PsDateTools/Find-Weekday.ps1 at master · RFAInc/PsDateTools · GitHub

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<#
.Synopsis
   Determines the previous or next date from the current or imported date.
.DESCRIPTION
   Calulates a date based on a start date, a day of the week, and an offset in weeks.
.INPUTS
   Inputs to this cmdlet (if any)
.OUTPUTS
   Output from this cmdlet (if any)
#>
function Find-Weekday
{
    [CmdletBinding(DefaultParameterSetName='AnyWeekday')]
    [OutputType([datetime])]
    Param
    (
        # The date from which to start the find
        [Parameter(ValueFromPipeline=$true,
                   ValueFromPipelineByPropertyName=$true,
                   ValueFromRemainingArguments=$false,
                   Position=0)]
        [ValidateNotNull()]
        [ValidateNotNullOrEmpty()]
        [datetime]
        [Alias('ReportDate','Last_Start','Next_Start')]
        $Date,

        # Day of week to find, any in the past or future
        [Parameter(Mandatory=$true,
                   Position=1,
                   ParameterSetName='AnyWeekday')]
        [ValidateSet('Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday',
            'Saturday','Sun', 'Mon', 'Tue', 'Tues', 'Wed', 'Weds', 'Thu', 'Thur', 'Thurs', 'Fri', 'Sat')]
        [string]
        $DayOfWeek,

        # Look in the past (neg) direction
        [Parameter(ParameterSetName='AnyWeekday')]
        [switch]
        $Backwards=$false,

        # Find the next weekday in the future
        [Parameter(ParameterSetName='NextWeekday')]
        [switch]
        $Next=$false,

        # Find the last weekday in the past
        [Parameter(ParameterSetName='LastWeekday')]
        [switch]
        $Last=$false,

        # A collection of more dates of which to exclude
        [datetime[]]
        $ExcludeHolidays
    )

    Begin
    {

    }
    Process
    {
        if($PSCmdlet.ParameterSetName -eq 'AnyWeekday'){
            $UpOrDown = if($Backwards){-1}else{1}
            Do{
                $Date = $Date.AddDays($UpOrDown)
            }until(
                ($DayOfWeek -like
                    "$(([regex]::Match((($Date).DayOfWeek),'...')).value)*") -and
                ($ExcludeHolidays -notcontains $Date)
            )
        }elseif($PSCmdlet.ParameterSetName -eq 'NextWeekday'){
            Do{
                $Date = $Date.AddDays(1)
            }until(
                ($ExcludeHolidays -notcontains $Date) -and
                (@('Saturday','Sunday') -notcontains ($Date).DayOfWeek)
            )
        }elseif($PSCmdlet.ParameterSetName -eq 'LastWeekday'){
            Do{
                $Date = $Date.AddDays(-1)
            }until(
                ($ExcludeHolidays -notcontains $Date) -and
                (@('Saturday','Sunday') -notcontains ($Date).DayOfWeek)
            )
        }
    }
    End
    {
        $Date
    }
}