invoke-DbaDbRestoreSeeding.ps1

function Invoke-DbaDBRestoreSeeding
{
<#
.SYNOPSIS
Syncs 2 databases ready for database mirroring or Availability Group setup

.DESCRIPTION
Scans the database backup history on the Source SQL Instance, and restores them onto the source Instance
If more transanction backups occur before the restores complete, these will then be applied afterwards.
The function may also be used to resume an already partially restored databas as long as it's based on the same full database backup chain

Returns $true on success, and $false otherwise

.PARAMETER SourceSqlInstance
The source SQL instance for the database to be seeded from

.PARAMETER SourceSqlCredential
A PSCredential object to authenticate to the Source SQL instance. If not provided Trusted auth will be used

.PARAMETER DestinationSqlInstance
The destination SQL instance for the database to be seeded to

.PARAMETER DestinationSqlCredential
A PSCredential object to authenticate to the Destsination SQL instance. If not provided Trusted auth will be used

.PARAMETER Database
The name of the database to be seeded

.PARAMETER Replace
A switch to indicate that if the database already exists on the Destination instance it should be overwritten

.PARAMETER Resume
A switch to indicated that the seeding should carry on from an earlier attempt if possible
#>
	[CmdletBinding()]
	Param (
		[parameter(Mandatory = $true)]
		[object]$SourceSqlInstance,
		[parameter(Mandatory = $true)]
		[object]$DestinationSqlInstance,
		[System.Management.Automation.PSCredential]$SourceSqlCredential,
		[System.Management.Automation.PSCredential]$DestinationSqlCredential,
        [String]$Database,
		[Switch]$Replace,
		[Switch]$Resume

	)

        $FunctionName = "Invoke-DbaDBRestoreSeeding"
        Write-Verbose "$FunctionName - Starting"

		Try
		{
			$SourceServer = Connect-SqlServer -SqlServer $SourceSqlInstance -SqlCredential	$SourceSqlCredential
		}
		Catch
		{
			Write-Error "$FunctionName - Can't connect to Source Instance"
			return $false
		}

		Try
		{
			$DestServer = Connect-SqlServer -SqlServer $DestinationSqlInstance -SqlCredential $DestinationSqlCredential
		}
		Catch
		{
			Write-Error "$FunctionName - Can't connect to Destination Instance"
			return $false
		}


		if (($DestServer.databases[$Database].length -ne 0) -and ($Replace -eq $false -or $resume -eq $false ))
		{
			Write-Error "$FunctionName - Database exists, and we've not been told to replace it."
			return $false
			break
		}

        $LastFullBackup = (Get-DbaBackupHistory -SqlServer $SourceSqlInstance -Databases $Database -LastFull -credential $SourceSqlCredential).start 

        $BackupHistory = get-dbabackuphistory -SqlServer $SourceSqlInstance -databases $Database -since $LastFullBackup -credential $SourceSqlCredential
        
        $RestoreFiles = $BackupHistory | select @{Name="Fullname";Expression={$_.path}} | Get-FilteredRestoreFile -SqlServer $SourceSqlInstance -Credential $SourceSqlCredential
		
		if ($resume -eq $True -and $DestServer.DataBases[$Database].length -ne 0 -and $DestServer.DataBases[$Database].length -eq 'Restoring')
		{
			#Get dest LSN and filter restore files appropriately.
			$DestinationLastLSN = $DestinationSqlInstance.Databases[$Database].EnumBackupSets() | sort-object -Descending -Property LastLSN | select-object -property LastLSN -First 1
			$RestoreFiles = $RestoreFiles | Where-Object {$_.LastLSN -gt $DestinationLastLSN}
		}
		elseif ($resume -eq $true -and ($DestServer.DataBases[$Database].length -eq 0 -or $DestServer.DataBases[$Database].length -ne 'Restoring')) 
		{
			Write-Error "$FunctionName - Cannot resume if Database does not exist or is not in restoring mode"
			return $false
		}
		
		try 
		{
        	$RestoreFiles | Restore-DbFromFilteredArray -SqlServer $DestinationSqlInstance -SqlCredential $DestinationSqlCredential -Databases $Database -NoRecovery -Replace:$Replace
		}
		catch
		{
			Write-Error "$FunctionName - Failure in restore proccess"
			return $false
		}
		$SourceLastLSN = $SourceSqlInstance.Databases[$Database].EnumBackupSets() | sort-object -Descending -Property LastLSN | select-object -property LastLSN -First 1
		$DestinationLastLSN = $DestinationSqlInstance.Databases[$Database].EnumBackupSets() | sort-object -Descending -Property LastLSN | select-object -property LastLSN -First 1
		if ($SourceLastLSN -gt $DestinationLastLSN)
		{
			$recurse = Invoke-DbaDBRestoreSeeding -Source $SourceSqlInstance -Destination $DestinationSqlInstance -SourceSqlCredential $SourceSqlCredential -DestinationSqlCredential $DestinationSqlCredential -Database $Database -Resume:True
			if ($recurse -eq $true)
			{
				return $true
			}
		} 
		elseif ($SourceLstLSN -lt $DestinationLastLSN) 
		{
			Write-Error "$FunctionName - Ahead of Source database, aborting"
			return $false
		} 
		else
		{
			#We're done, notify, or set up mirroing/AG
			return $true
		}