function CheckFor-MicrosoftTeamsVersion
{
    if (!(((Get-Module -Name "MicrosoftTeams") -ne $null) -or ((Get-InstalledModule -Name "MicrosoftTeams" -ErrorAction SilentlyContinue) -ne $null))) {
        Write-Host
        $msg = "INFO: MicrosoftTeams PowerShell module not installed."
        Write-Host $msg     
        $msg = "INFO: Installing MicrosoftTeams PowerShell module."
        Write-Host $msg
        
        try{
            Install-Module -Name MicrosoftTeams -RequiredVersion 1.1.3-preview -AllowPrerelease
        }
        catch{
            $msg = "ERROR: Failed to install MicrosoftTeams module. Script will abort."
            Write-Host -ForegroundColor Red $msg
            Write-Host
            $msg = "ACTION: Run this script 'As administrator' to intall the MicrosoftTeams module."
            Write-Host -ForegroundColor Yellow $msg
            Exit
        }
    }
    else{
        $MicrosoftTeamsVersion = if ((Get-Module -Name "MicrosoftTeams") -ne $null) { (Get-Module -Name "MicrosoftTeams").Version } else { (Get-InstalledModule -Name "MicrosoftTeams").Version }
        if(($MicrosoftTeamsVersion -ne '1.1.3') -and ($MicrosoftTeamsVersion -ne '1.1.3-preview')) {
            Write-Host
            $msg = "INFO: MicrosoftTeams PowerShell module not using the right version. Current version $MicrosoftTeamsVersion"
            Write-Host $msg            
            Write-Host "MicrosoftTeams PowerShell module needs to be updated to run operations related to Private Channels since the current version is incompatible."  
            $confirm = (Read-Host -prompt "Do you want to update MicrosoftTeams PowerShell module?  [Y]es or [N]o")
            if($confirm.ToLower() -eq "y") {
                $msg = "INFO: Updating MicrosoftTeams PowerShell module."
                Write-Host $msg
                try {
                    Uninstall-Module -Name MicrosoftTeams -Force -ErrorAction Stop
                    Install-Module -Name MicrosoftTeams -RequiredVersion 1.1.3-preview -AllowPrerelease
                }
                catch{
                    $msg = "ERROR: Failed to update MicrosoftTeams module."
                    Write-Host -ForegroundColor Red $msg
                    Write-Host
                    $msg = "ACTION: Run this script 'As administrator' to intall the MicrosoftTeams module."
                    Write-Host -ForegroundColor Yellow $msg
                    Exit
                }
            }
        }    
    }
}

function Show-Menu
{
     param (
           [string]$Title = 'Options'
     )
     Write-Host "================ $Title ================"
    
     Write-Host "1: Press '1' to get list of teams with private channels at source tenant."
     Write-Host "2: Press '2' to get owners and members of private channels in selected teams from source tenant."
     Write-Host "3: Press '3' to add owners and members into private channels of the corresponding teams in the destination tenant."
}

function GetTeamsWithPrivatechannel-InSourceTenant
{
    if(!(Test-Path Variable::global:SourceGlobalCred)-or($global:SourceGlobalCred-isnot[pscredential])){
        $global:SourceGlobalCred=Get-Credential -Message 'Please enter the GA credentials for your Source tenant.'
    }
    $SourceCred=$global:SourceGlobalCred
    Connect-MicrosoftTeams -Credential $SourceCred

    $teamsWithPrivateChannels =  @()
    $counter = 0
    $teams = Get-Team
    Write-Output "Teams count" $teams.count
    ForEach ($team in $teams)
    {        
        $teamWithPrivateChannels = Get-TeamChannel -GroupId $team.GroupId -MembershipType Private
        if ($teamWithPrivateChannels)
        {
            Write-Host $team.DisplayName "has private channels"
            $teamsWithPrivateChannels +=   New-Object -TypeName PSObject -Property @{ mailNickName = $team.MailNickName }
        }

        $counter += 1
        if ($counter % 10 -eq 0)
        {
            Write-Host "Scanned" $counter "teams for private channels"
        }
    }

    if ($teamsWithPrivateChannels)
    {
        $teamsWithPrivateChannels | Export-Csv -NoTypeInformation -Path .\ListOfTeamsWithPrivateChannels.csv -Encoding UTF8
        Write-Host "Exported all teams with private channels into ListOfTeamsWithPrivateChannels.csv" 
        Write-Host "`nPlease remove teams' mailNickName from ListOfTeamsWithPrivateChannels.csv for those teams whose private channel membership you do not wish to migrate over to desitnation tenant" -ForegroundColor Yellow
        Write-Host "`nThen run option 2 in the script to retreive all owners and members of private channels for the respective teams in ListOfTeamsWithPrivateChannels.csv" -ForegroundColor Yellow
    }
}

function GetOwnerMember-OfPrivateChannelsSouceTenant 
{
    if(!(Test-Path Variable::global:SourceGlobalCred)-or($global:SourceGlobalCred-isnot[pscredential])){
        $global:SourceGlobalCred=Get-Credential -Message 'Please enter the GA credentials for your source tenant.'
    }
    $SourceCred=$global:SourceGlobalCred
    Connect-MicrosoftTeams -Credential $SourceCred

