% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License. You may obtain a copy of
% the License at
%
%   http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.

-module(fabric_db_doc_count).

-export([go/1]).

-include_lib("fabric/include/fabric.hrl").
-include_lib("mem3/include/mem3.hrl").
-include_lib("couch/include/couch_db.hrl").

go(DbName) ->
    Shards = mem3:shards(DbName),
    Workers = fabric_util:submit_jobs(Shards, get_doc_count, []),
    RexiMon = fabric_util:create_monitors(Shards),
    Acc0 = {fabric_dict:init(Workers, nil), 0},
    try
        fabric_util:recv(Workers, #shard.ref, fun handle_message/3, Acc0)
    after
        rexi_monitor:stop(RexiMon)
    end.

handle_message({rexi_DOWN, _, {_,NodeRef},_}, _Shard, {Counters, Acc}) ->
    case fabric_util:remove_down_workers(Counters, NodeRef) of
    {ok, NewCounters} ->
        {ok, {NewCounters, Acc}};
    error ->
        {error, {nodedown, <<"progress not possible">>}}
    end;

handle_message({rexi_EXIT, Reason}, Shard, {Counters, Acc}) ->
    NewCounters = lists:keydelete(Shard, #shard.ref, Counters),
    case fabric_view:is_progress_possible(NewCounters) of
    true ->
        {ok, {NewCounters, Acc}};
    false ->
        {error, Reason}
    end;

handle_message({ok, Count}, Shard, {Counters, Acc}) ->
    case fabric_dict:lookup_element(Shard, Counters) of
    undefined ->
        % already heard from someone else in this range
        {ok, {Counters, Acc}};
    nil ->
        C1 = fabric_dict:store(Shard, ok, Counters),
        C2 = fabric_view:remove_overlapping_shards(Shard, C1),
        case fabric_dict:any(nil, C2) of
        true ->
            {ok, {C2, Count+Acc}};
        false ->
            {stop, Count+Acc}
        end
    end;
handle_message(_, _, Acc) ->
    {ok, Acc}.