Automatically Sync ACF Fields on dev environments

functions.php

<?php
/*
Plugin Name:  Zing ACF Auto Sync
Plugin URI:
Description:  Plugin that automatically syncs the database with local json for .test urls
Version:      20180419
Author:       Noah Duncan <noah@zingstudios.com>
 */

/* Put in /wp-content/mu-plugins/zing-acf-auto-sync/zing-acf-auto-sync.php if you want as a plugin */


/**
 * Function that will update ACF fields via JSON file update.  
 * It would be better to hook into ACF's own update function...but 
 * this works for now.
 */

function zing_sync_acf_fields() {
    error_log('syncing acf fields');

    // vars
    $groups = acf_get_field_groups();
    $sync     = array();

    // bail early if no field groups
    if( empty( $groups ) )
        return;

    // find JSON field groups which have not yet been imported
    foreach( $groups as $group ) {

        // vars
        $local         = acf_maybe_get( $group, 'local', false );
        $modified     = acf_maybe_get( $group, 'modified', 0 );
        $private     = acf_maybe_get( $group, 'private', false );

        // ignore DB / PHP / private field groups
        if( $local !== 'json' || $private ) {

            // do nothing

        } elseif( ! $group[ 'ID' ] ) {

            $sync[ $group[ 'key' ] ] = $group;

        } elseif( $modified && $modified > get_post_modified_time( 'U', true, $group[ 'ID' ], true ) ) {

            $sync[ $group[ 'key' ] ]  = $group;
        }
    }

    // bail if no sync needed
    if( empty( $sync ) )
        return;

    if( ! empty( $sync ) ) { //if( ! empty( $keys ) ) {

        // vars
        $new_ids = array();

        foreach( $sync as $key => $v ) { //foreach( $keys as $key ) {

            // append fields
            if( acf_have_local_fields( $key ) ) {

                $sync[ $key ][ 'fields' ] = acf_get_local_fields( $key );

            }
            // import
            $field_group = acf_import_field_group( $sync[ $key ] );
        }
    }
}

if (preg_match('/\.(test|dev)$/', $_SERVER['HTTP_HOST'])) {
    add_action( 'admin_init', 'zing_sync_acf_fields' );
}