Add gradient fill support to resolve EPPlus color reading limitations

GRADIENT_GUIDE.md

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+# Working with Gradient Fills in ImportExcel
+
+## Overview
+
+ImportExcel now provides enhanced support for working with Excel gradient fills through three new functions that address EPPlus 4.x limitations with gradient color reading.
+
+## The Issue
+
+In EPPlus 4.x (used by ImportExcel), while gradient colors can be set using `SetColor()`, they cannot be read back via properties like `Rgb`, `Top`, `Bottom`, `Left`, `Right`. This prevents copying gradients between cells.
+
+## The Solution
+
+Three new functions provide a complete gradient workflow:
+
+### Set-ExcelGradientFill
+Sets gradient fill properties for Excel ranges.
+
+```powershell
+# Basic linear gradient
+Set-ExcelGradientFill -Range $ws.Cells["A1"] -Type Linear -Degree 90 -Color1 Blue -Color2 Green
+
+# Path gradient
+Set-ExcelGradientFill -Range $ws.Cells["B1"] -Type Path -Color1 Red -Color2 Yellow
+
+# Advanced linear gradient with positioning
+Set-ExcelGradientFill -Range $ws.Cells["C1"] -Type Linear -Degree 45 -Color1 Purple -Color2 Orange -Top 0.1 -Bottom 0.9
+```
+
+### Get-ExcelGradientFill
+Reads gradient properties that can be reliably extracted from EPPlus.
+
+```powershell
+$gradient = Get-ExcelGradientFill -Range $ws.Cells["A1"]
+# Returns: Type, Degree, Top, Bottom, Left, Right
+# Note: Color1 and Color2 are null due to EPPlus limitations
+```
+
+### Copy-ExcelGradientFill
+Copies gradient fills between ranges using two approaches:
+
+#### Approach 1: Copy Geometric Properties Only
+```powershell
+# Copies Type, Degree, and positioning but warns about colors
+Copy-ExcelGradientFill -SourceRange $ws.Cells["A1"] -TargetRange $ws.Cells["B1"]
+```
+
+#### Approach 2: Complete Gradient Definition
+```powershell
+# Create a complete gradient definition
+$gradientDef = @{
+    Type = "Linear"
+    Degree = 45
+    Color1 = [System.Drawing.Color]::Blue
+    Color2 = [System.Drawing.Color]::Green
+    Top = 0.2
+    Bottom = 0.8
+}
+
+Copy-ExcelGradientFill -TargetRange $ws.Cells["C1:E3"] -GradientDefinition $gradientDef
+```
+
+## Complete Example
+
+```powershell
+Import-Module ImportExcel
+
+$xl = Open-ExcelPackage -Path "gradients.xlsx" -Create
+$ws = Add-WorkSheet -ExcelPackage $xl -WorksheetName "Gradients"
+
+# Set original gradient
+Set-ExcelGradientFill -Range $ws.Cells["A1"] -Type Linear -Degree 90 -Color1 Blue -Color2 Green
+
+# Get gradient properties (geometric only)
+$gradientInfo = Get-ExcelGradientFill -Range $ws.Cells["A1"]
+
+# Create complete definition for copying
+$completeDef = @{
+    Type = $gradientInfo.Type
+    Degree = $gradientInfo.Degree
+    Top = $gradientInfo.Top
+    Bottom = $gradientInfo.Bottom
+    Left = $gradientInfo.Left
+    Right = $gradientInfo.Right
+    Color1 = [System.Drawing.Color]::Blue    # Must specify colors
+    Color2 = [System.Drawing.Color]::Green
+}
+
+# Copy to other cells
+Copy-ExcelGradientFill -TargetRange $ws.Cells["B1:D3"] -GradientDefinition $completeDef
+
+Close-ExcelPackage -ExcelPackage $xl -SaveAs "gradients.xlsx"
+```
+
+## Migration from Direct EPPlus Access
+
+### Before (Limited by EPPlus 4.x):
+```powershell
+# Setting worked
+$Sheet.Cells["A1"].Style.Fill.Gradient.Color1.SetColor("BLUE")
+$Sheet.Cells["A1"].Style.Fill.Gradient.Color2.SetColor("GREEN")
+
+# Reading failed - returned empty values
+$rgb = $Sheet.Cells["A1"].Style.Fill.Gradient.Color1.Rgb  # Empty!
+```
+
+### After (Using ImportExcel functions):
+```powershell
+# Setting is easier and more robust
+Set-ExcelGradientFill -Range $Sheet.Cells["A1"] -Type Linear -Degree 90 -Color1 Blue -Color2 Green
+
+# Reading works for geometric properties
+$gradient = Get-ExcelGradientFill -Range $Sheet.Cells["A1"]
+# $gradient.Type, $gradient.Degree work; colors need to be specified separately
+
+# Copying now possible with complete definitions
+$gradientDef = @{
+    Type = $gradient.Type
+    Degree = $gradient.Degree
+    Color1 = [System.Drawing.Color]::Blue
+    Color2 = [System.Drawing.Color]::Green
+}
+Copy-ExcelGradientFill -TargetRange $Sheet.Cells["B1"] -GradientDefinition $gradientDef
+```
+
+## Parameters Reference
+
+### Set-ExcelGradientFill Parameters
+- **Range**: Target Excel range (required)
+- **Type**: "Linear" or "Path" (required)
+- **Degree**: Angle for linear gradients (0-360, default 90)
+- **Color1**: First color - Color object or string name (required)
+- **Color2**: Second color - Color object or string name (required)
+- **Top/Bottom/Left/Right**: Position values (0-1, optional)
+
+### Copy-ExcelGradientFill Parameters
+- **SourceRange**: Source range (for copying geometric properties)
+- **TargetRange**: Target range (required)
+- **GradientDefinition**: Hashtable with gradient properties (alternative to SourceRange)
+
+## Limitations
+
+- Color properties cannot be read from existing gradients due to EPPlus 4.x limitations
+- When copying gradients, colors must be specified manually in the gradient definition
+- Functions provide warnings when color limitations affect operations
+
+## Benefits
+
+- Clean, PowerShell-friendly interface for gradient operations
+- Comprehensive parameter validation
+- Clear error messages and warnings
+- Supports both string color names and Color objects
+- Enables gradient copying workflows that weren't possible before

