-module(tbray_qsort).
-export([start/2]).

find_match("/ongoing/When/" ++ Last, Matches) ->
    case lists:member($., Last) of
        false -> Matches ++ [Last];
        true -> Matches
    end;
find_match(_, Matches) -> Matches.

process_binary(Pid, Bin) ->
    spawn(fun() ->
        L = string:tokens(binary_to_list(Bin), "\n"),
        V = lists:foldl(
            fun(Line, Matches) ->
                find_match(lists:nth(7, string:tokens(Line, " ")), Matches) end,
            [], L),
        Pid ! V
        end).

split_on_newline(Bin, N, All) when size(Bin) < N ->
    All ++ [Bin];
split_on_newline(Bin, N, All) ->
    {_, <<C:8, _/binary>>} = split_binary(Bin, N),
    case C of
        $\n ->
          {B21, B22} = split_binary(Bin, N+1),
          split_on_newline(B22, N, All ++ [B21]);
        _ -> split_on_newline(Bin, N+1, All)
    end.
split_on_newline(Bin, N) when N == size(Bin) -> [Bin];
split_on_newline(Bin, N) -> split_on_newline(Bin, N, []).

sort([Pivot|T]) ->
    sort([ X || X <- T, X < Pivot]) ++
    [Pivot] ++
    sort([ X || X <- T, X >= Pivot]);
sort([]) -> [].


-record(count, {url, hits}).

sort_count([Pivot|T]) ->
    sort_count([ X || X <- T, X#count.hits >= Pivot#count.hits]) ++
    [Pivot] ++
    sort_count([ X || X <- T, X#count.hits < Pivot#count.hits]);
sort_count([]) -> [].


start(Num, Input) ->
    {ok, Data} = file:read_file(Input),
    Bins = split_on_newline(Data, size(Data) div Num),
    Me = self(),
    Pids = [process_binary(Me, B) || B <- Bins],
    {Counts, _, _} = lists:foldl(
        fun(Url, S) -> {Counts, Last, LastCount} = S,
            if
                Url == Last -> {Counts, Url, LastCount + 1};
                true -> { Counts ++ [#count{hits = LastCount, url = Last}], Url, 1 }
        end end, {[], [], 0}, sort(lists:foldl(
        fun(_, Total) -> receive X -> Total ++ X end end,
        [], Pids))++[[]]),
    {Popular, _} = lists:split(10, sort_count(Counts)),
    lists:foreach(fun(X) -> io:format("~w : ~s~n", [X#count.hits, X#count.url]) end, Popular).