Pro Sites - Limit plugins per level

ps-limit-plugins.php

<?php
/*
Plugin Name: Pro Sites - Limit plugins per level
Plugin URI: https://premium.wpmudev.org/
Description: Allow specific number of plugins to be available per level. Requires Pro Sites plugin
Author: Panos Lyrakis @ WPMUDEV
Author URI: https://premium.wpmudev.org/
License: GPLv2 or later
*/

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

if ( ! class_exists( 'WPMUDEV_PS_Limit_Plugins' ) ) {

	class WPMUDEV_PS_Limit_Plugins {

		private static $_instance = null;
		public 	$levels = null,
				$active_plugins_count = null,
				$blog_level = null,
				$allowed_plugins_num = null;


		public static function get_instance() {
			if( is_null( self::$_instance ) ){
				self::$_instance = new WPMUDEV_PS_Limit_Plugins();
			}
			return self::$_instance;
		}


		public function __construct() {

			if( ! $this->is_plugins_page() ){
				return;
			}

			$this->levels = self::get_levels();
			$this->active_plugins_count = $this->count_blog_active_plugins();
			$this->blog_level = $this->get_blog_level();
			$this->allowed_plugins_num = $this->get_allowed_plugins_num();			

			add_action( 'admin_notices', array( $this, 'admin_notice' ) );
			add_action( 'activated_plugin', array( $this, 'maybe_deactivate_plugin' ), 10, 2 );
			add_filter( 'plugin_action_links', array( $this, 'maybe_remove_activation_links' ), 10, 4 );

		}


		public function plugins_per_level(){

			$plugins_per_level = array(
				0 => 1, //0 not a pro site, no level...
				1 => 2,
				2 => 4,
				3 => '-' //'-' has no limit
			);

			return $plugins_per_level;

		}

		public function blog_can_have_more_plugins(){
			$plugins_by_super = count( get_option( 'wpmudev_plugins_by_super', array() ) );
			return $this->allowed_plugins_num == '-' || (int)$this->allowed_plugins_num > ( (int)$this->active_plugins_count - (int)$plugins_by_super );
		}


		public function admin_notice(){

			global $blog_id, $psts;

			if( $this->blog_can_have_more_plugins() ){
				return;
			}

			$upgrade_link   = '<a href="' . $psts->checkout_url( $blog_id ) . '" target="_parent" class="activatelink nonpsts button-primary" t">' . __( 'upgrade level', 'psts' ) . '</a>';
			?>
			<div class="notice notice-error is-dismissible">
		        <p><?php echo sprintf( __( 'You are not allowed to activate any other plugins. If you need to activate a new one you can either deactivate one or %s', 'psts' ), $upgrade_link  ); ?></p>
		    </div>
			<?php

		}


		public function maybe_deactivate_plugin( $plugin, $network_wide ){

			if( $network_wide )	{
				return;
			}

			if( is_super_admin( get_current_user_id() ) ){
				global $blog_id;
				$plugins_by_super = get_option( 'wpmudev_plugins_by_super', array() );
				$plugins_by_super[] = $plugin;
				update_option( 'wpmudev_plugins_by_super', $plugins_by_super );
				return;
			}

			if( ! $this->blog_can_have_more_plugins() ){
				if( ! is_plugin_active_for_network( $plugin ) ){
					deactivate_plugins( $plugin );
				}				
			}
		}


		public function maybe_remove_activation_links( $actions, $plugin_file, $plugin_data, $context ){

			if( is_super_admin( get_current_user_id() ) ){
				return $actions;
			}

			if ( ! $this->blog_can_have_more_plugins() && array_key_exists( 'activate', $actions ) ){
				unset( $actions['activate'] );
			}
			return $actions;

		}


		public function get_allowed_plugins_num(){

			$plugins_per_level = $this->plugins_per_level();
			return $plugins_per_level[ $this->blog_level ];

		}


		public function count_blog_active_plugins(){

			$blog_plugins = count( $this->get_blog_plugins() );
			//$network_plugins = count( $this->get_network_plugins() );

			//return $blog_plugins + $network_plugins;
			return $blog_plugins;
		}


		public function get_blog_level( $blog_id = null ){
			global $psts;
			if( $blog_id == null ){
				global $blog_id;
			}

			return $psts->get_level( $blog_id );
		}


		public function get_blog_plugins(){

			return get_option( 'active_plugins', array() );

		}


		public function get_network_plugins(){

			return get_site_option('active_sitewide_plugins');

		}


		public static function get_levels(){

			$levels = (array) get_site_option( 'psts_levels' );
			if ( ! ( defined( 'PSTS_DONT_REVERSE_LEVELS' ) && PSTS_DONT_REVERSE_LEVELS ) ) {
				$levels = array_reverse( $levels, true );
			}
			foreach ( $levels as $level_id => $level ) {
				$is_visible = isset( $level['is_visible'] ) ? (bool) $level['is_visible'] : true;
				if ( $is_visible ) {
					continue;
				}
				unset( $levels[ $level_id ] );
			}

			return $levels;	
		}


		public function is_plugins_page(){

			if( ! is_admin() || ! class_exists( 'ProSites' ) ){
				return false;
			}

			global $pagenow;
			return $pagenow == 'plugins.php';

		}


		public function get_plugins(){
			return get_plugins();
		}

	}


	add_action( 'plugins_loaded', function(){
		$GLOBALS['WPMUDEV_PS_Limit_Plugins'] = WPMUDEV_PS_Limit_Plugins::get_instance();
	}, 10 );

}

First thing to set is the array with levels and number of plugins:

		```$plugins_per_level = array(
			0 => 1, //0 not a pro site, no level...
			1 => 2,
			2 => 4,
			3 => '-' //'-' has no limit
		);```

Currently it counts the network active plugins too. If you only need to count plugins per blog only comment/delete line

return $blog_plugins + $network_plugins;

and uncomment line

//return $blog_plugins;