jsonpatch.php

<?php

$old = [
    'name' => 'Old name',
    'active' => true,
    'description' => 'This is a description',
    'items' => [
        [
            'name' => 'Old item name',
            'active' => true,
        ],
    ],
];

$new = [
    'name' => 'new name',
    'active' => true,
    'categories' => [1, 2],
    'items' => [
        [
            'name' => 'Old item name',
            'active' => false,
        ],
        [
            'name' => 'New item name',
            'active' => true,
        ],
    ],
];

$changes = getChanges($old, $new);

echo '<pre>';

echo json_encode($changes, JSON_UNESCAPED_SLASHES | JSON_PRETTY_PRINT);

print_r(applyChanges($old, $changes));

function getChanges(array $old, array $new, string $path = ''): array
{
    $changes = [];

    foreach ($new as $key => $newValue) {
        if (isset($old[$key])) {
            $oldValue = $old[$key];
            if ($oldValue !== $newValue) {
                if (is_array($oldValue) && is_array($newValue)) {
                    foreach (getChanges($oldValue, $newValue, $path.'/'.$key) as $change) {
                        $changes[] = $change;
                    }
                } else {
                    $changes[] = ['op' => 'replace', 'path' => $path.'/'.$key, 'value' => $newValue];
                }
            }
        } else {
            $changes[] = ['op' => 'add', 'path' => $path.'/'.$key, 'value' => $newValue];
        }

        unset($old[$key]);
    }

    foreach ($old as $key => $oldValue) {
        $changes[] = ['op' => 'remove', 'path' => $path.'/'.$key];
    }

    return $changes;
}

function applyChanges(array $old, array $changes): array
{
    foreach ($changes as $change) {
        switch ($change['op']) {
            case 'add':
                replace($old, $change['path'], $change['value']);
                break;
            case 'replace':
                replace($old, $change['path'], $change['value']);
                break;
            case 'remove':
                remove($old, $change['path']);
        }
    }

    return $old;
}

function add(array &$data, string $path, $value)
{
    $pathParts = explode('/', trim($path, '/'));
    $lastPart = array_pop($pathParts);

    $reference = &$data;
    foreach ($pathParts as $pathPart) {
        if ($pathPart === (string) (int) $pathPart) {
            $pathPart = (int) $pathPart;
        }

        if (!isset($reference[$pathPart])) {
            $reference[$pathPart] = [];
        }

        $reference = &$reference[$pathPart];
    }

    if (is_array($value) && is_array($reference[$lastPart])) {
        $reference[$lastPart] = array_replace_recursive($reference[$lastPart], $value);
    } else {
        $reference[$lastPart] = $value;
    }
}

function replace(array &$data, string $path, $value)
{
    $pathParts = explode('/', trim($path, '/'));
    $lastPart = array_pop($pathParts);

    $reference = &$data;
    foreach ($pathParts as $pathPart) {
        if ($pathPart === (string) (int) $pathPart) {
            $pathPart = (int) $pathPart;
        }

        if (!isset($reference[$pathPart])) {
            $reference[$pathPart] = [];
        }

        $reference = &$reference[$pathPart];
    }

    $reference[$lastPart] = $value;
}

function remove(array &$data, string $path)
{
    $pathParts = explode('/', trim($path, '/'));
    $lastPart = array_pop($pathParts);

    $reference = &$data;
    foreach ($pathParts as $pathPart) {
        if ($pathPart === (string) (int) $pathPart) {
            $pathPart = (int) $pathPart;
        }

        if (!isset($reference[$pathPart])) {
            return;
        }
    }

    unset($reference[$lastPart]);
}