Migrate SharePoint Site Designs and Scripts to a new Tenant

Clear-Host
# Settings - UPDATE THESE TO YOUR SITE AND TENANT
# Connect to your SharePoint tenant
$siteUrl = "https://pieterveenstraMVP-admin.sharepoint.com"
#Tenant ID
$tenant = "pieterveenstraMVP.onmicrosoft.com"
# Export each site design
$exportPath = "C:\projects\SiteDesignMigration\Exports"
# End of Settings

# Install PnP.PowerShell if not already installed. Script has been tested with version 3.1.0,
# so we will check for that specific version and install or upgrade as needed.
If( (Get-Module PnP.PowerShell).Version -eq "3.1.0") 
{
    Write-Host "PnP.PowerShell version 3.1.0 is already installed." -ForegroundColor Green
}
else { 
    if (!(Get-Module PnP.PowerShell))
    {
            Write-Host "Installing PnP.PowerShell..." -ForegroundColor Yellow
            Install-Module PnP.PowerShell -Scope CurrentUser -Force   
    } elsif  (Get-Module PnP.PowerShell).Version -ne "3.1.0" 
    {    
            Upgrade-Module PnP.PowerShell -Scope CurrentUser -Force   
    }
}

Write-Host "Registering PnP.PowerShell app for interactive login..." -ForegroundColor Yellow
# Register the PnP.PowerShell app for interactive login and connect to the tenant
$AppRegistration = Register-PnPEntraIDAppForInteractiveLogin -ApplicationName "PnP.PowerShell" -Tenant $tenant -GraphDelegatePermissions "Sites.Read.All","User.Read" -SharePointDelegatePermissions "AllSites.FullControl" -ErrorAction SilentlyContinue  | Out-Null
# Get the Client ID from the app registration
$ClientID = $AppRegistration.'AzureAppId/ClientId'
# Connect to the SharePoint tenant using the registered app
Connect-PnPOnline -Url $siteUrl -ClientId  $ClientID

# Get all site designs
$ExistingSiteDesigns = Get-PnPSiteDesign

# Check if export directory exists, if not create it
if (-not (Test-Path $exportPath)) {
  Write-Host "Export Directory not found" -ForegroundColor Red
  Exit
}

# Export Site Designs and Site Scripts
foreach ($design in $siteDesigns) {
    try {
        # Get the full site design information, including the associated site script IDs, and export it to a JSON file
        $designJson = Get-PnPSiteDesign -Identity $design.Id
        $fileName = "$($design.Title -replace '[\\/:*?"<>|]', '_')_SiteDesign.json"
        $filePath = Join-Path $exportPath $fileName
        # The Get-PnPSiteDesign cmdlet returns a complex object that includes properties that are not serializable to JSON, such as the Id property which is a GUID object. To export the site design to JSON, we need to create a custom object that only includes the properties we want to export and convert the GUID to a string.
        $designJson | ConvertTo-Json | Out-File -FilePath $filePath -Encoding UTF8
        Write-Host "Exported: $($design.Title)" -ForegroundColor Green
        # After exporting the site design, we will export each associated site script to a separate JSON file. We will use the site design ID in the file name to link the site scripts to the site design.
        $DesignId = $design.Id.Guid
        # For each site script ID associated with the site design, we will get the site script information and export it to a JSON file. We will use the same naming convention as the site design file, but with "_SiteScript" in the name to differentiate it from the site design file.
        foreach ($siteScriptId in $design.SiteScriptIds) {
            try {
                $siteScriptJson = Get-PnPSiteScript -Identity $siteScriptId
                
                $scriptFileName = "$($design.Title -replace '[\\/:*?"<>|]', '_')_SiteScript_$DesignId.json"
                $scriptFilePath = Join-Path $exportPath $scriptFileName
                
                $siteScriptJson| ConvertTo-Json | Out-File -FilePath $scriptFilePath -Encoding UTF8
                Write-Host "Exported Site Script: $($siteScriptId) for design: $($design.Title)" -ForegroundColor Green
            }
            catch {
                Write-Host "Error exporting site script $siteScriptId for design $($design.Title): $_" -ForegroundColor Red
            }
        }
    }
    catch {
        Write-Host "Error exporting $($design.Title): $_" -ForegroundColor Red
    }
}

# Import Site Designs and Site Scripts
Get-Childitem $exportPath -Filter *_SiteDesign.json | ForEach-Object {
    # For each site design JSON file, read the content and convert it from JSON to a PowerShell object
    $filePath = $_.FullName
    $fileContent = Get-Content -Path $filePath -Raw
    $siteDesignData = $fileContent | ConvertFrom-Json
    $DesignId = $siteDesignData.Id
    # Check if the site design already exists
    $existingDesign = $ExistingSiteDesigns | Where-Object { $_.Title -eq $siteDesignData.Title }
    # If the site design already exists, skip the import. Otherwise, import the site design and its associated site scripts.
    if ($existingDesign) {
        Write-Host "Site Design '$($siteDesignData.Title)' already exists. Skipping import." -ForegroundColor Yellow
    } else {
        # Import the site design
        try {
            # The Add-PnPSiteDesign cmdlet does not support specifying the ID, so we will create the site design without the ID and then update it with the correct site script IDs after importing the site scripts.
            $NewDesignData = Add-PnPSiteDesign -Title $siteDesignData.Title -Description $siteDesignData.Description -SiteScriptIds $siteDesignData.SiteScriptIds -WebTemplate $siteDesignData.WebTemplate -PreviewImageUrl $siteDesignData.PreviewImageUrl
            Write-Host "Imported Site Design: '$($siteDesignData.Title)'" -ForegroundColor Green
            
            # After importing the site design, we need to import the associated site scripts and update the site design with the correct site script IDs.
            Get-Childitem $exportPath -Filter *_SiteScript_$DesignId.json | ForEach-Object {
                $scriptFilePath = $_.FullName
                $scriptFileContent = Get-Content -Path $scriptFilePath -Raw
                $siteScriptData = $scriptFileContent | ConvertFrom-Json
                
                # Check if the site script already exists
                $existingScript = Get-PnPSiteScript | Where-Object { $_.Title -eq $siteScriptData.Title }
                if ($existingScript) {
                    # If the site script already exists, we will skip importing it and just update the site design to reference the existing site script ID.
                    Write-Host "Site Script '$($siteScriptData.Title)' already exists. Skipping import." -ForegroundColor Yellow
                    Set-PnPSiteDesign -Identity $NewDesignData.Id -SiteScriptIds $existingScript.Id
                } else {
                    # If the site script does not exist, we will import it and then update the site design to reference the new site script ID.
                    $NewScriptData = Add-PnPSiteScript -Title $siteScriptData.Title -Description $siteScriptData.Description -Content $siteScriptData.Content
                    Write-Host "Imported Site Script: '$($siteScriptData.Title)'" -ForegroundColor Green
                    Set-PnPSiteDesign -Identity $NewDesignData.Id -SiteScriptIds $NewScriptData.Id
                }            
            }
            
        } catch {
            Write-Host "Error importing Site Design '$($siteDesignData.Title)': $_" -ForegroundColor Red
        }
    }
}

Get-PnPSiteDesign
Get-PnPSiteScript