-module(prometheus_process_collector).
-if(?OTP_RELEASE >= 27).
-define(MODULEDOC(Str), -moduledoc(Str)).
-define(DOC(Str), -doc(Str)).
-else.
-define(MODULEDOC(Str), -compile([])).
-define(DOC(Str), -compile([])).
-endif.
?MODULEDOC("Prometheus OS process collector API").

-on_load(init/0).
-nifs([get_process_info/0]).
-export([deregister_cleanup/1, collect_mf/2, collect_metrics/2]).
-export([get_process_info/0]).

-behaviour(prometheus_collector).

-define(APPNAME, prometheus_process_collector).
-define(LIBNAME, prometheus_process_collector).

-define(METRICS, [
    {process_open_fds, gauge, "Number of open file descriptors."},
    {process_max_fds, gauge, "Maximum number of open file descriptors."},
    {process_start_time_seconds, gauge, "Start time of the process since unix epoch in seconds."},
    {process_uptime_seconds, counter, "Process uptime in seconds."},
    {process_threads_total, gauge, "Process Threads count."},
    {process_virtual_memory_bytes, gauge, "Virtual memory size in bytes."},
    {process_resident_memory_bytes, gauge, "Resident memory size in bytes."},
    {process_cpu_seconds_total, counter, "Process CPU seconds total.", fun(Info) ->
        prometheus_model_helpers:counter_metrics([
            {[{kind, utime}], proplists:get_value(process_utime_seconds, Info)},
            {[{kind, stime}], proplists:get_value(process_stime_seconds, Info)}
        ])
    end},
    {process_max_resident_memory_bytes, gauge, "Maximum resident set size used."},
    {process_noio_pagefaults_total, counter,
        "Number of page faules serviced without any I/O activity."},
    {process_io_pagefaults_total, counter,
        "Number of page faults serviced that required I/O activity."},
    {process_swaps_total, counter, "Number of times a process was \"swapped\" out of main memory."},
    {process_disk_reads_total, counter, "Number of times the file system had to perform input."},
    {process_disk_writes_total, counter, "Number of times the file system had to perform output."},
    {process_signals_delivered_total, counter, "Number of signals delivered."},
    {process_voluntary_context_switches_total, counter,
        "Number of times a context switch resulted due to a "
        "process voluntarily giving up the processor."},
    {process_involuntary_context_switches_total, counter,
        "Number of times a context switch resulted due to a "
        "higher priority process becoming runnable or because the "
        "current process exceeded its time slice."}
]).

%%====================================================================
%% Collector API
%%====================================================================

?DOC("Deregister collector. No cleanup logic needed.").
-spec deregister_cleanup(Registry) -> ok when
    Registry :: prometheus_registry:registry().
deregister_cleanup(_) ->
    ok.

?DOC("Calls `Callback` for each `MetricFamily` of this collector").
-spec collect_mf(Registry, Callback) -> ok when
    Registry :: prometheus_registry:registry(),
    Callback :: prometheus_collector:collect_mf_callback().
collect_mf(_Registry, Callback) ->
    ProcessInfo = get_process_info(),
    [mf(Callback, Metric, ProcessInfo) || Metric <- ?METRICS],
    ok.

?DOC("Returns Metric list for each MetricFamily identified by `Name`.").
-spec collect_metrics(Name, Data) -> Metrics when
    Name :: prometheus_metric:name(),
    Data :: prometheus_collector:data(),
    Metrics :: prometheus_model:'Metric'() | [prometheus_model:'Metric'()].
collect_metrics(_, {Fun, Proplist}) ->
    Fun(Proplist).

mf(Callback, Metric, Proplist) ->
    {Name, Type, Help, Fun} =
        case Metric of
            {Key, Type1, Help1} ->
                {Key, Type1, Help1, fun(Proplist1) ->
                    metric(Type1, [], proplists:get_value(Key, Proplist1))
                end};
            {Key, Type1, Help1, Fun1} ->
                {Key, Type1, Help1, Fun1}
        end,
    Callback(prometheus_model_helpers:create_mf(Name, Help, Type, ?MODULE, {Fun, Proplist})).

%%====================================================================
%% Private Parts
%%====================================================================

metric(counter, Labels, Value) ->
    prometheus_model_helpers:counter_metric(Labels, Value);
metric(gauge, Labels, Value) ->
    prometheus_model_helpers:gauge_metric(Labels, Value).

?DOC("Get process info callback").
-spec get_process_info() -> proplists:proplist().
get_process_info() ->
    erlang:nif_error("NIF library not loaded").

init() ->
    SoName =
        case code:priv_dir(?APPNAME) of
            {error, bad_name} ->
                case filelib:is_dir(filename:join(["..", priv])) of
                    true ->
                        filename:join(["..", priv, ?LIBNAME]);
                    _ ->
                        filename:join([priv, ?LIBNAME])
                end;
            Dir ->
                filename:join(Dir, ?LIBNAME)
        end,
    erlang:load_nif(SoName, 0).