<#
.SYNOPSIS
    Identifie duplicate files in a comparison folder based on the contents of a source folder.
.DESCRIPTION
    This script calculates the hash values of files in a source folder and compares them against the files in a comparison folder.
    If duplicates are found, it optionally renames the duplicate files in the comparison folder by prepending "Duplicate-" to their filenames.
.PARAMETER SourceFolder
    The path to the source folder containing the original files.
.PARAMETER ComparisonFolder
    The path to the comparison folder where duplicate files will be identified.
.PARAMETER RenameDuplicates
    An optional switch parameter. If specified, the script renames duplicate files in the comparison folder by prepending "Duplicate-" to their filenames.
.EXAMPLE
    .\Find-DuplicateFiles.ps1 -SourceFolder "C:\path\to\source\folder" -ComparisonFolder "C:\path\to\compare\folder"
    This command will identify duplicate files in the "C:\path\to\backup" folder based on the files in the "C:\path\to\main" folder.
.EXAMPLE
    .\Find-DuplicateFiles.ps1 -SourceFolder "C:\path\to\source\folder" -ComparisonFolder "C:\path\to\compare\folder" -RenameDuplicates
    This command will identify and rename duplicate files in the "C:\path\to\compare\folder" folder by prepending "Duplicate-" to their filenames based on the files in the "C:\path\to\main" folder.
.NOTES
    Date: 2024-05-26
#>
param (
    [Parameter(Mandatory = $true)]
    [string]$SourceFolder,  # Main folder

    [Parameter(Mandatory = $true)]
    [string]$ComparisonFolder,  # Backup folder

    [Parameter(Mandatory = $false)]
    [switch]$RenameDuplicates  # Optional switch to rename duplicates
)

# Function to calculate the hash of a file
function Get-CustomFileHash {
    param (
        [string]$filePath
    )
    $hash = Get-FileHash -Algorithm MD5 -Path $filePath
    return $hash.Hash
}

$sourceFiles = Get-ChildItem -Path $SourceFolder -File
$comparisonFiles = Get-ChildItem -Path $ComparisonFolder -File
$sourceFileHashes = @{}

foreach ($file in $sourceFiles) {
    $hash = Get-CustomFileHash -filePath $file.FullName
    $sourceFileHashes[$hash] = $file.FullName
}

$duplicateFiles = @()
$index = 1
foreach ($file in $comparisonFiles) {
    $hash = Get-CustomFileHash -filePath $file.FullName
    if ($sourceFileHashes.ContainsKey($hash)) {
        $newFileName = $null
        if ($RenameDuplicates) {
            $newFileName = Join-Path -Path $ComparisonFolder -ChildPath ("Duplicate-" + $file.Name)
            Rename-Item -Path $file.FullName -NewName $newFileName
        }

        $duplicateFiles += [PSCustomObject]@{
            Number         = $index
            ComparisonFile = $file.FullName
            SourceFile     = $sourceFileHashes[$hash]
            RenamedTo      = $newFileName
        }
        $index++
    }
}

$duplicateFiles | Format-Table -AutoSize