From 618d9f31a0c70152226f3546e1d802eefa9d372b Mon Sep 17 00:00:00 2001
From: Staffan Gustafsson <staffangu@outlook.com>
Date: Thu, 9 Aug 2018 20:59:54 +0200
Subject: [PATCH] Add '-SkipIndex' parameter to 'Select-Object' (#7483)

---
 .../commands/utility/select-object.cs         | 125 ++++++++++++++----
 .../Select-Object.Tests.ps1                   |  12 ++
 2 files changed, 110 insertions(+), 27 deletions(-)

diff --git a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/select-object.cs b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/select-object.cs
index 4b31897411..aece2f1466 100644
--- a/src/Microsoft.PowerShell.Commands.Utility/commands/utility/select-object.cs
+++ b/src/Microsoft.PowerShell.Commands.Utility/commands/utility/select-object.cs
@@ -161,7 +161,7 @@ namespace Microsoft.PowerShell.Commands
         public SwitchParameter Wait { get; set; }
 
         /// <summary>
-        /// Used to display the object at specified index.
+        /// Used to display the object at the specified index.
         /// </summary>
         /// <value></value>
         [Parameter(ParameterSetName = "IndexParameter")]
@@ -177,11 +177,36 @@ namespace Microsoft.PowerShell.Commands
             {
                 _index = value;
                 _indexSpecified = true;
+                _isIncludeIndex = true;
                 Array.Sort(_index);
             }
         }
+
+        /// <summary>
+        /// Used to display all objects at the specified indices.
+        /// </summary>
+        /// <value></value>
+        [Parameter(ParameterSetName = "SkipIndexParameter")]
+        [ValidateRangeAttribute(0, int.MaxValue)]
+        [SuppressMessage("Microsoft.Performance", "CA1819:PropertiesShouldNotReturnArrays")]
+        public int[] SkipIndex
+        {
+            get
+            {
+                return _index;
+            }
+            set
+            {
+                _index = value;
+                _indexSpecified = true;
+                _isIncludeIndex = false;
+                Array.Sort(_index);
+            }
+        }
+
         private int[] _index;
         private bool _indexSpecified;
+        private bool _isIncludeIndex;
 
         #endregion
 
@@ -641,15 +666,18 @@ namespace Microsoft.PowerShell.Commands
             _selectObjectQueue = new SelectObjectQueue(_first, _last, Skip, SkipLast, _firstOrLastSpecified);
         }
 
-        private int _indexOfCurrentObject = 0;
-        private int _indexCount = 0;
         /// <summary>
+        /// Handles processing of InputObject.
         /// </summary>
         protected override void ProcessRecord()
         {
             if (InputObject != AutomationNull.Value && InputObject != null)
             {
-                if (!_indexSpecified)
+                if (_indexSpecified)
+                {
+                    ProcessIndexed();
+                }
+                else
                 {
                     _selectObjectQueue.Enqueue(InputObject);
                     PSObject streamingInputObject = _selectObjectQueue.StreamingDequeue();
@@ -657,39 +685,82 @@ namespace Microsoft.PowerShell.Commands
                     {
                         ProcessObjectAndHandleErrors(streamingInputObject);
                     }
+
                     if (_selectObjectQueue.AllRequestedObjectsProcessed && !this.Wait)
                     {
                         this.EndProcessing();
                         throw new StopUpstreamCommandsException(this);
                     }
                 }
-                else
-                {
-                    if (_indexOfCurrentObject < _index.Length)
-                    {
-                        int currentlyRequestedIndex = _index[_indexOfCurrentObject];
-                        if (_indexCount == currentlyRequestedIndex)
-                        {
-                            ProcessObjectAndHandleErrors(InputObject);
-                            while ((_indexOfCurrentObject < _index.Length) && (_index[_indexOfCurrentObject] == currentlyRequestedIndex))
-                            {
-                                _indexOfCurrentObject++;
-                            }
-                        }
-                    }
-
-                    if (!this.Wait && _indexOfCurrentObject >= _index.Length)
-                    {
-                        this.EndProcessing();
-                        throw new StopUpstreamCommandsException(this);
-                    }
-
-                    _indexCount++;
-                }
             }
         }
 
         /// <summary>
+        /// The index of the active index filter.
+        /// </summary>
+        private int _currentFilterIndex;
+
+        /// <summary>
+        /// The index of the object being processed.
+        /// </summary>
+        private int _currentObjectIndex;
+
+        /// <summary>
+        /// Handles processing of InputObject if -Index or -SkipIndex is specified.
+        /// </summary>
+        private void ProcessIndexed()
+        {
+            if (_isIncludeIndex)
+            {
+                if (_currentFilterIndex < _index.Length)
+                {
+                    int nextIndexToOutput = _index[_currentFilterIndex];
+                    if (_currentObjectIndex == nextIndexToOutput)
+                    {
+                        ProcessObjectAndHandleErrors(InputObject);
+                        while ((_currentFilterIndex < _index.Length) && (_index[_currentFilterIndex] == nextIndexToOutput))
+                        {
+                            _currentFilterIndex++;
+                        }
+                    }
+                }
+
+                if (!Wait && _currentFilterIndex >= _index.Length)
+                {
+                    EndProcessing();
+                    throw new StopUpstreamCommandsException(this);
+                }
+
+                _currentObjectIndex++;
+            }
+            else
+            {
+                if (_currentFilterIndex < _index.Length)
+                {
+                    int nextIndexToSkip = _index[_currentFilterIndex];
+                    if (_currentObjectIndex != nextIndexToSkip)
+                    {
+                        ProcessObjectAndHandleErrors(InputObject);
+                    }
+                    else
+                    {
+                        while ((_currentFilterIndex < _index.Length) && (_index[_currentFilterIndex] == nextIndexToSkip))
+                        {
+                            _currentFilterIndex++;
+                        }
+                    }
+                }
+                else
+                {
+                    ProcessObjectAndHandleErrors(InputObject);
+                }
+
+                _currentObjectIndex++;
+            }
+        }
+
+        /// <summary>
+        /// Completes the processing of Input.
         /// </summary>
         protected override void EndProcessing()
         {
diff --git a/test/powershell/Modules/Microsoft.PowerShell.Utility/Select-Object.Tests.ps1 b/test/powershell/Modules/Microsoft.PowerShell.Utility/Select-Object.Tests.ps1
index 8565b3ccae..872b785049 100644
--- a/test/powershell/Modules/Microsoft.PowerShell.Utility/Select-Object.Tests.ps1
+++ b/test/powershell/Modules/Microsoft.PowerShell.Utility/Select-Object.Tests.ps1
@@ -244,6 +244,18 @@ Describe "Select-Object DRT basic functionality" -Tags "CI" {
 		$results[0] | Should -BeExactly "3"
 	}
 
+    It "Select-Object with SkipIndex should work" {
+        $results = "1", "2", "3" | Select-Object -SkipIndex 0, 2
+        $results | Should -HaveCount 1
+        $results[0] | Should -BeExactly "2"
+    }
+
+    It "Select-Object with SkipIndex should work with index out of range" {
+        $results = 0..10 | Select-Object -SkipIndex 5, 6, 7, 8, 11
+        $results | Should -HaveCount 7
+        $results -join ',' | Should -BeExactly "0,1,2,3,4,9,10"
+    }
+
     It "Select-Object should handle dynamic (DLR) properties"{
         $dynObj = [TestDynamic]::new()
         $results = $dynObj, $dynObj | Select-Object -ExpandProperty FooProp