Develop an offline data layer for a simple HTML5 app that is currently online-only -- 4

We currently have a simple and working CRUD professional mobile HTML5 app with jQuery Mobile. It lists customers "around me", allowing the employee to filter the list, edit & upload the customer's information, and create a new customer not found on the list. All this information is retrieved in real time from a JSON web services layer in our servers, which provides the basic methods: list, getInfo, and save. It also provides authentication via user, password, and delivering a temporary token that must be sent on each WS call. The problem with this architecture is that the app is rendered useless when there is no mobile coverage. What we require is to modify this app so that it: - Loads information when there is coverage and stores it locally in the phone / mobile device. Loading should be a background process. It should start with those records "closest around me" (that is, asking the WS with my current position and a lower radius, for example 200m), and proceed with farther away records (500meters, 1 km, 2km, 5km...). Closest records should also be updated frequently in case another user changes their information. - The above should have a limit on the number of records based on the available local memory, not on distance. The idea is that users with few records per city, can download hundreds or thousands of kilometers wide, whereas users with many records will only be able to download to their devices few kilometers. - Saving & updating should first change local information, plus create an "upload queue" to send this information to the server via WS calls - Updating the local database for records that have been changed locally should only happen after they have been properly updated in the server (the queue has been emptied). - A new page should be added to the app to manage pending "upload queue" messages, as well as for checking current download status. Please don't hesitate to propose variations of the above idea. We are also interested in further developing this app, so if we find a good freelancer for this project, we would go on working with him or her on future developments.