function Connect-SharePoint {
    param($SiteUrl)
    try {
        Connect-PnPOnline -Url $SiteUrl -UseWebLogin
        return $true
    }
    catch {
        $script:txtStatus.Text += "Error connecting: $_`n"
        return $false
    }
}

function List-XlsFiles {
    if (-not (Connect-SharePoint -SiteUrl "https://yoursite.sharepoint.com")) {
        return
    }
    
    $tempLibrary = "Documents/Temp"
    $fileList = @()
    
    $items = Get-PnPListItem -List "Documents" -PageSize 2000 | Where {
        ($_.FieldValues.FileRef -like "*.xls") -and (-not $_.FieldValues.FileRef.Contains(".xlsx"))
    }
    
    foreach ($item in $items) {
        $fileList += [PSCustomObject]@{
            OriginalPath = $item.FieldValues.FileRef
            TempPath = "$tempLibrary/$($item.FieldValues.FileLeafRef)"
        }
    }
    
    $fileList | ConvertTo-Json | Set-PnPFileContent -Folder $tempLibrary -FileName "FileList.json"
    $script:txtStatus.Text += "Found $($fileList.Count) XLS files`n"
}

function Convert-Files {
    if (-not (Connect-SharePoint -SiteUrl "https://yoursite.sharepoint.com")) {
        return
    }
    
    $excel = New-Object -ComObject Excel.Application
    $excel.Visible = $false
    
    try {
        Get-PnPFile -Url "/sites/yoursite/Documents/Temp/FileList.json" -Path $env:TEMP -Filename "FileList.json"
        $files = Get-Content "$env:TEMP\FileList.json" | ConvertFrom-Json
        
        foreach ($file in $files) {
            try {
                $workbook = $excel.Workbooks.Open((Convert-PnPFile -Url $file.OriginalPath -Path $env:TEMP -Filename $file.OriginalFileName))
                $newName = [System.IO.Path]::ChangeExtension($file.OriginalFileName, ".xlsx")
                $workbook.SaveAs([System.IO.Path]::Combine($env:TEMP, $newName), 51) # 51 = xlsx
                Add-PnPFile -Folder "Documents" -Path "$env:TEMP\$newName"
                $script:txtStatus.Text += "Converted $($file.OriginalFileName) to XLSX`n"
            }
            finally {
                $workbook.Close()
            }
        }
    }
    finally {
        $excel.Quit()
    }
}

function Move-Files {
    if (-not (Connect-SharePoint -SiteUrl "https://yoursite.sharepoint.com")) {
        return
    }
    
    $files = Get-Content "$env:TEMP\FileList.json" | ConvertFrom-Json
    
    foreach ($file in $files) {
        Move-PnPFile -SourceUrl $file.OriginalPath -TargetUrl $file.TempPath -Force
        $xlsxPath = [System.IO.Path]::ChangeExtension($file.OriginalPath, ".xlsx")
        Move-PnPFile -SourceUrl "$tempLibrary/$xlsxPath" -TargetUrl $xlsxPath -Force
        $script:txtStatus.Text += "Moved $($file.OriginalFileName) and its XLSX version`n"
    }
}