-module(prometheus_summary).
-compile({parse_transform, prometheus_pt}).
-moduledoc """
Summary metric, to track the size of events.

Example use cases for Summaries: - Response latency; - Request size; - Response size.

Example:

```erlang
-module(my_proxy_instrumenter).

setup() ->
    prometheus_summary:declare([{name, request_size_bytes},
                                {help, \"Request size in bytes.\"}]),
    prometheus_summary:declare([{name, response_size_bytes},
                                {help, \"Response size in bytes.\"}]).

observe_request(Size) ->
    prometheus_summary:observe(request_size_bytes, Size).

observe_response(Size) ->
    prometheus_summary:observe(response_size_bytes, Size).

```
""".

%%% metric
-export([
    new/1,
    declare/1,
    deregister/1,
    deregister/2,
    set_default/2,
    observe/2,
    observe/3,
    observe/4,
    observe_duration/2,
    observe_duration/3,
    observe_duration/4,
    remove/1,
    remove/2,
    remove/3,
    reset/1,
    reset/2,
    reset/3,
    value/1,
    value/2,
    value/3,
    values/2
]).

%%% collector
-export([
    deregister_cleanup/1,
    collect_mf/2,
    collect_metrics/2
]).

-include("prometheus.hrl").

-behaviour(prometheus_metric).
-behaviour(prometheus_collector).

-define(TABLE, ?PROMETHEUS_SUMMARY_TABLE).
-define(ISUM_POS, 3).
-define(FSUM_POS, 4).
-define(COUNTER_POS, 2).
-define(WIDTH, 16).

-type conflict_cb() :: fun(
    (
        prometheus_registry:registry(),
        prometheus_metric:name(),
        prometheus_metric:labels(),
        number()
    ) -> ok
).

-doc """
Creates a summary using `Spec`.

Raises:
* `{missing_metric_spec_key, Key, Spec}` error if required `Spec` key is missing.
* `{invalid_metric_name, Name, Message}` error if metric `Name` is invalid.
* `{invalid_metric_help, Help, Message}` error if metric `Help` is invalid.
* `{invalid_metric_labels, Labels, Message}` error if `Labels` isn't a list.
* `{invalid_label_name, Name, Message}` error if `Name` isn't a valid label name.
* `{invalid_value_error, Value, Message}` error if `duration_unit` is unknown or doesn't match metric name.
* `{mf_already_exists, {Registry, Name}, Message}` error if a summary with the same `Spec` already exists.
""".
-spec new(prometheus_metric:spec()) -> ok.
new(Spec) ->
    validate_summary_spec(Spec),
    prometheus_metric:insert_new_mf(?TABLE, ?MODULE, Spec).

-doc """
Creates a summary using `Spec`. If a summary with the same `Spec` exists returns `false`.

Raises:
* `{missing_metric_spec_key, Key, Spec}` error if required `Spec` key is missing.
* `{invalid_metric_name, Name, Message}` error if metric `Name` is invalid.
* `{invalid_metric_help, Help, Message}` error if metric `Help` is invalid.
* `{invalid_metric_labels, Labels, Message}` error if `Labels` isn't a list.
* `{invalid_label_name, Name, Message}` error if `Name` isn't a valid label name.
* `{invalid_value_error, Value, MessagE}` error if `duration_unit` is unknown or doesn't match metric name.
""".
-spec declare(prometheus_metric:spec()) -> boolean().
declare(Spec) ->
    Spec1 = validate_summary_spec(Spec),
    prometheus_metric:insert_mf(?TABLE, ?MODULE, Spec1).

-doc #{equiv => deregister(default, Name)}.
-spec deregister(prometheus_metric:name()) -> {boolean(), boolean()}.
deregister(Name) ->
    deregister(default, Name).

-doc """
Removes all summary series with name `Name` and removes Metric Family from `Registry`.

After this call new/1 for `Name` and `Registry` will succeed.

Returns `{true, _}` if `Name` was a registered summary. Otherwise returns `{false, _}`.
""".
-spec deregister(prometheus_registry:registry(), prometheus_metric:name()) ->
    {boolean(), boolean()}.
deregister(Registry, Name) ->
    MFR = prometheus_metric:deregister_mf(?TABLE, Registry, Name),
    NumDeleted = ets:select_delete(?TABLE, deregister_select(Registry, Name)),
    {MFR, NumDeleted > 0}.

