<?php
	
	// post ID
	$post_id = 123;
	// reference of the post, the images will be uploaded in a folder named after it, could be replaced by the post ID if you don't have a reference
	$reference = 'TEST-REF';
	// array of images URLs to attach
	$images = array(
		'https://static5.immomigsa.ch/s/710e6/1/pictures/objects/1_5e6895ada6a599.35609643.jpg',
		'https://static3.immomigsa.ch/s/c9e4c/1/pictures/objects/1_5e6895ade6a061.09425577.jpg',
		'https://static3.immomigsa.ch/s/11761/1/pictures/objects/1_5e6895ae1bba80.89092542.jpg',
	);
	
	// key of the ACF to update
	$acf_key = 'images';
	
	// declaring upload base directory, images will be uploaded within subfolder of this folder, created un the "uploads" folder
	$base_upload_folder = 'immomig';
	
	// getting WP uploads path
	$wp_upload_path = wp_upload_dir()['basedir'];
	// if base folder doesn't exist, it is created
	if (!is_dir($wp_upload_path.'/'.$base_upload_folder.'/'))
		mkdir($wp_upload_path.'/'.$base_upload_folder.'/');
	// removing the previously attached images
	$attachedz = get_field_object($acf_key, $post_id, false, true); // getting the list of images linked to this post through this ACF
	if ($attachedz[0]) { // if there are several in the main array...
		foreach($attachedz as $attached) // ...then for each...
			wp_delete_attachment(is_numeric($attached['value'])?$attached['value']:$attached['ID'], true); // ...we delete it
	}
	elseif (is_array($attachedz['value'])) { // or if there are several in a sub array...
		foreach($attachedz['value'] as $attached_id) // ...then for each...
			wp_delete_attachment($attached_id, true); // ...we delete it
	}
	else { // or if there is a single one...
		wp_delete_attachment(is_numeric($attachedz['value'])?$attachedz['value']:$attachedz['ID'], true); // ...we delete it
	}
	// initiating array of attached images IDs
	$attach_idz = array();
	// looping on each image URL
	foreach($images as $url) {
		// getting filename
		$filename = basename($url);
		// getting upload path directory
		$upload_path_dir = $wp_upload_path.'/'.$base_upload_folder.'/'.$reference.'/';
		// if directory doesn't existe, it is created
		if (!is_dir($upload_path_dir))
			mkdir($upload_path_dir);
		// getting complete upload path for the file
		$upload_path = $upload_path_dir.$filename;
		// if a file with the same name already exists, it is renamed with a trailing number
		$n = 2;
		while(is_file($upload_path))
			$upload_path = $upload_path_dir.pathinfo($filename,PATHINFO_FILENAME).'-'.($n++).'.'.pathinfo($filename,PATHINFO_EXTENSION);
		// uploading file to folder
		file_put_contents($upload_path, file_get_contents($url));
		// getting file type
		$filetype = wp_check_filetype(basename($upload_path), null);
		// iniatiating attachment datas
		$attachment = array(
			'guid'           => $upload_path, 
			'post_mime_type' => $filetype['type'],
			'post_title'     => preg_replace('/\.[^.]+$/', '', $filename),
			'post_content'   => '',
			'post_status'    => 'inherit'
		);
		// attaching the file to the post
		$attach_id = wp_insert_attachment($attachment, $upload_path, $post_id);
		// loading admin image library
		require_once(ABSPATH.'wp-admin/includes/image.php');
		// genertating attachment metadata
		$attach_data = wp_generate_attachment_metadata($attach_id, $upload_path);
		// updating metadata on the attached image
		wp_update_attachment_metadata($attach_id, $attach_data);
		// adding attachment ID to the array of attached images IDs
		$attach_idz[] = $attach_id;
	}
	
	// updating ACF gallery with images IDs
	update_field($acf_key, $attach_idz, $post_id);