days are 0, they should say "day/year", rather than "days/years" respectively.

Examples:
2.2 years:             "2 years 73 days"
1.002738 years:   "1 year 1 day"
0.2 years:             "73 days"
2 years:                "2 years"

What I have works, but it is long:

private const decimal DaysInAYear = 365.242M;

public string LengthInYearsAndDays
{
    get
    {
        var lastDay = this.LastDay ?? DateTime.Today;
        var lengthValue = lastDay - this.FirstDay;

        var builder = new StringBuilder();

        var totalDays = (decimal)lengthValue.TotalDays;
        var totalYears = totalDays / DaysInAYear;
        var years = (int)Math.Floor(totalYears);

        totalDays -= (years * DaysInAYear);
        var days = (int)Math.Floor(totalDays);

        Func<int, string> sIfPlural = value =>
            value > 1 ? "s" : string.Empty;

        if (years > 0)
        {
            builder.AppendFormat(
                CultureInfo.InvariantCulture,
                "{0} year{1}",
                years,
                sIfPlural(years));

            if (days > 0)
            {
                builder.Append(" ");
            }
        }

        if (days > 0)
        {
            builder.AppendFormat(
                CultureInfo.InvariantCulture,
                "{0} day{1}",
                days,
                sIfPlural(days));
        }

        var length = builder.ToString();
        return length;
    }
}

Is there a more concise way of doing this (but still readable)?

Answer 1

A TimeSpan doesn't have a sensible concept of "years" because it depends on the start and end point. (Months is similar - how many months are there in 29 days? Well, it depends...)

To give a shameless plug, my Noda Time project makes this really simple though:

using System;
using NodaTime;

public class Test
{
    static void Main(string[] args)
    {
        LocalDate start = new LocalDate(2010, 6, 19);
        LocalDate end = new LocalDate(2013, 4, 11);
        Period period = Period.Between(start, end,
                                       PeriodUnits.Years | PeriodUnits.Days);

        Console.WriteLine("Between {0} and {1} are {2} years and {3} days",
                          start, end, period.Years, period.Days);
    }
}

Output:

Between 19 June 2010 and 11 April 2013 are 2 years and 296 days