wp_insert_user( array|object|WP_User $userdata )

function wp_insert_user( $userdata ) {
	global $wpdb;

	if ( $userdata instanceof stdClass ) {
		$userdata = get_object_vars( $userdata );
	} elseif ( $userdata instanceof WP_User ) {
		$userdata = $userdata->to_array();
	}

	// Are we updating or creating?
	if ( ! empty( $userdata['ID'] ) ) {
		$ID = (int) $userdata['ID'];
		$update = true;
		$old_user_data = get_userdata( $ID );

		if ( ! $old_user_data ) {
			return new WP_Error( 'invalid_user_id', __( 'Invalid user ID.' ) );
		}

		// hashed in wp_update_user(), plaintext if called directly
		$user_pass = ! empty( $userdata['user_pass'] ) ? $userdata['user_pass'] : $old_user_data->user_pass;
	} else {
		$update = false;
		// Hash the password
		$user_pass = wp_hash_password( $userdata['user_pass'] );
	}

	$sanitized_user_login = sanitize_user( $userdata['user_login'], true );

	/**
	 * Filters a username after it has been sanitized.
	 *
	 * This filter is called before the user is created or updated.
	 *
	 * @since WP-2.0.3
	 *
	 * @param string $sanitized_user_login Username after it has been sanitized.
	 */
	$pre_user_login = apply_filters( 'pre_user_login', $sanitized_user_login );

	//Remove any non-printable chars from the login string to see if we have ended up with an empty username
	$user_login = trim( $pre_user_login );

	// user_login must be between 0 and 60 characters.
	if ( empty( $user_login ) ) {
		return new WP_Error('empty_user_login', __('Cannot create a user with an empty login name.') );
	} elseif ( mb_strlen( $user_login ) > 60 ) {
		return new WP_Error( 'user_login_too_long', __( 'Username may not be longer than 60 characters.' ) );
	}

	if ( ! $update && username_exists( $user_login ) ) {
		return new WP_Error( 'existing_user_login', __( 'Sorry, that username already exists!' ) );
	}

	/**
	 * Filters the list of blacklisted usernames.
	 *
	 * @since WP-4.4.0
	 *
	 * @param array $usernames Array of blacklisted usernames.
	 */
	$illegal_logins = (array) apply_filters( 'illegal_user_logins', array() );

	if ( in_array( strtolower( $user_login ), array_map( 'strtolower', $illegal_logins ) ) ) {
		return new WP_Error( 'invalid_username', __( 'Sorry, that username is not allowed.' ) );
	}

	/*
	 * If a nicename is provided, remove unsafe user characters before using it.
	 * Otherwise build a nicename from the user_login.
	 */
	if ( ! empty( $userdata['user_nicename'] ) ) {
		$user_nicename = sanitize_user( $userdata['user_nicename'], true );
		if ( mb_strlen( $user_nicename ) > 50 ) {
			return new WP_Error( 'user_nicename_too_long', __( 'Nicename may not be longer than 50 characters.' ) );
		}
	} else {
		$user_nicename = mb_substr( $user_login, 0, 50 );
	}

	$user_nicename = sanitize_title( $user_nicename );

	// Store values to save in user meta.
	$meta = array();

	/**
	 * Filters a user's nicename before the user is created or updated.
	 *
	 * @since WP-2.0.3
	 *
	 * @param string $user_nicename The user's nicename.
	 */
	$user_nicename = apply_filters( 'pre_user_nicename', $user_nicename );

	$raw_user_url = empty( $userdata['user_url'] ) ? '' : $userdata['user_url'];

	/**
	 * Filters a user's URL before the user is created or updated.
	 *
	 * @since WP-2.0.3
	 *
	 * @param string $raw_user_url The user's URL.
	 */
	$user_url = apply_filters( 'pre_user_url', $raw_user_url );

	$raw_user_email = empty( $userdata['user_email'] ) ? '' : $userdata['user_email'];

	/**
	 * Filters a user's email before the user is created or updated.
	 *
	 * @since WP-2.0.3
	 *
	 * @param string $raw_user_email The user's email.
	 */
	$user_email = apply_filters( 'pre_user_email', $raw_user_email );

	/*
	 * If there is no update, just check for `email_exists`. If there is an update,
	 * check if current email and new email are the same, or not, and check `email_exists`
	 * accordingly.
	 */
	if ( ( ! $update || ( ! empty( $old_user_data ) && 0 !== strcasecmp( $user_email, $old_user_data->user_email ) ) )
		&& ! defined( 'WP_IMPORTING' )
		&& email_exists( $user_email )
	) {
		return new WP_Error( 'existing_user_email', __( 'Sorry, that email address is already used!' ) );
	}
	$nickname = empty( $userdata['nickname'] ) ? $user_login : $userdata['nickname'];

