overlap.ps1

$sample = @(
    [PSCustomObject]@{
        From = [datetime]::Parse("01.01.2022 00:00:00")
        To   = [datetime]::Parse("10.01.2022 23:59:59")
    }
    [PSCustomObject]@{
        From = [datetime]::Parse("05.01.2022 00:00:00")
        To   = [datetime]::Parse("15.01.2022 23:59:59")
    }
    [PSCustomObject]@{
        From = [datetime]::Parse("08.01.2022 00:00:00")
        To   = [datetime]::Parse("09.01.2022 23:59:59")
    }
    [PSCustomObject]@{
        From = [datetime]::Parse("20.01.2022 00:00:00")
        To   = [datetime]::Parse("25.01.2022 23:59:59")
    }    
    [PSCustomObject]@{
        From = [datetime]::Parse("24.01.2022 00:00:00")
        To   = [datetime]::Parse("31.01.2022 23:59:59")
    }        
)

$main = {

    Clear-Host

    getOverlapsFrom($sample)

}

function getOverlapsFrom($List) {

    process {
        
        $sorted = $List | Sort-Object -Property From
    
        $head = $sorted | Select-Object -First 1
        $tail = $sorted | Select-Object -Skip 1
    
        $tail | getOverlapsStartingWith $head
    }    
}

function getOverlapsStartingWith($init) {
    begin {
        $last   = $init
        $result = @()
    }

    process {

        if(-not ($_ | isOverlapping $last)) {
            $last = $_
            return
        }

        $result += [PSCustomObject]@{
            From = if($last.From -lt $_.From ) { $_.From } else { $last.From }
            To   = if($_.To      -lt $last.To) { $_.To   } else { $last.To }
        }

        if($_.To -lt $last.To) {
            $last =  $_ 
        } 
    }

    end {
        $result
    }
}

function isOverlapping($that) {
    process {
        return $that.From -lt $_.To -and $_.From -le $that.To
    }
}

&$main