Discover New Music – Band Info

class Discover_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(
			'bandinfo',
			__( 'Band Info', 'text_domain' ),
			array( $this, 'render_metabox' ),
			'post',
			'advanced',
			'default'
		);

	}

	public function render_metabox( $post ) {

		// Retrieve an existing value from the database.
		$discover_website = get_post_meta( $post->ID, 'discover_website', true );
		$discover_facebook = get_post_meta( $post->ID, 'discover_facebook', true );
		$discover_twitter = get_post_meta( $post->ID, 'discover_twitter', true );
		$discover_instagram = get_post_meta( $post->ID, 'discover_instagram', true );
		$discover_youtube = get_post_meta( $post->ID, 'discover_youtube', true );

		// Set default values.
		if( empty( $discover_website ) ) $discover_website = '';
		if( empty( $discover_facebook ) ) $discover_facebook = '';
		if( empty( $discover_twitter ) ) $discover_twitter = '';
		if( empty( $discover_instagram ) ) $discover_instagram = '';
		if( empty( $discover_youtube ) ) $discover_youtube = '';

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

		echo '	<tr>';
		echo '		<th><label for="discover_website" class="discover_website_label">' . __( 'Website', 'text_domain' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="url" id="discover_website" name="discover_website" class="discover_website_field" placeholder="' . esc_attr__( '', 'text_domain' ) . '" value="' . esc_attr( $discover_website ) . '">';
		echo '			<p class="description">' . __( 'Website URL', 'text_domain' ) . '</p>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="discover_facebook" class="discover_facebook_label">' . __( 'Facebook', 'text_domain' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="url" id="discover_facebook" name="discover_facebook" class="discover_facebook_field" placeholder="' . esc_attr__( '', 'text_domain' ) . '" value="' . esc_attr( $discover_facebook ) . '">';
		echo '			<p class="description">' . __( 'Facebook URL', 'text_domain' ) . '</p>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="discover_twitter" class="discover_twitter_label">' . __( 'Twitter', 'text_domain' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="url" id="discover_twitter" name="discover_twitter" class="discover_twitter_field" placeholder="' . esc_attr__( '', 'text_domain' ) . '" value="' . esc_attr( $discover_twitter ) . '">';
		echo '			<p class="description">' . __( 'Twitter URL', 'text_domain' ) . '</p>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="discover_instagram" class="discover_instagram_label">' . __( 'Instagram', 'text_domain' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="url" id="discover_instagram" name="discover_instagram" class="discover_instagram_field" placeholder="' . esc_attr__( '', 'text_domain' ) . '" value="' . esc_attr( $discover_instagram ) . '">';
		echo '			<p class="description">' . __( 'Instagram URL', 'text_domain' ) . '</p>';
		echo '		</td>';
		echo '	</tr>';

		echo '	<tr>';
		echo '		<th><label for="discover_youtube" class="discover_youtube_label">' . __( 'YouTube', 'text_domain' ) . '</label></th>';
		echo '		<td>';
		echo '			<input type="url" id="discover_youtube" name="discover_youtube" class="discover_youtube_field" placeholder="' . esc_attr__( '', 'text_domain' ) . '" value="' . esc_attr( $discover_youtube ) . '">';
		echo '			<p class="description">' . __( 'YouTube URL', 'text_domain' ) . '</p>';
		echo '		</td>';
		echo '	</tr>';

		echo '</table>';

	}

	public function save_metabox( $post_id, $post ) {

		// Check if it's not an autosave.
		if ( wp_is_post_autosave( $post_id ) )
			return;

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

		// Sanitize user input.
		$discover_new_website = isset( $_POST[ 'discover_website' ] ) ? sanitize_text_field( $_POST[ 'discover_website' ] ) : '';
		$discover_new_facebook = isset( $_POST[ 'discover_facebook' ] ) ? sanitize_text_field( $_POST[ 'discover_facebook' ] ) : '';
		$discover_new_twitter = isset( $_POST[ 'discover_twitter' ] ) ? sanitize_text_field( $_POST[ 'discover_twitter' ] ) : '';
		$discover_new_instagram = isset( $_POST[ 'discover_instagram' ] ) ? sanitize_text_field( $_POST[ 'discover_instagram' ] ) : '';
		$discover_new_youtube = isset( $_POST[ 'discover_youtube' ] ) ? sanitize_text_field( $_POST[ 'discover_youtube' ] ) : '';

		// Update the meta field in the database.
		update_post_meta( $post_id, 'discover_website', $discover_new_website );
		update_post_meta( $post_id, 'discover_facebook', $discover_new_facebook );
		update_post_meta( $post_id, 'discover_twitter', $discover_new_twitter );
		update_post_meta( $post_id, 'discover_instagram', $discover_new_instagram );
		update_post_meta( $post_id, 'discover_youtube', $discover_new_youtube );

	}

}

new Discover_Meta_Box;