PHP daya sync process (Prestashop data)

We need to develop a two-systems data synchronization PHP process. One system is a Prestashop online store, and the other is an unspecific product and sales management system which provides a documented REST API. The requested product consists of a PHP system which will be able to query both the Prestashop data and the other system's data, the syncronizations registries, the modification dates, then compute all the additions, editions and deletions, and finally perform a sync process. System must understand sync priority rules, sync direction rules, and datum dependencies in order to syncronize groups of dependent data, or synchronize single required items before continuing the current sync process... The system must also be able to work with a single or multiple execution threads. The sync process must be ready to react to in-sync unexpected data modifications. The data to sync will be products, variants, attibutes, prices, discounts, users, addresses and orders, at least. The final product must be packaged as a Prestashop plugin, the processes must run under the Prestashop install, and it must create and manage sync tables (process control, data mapping between systems...) in the Prestashop database. It must be compatible with both Prestashop 1.6 and 1.7, and PHP versions from 5.4 to 7.2. PHP code must be PSR-4 compliant. The process must run súper agile, sync the data very efficiently and fast, and run errorless 24/7. All unexpected situations must be logged. A process results log must be recorded. Code must be committed daily. Code must include tests. Project is estimated to about 86h, but if the work is excellent, the project is very likely to be continued for approximately 6 months, and we will take you in account for our constant new projects. We need committed professionals with minimum 40h/week availability.