% 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_task_status).
-behaviour(gen_server).

% This module allows is used to track the status of long running tasks.
% Long running tasks register (add_task/3) then update their status (update/1)
% and the task and status is added to tasks list. When the tracked task dies
% it will be automatically removed the tracking. To get the tasks list, use the
% all/0 function

-export([start_link/0,init/1,terminate/2,handle_call/3,handle_cast/2,handle_info/2,
    code_change/3,add_task/3,update/1,update/2,all/0,set_update_frequency/1]).

-include("couch_db.hrl").
    
start_link() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

to_binary(L) when is_list(L) ->
    ?l2b(L);
to_binary(B) when is_binary(B) ->
    B.

add_task(Type, TaskName, StatusText) ->
    put(task_status_update, {{0,0,0}, 0}),
    gen_server:call(?MODULE, {add_task, to_binary(Type),
            to_binary(TaskName), to_binary(StatusText)}).

set_update_frequency(Msecs) ->
    put(task_status_update, {{0,0,0}, Msecs * 1000}).

update(StatusText) ->
    update("~s", [StatusText]).
    
update(Format, Data) ->
    {LastUpdateTime, Frequency} = get(task_status_update),
    
    case timer:now_diff(Now = now(), LastUpdateTime) >= Frequency of
    true ->
        put(task_status_update, {Now, Frequency}),
        gen_server:cast(?MODULE, {update_status, self(), ?l2b(io_lib:format(Format, Data))});
    false ->
        ok
    end.
    

% returns a list of proplists. Each proplist describes a running task.
all() ->
    [[{type,Type},
        {task,Task},
        {status,Status},
        {pid,?l2b(pid_to_list(Pid))}] ||
            {Pid, {Type,Task,Status}} <- ets:tab2list(tasks_by_pid)].
    
init([]) ->
    % read configuration settings and register for configuration changes
    ets:new(tasks_by_pid, [ordered_set, protected, named_table]),
    {ok, nil}.

terminate(_Reason,_State) ->
    ok.


handle_call({add_task,Type,TaskName,StatusText}, {From, _}, Server) ->
    case ets:lookup(tasks_by_pid, From) of
    [] ->
        true = ets:insert(tasks_by_pid, {From,{Type,TaskName,StatusText}}),
        erlang:monitor(process, From),
        {reply, ok, Server};
    [_] ->
        {reply, {add_task_error, already_registered}, Server}
    end.
    
handle_cast({update_status, Pid, StatusText}, Server) ->
    [{Pid, {Type,TaskName,_StatusText}}] = ets:lookup(tasks_by_pid, Pid),
    true = ets:insert(tasks_by_pid, {Pid, {Type,TaskName,StatusText}}),
    {noreply, Server}.

handle_info({'DOWN', _MonitorRef, _Type, Pid, _Info}, Server) ->
    ets:delete(tasks_by_pid, Pid),
    {noreply, Server}.

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