Mimic ACF flexible content fields with Field Manager

flexible-content.php

<?php
/**
 * Mimic ACF flexible content fields with Field Manager
 */

add_action( 'fm_post_post', function() {

	$fm = new Fieldmanager_Group( [
		'name' => 'flexible-content',
		'label' => __( 'Content Section', 'your-textdomain' ),
		'limit' => 0,
		'sortable' => 1,
		'add_more_label' => __( 'Add Content Section', 'your-textdomain' ),
		'children' => [
			'section-title' => new Fieldmanager_TextField( __( 'Section Title', 'your-textdomain' ) ),
		],
	] );
	$flexible_content_select = new Fieldmanager_Select( __( 'Section Type', 'your-textdomain' ), [ 'name' => 'section_type' ] );
	$fm->add_child( $flexible_content_select );

	$flexfields = [];

	$flexfields[] = new Fieldmanager_Group( [
		'name' => 'demo-group',
		'label' => __( 'Demo Section', 'your-textdomain' ),
		'children' => [
			'field-one' => new Fieldmanager_TextField( __( 'First Field', 'your-textdomain' ) ),
			'field-two' => new Fieldmanager_TextField( __( 'Second Field', 'your-textdomain' ) ),
		],
	] );

	$flexfields[] = new Fieldmanager_Group( [
		'name' => 'youtube',
		'label' => __( 'YouTube Video', 'your-textdomain' ),
		'children' => [
			'youtube-url' => new Fieldmanager_TextField( __( 'YouTube URL', 'your-textdomain' ) ),
			'preview-image' => new Fieldmanager_Media( __( 'Preview Image', 'your-textdomain' ), [
				'preview_size' => 'medium',
			] ),
		],
	] );

	$flexfields[] = new Fieldmanager_Group( [
		'name' => 'all-fields',
		'label' => __( 'All Field Types', 'your-textdomain' ),
		'children' => [
			'autocomplete' => new Fieldmanager_Autocomplete( __( 'Autocomplete', 'your-textdomain' ), [ 'datasource' => new Fieldmanager_Datasource( [ 'options' => [ 'alt1' => __( 'Alternative One', 'your-textdomain' ), 'alt2' => __( 'Alternative Two', 'your-textdomain' ), 'alt3' => __( 'Alternative Three', 'your-textdomain' ) ] ] ) ] ),
			'checkbox' => new Fieldmanager_Checkbox( __( 'Checkbox', 'your-textdomain' ) ),
			'checkboxes' => new Fieldmanager_Checkboxes( __( 'Checkboxes', 'your-textdomain' ), [ 'options' => [ 'alt1' => __( 'Alternative One', 'your-textdomain' ), 'alt2' => __( 'Alternative Two', 'your-textdomain' ), 'alt3' => __( 'Alternative Three', 'your-textdomain' ) ] ] ),
			'colorpicker' => new Fieldmanager_Colorpicker( __( 'Colorpicker', 'your-textdomain' ) ),
			'datepicker' => new Fieldmanager_Datepicker( __( 'Datepicker', 'your-textdomain' ) ),
			'draggablepost' => new Fieldmanager_DraggablePost( __( 'DraggablePost', 'your-textdomain' ), [ 'repositories' => [ [ 'label' => __( 'Available posts', 'your-textdomain' ), 'post_type' => 'post' ], [ 'label' => __( 'Available pages', 'your-textdomain' ), 'post_type' => 'page' ] ], 'bins' => [ 'featured_posts' => __( 'Featured Posts', 'your-textdomain' ), 'really_featured_posts' => __( 'Really Featured Posts', 'your-textdomain' ) ] ] ),
			'grid' => new Fieldmanager_Grid( __( 'Grid', 'your-textdomain' ) ),
			'link' => new Fieldmanager_Link( __( 'Link', 'your-textdomain' ) ),
			'media' => new Fieldmanager_Media( __( 'Media', 'your-textdomain' ) ),
			'password' => new Fieldmanager_Password( __( 'Password', 'your-textdomain' ) ),
			'radios' => new Fieldmanager_Radios( __( 'Radios', 'your-textdomain' ), [ 'options' => [ 'alt1' => __( 'Alternative One', 'your-textdomain' ), 'alt2' => __( 'Alternative Two', 'your-textdomain' ), 'alt3' => __( 'Alternative Three', 'your-textdomain' ) ] ] ),
			'richTextArea' => new Fieldmanager_RichTextArea( __( 'RichTextArea', 'your-textdomain' ) ),
			'select' => new Fieldmanager_Select( __( 'Select', 'your-textdomain' ), [ 'options' => [ 'alt1' => __( 'Alternative One', 'your-textdomain' ), 'alt2' => __( 'Alternative Two', 'your-textdomain' ), 'alt3' => __( 'Alternative Three', 'your-textdomain' ) ] ] ),
			'textarea' => new Fieldmanager_TextArea( __( 'TextArea', 'your-textdomain' ) ),
			'textfield' => new Fieldmanager_TextField( __( 'TextField', 'your-textdomain' ) ),
		],
	] );

	foreach ( $flexfields as $flexfield ) {
		$flexible_content_select->add_options( [ $flexfield->name => $flexfield->label ] );
		$flexfield->display_if = [ 'src' => 'section_type', 'value' => $flexfield->name ];
		$fm->add_child( $flexfield );
	}

	$fm->add_meta_box( __( 'Flexible Content', 'your-textdomain' ), 'post' );

} );