% 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_view_all_docs).

-export([go/5]).
-export([open_doc/4]). % exported for spawn

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

go(DbName, Options, #mrargs{keys=undefined} = QueryArgs, Callback, Acc0) ->
    Workers = fabric_util:submit_jobs(mem3:shards(DbName),all_docs,[Options, QueryArgs]),
    #mrargs{limit = Limit, skip = Skip} = QueryArgs,
    State = #collector{
        query_args = QueryArgs,
        callback = Callback,
        counters = fabric_dict:init(Workers, 0),
        skip = Skip,
        limit = Limit,
        user_acc = Acc0
    },
    RexiMon = fabric_util:create_monitors(Workers),
    try rexi_utils:recv(Workers, #shard.ref, fun handle_message/3,
        State, infinity, 5000) of
    {ok, NewState} ->
        {ok, NewState#collector.user_acc};
    {timeout, NewState} ->
        Callback({error, timeout}, NewState#collector.user_acc);
    {error, Resp} ->
        {ok, Resp}
    after
        rexi_monitor:stop(RexiMon),
        fabric_util:cleanup(Workers)
    end;


go(DbName, Options, QueryArgs, Callback, Acc0) ->
    #mrargs{
        direction = Dir,
        include_docs = IncludeDocs,
        limit = Limit,
        skip = Skip,
        keys = Keys0
    } = QueryArgs,
    {_, Ref0} = spawn_monitor(fun() -> exit(fabric:get_doc_count(DbName)) end),
    SpawnFun = fun(Key) ->
        spawn_monitor(?MODULE, open_doc, [DbName, Options, Key, IncludeDocs])
    end,
    MaxJobs = all_docs_concurrency(),
    Keys1 = case Dir of
        fwd -> Keys0;
        _ -> lists:reverse(Keys0)
    end,
    Keys2 = case Skip < length(Keys1) of
        true -> lists:nthtail(Skip, Keys1);
        false -> []
    end,
    Keys3 = case Limit < length(Keys2) of
        true -> lists:sublist(Keys2, Limit);
        false -> Keys2
    end,
    receive {'DOWN', Ref0, _, _, {ok, TotalRows}} ->
        {ok, Acc1} = Callback({meta, [{total, TotalRows}]}, Acc0),
        {ok, Acc2} = doc_receive_loop(
            Keys3, queue:new(), SpawnFun, MaxJobs, Callback, Acc1
        ),
        Callback(complete, Acc2)
    after 10000 ->
        Callback(timeout, Acc0)
    end.

handle_message({rexi_DOWN, _, {_, NodeRef}, _}, _, State) ->
    fabric_view:remove_down_shards(State, NodeRef);

handle_message({rexi_EXIT, Reason}, Worker, State) ->
    #collector{callback=Callback, counters=Counters0, user_acc=Acc} = State,
    Counters = fabric_dict:erase(Worker, Counters0),
    case fabric_view:is_progress_possible(Counters) of
    true ->
        {ok, State#collector{counters = Counters}};
    false ->
        {ok, Resp} = Callback({error, fabric_util:error_info(Reason)}, Acc),
        {error, Resp}
    end;

handle_message({meta, Meta0}, {Worker, From}, State) ->
    Tot = couch_util:get_value(total, Meta0, 0),
    Off = couch_util:get_value(offset, Meta0, 0),
    #collector{
        callback = Callback,
        counters = Counters0,
        total_rows = Total0,
        offset = Offset0,
        user_acc = AccIn
    } = State,
    case fabric_dict:lookup_element(Worker, Counters0) of
    undefined ->
        % this worker lost the race with other partition copies, terminate
        gen_server:reply(From, stop),
        {ok, State};
    0 ->
        gen_server:reply(From, ok),
        Counters1 = fabric_dict:update_counter(Worker, 1, Counters0),
        Counters2 = fabric_view:remove_overlapping_shards(Worker, Counters1),
        Total = Total0 + Tot,
        Offset = Offset0 + Off,
        case fabric_dict:any(0, Counters2) of
        true ->
            {ok, State#collector{
                counters = Counters2,
                total_rows = Total,
                offset = Offset
            }};
        false ->
            FinalOffset = erlang:min(Total, Offset+State#collector.skip),
            Meta = [{total, Total}, {offset, FinalOffset}],
            {Go, Acc} = Callback({meta, Meta}, AccIn),
            {Go, State#collector{
                counters = fabric_dict:decrement_all(Counters2),
                total_rows = Total,
                offset = FinalOffset,
                user_acc = Acc
            }}
        end
    end;

