Set A Featured Image By Image URL

<?php
$image_url        = $_POST['imageUrl'];
$image_name       = basename($image_url);
$upload_dir       = wp_upload_dir();
$image_data       = file_get_contents($image_url);
$genrate_unique_file_name = wp_unique_filename( $upload_dir['path'], $image_name );
$filename         = basename( $genrate_unique_file_name );
if( wp_mkdir_p( $upload_dir['path'] ) ) {
    $file = $upload_dir['path'] . '/' . $filename;
} else {
    $file = $upload_dir['basedir'] . '/' . $filename;
}
file_put_contents( $file, $image_data );
$wp_filetype = wp_check_filetype( $filename, null );

$attachment = array(
    'post_mime_type' => $wp_filetype['type'],
    'post_title'     => sanitize_file_name( $filename ),
    'post_content'   => '',
    'post_status'    => 'inherit'
);

$attach_id = wp_insert_attachment( $attachment, $file, $post_id );
require_once(ABSPATH . 'wp-admin/includes/image.php');
$attach_data = wp_generate_attachment_metadata( $attach_id, $file );
wp_update_attachment_metadata( $attach_id, $attach_data );
set_post_thumbnail( $post_id, $attach_id );
?>
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Let me know your thoughts and questions in the comments.
Email: vyasankit2008@gmail.com