-doc false.
-spec set_default(prometheus_registry:registry(), prometheus_metric:name()) -> boolean().
set_default(Registry, Name) ->
    ets:insert_new(?TABLE, {key(Registry, Name, []), 0, 0, 0}).

-doc #{equiv => observe(default, Name, [], Value)}.
-spec observe(prometheus_metric:name(), number()) -> ok.
observe(Name, Value) ->
    observe(default, Name, [], Value).

-doc #{equiv => observe(default, Name, LabelValues, Value)}.
-spec observe(prometheus_metric:name(), prometheus_metric:labels(), number()) -> ok.
observe(Name, LabelValues, Value) ->
    observe(default, Name, LabelValues, Value).

-doc """
Observes the given `Value`.

Raises:
* `{invalid_value, Value, Message}` if `Value` isn't an integer.
* `{unknown_metric, Registry, Name}` error if summary with named `Name` can't be found in `Registry`.
* `{invalid_metric_arity, Present, Expected}` error if labels count mismatch.
""".
-spec observe(Registry, Name, LabelValues, Value) -> ok when
    Registry :: prometheus_registry:registry(),
    Name :: prometheus_metric:name(),
    LabelValues :: prometheus_metric:labels(),
    Value :: number().
observe(Registry, Name, LabelValues, Value) when is_integer(Value) ->
    Key = key(Registry, Name, LabelValues),
    Spec = [{?COUNTER_POS, 1}, {?ISUM_POS, Value}],
    try
        ets:update_counter(?TABLE, Key, Spec)
    catch
        error:badarg ->
            insert_metric(Registry, Name, LabelValues, Value, fun observe/4)
    end,
    ok;
observe(Registry, Name, LabelValues, Value) when is_number(Value) ->
    Key = key(Registry, Name, LabelValues),
    Spec = [{{Key, '$1', '$2', '$3'}, [], [{{{Key}, {'+', '$1', 1}, '$2', {'+', '$3', Value}}}]}],
    case ets:select_replace(?TABLE, Spec) of
        0 ->
            insert_metric(Registry, Name, LabelValues, Value, fun observe/4);
        1 ->
            ok
    end;
observe(_Registry, _Name, _LabelValues, Value) ->
    erlang:error({invalid_value, Value, "observe accepts only numbers"}).

-doc #{equiv => observe_duration(default, Name, [], Fun)}.
-spec observe_duration(prometheus_metric:name(), fun(() -> term())) -> term().
observe_duration(Name, Fun) ->
    observe_duration(default, Name, [], Fun).

-doc #{equiv => observe_duration(default, Name, LabelValues, Fun)}.
-spec observe_duration(prometheus_metric:name(), prometheus_metric:labels(), fun(() -> term())) ->
    term().
observe_duration(Name, LabelValues, Fun) ->
    observe_duration(default, Name, LabelValues, Fun).

-doc """
Tracks the amount of time spent executing `Fun`.

Raises:
* `{unknown_metric, Registry, Name}` error if summary with named `Name` can't be found in `Registry`.
* `{invalid_metric_arity, Present, Expected}` error if labels count mismatch.
* `{invalid_value, Value, Message}` if `Fun` isn't a function.
""".
-spec observe_duration(Registry, Name, LabelValues, Fun) -> any() when
    Registry :: prometheus_registry:registry(),
    Name :: prometheus_metric:name(),
    LabelValues :: prometheus_metric:labels(),
    Fun :: fun(() -> any()).
observe_duration(Registry, Name, LabelValues, Fun) when is_function(Fun) ->
    Start = erlang:monotonic_time(),
    try
        Fun()
    after
        observe(Registry, Name, LabelValues, erlang:monotonic_time() - Start)
    end;
observe_duration(_Regsitry, _Name, _LabelValues, Fun) ->
    erlang:error({invalid_value, Fun, "observe_duration accepts only functions"}).

-doc #{equiv => remove(default, Name, [])}.
-spec remove(prometheus_metric:name()) -> boolean().
remove(Name) ->
    remove(default, Name, []).

-doc #{equiv => remove(default, Name, LabelValues)}.
-spec remove(prometheus_metric:name(), prometheus_metric:labels()) -> boolean().
remove(Name, LabelValues) ->
    remove(default, Name, LabelValues).

-doc """
Removes summary series identified by `Registry`, `Name` and `LabelValues`.

