using System;
using System.Collections;
using System.Collections.ObjectModel;
using System.Management.Automation;
using System.Management.Automation.Runspaces;

namespace CustomPowerShellCmdlet
{
    class Program
    {
        static void Main(string[] args)
        {
            string powerShellScript = @"
Write-Output ('PowerShell Version is ' + $PSVersionTable.PSVersion)

$A  = New-Object System.Collections.ArrayList
$A.Add('3') | Out-Null
Write-Output  ('Count is ' + $A.Count)

$B  = New-Object System.Collections.ArrayList
Add-CollectionItem -Collection $B -Item '1'
Add-CollectionItem -Collection $B -Item '2'
foreach ($Item in $B) {
    Write-Output $Item
}
Write-Output  ('Count is ' + $B.Count)
";

            var output = RunPowerShellScript(powerShellScript);

            foreach (PSObject psObject in output)
            {
                Console.WriteLine(psObject.BaseObject.ToString());
            }
        }

        private static Collection<PSObject> RunPowerShellScript(string powerShellScript)
        {
            InitialSessionState initialSessionState = InitialSessionState.CreateDefault();
            initialSessionState.Commands.Add(new SessionStateCmdletEntry("Add-CollectionItem", typeof(AddCollectionItemCmdlet), null));

            using (var runspace = RunspaceFactory.CreateRunspace(initialSessionState))
            {
                runspace.Open();

                using (var ps = PowerShell.Create())
                {
                    ps.Runspace = runspace;

                    ps.AddScript(powerShellScript);


                    return ps.Invoke();
                }
            }
        }

        [Cmdlet(VerbsCommon.Add, "CollectionItem")]
        public class AddCollectionItemCmdlet : Cmdlet
        {
            [Parameter(Mandatory = true)]
            [AllowEmptyCollection]
            public ArrayList Collection { get; set; }

            [Parameter(Mandatory = true)]
            public object Item { get; set; }

            protected override void BeginProcessing()
            {
                Collection.Add(Item);
            }
        }
    }
}