    $OwnersAndMembersInPrivateChannels = @()
    $mailNickNames = Import-Csv -Path .\ListOfTeamsWithPrivateChannels.csv
    $teamsWithPrivateChannels = $mailNickNames | Get-Team
    ForEach ($teamWithPrivateChannels in $teamsWithPrivateChannels)
    {
        Write-Host "Scanning owners and members of private channels in team " $teamWithPrivateChannels.DisplayName
        $privateChannelsInTeam = Get-TeamChannel -GroupId $teamWithPrivateChannels.GroupId -MembershipType Private
        ForEach ($privateChannelInTeam in $privateChannelsInTeam)
        {
            $ownerMemberOfPrivateChannel = $privateChannelInTeam | 
                                                Get-TeamChannelUser -GroupId $teamWithPrivateChannels.GroupId | 
                                                Select-Object User, Role, @{n='PrivateChannelDisplayName';e={$privateChannelInTeam.DisplayName}}, @{n='TeamMailNickName';e={$teamWithPrivateChannels.MailNickName}}
            $ownersAndMembersInPrivateChannels += $ownerMemberOfPrivateChannel
        }
    }

    if ($ownersAndMembersInPrivateChannels)
    {
        $ownersAndMembersInPrivateChannels | Export-Csv -NoTypeInformation -Path .\OwnersAndMembersOfPrivateChannels.csv -Encoding UTF8
        Write-Host "Exported all owners and members of private channels into OwnersAndMembersOfPrivateChannels.csv"
        Write-Host "`nChange the user's domain, apply user mapping (if any) and apply teams mapping (if any) in OwnersAndMembersOfPrivateChannels.csv before running option 3 in the script." -ForegroundColor Yellow
    }
}

function AddOwnerMember-ToPrivateChannelDestinationTenant
{

    if(!(Test-Path Variable::global:DestinationGlobalCred)-or($global:DestinationGlobalCred-isnot[pscredential])){
        $global:DestinationGlobalCred=Get-Credential -Message 'Please enter the GA credentials for your destination tenant.'
    }
    $DestCred=$global:DestinationGlobalCred
    Connect-MicrosoftTeams -Credential $DestCred

    $mapOfTeamNickNameToGroupId = @{}
    $ownersAndMembersInPrivateChannels = Import-Csv -Path .\OwnersAndMembersOfPrivateChannels.csv
    ForEach ($item in $ownersAndMembersInPrivateChannels)
    {
        try
        {
            if ($mapOfTeamNickNameToGroupId[$item.TeamMailNickName] -eq $null)
            {
                $team =  Get-Team -MailNickName $item.TeamMailNickName
                $mapOfTeamNickNameToGroupId[$item.TeamMailNickName] = $team.GroupId
            }

            Add-TeamChannelUser -GroupId $mapOfTeamNickNameToGroupId[$item.TeamMailNickName] -DisplayName $item.PrivateChannelDisplayName -User $item.User
            if ($item.Role -eq "Owner")
            {
                Add-TeamChannelUser -GroupId $mapOfTeamNickNameToGroupId[$item.TeamMailNickName] -DisplayName $item.PrivateChannelDisplayName -User $item.User -Role Owner
            }
            Write-Host "Added user" $item.User "to private channel" $item.PrivateChannelDisplayName "in team" $item.TeamMailNickName "as" $item.Role
        }
        catch 
        {
            # Convert common exception messages into human understandable form

            if ($_.Exception.Message.contains("Cannot bind argument to parameter 'GroupId' because it is null"))
            {
                $errMessage = "Team is not found in the tenant."
            }
            elseif ($_.Exception.Message.contains("does not exist or one of its queried reference-property objects"))
            {
                $errMessage = "User is not found in the tenant."
            }
            elseif ($_.Exception.Message.contains("Failed to execute backend request"))
            {
                $errMessage = "User is already in the private channel."
            }
            elseif ($_.Exception.Message.contains("User is not found in the team"))
            {
                $errMessage = "User is not found in the team."
            }
            else
            {
                $errMessage = $_.Exception.Message
            }


            Write-Host "Could not add user" $item.User "to private channel" $item.PrivateChannelDisplayName "in team" $item.TeamMailNickName "because" $errMessage -ForegroundColor red
        }
    }
}

$ErrorActionPreference="Stop"
CheckFor-MicrosoftTeamsVersion
Import-Module MicrosoftTeams
Show-Menu
$input = Read-Host "Please make a selection"
switch ($input)
{
    '1' {
        GetTeamsWithPrivatechannel-InSourceTenant
    } '2' {
        GetOwnerMember-OfPrivateChannelsSouceTenant
    } '3' {
        AddOwnerMember-ToPrivateChannelDestinationTenant
    } 
}