Raises:
* `{unknown_metric, Registry, Name}` error if summary with name `Name` can't be found in `Registry`.
* `{invalid_metric_arity, Present, Expected}` error if labels count mismatch.
""".
-spec remove(prometheus_registry:registry(), prometheus_metric:name(), prometheus_metric:labels()) ->
    boolean().
remove(Registry, Name, LabelValues) ->
    prometheus_metric:check_mf_exists(?TABLE, Registry, Name, LabelValues),
    case
        lists:flatten([
            ets:take(
                ?TABLE,
                {Registry, Name, LabelValues, Scheduler}
            )
         || Scheduler <- schedulers_seq()
        ])
    of
        [] -> false;
        _ -> true
    end.

-doc #{equiv => reset(default, Name, [])}.
-spec reset(prometheus_metric:name()) -> boolean().
reset(Name) ->
    reset(default, Name, []).

-doc #{equiv => reset(default, Name, LabelValues)}.
-spec reset(prometheus_metric:name(), prometheus_metric:labels()) -> boolean().
reset(Name, LabelValues) ->
    reset(default, Name, LabelValues).

-doc """
Resets the value of the summary identified by `Registry`, `Name` and `LabelValues`.

Raises:
* `{unknown_metric, Registry, Name}` error if summary with name `Name` can't be found in `Registry`.
* `{invalid_metric_arity, Present, Expected}` error if labels count mismatch.
""".
-spec reset(prometheus_registry:registry(), prometheus_metric:name(), prometheus_metric:labels()) ->
    boolean().
reset(Registry, Name, LabelValues) ->
    prometheus_metric:check_mf_exists(?TABLE, Registry, Name, LabelValues),
    case
        lists:usort([
            ets:update_element(
                ?TABLE,
                {Registry, Name, LabelValues, Scheduler},
                [{?COUNTER_POS, 0}, {?ISUM_POS, 0}, {?FSUM_POS, 0}]
            )
         || Scheduler <- schedulers_seq()
        ])
    of
        [_, _] -> true;
        [true] -> true;
        _ -> false
    end.

-doc #{equiv => value(default, Name, [])}.
-spec value(prometheus_metric:name()) -> {integer(), number()} | undefined.
value(Name) ->
    value(default, Name, []).

-doc #{equiv => value(default, Name, LabelValues)}.
-spec value(prometheus_metric:name(), prometheus_metric:labels()) ->
    {integer(), number()} | undefined.
value(Name, LabelValues) ->
    value(default, Name, LabelValues).

-doc """
Returns the value of the summary identified by `Registry`, `Name` and `LabelValues`.
If there is no summary for `LabelValues`, returns `undefined`.

If duration unit set, sum will be converted to the duration unit.
[Read more here.](`m:prometheus_time`)

Raises:
* `{unknown_metric, Registry, Name}` error if summary named `Name` can't be found in `Registry`.
* `{invalid_metric_arity, Present, Expected}` error if labels count mismatch.
""".
-spec value(prometheus_registry:registry(), prometheus_metric:name(), prometheus_metric:labels()) ->
    {integer(), number()} | undefined.
value(Registry, Name, LabelValues) ->
    MF = prometheus_metric:check_mf_exists(?TABLE, Registry, Name, LabelValues),
    DU = prometheus_metric:mf_duration_unit(MF),
    case
        ets:select(?TABLE, [{{{Registry, Name, LabelValues, '_'}, '$1', '$2', '$3'}, [], ['$$']}])
    of
        [] ->
            undefined;
        Values ->
            {Count, Sum} = reduce_values(Values),
            {Count, prometheus_time:maybe_convert_to_du(DU, Sum)}
    end.

-spec values(prometheus_registry:registry(), prometheus_metric:name()) ->
    [prometheus_model:'Summary'()].
values(Registry, Name) ->
    case prometheus_metric:check_mf_exists(?TABLE, Registry, Name) of
        false ->
            [];
        MF ->
            DU = prometheus_metric:mf_duration_unit(MF),
            Labels = prometheus_metric:mf_labels(MF),
            MFValues = load_all_values(Registry, Name),
            Foldl = fun([L, C, IS, FS], ResAcc) ->
                {PrevCount, PrevSum} = maps:get(L, ResAcc, {0, 0}),
                ResAcc#{L => {PrevCount + C, PrevSum + IS + FS}}
            end,
            ReducedMap = lists:foldl(Foldl, #{}, MFValues),
            ReducedMapList = lists:sort(maps:to_list(ReducedMap)),
            Foldr = fun({LabelValues, {Count, Sum}}, Acc) ->
                [
                    {
                        lists:zip(Labels, LabelValues),
                        Count,
                        prometheus_time:maybe_convert_to_du(DU, Sum)
                    }
                    | Acc
                ]
            end,
            lists:foldr(Foldr, [], ReducedMapList)
    end.