ImportExcel.psd1

@@ -46,6 +46,7 @@ Check out the How To Videos https://www.youtube.com/watch?v=U3Ne_yX4tYo&list=PL5
         'ConvertFrom-ExcelSheet',
         'ConvertFrom-ExcelToSQLInsert',
         'ConvertTo-ExcelXlsx',
+        'Copy-ExcelGradientFill',
         'Copy-ExcelWorksheet',
         'DoChart',
         'Enable-ExcelAutoFilter',
@@ -56,6 +57,7 @@ Check out the How To Videos https://www.youtube.com/watch?v=U3Ne_yX4tYo&list=PL5
         'Get-ExcelColumnName',
         'Get-ExcelFileSchema',
         'Get-ExcelFileSummary', 
+        'Get-ExcelGradientFill',
         'Get-ExcelSheetDimensionAddress',       
         'Get-ExcelSheetInfo',
         'Get-ExcelWorkbookInfo',
@@ -92,6 +94,7 @@ Check out the How To Videos https://www.youtube.com/watch?v=U3Ne_yX4tYo&list=PL5
         'Set-CellComment',
         'Set-CellStyle',
         'Set-ExcelColumn',
+        'Set-ExcelGradientFill',
         'Set-ExcelRange',
         'Set-ExcelRow',
         'Set-WorksheetProtection',

