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-module(fabric_view).
-export([is_progress_possible/1, remove_overlapping_shards/2, maybe_send_row/1,
maybe_pause_worker/3, maybe_resume_worker/2, transform_row/1, keydict/1]).
-include("fabric.hrl").
%% @doc looks for a fully covered keyrange in the list of counters
-spec is_progress_possible([{#shard{}, non_neg_integer()}]) -> boolean().
is_progress_possible(Counters) ->
Ranges = fabric_dict:fold(fun(#shard{range=[X,Y]}, _, A) -> [{X,Y}|A] end,
[], Counters),
[First | Rest] = lists:ukeysort(1, Ranges),
{Head, Tail} = lists:foldl(fun
(_, {Head, Tail}) when Head =:= Tail ->
% this is the success condition, we can fast-forward
{Head, Tail};
(_, {foo, bar}) ->
% we've already declared failure
{foo, bar};
({X,_}, {Head, Tail}) when Head < Tail, X > Tail ->
% gap in the keyrange, we're dead
{foo, bar};
({X,Y}, {Head, Tail}) when Head < Tail, X < Y ->
% the normal condition, adding to the tail
{Head, erlang:max(Tail, Y)};
({X,Y}, {Head, Tail}) when Head < Tail, X > Y, Y >= Head ->
% we've wrapped all the way around, trigger success condition
{Head, Head};
({X,Y}, {Head, Tail}) when Head < Tail, X > Y ->
% this wraps the keyspace, but there's still a gap. We're dead
% TODO technically, another shard could be a superset of this one, and
% we could still be alive. Pretty unlikely though, and impossible if
% we don't allow shards to wrap around the boundary
{foo, bar}
end, First, Rest),
Head =:= Tail.
-spec remove_overlapping_shards(#shard{}, [#shard{}]) -> [#shard{}].
remove_overlapping_shards(#shard{range=[A,B]} = Shard0, Shards) ->
fabric_dict:filter(fun(#shard{range=[X,Y]} = Shard, _Value) ->
if Shard =:= Shard0 ->
% we can't remove ourselves
true;
A < B, X >= A, X < B ->
% lower bound is inside our range
false;
A < B, Y > A, Y =< B ->
% upper bound is inside our range
false;
B < A, X >= A orelse B < A, X < B ->
% target shard wraps the key range, lower bound is inside
false;
B < A, Y > A orelse B < A, Y =< B ->
% target shard wraps the key range, upper bound is inside
false;
true ->
true
end
end, Shards).
maybe_pause_worker(Worker, From, State) ->
#collector{buffer_size = BufferSize, counters = Counters} = State,
case fabric_dict:lookup_element(Worker, Counters) of
BufferSize ->
State#collector{blocked = [{Worker,From} | State#collector.blocked]};
_Count ->
gen_server:reply(From, ok),
State
end.
maybe_resume_worker(Worker, State) ->
#collector{buffer_size = Buffer, counters = C, blocked = B} = State,
case fabric_dict:lookup_element(Worker, C) of
Count when Count < Buffer/2 ->
case couch_util:get_value(Worker, B) of
undefined ->
State;
From ->
gen_server:reply(From, ok),
State#collector{blocked = lists:keydelete(Worker, 1, B)}
end;
_Other ->
State
end.
maybe_send_row(#collector{limit=0} = State) ->
#collector{user_acc=AccIn, callback=Callback} = State,
{_, Acc} = Callback(complete, AccIn),
{stop, State#collector{user_acc=Acc}};
maybe_send_row(State) ->
#collector{
callback = Callback,
counters = Counters,
skip = Skip,
limit = Limit,
user_acc = AccIn
} = State,
case fabric_dict:any(0, Counters) of
true ->
{ok, State};
false ->
case get_next_row(State) of
complete ->
{_, Acc} = Callback(complete, AccIn),
{stop, State#collector{user_acc=Acc}};
{_, NewState} when Skip > 0 ->
maybe_send_row(NewState#collector{skip=Skip-1, limit=Limit-1});
{Row, NewState} ->
case Callback(transform_row(Row), AccIn) of
{stop, Acc} ->
{stop, NewState#collector{user_acc=Acc, limit=Limit-1}};
{ok, Acc} ->
maybe_send_row(NewState#collector{user_acc=Acc, limit=Limit-1})
end
end
end.
keydict(nil) ->
undefined;
keydict(Keys) ->
{Dict,_} = lists:foldl(fun(K, {D,I}) -> {dict:store(K,I,D), I+1} end,
{dict:new(),0}, Keys),
Dict.
%% internal %%
get_next_row(#collector{rows = []}) ->
complete;
get_next_row(State) ->
#collector{
rows = [Row|Rest],
counters = Counters0,
stop_fun = Stop
} = State,
Worker = Row#view_row.worker,
Counters1 = fabric_dict:update_counter(Worker, -1, Counters0),
NewState = maybe_resume_worker(Worker, State#collector{counters=Counters1}),
case Stop(Row) of
true ->
complete;
false ->
{Row, NewState#collector{rows = Rest}}
end.
transform_row(#view_row{key=Key, id=undefined}) ->
{row, {[{key,Key}, {error,not_found}]}};
transform_row(#view_row{key=Key, id=Id, value=Value, doc=undefined}) ->
{row, {[{key,Key}, {id,Id}, {value,Value}]}};
transform_row(#view_row{key=Key, id=Id, value=Value, doc={error,Reason}}) ->
{row, {[{key,Key}, {id,Id}, {value,Value}, {error,Reason}]}};
transform_row(#view_row{key=Key, id=Id, value=Value, doc=Doc}) ->
{row, {[{key,Key}, {id,Id}, {value,Value}, {doc,Doc}]}}.
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