PowerShell/src/Microsoft.PowerShell.Commands.Utility/commands/utility/GetUnique.cs at master · powercode/PowerShell · GitHub

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// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

using System;
using System.Globalization;
using System.Management.Automation;
using System.Management.Automation.Internal;

namespace Microsoft.PowerShell.Commands
{
    /// <summary>
    /// </summary>
    [Cmdlet(VerbsCommon.Get, "Unique", DefaultParameterSetName = "AsString",
        HelpUri = "https://go.microsoft.com/fwlink/?LinkID=2097028", RemotingCapability = RemotingCapability.None)]
    public sealed class GetUniqueCommand : PSCmdlet
    {
        #region Parameters
        /// <summary>
        /// </summary>
        /// <value></value>
        [Parameter(ValueFromPipeline = true)]
        public PSObject InputObject { get; set; } = AutomationNull.Value;

        /// <summary>
        /// This parameter specifies that objects should be converted to
        /// strings and the strings should be compared.
        /// </summary>
        /// <value></value>
        [Parameter(ParameterSetName = "AsString")]
        public SwitchParameter AsString
        {
            get { return _asString; }

            set { _asString = value; }
        }

        private bool _asString;

        /// <summary>
        /// This parameter specifies that just the types of the objects
        /// should be compared.
        /// </summary>
        /// <value></value>
        [Parameter(ParameterSetName = "UniqueByType")]
        public SwitchParameter OnType
        {
            get { return _onType; }

            set { _onType = value; }
        }

        private bool _onType = false;

        /// <summary>
        /// Gets or sets case insensitive switch for string comparison.
        /// </summary>
        [Parameter]
        public SwitchParameter CaseInsensitive { get; set; }

        #endregion Parameters

        #region Overrides
        /// <summary>
        /// </summary>
        protected override void ProcessRecord()
        {
            bool isUnique = true;
            if (_lastObject == null)
            {
                // always write first object, but return nothing
                // on "MSH> get-unique"
                if (AutomationNull.Value == InputObject)
                    return;
            }
            else if (OnType)
            {
                isUnique = (InputObject.InternalTypeNames[0] != _lastObject.InternalTypeNames[0]);
            }
            else if (AsString)
            {
                string inputString = InputObject.ToString();
                _lastObjectAsString ??= _lastObject.ToString();

                if (string.Equals(
                    inputString,
                    _lastObjectAsString,
                    CaseInsensitive.IsPresent ? StringComparison.CurrentCultureIgnoreCase : StringComparison.CurrentCulture))
                {
                    isUnique = false;
                }
                else
                {
                    _lastObjectAsString = inputString;
                }
            }
            else // compare as objects
            {
                _comparer ??= new ObjectCommandComparer(
                    ascending: true,
                    CultureInfo.CurrentCulture,
                    caseSensitive: !CaseInsensitive.IsPresent);

                isUnique = (_comparer.Compare(InputObject, _lastObject) != 0);
            }

            if (isUnique)
            {
                WriteObject(InputObject);
                _lastObject = InputObject;
            }
        }
        #endregion Overrides

        #region Internal
        private PSObject _lastObject = null;
        private string _lastObjectAsString = null;
        private ObjectCommandComparer _comparer = null;
        #endregion Internal
    }
}