Public/Copy-ExcelGradientFill.ps1

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+function Copy-ExcelGradientFill {
+    <#
+    .SYNOPSIS
+    Copies gradient fill settings from one Excel range to another.
+
+    .DESCRIPTION
+    Due to limitations in EPPlus 4.x, gradient color properties cannot be read directly.
+    This function provides a workaround by storing gradient definitions and applying them
+    to target ranges.
+
+    .PARAMETER SourceRange
+    The source range with the gradient fill to copy.
+
+    .PARAMETER TargetRange
+    The target range where the gradient fill should be applied.
+
+    .PARAMETER GradientDefinition
+    A hashtable containing gradient definition with properties:
+    - Type: Linear or Path
+    - Degree: Angle for linear gradients (0-360)
+    - Top, Bottom, Left, Right: Position values (0-1)
+    - Color1: First color (System.Drawing.Color or color name)
+    - Color2: Second color (System.Drawing.Color or color name)
+
+    .EXAMPLE
+    # Copy gradient from A1 to B1:C2
+    Copy-ExcelGradientFill -SourceRange $ws.Cells["A1"] -TargetRange $ws.Cells["B1:C2"]
+
+    .EXAMPLE
+    # Apply a custom gradient definition
+    $gradient = @{
+        Type = "Linear"
+        Degree = 45
+        Color1 = [System.Drawing.Color]::Blue
+        Color2 = [System.Drawing.Color]::Green
+        Top = 0
+        Bottom = 1
+        Left = 0
+        Right = 1
+    }
+    Copy-ExcelGradientFill -TargetRange $ws.Cells["A1:B2"] -GradientDefinition $gradient
+
+    .NOTES
+    This function works around EPPlus 4.x limitations with gradient color reading.
+    #>
+    [CmdletBinding(DefaultParameterSetName = 'CopyFromSource')]
+    param(
+        [Parameter(ParameterSetName = 'CopyFromSource', Mandatory)]
+        $SourceRange,
+
+        [Parameter(Mandatory)]
+        $TargetRange,
+
+        [Parameter(ParameterSetName = 'ApplyDefinition', Mandatory)]
+        [hashtable]$GradientDefinition
+    )
+
+    if ($PSCmdlet.ParameterSetName -eq 'CopyFromSource') {
+        # Extract gradient properties from source
+        $sourceGradient = $SourceRange.Style.Fill.Gradient
+
+        # Create gradient definition from source
+        $GradientDefinition = @{
+            Type = $sourceGradient.Type
+            Degree = $sourceGradient.Degree
+            Top = $sourceGradient.Top
+            Bottom = $sourceGradient.Bottom
+            Left = $sourceGradient.Left
+            Right = $sourceGradient.Right
+        }
+
+        # Note: Colors cannot be copied due to EPPlus limitation
+        Write-Warning "Gradient colors cannot be copied due to EPPlus 4.x limitations. Only geometric properties (Type, Degree, positioning) are copied. Please use Set-ExcelGradientFill to set colors."
+    }
+
+    # Apply gradient definition to target
+    $targetGradient = $TargetRange.Style.Fill.Gradient
+
+    if ($GradientDefinition.Type) {
+        $targetGradient.Type = [OfficeOpenXml.Style.ExcelFillGradientType]::$($GradientDefinition.Type)
+    }
+
+    if ($GradientDefinition.ContainsKey('Degree')) {
+        $targetGradient.Degree = $GradientDefinition.Degree
+    }
+
+    if ($GradientDefinition.ContainsKey('Top')) {
+        $targetGradient.Top = $GradientDefinition.Top
+    }
+
+    if ($GradientDefinition.ContainsKey('Bottom')) {
+        $targetGradient.Bottom = $GradientDefinition.Bottom
+    }
+
+    if ($GradientDefinition.ContainsKey('Left')) {
+        $targetGradient.Left = $GradientDefinition.Left
+    }
+
+    if ($GradientDefinition.ContainsKey('Right')) {
+        $targetGradient.Right = $GradientDefinition.Right
+    }
+
+    # Set colors if provided
+    if ($GradientDefinition.Color1) {
+        $color1 = $GradientDefinition.Color1
+        if ($color1 -is [string]) {
+            $color1 = [System.Drawing.Color]::$color1
+        }
+        $targetGradient.Color1.SetColor($color1)
+    }
+
+    if ($GradientDefinition.Color2) {
+        $color2 = $GradientDefinition.Color2
+        if ($color2 -is [string]) {
+            $color2 = [System.Drawing.Color]::$color2
+        }
+        $targetGradient.Color2.SetColor($color2)
+    }
+}

Public/Get-ExcelGradientFill.ps1

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+function Get-ExcelGradientFill {
+    <#
+    .SYNOPSIS
+    Gets gradient fill properties from an Excel range.
+
+    .DESCRIPTION
+    This function extracts gradient fill properties that can be reliably read from EPPlus 4.x.
+    Due to EPPlus limitations, gradient colors cannot be read directly and will return $null.
+
+    .PARAMETER Range
+    The Excel range to read gradient properties from.
+
+    .EXAMPLE
+    # Get gradient properties from a cell
+    $gradientInfo = Get-ExcelGradientFill -Range $ws.Cells["A1"]
+
+    .EXAMPLE
+    # Get gradient properties and use them to copy to another range
+    $gradient = Get-ExcelGradientFill -Range $ws.Cells["A1"]
+    # Add colors since they can't be read
+    $gradient.Color1 = [System.Drawing.Color]::Blue
+    $gradient.Color2 = [System.Drawing.Color]::Green
+    Copy-ExcelGradientFill -TargetRange $ws.Cells["B1:C2"] -GradientDefinition $gradient
+
+    .NOTES
+    Due to EPPlus 4.x limitations, Color1 and Color2 properties will always be $null.
+    This function is provided for completeness and to work with Copy-ExcelGradientFill.
+    #>
+    [CmdletBinding()]
+    param(
+        [Parameter(Mandatory, ValueFromPipeline)]
+        $Range
+    )
+
+    process {
+        $gradient = $Range.Style.Fill.Gradient
+
+        $result = [PSCustomObject]@{
+            Type = $gradient.Type
+            Degree = $gradient.Degree
+            Top = $gradient.Top
+            Bottom = $gradient.Bottom
+            Left = $gradient.Left
+            Right = $gradient.Right
+            Color1 = $null  # Cannot be read due to EPPlus 4.x limitation
+            Color2 = $null  # Cannot be read due to EPPlus 4.x limitation
+            ColorLimitationNote = "Color properties cannot be read due to EPPlus 4.x limitations"
+        }
+
+        return $result
+    }
+}