	/**
	 * Filters a user's nickname before the user is created or updated.
	 *
	 * @since WP-2.0.3
	 *
	 * @param string $nickname The user's nickname.
	 */
	$meta['nickname'] = apply_filters( 'pre_user_nickname', $nickname );

	$first_name = empty( $userdata['first_name'] ) ? '' : $userdata['first_name'];

	/**
	 * Filters a user's first name before the user is created or updated.
	 *
	 * @since WP-2.0.3
	 *
	 * @param string $first_name The user's first name.
	 */
	$meta['first_name'] = apply_filters( 'pre_user_first_name', $first_name );

	$last_name = empty( $userdata['last_name'] ) ? '' : $userdata['last_name'];

	/**
	 * Filters a user's last name before the user is created or updated.
	 *
	 * @since WP-2.0.3
	 *
	 * @param string $last_name The user's last name.
	 */
	$meta['last_name'] = apply_filters( 'pre_user_last_name', $last_name );

	if ( empty( $userdata['display_name'] ) ) {
		if ( $update ) {
			$display_name = $user_login;
		} elseif ( $meta['first_name'] && $meta['last_name'] ) {
			/* translators: 1: first name, 2: last name */
			$display_name = sprintf( _x( '%1$s %2$s', 'Display name based on first name and last name' ), $meta['first_name'], $meta['last_name'] );
		} elseif ( $meta['first_name'] ) {
			$display_name = $meta['first_name'];
		} elseif ( $meta['last_name'] ) {
			$display_name = $meta['last_name'];
		} else {
			$display_name = $user_login;
		}
	} else {
		$display_name = $userdata['display_name'];
	}

	/**
	 * Filters a user's display name before the user is created or updated.
	 *
	 * @since WP-2.0.3
	 *
	 * @param string $display_name The user's display name.
	 */
	$display_name = apply_filters( 'pre_user_display_name', $display_name );

	$description = empty( $userdata['description'] ) ? '' : $userdata['description'];

	/**
	 * Filters a user's description before the user is created or updated.
	 *
	 * @since WP-2.0.3
	 *
	 * @param string $description The user's description.
	 */
	$meta['description'] = apply_filters( 'pre_user_description', $description );

	$meta['rich_editing'] = empty( $userdata['rich_editing'] ) ? 'true' : $userdata['rich_editing'];

	$meta['syntax_highlighting'] = empty( $userdata['syntax_highlighting'] ) ? 'true' : $userdata['syntax_highlighting'];

	$meta['comment_shortcuts'] = empty( $userdata['comment_shortcuts'] ) || 'false' === $userdata['comment_shortcuts'] ? 'false' : 'true';

	$admin_color = empty( $userdata['admin_color'] ) ? 'fresh' : $userdata['admin_color'];
	$meta['admin_color'] = preg_replace( '|[^a-z0-9 _.\-@]|i', '', $admin_color );

	$meta['use_ssl'] = empty( $userdata['use_ssl'] ) ? 0 : $userdata['use_ssl'];

	$user_registered = empty( $userdata['user_registered'] ) ? gmdate( 'Y-m-d H:i:s' ) : $userdata['user_registered'];

	$meta['show_admin_bar_front'] = empty( $userdata['show_admin_bar_front'] ) ? 'true' : $userdata['show_admin_bar_front'];

	$meta['locale'] = isset( $userdata['locale'] ) ? $userdata['locale'] : '';

	$user_nicename_check = $wpdb->get_var( $wpdb->prepare("SELECT ID FROM $wpdb->users WHERE user_nicename = %s AND user_login != %s LIMIT 1" , $user_nicename, $user_login));

	if ( $user_nicename_check ) {
		$suffix = 2;
		while ($user_nicename_check) {
			// user_nicename allows 50 chars. Subtract one for a hyphen, plus the length of the suffix.
			$base_length = 49 - mb_strlen( $suffix );
			$alt_user_nicename = mb_substr( $user_nicename, 0, $base_length ) . "-$suffix";
			$user_nicename_check = $wpdb->get_var( $wpdb->prepare("SELECT ID FROM $wpdb->users WHERE user_nicename = %s AND user_login != %s LIMIT 1" , $alt_user_nicename, $user_login));
			$suffix++;
		}
		$user_nicename = $alt_user_nicename;
	}