handle_message(#view_row{} = Row, {Worker, From}, State) ->
    #collector{query_args = Args, counters = Counters0, rows = Rows0} = State,
    Dir = Args#mrargs.direction,
    Rows = merge_row(Dir, Row#view_row{worker={Worker, From}}, Rows0),
    Counters1 = fabric_dict:update_counter(Worker, 1, Counters0),
    State1 = State#collector{rows=Rows, counters=Counters1},
    fabric_view:maybe_send_row(State1);

handle_message(complete, Worker, State) ->
    Counters = fabric_dict:update_counter(Worker, 1, State#collector.counters),
    fabric_view:maybe_send_row(State#collector{counters = Counters}).


merge_row(fwd, Row, Rows) ->
    lists:keymerge(#view_row.id, [Row], Rows);
merge_row(rev, Row, Rows) ->
    lists:rkeymerge(#view_row.id, [Row], Rows).

all_docs_concurrency() ->
    Value = config:get("fabric", "all_docs_concurrency", "10"),
    try
        list_to_integer(Value)
    catch _:_ ->
        10
    end.

doc_receive_loop(Keys, Pids, SpawnFun, MaxJobs, Callback, AccIn) ->
    case {Keys, queue:len(Pids)} of
    {[], 0} ->
        {ok, AccIn};
    {[K | RKeys], Len} when Len < MaxJobs ->
        Pids1 = queue:in(SpawnFun(K), Pids),
        doc_receive_loop(RKeys, Pids1, SpawnFun, MaxJobs, Callback, AccIn);
    _ ->
        {{value, {Pid, Ref}}, RestPids} = queue:out(Pids),
        receive {'DOWN', Ref, process, Pid, #view_row{} = Row} ->
            case Callback(fabric_view:transform_row(Row), AccIn) of
            {ok, Acc} ->
                doc_receive_loop(
                    Keys, RestPids, SpawnFun, MaxJobs, Callback, Acc
                );
            {stop, Acc} ->
                cancel_read_pids(RestPids),
                {ok, Acc}
            end
        after 10000 ->
            timeout
        end
    end.

open_doc(DbName, Options, Id, IncludeDocs) ->
    Row = case fabric:open_doc(DbName, Id, [deleted | Options]) of
    {not_found, missing} ->
        Doc = undefined,
        #view_row{key=Id};
    {ok, #doc{deleted=true, revs=Revs}} ->
        Doc = null,
        {RevPos, [RevId|_]} = Revs,
        Value = {[{rev,couch_doc:rev_to_str({RevPos, RevId})}, {deleted,true}]},
        #view_row{key=Id, id=Id, value=Value};
    {ok, #doc{revs=Revs} = Doc0} ->
        Doc = couch_doc:to_json_obj(Doc0, []),
        {RevPos, [RevId|_]} = Revs,
        Value = {[{rev,couch_doc:rev_to_str({RevPos, RevId})}]},
        #view_row{key=Id, id=Id, value=Value}
    end,
    exit(if IncludeDocs -> Row#view_row{doc=Doc}; true -> Row end).

cancel_read_pids(Pids) ->
    case queue:out(Pids) of
        {{value, {Pid, Ref}}, RestPids} ->
            exit(Pid, kill),
            erlang:demonitor(Ref, [flush]),
            cancel_read_pids(RestPids);
        {empty, _} ->
            ok
    end.