MNI metabox

class MNI_Meta_Box {

	public function __construct() {

		if ( is_admin() ) {
			add_action( 'load-post.php',     array( $this, 'init_metabox' ) );
			add_action( 'load-post-new.php', array( $this, 'init_metabox' ) );
		}

	}

	public function init_metabox() {

		add_action( 'add_meta_boxes', array( $this, 'add_metabox'  )        );
		add_action( 'save_post',      array( $this, 'save_metabox' ), 10, 2 );

	}

	public function add_metabox() {

		add_meta_box(
			'mni_metabox',
			__( 'Advanced Options', 'mni' ),
			array( $this, 'render_metabox' ),
			'page',
			'side',
			'high'
		);

	}

	public function render_metabox( $post ) {

		// Retrieve an existing value from the database.
		$mni_contact_form = get_post_meta( $post->ID, 'mni_contact_form', true );
		$mni_text = get_post_meta( $post->ID, 'mni_text', true );
		$mni_1 = get_post_meta( $post->ID, 'mni_1', true );
		$mni_2 = get_post_meta( $post->ID, 'mni_2', true );
		$mni_radio = get_post_meta( $post->ID, 'mni_radio', true );
		$mni_date = get_post_meta( $post->ID, 'mni_date', true );

		// Set default values.
		if( empty( $mni_contact_form ) ) $mni_contact_form = '';
		if( empty( $mni_text ) ) $mni_text = '';
		if( empty( $mni_radio ) ) $mni_radio = '';
		if( empty( $mni_date ) ) $mni_date = '';

		// Form fields.
		echo '<table class="form-table">';

		echo '	<tr>';
		echo '		<th><label for="mni_contact_form" class="mni_contact_form_label">' . __( 'Contact form 7', 'mni' ) . '</label></th>';
		echo '		<td>';
		echo '			<select id="mni_contact_form" name="mni_contact_form" class="mni_contact_form_field">';
		echo '			<option value="mni_value1" ' . selected( $mni_contact_form, 'mni_value1', false ) . '> ' . __( ' form1', 'mni' );
		echo '			<option value="mni_value2" ' . selected( $mni_contact_form, 'mni_value2', false ) . '> ' . __( ' form2', 'mni' );
		echo '			</select>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="mni_text" class="mni_text_label">' . __( 'Text', 'mni' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="text" id="mni_text" name="mni_text" class="mni_text_field" placeholder="' . esc_attr__( 'placeholder', 'mni' ) . '" value="' . esc_attr__( $mni_text ) . '">';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="mni_checkbox" class="mni_checkbox_label">' . __( 'Checkbox', 'mni' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="checkbox" name="mni_1" class="mni_checkbox_field" value="' . $mni_1 . '" ' . checked( $mni_1, 'checked', false ) . '> ' . __( '1', 'mni' ) . '<br>';
		echo '			<input type="checkbox" name="mni_2" class="mni_checkbox_field" value="' . $mni_2 . '" ' . checked( $mni_2, 'checked', false ) . '> ' . __( '2', 'mni' ) . '<br>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="mni_radio" class="mni_radio_label">' . __( 'Radio', 'mni' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="radio" name="mni_radio" class="mni_radio_field" value="mni_1" ' . checked( $mni_radio, 'mni_1', false ) . '> ' . __( '1', 'mni' ) . '<br>';
		echo '			<input type="radio" name="mni_radio" class="mni_radio_field" value="mni_1" ' . checked( $mni_radio, 'mni_1', false ) . '> ' . __( '1', 'mni' ) . '<br>';
		echo '			<input type="radio" name="mni_radio" class="mni_radio_field" value="mni_1" ' . checked( $mni_radio, 'mni_1', false ) . '> ' . __( '1', 'mni' ) . '<br>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="mni_date" class="mni_date_label">' . __( 'Date', 'mni' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="date" id="mni_date" name="mni_date" class="mni_date_field" placeholder="' . esc_attr__( 'date', 'mni' ) . '" value="' . esc_attr__( $mni_date ) . '">';
		echo '		</td>';
		echo '	</tr>';

		echo '</table>';

	}

	public function save_metabox( $post_id, $post ) {

		// Check if it's not a revision.
		if ( wp_is_post_revision( $post_id ) )
			return;

		// Sanitize user input.
		$mni_new_contact_form = isset( $_POST[ 'mni_contact_form' ] ) ? $_POST[ 'mni_contact_form' ] : '';
		$mni_new_text = isset( $_POST[ 'mni_text' ] ) ? sanitize_text_field( $_POST[ 'mni_text' ] ) : '';
		$mni_new_1 = isset( $_POST[ 'mni_1' ] ) ? 'checked' : '';
		$mni_new_2 = isset( $_POST[ 'mni_2' ] ) ? 'checked' : '';
		$mni_new_radio = isset( $_POST[ 'mni_radio' ] ) ? $_POST[ 'mni_radio' ] : '';
		$mni_new_date = isset( $_POST[ 'mni_date' ] ) ? sanitize_text_field( $_POST[ 'mni_date' ] ) : '';

		// Update the meta field in the database.
		update_post_meta( $post_id, 'mni_contact_form', $mni_new_contact_form );
		update_post_meta( $post_id, 'mni_text', $mni_new_text );
		update_post_meta( $post_id, 'mni_1', $mni_new_1 );
		update_post_meta( $post_id, 'mni_2', $mni_new_2 );
		update_post_meta( $post_id, 'mni_radio', $mni_new_radio );
		update_post_meta( $post_id, 'mni_date', $mni_new_date );

	}

}

new MNI_Meta_Box;