How to Limit BuddyPress Activity Messages | https://www.ibenic.com/limit-buddypress-activity-messages

before_save.php

<?php

// .../wp-content/plugins/buddypress/bp-activity/classes/class-bp-activity-activity.php

// ...

/**
 * Database interaction class for the BuddyPress activity component.
 * Instance methods are available for creating/editing an activity,
 * static methods for querying activities.
 *
 * @since 1.0.0
 */
class BP_Activity_Activity {

	// ...

	/**
	 * Save the activity item to the database.
	 *
	 * @since 1.0.0
	 *
	 * @return WP_Error|bool True on success.
	 */
	public function save() {
		global $wpdb;

		$bp = buddypress();

		$this->id                = apply_filters_ref_array( 'bp_activity_id_before_save',                array( $this->id,                &$this ) );
		$this->item_id           = apply_filters_ref_array( 'bp_activity_item_id_before_save',           array( $this->item_id,           &$this ) );
		$this->secondary_item_id = apply_filters_ref_array( 'bp_activity_secondary_item_id_before_save', array( $this->secondary_item_id, &$this ) );
		$this->user_id           = apply_filters_ref_array( 'bp_activity_user_id_before_save',           array( $this->user_id,           &$this ) );
		$this->primary_link      = apply_filters_ref_array( 'bp_activity_primary_link_before_save',      array( $this->primary_link,      &$this ) );
		$this->component         = apply_filters_ref_array( 'bp_activity_component_before_save',         array( $this->component,         &$this ) );
		$this->type              = apply_filters_ref_array( 'bp_activity_type_before_save',              array( $this->type,              &$this ) );
		$this->action            = apply_filters_ref_array( 'bp_activity_action_before_save',            array( $this->action,            &$this ) );
		$this->content           = apply_filters_ref_array( 'bp_activity_content_before_save',           array( $this->content,           &$this ) );
		$this->date_recorded     = apply_filters_ref_array( 'bp_activity_date_recorded_before_save',     array( $this->date_recorded,     &$this ) );
		$this->hide_sitewide     = apply_filters_ref_array( 'bp_activity_hide_sitewide_before_save',     array( $this->hide_sitewide,     &$this ) );
		$this->mptt_left         = apply_filters_ref_array( 'bp_activity_mptt_left_before_save',         array( $this->mptt_left,         &$this ) );
		$this->mptt_right        = apply_filters_ref_array( 'bp_activity_mptt_right_before_save',        array( $this->mptt_right,        &$this ) );
		$this->is_spam           = apply_filters_ref_array( 'bp_activity_is_spam_before_save',           array( $this->is_spam,           &$this ) );

		/**
		 * Fires before the current activity item gets saved.
		 *
		 * Please use this hook to filter the properties above. Each part will be passed in.
		 *
		 * @since 1.0.0
		 *
		 * @param BP_Activity_Activity $this Current instance of the activity item being saved. Passed by reference.
		 */
		do_action_ref_array( 'bp_activity_before_save', array( &$this ) );

		if ( 'wp_error' === $this->error_type && $this->errors->get_error_code() ) {
			return $this->errors;
		}
    
    // ...
  }
  
  // ...
}

// ...

can_mention.php

<?php

/**
 * We will return false if we're trying to mention ourselves.
 */
function can_this_user_be_mentioned( $user_id ) {
  /* This function can contain various checks such as:
   - user roles
   - user levels
   - capabilities
   - and a lot more...
  */
  $current_user_id = get_current_user_id();
  if ( $current_user_id !== $user_id ) {
    return true;
  }
  
  return false;
}

disable_save.php

<?php

add_action( 'bp_activity_before_save', 'yourplugin_disable_activity_on_save' );

/**
 * If a user can't be mentioned, add an error to Activity object.
 *
 * @param BP_Activity_Activity $activity Activity object.
 *
 * @return void
 */
function yourplugin_disable_activity_on_save( $activity ) {
  $unavailable_username = '';
  
  $user_ids = bp_activity_find_mentions( $activity->content );
  if ( ! $user_ids ) { 
    return;
  }

  foreach( $user_ids as $user_id => $username ) {
    if ( ! can_this_user_be_mentioned( $user_id ) ) {
      $unavailable_username = $username;
      break;
    }
  }
  if ( $unavailable_username ) {
    $activity->error_type = 'wp_error';
    $activity->errors = new WP_Error( 'no-user-mention', sprintf( __( 'You can\'t mention %s.', 'your_textdomain' ), $unavailable_username ) );
  }
}

disable_update.php

<?php

add_action( 'bp_activity_post_update_content', 'myplugin_disable_activity_mention_user' );

/**
 * If a username can't be mentioned, we will return an empty content and a message.
 *
 * @param string $content Content.
 *
 * @return string
 */
function myplugin_disable_activity_mention_user( $content ) {
  $user_ids = bp_activity_find_mentions( $content );
  if ( ! $user_ids ) { 
    return $content;
  }

  foreach( $user_ids as $user_id => $username ) {
    if ( ! can_this_user_be_mentioned( $user_id ) ) {
      $content = '';
      bp_core_add_message( sprintf( __( 'You can\t mention %s.', 'your_textdomain' ), $username ), 'error' );
      break;
    }
  }

  return $content;
}

update.php

<?php

// .../wp-content/plugins/buddypress/bp-activity/actions/post.php

// ...

function bp_activity_action_post_update() {
	// Do not proceed if user is not logged in, not viewing activity, or not posting.
	if ( !is_user_logged_in() || !bp_is_activity_component() || !bp_is_current_action( 'post' ) )
		return false;

	// Check the nonce.
	check_admin_referer( 'post_update', '_wpnonce_post_update' );

	/**
	 * Filters the content provided in the activity input field.
	 *
	 * @since 1.2.0
	 *
	 * @param string $value Activity message being posted.
	 */
	$content = apply_filters( 'bp_activity_post_update_content', $_POST['whats-new'] );
  
  // ...

}

// ...