Delete Parse duplicated Installation object for Android app

readme

Context:

When you install an app on Android, it creates an entry (Installation) in the database.
If you uninstall the app, then re-install it, another entry is created. If you subscribe to a channel, you'll get 2 push notifications.

On iOS, this problem doesn't exist, and with UrbanAirship, there's no problem either.

Solution:

The idea is to remove all the entries that matches a "unique Id" created for each device.
Gist based on [this post](https://www.parse.com/questions/check-for-duplicate-installations-of-same-user-on-re-installation-of-app)

I chose to use the Wifi mac address as unique key, because based on [that post](http://stackoverflow.com/questions/2785485/is-there-a-unique-android-device-id),
there's no good way to get a unique Id.

Application.java

// Android app
private void setupParse(Context context) {
  Parse.initialize(this, <PARSE_APP_ID>, <PARSE_CLIENT_KEY>);
  ParseInstallation.getCurrentInstallation().put("uniqueId", getWifiMacAddress(context));
  ParseInstallation.getCurrentInstallation().saveInBackground();
}

private String getWifiMacAddress(Context context) {
  WifiManager wifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
  if (wifiManager != null && wifiManager.getConnectionInfo() != null) {
      return wifiManager.getConnectionInfo().getMacAddress();
  }

  return "";
}

main.js

// Parse CloudCode
Parse.Cloud.beforeSave(Parse.Installation, function(request, response) {
  Parse.Cloud.useMasterKey();

  var uniqueId = request.object.get("uniqueId");
  if (uniqueId == null || uniqueId == "") {
    console.warn("No uniqueId found, exit");
    response.success();
  }

  var query = new Parse.Query(Parse.Installation);
  query.equalTo("uniqueId", uniqueId);
  query.addAscending("createdAt");
  query.find().then(function(results) {
    for (var i = 0; i < results.length; ++i) {
      if (results[i].get("installationId") != request.object.get("installationId")) {
        console.warn("App id " + results[i].get("installationId") + ", delete!");
        results[i].destroy().then(function() {
            console.warn("Delete success");
          },
          function() {
            console.warn("Delete error");
          }
        );
      } else {
        console.warn("Current App id " + results[i].get("installationId") + ", dont delete");
      }
    }
    response.success();
    },
    function(error) {
      response.error("Can't find Installation objects");
    }
  );
});