bp_groups_user_can_filter( bool $retval, int $user_id, string $capability, int $site_id, array $args )

function bp_groups_user_can_filter( $retval, $user_id, $capability, $site_id, $args ) {
	if ( empty( $args['group_id'] ) ) {
		$group_id = bp_get_current_group_id();
	} else {
		$group_id = (int) $args['group_id'];
	}

	switch ( $capability ) {
		case 'groups_join_group':
			// Return early if the user isn't logged in or the group ID is unknown.
			if ( ! $user_id || ! $group_id ) {
				break;
			}

			// Set to false to begin with.
			$retval = false;

			// The group must allow joining, and the user should not currently be a member.
			$group = groups_get_group( $group_id );
			if ( ( 'public' === bp_get_group_status( $group )
				&& ! groups_is_user_member( $user_id, $group->id )
				&& ! groups_is_user_banned( $user_id, $group->id ) )
				// Site admins can join any group they are not a member of.
				|| ( bp_user_can( $user_id, 'bp_moderate' )
				&& ! groups_is_user_member( $user_id, $group->id ) )
			) {
				$retval = true;
			}
			break;

		case 'groups_request_membership':
			// Return early if the user isn't logged in or the group ID is unknown.
			if ( ! $user_id || ! $group_id ) {
				break;
			}

			// Set to false to begin with.
			$retval = false;

			/*
			* The group must accept membership requests, and the user should not
			* currently be a member or be banned.
			*/
			$group = groups_get_group( $group_id );
			if ( 'private' === bp_get_group_status( $group )
				&& ! groups_is_user_member( $user_id, $group->id )
			    && ! groups_check_for_membership_request( $user_id, $group->id )
				&& ! groups_is_user_banned( $user_id, $group->id )
			) {
				$retval = true;
			}
			break;

		case 'groups_send_invitation':
			// Return early if the user isn't logged in or the group ID is unknown.
			if ( ! $user_id || ! $group_id ) {
				break;
			}

			/*
			* The group must allow invitations, and the user should not
			* currently be a member or be banned from the group.
			*/
			// Users with the 'bp_moderate' cap can always send invitations.
			if ( bp_user_can( $user_id, 'bp_moderate' ) ) {
				$retval = true;
			} else {
				$invite_status = bp_group_get_invite_status( $group_id );

				switch ( $invite_status ) {
					case 'admins' :
						if ( groups_is_user_admin( $user_id, $group_id ) ) {
							$retval = true;
						}
						break;

					case 'mods' :
						if ( groups_is_user_mod( $user_id, $group_id ) || groups_is_user_admin( $user_id, $group_id ) ) {
							$retval = true;
						}
						break;

					case 'members' :
						if ( groups_is_user_member( $user_id, $group_id ) ) {
							$retval = true;
						}
						break;
				}
			}
			break;

		case 'groups_receive_invitation':
			// Return early if the user isn't logged in or the group ID is unknown.
			if ( ! $user_id || ! $group_id ) {
				break;
			}

			// Set to false to begin with.
			$retval = false;

			/*
			* The group must allow invitations, and the user should not
			* currently be a member or be banned from the group.
			*/
			$group = groups_get_group( $group_id );
			if ( in_array( bp_get_group_status( $group ), array( 'private', 'hidden' ), true )
				&& ! groups_is_user_member( $user_id, $group->id )
				&& ! groups_is_user_banned( $user_id, $group->id )
			) {
				$retval = true;
			}
			break;

		case 'groups_access_group':
			// Return early if the group ID is unknown.
			if ( ! $group_id ) {
				break;
			}

			$group = groups_get_group( $group_id );

			// If the check is for the logged-in user, use the BP_Groups_Group property.
			if ( $user_id === bp_loggedin_user_id() ) {
				$retval = $group->user_has_access;

			/*
			 * If the check is for a specified user who is not the logged-in user
			 * run the check manually.
			 */
			} elseif ( 'public' === bp_get_group_status( $group ) || groups_is_user_member( $user_id, $group->id ) ) {
				$retval = true;
			}
			break;

		case 'groups_see_group':
			// Return early if the group ID is unknown.
			if ( ! $group_id ) {
				break;
			}

			$group = groups_get_group( $group_id );

			// If the check is for the logged-in user, use the BP_Groups_Group property.
			if ( $user_id === bp_loggedin_user_id() ) {
				$retval = $group->is_visible;

			/*
			 * If the check is for a specified user who is not the logged-in user
			 * run the check manually.
			 */
			} elseif ( 'hidden' !== bp_get_group_status( $group ) || groups_is_user_member( $user_id, $group->id ) ) {
				$retval = true;
			}
			break;
	}

	return $retval;

}