reset / fix broken/partial download of dictionary

[megahirt]

I have observed users who only received part of the dictionary to the client due to flaky/inconsistent internet. This results in a broken language forge for the user which they cannot fix by themselves without using the Dev Tools and clearing the IndexDB cache. What they experience is that the number of entries is less on their install vs the actual number of entries (some failed to download).

The current code uses a timestamp to determine if it should download all the dictionary or just updates since a timestamp.

Possible solutions:

• Evaluate if the number of entries on the client is equal to the number of entries on the server. If they are not equal, delete the timestamp and redownload.
• Don't save the timestamp on download until it is confirmed that the entries are equal on client and server.

[rmunn]

Number of entries should be simple to calculate, as array length is an O(1) operation in Javascript (and should be O(1) in PHP as well, though we'd have to make sure that our PHP array wasn't some instance of a class where count() has to iterate through it to obtain the count. A simple PHP array can be counted in O(1) time, but if we somehow end up with a Mongo query result object that has to pull in all the results to do a count() then it would be inefficient).

[megahirt]

The title of this issue points suggests that we need a button in settings to "fix" the problem for users where this happens occasionally. But it would be nice if the app was more robust in the first place that this just doesn't happen. That's where my suggestions come into play. I have done user support before for users who got their browser into a partial-dictionary state where the only solution was to delete the browser application cache (IndexDB) and start over. That resolves it.