sudocode

# a noble start!
make server socket (say which port to accept connections on) for clients
make server socket for info providers
make a list of challenged data-providers
make a list of accepted data-providers
make a list of clients
make a list of ALL SOCKETS. Server sockets, clients, data providers,
*everything*.

make some sort of efficient data structure to keep spawn info in. Big enough to
keep the last <maximum pokemon spawn duration> minutes of spawns logged.

make an associative data structure associating clients with subscriptions and
how up-to-date they are on each pokemon type.

in a loop as long as the server runs...
    wait until something new happens with ALL SOCKETS.
    # A socket represents an endpoint of a connection. This can be what is
    # called a "server" socket (represents the "us" end of a connection) or what's
    # just called a plain old "socket" (represents the "them" end of a
    # connection). There should be functions that let you "wait" on a list of
    # sockets (that is, the function will block until any of them have something
    # new). In classic unix sockets, this is called select()
    # https://en.wikipedia.org/wiki/Berkeley_sockets#Socket_API_functions

    # Okay, so we know something has happened now! It might be a new client
    # giving us data, or it might be a new client to give data to. Or a client
    # might have disconnected.

    Check for disconnected sockets. Remove them from their associated lists and
    ALL SOCKETS, as well as the associative data structure.

    Check for new data-providers, challenge them, and add them to the challenged
    list (and the list of ALL SOCKETS).

    Check for a response from data-providers that have been challenged.
    if they succeeded, then
       move them to the list of accepted data-providers and tell them about our
       subscriptions (the kinds of pokemon we wanna see).
    otherwise
       throw them away (close the connection, remove them from ALL SOCKETS and
       the challenged data-providers).
    Of course, if they haven't answered, don't do anything.

    Check for new clients and happily add any newbies to the list of clients
    (and the list of ALL SOCKETS).

    Check if accepted data-providers have any new info, if so, store
    it. Optionally, if we wanna do a lot of analysis, store it in a database as
    well. Feel free to overwrite data older than <maximum pokemon spawn
    duration> in our shorter-term data structure. Send all new data to all
    clients according to their subscriptions (if they don't have one, don't send
    anything) and update how up-to-date they are for each pokemon type.

    Check if clients have any subscription info to give and update it if they
    do. For each new pokemon they're subscribed to, bring them up-to-date.