implement an ETL GenServer to orchestrate and automate archiving

[boonious]

Lastfm Archive currently provides a discrete set of "one-off" manual archiving functions, archive/1 all scrobbles including the latest one or archive/2 scrobbles of specific date range. It also provides functions to transform raw data into TSV files which can be loaded (imported) into Solr for querying.

These functions can be put into a use context via a GenServer to facilitate lifecycle of an ongoing archiving/ETL process, i.e. continuous and automatic archiving of latest scrobbles. It would also underpin other background processes such as data consolidation and backing up into files of other formats. The server can also be used to provide periodic reporting of basic Lastfm scrobble stats (later iterations).

Tasks

• update Lastfm Archive so that it makes use of Elixir/Erlang OTP capability: setting a supervision tree and a GenServer
• implement GenServer callback and client function that will initiate archiving on startup and on demand
• implement GenServer callback and client function for periodic archiving and syncing of latest scrobbles