Full circle jquery sortable structure to flat array and back to nested.

parse_jquery_sortable.php

<?php 

//updated gist for additional array wrapping and empty children arrays (required)

$json = '[{
		"name": "Item 1",
		"id": 0,
		"children": [
			[]
		]
	}, {
		"name": "Item 3",
		"id": 2,
		"children": [
			[]
		]
	}, {
		"name": "Item 4",
		"id": 3,
		"children": [
			[{
					"name": "Item 3.1",
					"id": 8,
					"children": [
						[]
					]
				}, {
					"name": "Item 2",
					"id": 1,
					"children": [
						[]
					]
				}, {
					"name": "Item 3.2",
					"id": "3-1",
					"children": [
						[]
					]
				}, {
					"name": "Item 3.3",
					"id": "3-2",
					"children": [
						[]
					]
				}, {
					"name": "Item 3.4",
					"id": "3-3",
					"children": [
						[]
					]
				}, {
					"name": "Item 3.5",
					"id": "3-4",
					"children": [
						[]
					]
				}, {
					"name": "Item 3.6",
					"id": "3-5",
					"children": [
						[]
					]
				}
			]
		]
	}
]';

// parse json to php array
$list = json_decode($json,true);
pre($list);

// flatten array to add parent and order
$flat = make_flat($list,0);
pre($flat,'flat');

// parse flat array to recreate nested strucure
$nested = make_nested($flat);
pre($nested,'nested');

//convert back to json
echo json_encode($nested);

function make_nested($flat) {
	$nested=[];
	foreach($flat as &$s){
		$s['children'][0]=[];
		$pid = $s['parent'];
		unset($s['parent']);
		unset($s['order']);
		if($pid==0){
			$nested[] = &$s;
		}else{
			if(isset($flat[$pid])){
				if (!isset($flat[$pid]['children'])){
					$flat[$pid]['children'][0] = [];
				}
				$flat[$pid]['children'][0][] = &$s;
			}
		}
	}
	return $nested;
}
function make_flat($list,$parent){  
	$r=[];     
	foreach($list as $ct => $arr){
		if(!empty($arr)){
			if(isset($arr['id'])){
				$ct++;
				$r[$arr['id']] = $arr;
				$r[$arr['id']]['parent'] = $parent;
				$r[$arr['id']]['order'] = $ct;
				if(isset($arr['children'][0])){
					unset($r[$arr['id']]['children']);
					$r = $r + make_flat($arr['children'][0],$arr['id']);
				}
			}
		}
	}
	return $r;
}
function pre($a,$h=false){
	echo $h ? '<h3 style="margin-bottom: 0px;">'.$h.'</h3><pre style="margin-top: 0px;">' : '<pre style="margin-top: 0px;">';
	print_r($a);
	echo '</pre>';
}
function prex($a,$h=false,$dbg=false){
	pre($a,$h);
	exit;
}