	$compacted = compact( 'user_pass', 'user_email', 'user_url', 'user_nicename', 'display_name', 'user_registered' );
	$data = wp_unslash( $compacted );

	if ( ! $update ) {
		$data = $data + compact( 'user_login' );
	}

	/**
	 * Filters user data before the record is created or updated.
	 *
	 * It only includes data in the wp_users table wp_user, not any user metadata.
	 *
	 * @since WP-4.9.0
	 *
	 * @param array    $data {
	 *     Values and keys for the user.
	 *
	 *     @type string $user_login      The user's login. Only included if $update == false
	 *     @type string $user_pass       The user's password.
	 *     @type string $user_email      The user's email.
	 *     @type string $user_url        The user's url.
	 *     @type string $user_nicename   The user's nice name. Defaults to a URL-safe version of user's login
	 *     @type string $display_name    The user's display name.
	 *     @type string $user_registered MySQL timestamp describing the moment when the user registered. Defaults to
	 *                                   the current UTC timestamp.
	 * }
	 * @param bool     $update Whether the user is being updated rather than created.
	 * @param int|null $id     ID of the user to be updated, or NULL if the user is being created.
	 */
	$data = apply_filters( 'wp_pre_insert_user_data', $data, $update, $update ? (int) $ID : null );

	if ( $update ) {
		if ( $user_email !== $old_user_data->user_email || $user_pass !== $old_user_data->user_pass ) {
			$data['user_activation_key'] = '';
		}
		$wpdb->update( $wpdb->users, $data, compact( 'ID' ) );
		$user_id = (int) $ID;
	} else {
		$wpdb->insert( $wpdb->users, $data );
		$user_id = (int) $wpdb->insert_id;
	}

	$user = new WP_User( $user_id );

	/**
 	 * Filters a user's meta values and keys immediately after the user is created or updated
 	 * and before any user meta is inserted or updated.
 	 *
 	 * Does not include contact methods. These are added using `wp_get_user_contact_methods( $user )`.
 	 *
 	 * @since WP-4.4.0
 	 *
 	 * @param array $meta {
 	 *     Default meta values and keys for the user.
 	 *
 	 *     @type string   $nickname             The user's nickname. Default is the user's username.
	 *     @type string   $first_name           The user's first name.
	 *     @type string   $last_name            The user's last name.
	 *     @type string   $description          The user's description.
	 *     @type bool     $rich_editing         Whether to enable the rich-editor for the user. False if not empty.
	 *     @type bool     $syntax_highlighting  Whether to enable the rich code editor for the user. False if not empty.
	 *     @type bool     $comment_shortcuts    Whether to enable keyboard shortcuts for the user. Default false.
	 *     @type string   $admin_color          The color scheme for a user's admin screen. Default 'fresh'.
	 *     @type int|bool $use_ssl              Whether to force SSL on the user's admin area. 0|false if SSL is
	 *                                          not forced.
	 *     @type bool     $show_admin_bar_front Whether to show the admin bar on the front end for the user.
	 *                                          Default true.
 	 * }
	 * @param WP_User $user   User object.
	 * @param bool    $update Whether the user is being updated rather than created.
 	 */
	$meta = apply_filters( 'insert_user_meta', $meta, $user, $update );

	// Update user meta.
	foreach ( $meta as $key => $value ) {
		update_user_meta( $user_id, $key, $value );
	}

	foreach ( wp_get_user_contact_methods( $user ) as $key => $value ) {
		if ( isset( $userdata[ $key ] ) ) {
			update_user_meta( $user_id, $key, $userdata[ $key ] );
		}
	}

	if ( isset( $userdata['role'] ) ) {
		$user->set_role( $userdata['role'] );
	} elseif ( ! $update ) {
		$user->set_role(get_option('default_role'));
	}
	wp_cache_delete( $user_id, 'users' );
	wp_cache_delete( $user_login, 'userlogins' );

	if ( $update ) {
		/**
		 * Fires immediately after an existing user is updated.
		 *
		 * @since WP-2.0.0
		 *
		 * @param int     $user_id       User ID.
		 * @param WP_User $old_user_data Object containing user's data prior to update.
		 */
		do_action( 'profile_update', $user_id, $old_user_data );
	} else {
		/**
		 * Fires immediately after a new user is registered.
		 *
		 * @since WP-1.5.0
		 *
		 * @param int $user_id User ID.
		 */
		do_action( 'user_register', $user_id );
	}

	return $user_id;
}