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

-doc false.
-spec deregister_cleanup(prometheus_registry:registry()) -> ok.
deregister_cleanup(Registry) ->
    prometheus_metric:deregister_mf(?TABLE, Registry),
    true = ets:match_delete(?TABLE, {{Registry, '_', '_', '_'}, '_', '_', '_'}),
    ok.

-doc false.
-spec collect_mf(prometheus_registry:registry(), prometheus_collector:collect_mf_callback()) -> ok.
collect_mf(Registry, Callback) ->
    [
        Callback(create_summary(Name, Help, {CLabels, Labels, Registry, DU}))
     || [Name, {Labels, Help}, CLabels, DU, _] <- prometheus_metric:metrics(?TABLE, Registry)
    ],
    ok.

-doc false.
-spec collect_metrics(prometheus_metric:name(), tuple()) ->
    [prometheus_model:'Metric'()].
collect_metrics(Name, {CLabels, Labels, Registry, DU}) ->
    MFValues = load_all_values(Registry, Name),
    ReducedMap = lists:foldl(
        fun([L, C, IS, FS], ResAcc) ->
            {PrevCount, PrevSum} = maps:get(L, ResAcc, {0, 0}),
            ResAcc#{L => {PrevCount + C, PrevSum + IS + FS}}
        end,
        #{},
        MFValues
    ),
    ReducedMapList = lists:sort(maps:to_list(ReducedMap)),
    lists:foldr(
        fun({LabelValues, {Count, Sum}}, Acc) ->
            [
                prometheus_model_helpers:summary_metric(
                    CLabels ++ lists:zip(Labels, LabelValues),
                    Count,
                    prometheus_time:maybe_convert_to_du(DU, Sum)
                )
                | Acc
            ]
        end,
        [],
        ReducedMapList
    ).

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

deregister_select(Registry, Name) ->
    [{{{Registry, Name, '_', '_'}, '_', '_', '_'}, [], [true]}].

validate_summary_spec(Spec) ->
    Labels = prometheus_metric_spec:labels(Spec),
    validate_summary_labels(Labels),
    Spec.

validate_summary_labels(Labels) ->
    [raise_error_if_quantile_label_found(Label) || Label <- Labels].

raise_error_if_quantile_label_found("quantile") ->
    erlang:error(
        {invalid_metric_label_name, "quantile", "summary cannot have a label named \"quantile\""}
    );
raise_error_if_quantile_label_found(Label) ->
    Label.

-spec insert_metric(Registry, Name, LabelValues, Value, ConflictCB) -> ok when
    Registry :: prometheus_registry:registry(),
    Name :: prometheus_metric:name(),
    LabelValues :: prometheus_metric:labels(),
    Value :: number(),
    ConflictCB :: conflict_cb().
insert_metric(Registry, Name, LabelValues, Value, ConflictCB) ->
    prometheus_metric:check_mf_exists(?TABLE, Registry, Name, LabelValues),
    case ets:insert_new(?TABLE, {key(Registry, Name, LabelValues), 1, 0, Value}) of
        %% some sneaky process already inserted
        false ->
            ConflictCB(Registry, Name, LabelValues, Value);
        true ->
            ok
    end.

load_all_values(Registry, Name) ->
    ets:match(?TABLE, {{Registry, Name, '$1', '_'}, '$2', '$3', '$4'}).

schedulers_seq() ->
    lists:seq(0, ?WIDTH - 1).

key(Registry, Name, LabelValues) ->
    X = erlang:system_info(scheduler_id),
    Rnd = X band (?WIDTH - 1),
    {Registry, Name, LabelValues, Rnd}.

-spec reduce_values([[number()]]) -> {number(), number()}.
reduce_values(Values) ->
    {lists:sum([C || [C, _, _] <- Values]), lists:sum([IS + FS || [_, IS, FS] <- Values])}.

create_summary(Name, Help, Data) ->
    prometheus_model_helpers:create_mf(Name, Help, summary, ?MODULE, Data).