$SiteUrl     = "https://zefiromethane.sharepoint.com/sites/contentTypeHub"
$Destination = "F:\TeamSite"

# Opens a Microsoft sign-in window.
Connect-MgGraph -Scopes "Sites.Read.All" -NoWelcome

function Get-GraphCollection {
    param([string]$Uri)

    do {
        $response = Invoke-MgGraphRequest -Method GET -Uri $Uri

        foreach ($item in @($response.value)) {
            Write-Output $item
        }

        $Uri = $response.'@odata.nextLink'
    }
    while ($Uri)
}

function Copy-GraphFolder {
    param(
        [string]$DriveId,
        [string]$ChildrenUri,
        [string]$LocalFolder
    )

    New-Item -ItemType Directory -Path $LocalFolder -Force |
        Out-Null

    foreach ($item in Get-GraphCollection -Uri $ChildrenUri) {
        $localPath = Join-Path $LocalFolder $item.name
        $escapedDriveId = [Uri]::EscapeDataString($DriveId)
        $escapedItemId  = [Uri]::EscapeDataString([string]$item.id)

        if ($null -ne $item.folder -or $null -ne $item.package) {
            # Create the folder, including empty folders.
            New-Item -ItemType Directory -Path $localPath -Force |
                Out-Null

            $childUri = `
                "https://graph.microsoft.com/v1.0/drives/" +
                "$escapedDriveId/items/$escapedItemId/children"

            Copy-GraphFolder `
                -DriveId $DriveId `
                -ChildrenUri $childUri `
                -LocalFolder $localPath
        }
        elseif ($null -ne $item.file) {
            if (Test-Path -LiteralPath $localPath) {
                Write-Host "Skipping existing file: $localPath"
                continue
            }

            Write-Host "Downloading: $localPath"

            $contentUri = `
                "https://graph.microsoft.com/v1.0/drives/" +
                "$escapedDriveId/items/$escapedItemId/content"

            Invoke-MgGraphRequest `
                -Method GET `
                -Uri $contentUri `
                -OutputFilePath $localPath
        }
        else {
            Write-Warning "Unsupported item skipped: $($item.name)"
        }
    }
}

# Resolve the SharePoint site from its URL.
$parsedSiteUrl = [Uri]$SiteUrl
$sitePath = $parsedSiteUrl.AbsolutePath.TrimEnd("/")

if ([string]::IsNullOrWhiteSpace($sitePath)) {
    $siteLookupUri = `
        "https://graph.microsoft.com/v1.0/sites/$($parsedSiteUrl.Host)"
}
else {
    $siteLookupUri = `
        "https://graph.microsoft.com/v1.0/sites/" +
        "$($parsedSiteUrl.Host):$sitePath"
}

$site = Invoke-MgGraphRequest -Method GET -Uri $siteLookupUri

New-Item -ItemType Directory -Path $Destination -Force |
    Out-Null

# A Graph "drive" represents a SharePoint document library.
$drivesUri = "https://graph.microsoft.com/v1.0/sites/$($site.id)/drives"

foreach ($drive in Get-GraphCollection -Uri $drivesUri) {
    $localLibrary = Join-Path $Destination $drive.name
    $escapedDriveId = [Uri]::EscapeDataString([string]$drive.id)

    Write-Host "Downloading library: $($drive.name)"

    $rootChildrenUri = `
        "https://graph.microsoft.com/v1.0/drives/" +
        "$escapedDriveId/root/children"

    Copy-GraphFolder `
        -DriveId $drive.id `
        -ChildrenUri $rootChildrenUri `
        -LocalFolder $localLibrary
}

Disconnect-MgGraph