hrynco-common/HrynCo.Common/Clock.cs

namespace HrynCo.Common;

public sealed class Clock : IClock
{
    private readonly DateTimeOffset _createdAt;
    private readonly DateTimeOffset _initialNow;
    private readonly DateTimeOffset _initialUtcNow;

    public Clock()
        : this(DateTimeOffset.UtcNow)
    {
    }

    public Clock(DateTimeOffset initialUtcNow)
    {
        _initialUtcNow = initialUtcNow;
        _initialNow = initialUtcNow.ToLocalTime();
        _createdAt = DateTimeOffset.UtcNow;
    }

    public DateTimeOffset Now => _initialNow + (DateTimeOffset.UtcNow - _createdAt);
    public DateTimeOffset UtcNow => _initialUtcNow + (DateTimeOffset.UtcNow - _createdAt);
    public DateOnly Today => DateOnly.FromDateTime(Now.DateTime);

    public DateOnly GetNextDayOfWeek(DayOfWeek dayOfWeek)
    {
        int daysToAdd = ((int)dayOfWeek - (int)Today.DayOfWeek + 7) % 7;
        return Today.AddDays(daysToAdd == 0 ? 7 : daysToAdd);
    }

    public DateOnly GetLastDayOfMonth()
    {
        return new DateOnly(Now.Year, Now.Month, 1).AddMonths(1).AddDays(-1);
    }

    public DateOnly GetNextMonthStart()
    {
        return new DateOnly(Now.Year, Now.Month, 1).AddMonths(1);
    }
}