% 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(couch_index_compactor).
-behaviour(gen_server).

%% API
-export([start_link/2, run/2, cancel/1, is_running/1, get_compacting_pid/1]).

%% gen_server callbacks
-export([init/1, terminate/2, code_change/3]).
-export([handle_call/3, handle_cast/2, handle_info/2]).

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

-record(st, {
    idx,
    mod,
    pid
}).

start_link(Index, Module) ->
    gen_server:start_link(?MODULE, {Index, Module}, []).

run(Pid, IdxState) ->
    gen_server:call(Pid, {compact, IdxState}).

cancel(Pid) ->
    gen_server:call(Pid, cancel).

is_running(Pid) ->
    gen_server:call(Pid, is_running).

get_compacting_pid(Pid) ->
    gen_server:call(Pid, get_compacting_pid).

init({Index, Module}) ->
    process_flag(trap_exit, true),
    {ok, #st{idx = Index, mod = Module}}.

terminate(_Reason, State) ->
    couch_util:shutdown_sync(State#st.pid),
    ok.

handle_call({compact, _}, _From, #st{pid = Pid} = State) when is_pid(Pid) ->
    {reply, {ok, Pid}, State};
handle_call({compact, IdxState}, _From, #st{idx = Idx} = State) ->
    Pid = spawn_link(fun() -> compact(Idx, State#st.mod, IdxState) end),
    {reply, {ok, Pid}, State#st{pid = Pid}};
handle_call(cancel, _From, #st{pid = undefined} = State) ->
    {reply, ok, State};
handle_call(cancel, _From, #st{pid = Pid} = State) ->
    unlink(Pid),
    exit(Pid, kill),
    {reply, ok, State#st{pid = undefined}};
handle_call(get_compacting_pid, _From, #st{pid = Pid} = State) ->
    {reply, {ok, Pid}, State};
handle_call(is_running, _From, #st{pid = Pid} = State) when is_pid(Pid) ->
    {reply, true, State};
handle_call(is_running, _From, State) ->
    {reply, false, State}.

handle_cast(_Mesg, State) ->
    {stop, unknown_cast, State}.

handle_info({'EXIT', Pid, normal}, #st{pid = Pid} = State) ->
    {noreply, State#st{pid = undefined}};
handle_info({'EXIT', Pid, Reason}, #st{pid = Pid} = State) ->
    #st{idx = Idx, mod = Mod} = State,
    {ok, IdxState} = gen_server:call(Idx, {compaction_failed, Reason}),
    DbName = Mod:get(db_name, IdxState),
    IdxName = Mod:get(idx_name, IdxState),
    Args = [DbName, IdxName, Reason],
    couch_log:error("Compaction failed for db: ~s idx: ~s reason: ~p", Args),
    {noreply, State#st{pid = undefined}};
handle_info({'EXIT', _Pid, normal}, State) ->
    {noreply, State};
handle_info({'EXIT', Pid, _Reason}, #st{idx = Pid} = State) ->
    {stop, normal, State};
handle_info(_Mesg, State) ->
    {stop, unknown_info, State}.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

compact(Parent, Mod, IdxState) ->
    DbName = Mod:get(db_name, IdxState),
    %% We use with_db here to make sure we hold db open
    %% during both phases of compaction
    %%  * compact
    %%  * recompact
    couch_util:with_db(DbName, fun(_) ->
        compact(Parent, Mod, IdxState, [])
    end).

compact(Idx, Mod, IdxState, Opts) ->
    DbName = Mod:get(db_name, IdxState),
    IndexName = Mod:get(idx_name, IdxState),
    erlang:put(io_priority, {view_compact, DbName, IndexName}),
    Args = [DbName, Mod:get(idx_name, IdxState)],
    couch_log:info("Compaction started for db: ~s idx: ~s", Args),
    {ok, NewIdxState} = couch_util:with_db(DbName, fun(Db) ->
        Mod:compact(Db, IdxState, Opts)
    end),
    ok = Mod:commit(NewIdxState),
    case gen_server:call(Idx, {compacted, NewIdxState}) of
        recompact ->
            couch_log:info("Compaction restarting for db: ~s idx: ~s", Args),
            compact(Idx, Mod, NewIdxState, [recompact]);
        _ ->
            couch_log:info("Compaction finished for db: ~s idx: ~s", Args),
            ok
    end.