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launchdarkly_server_sdk

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LaunchDarkly SDK for Erlang

Retired package: Deprecated - This version will not be able to connect to and communicate with LaunchDarkly after support for the HTTP/2 protocol is enabled.
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launchdarkly_server_sdk src ldclient_rollout.erl
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src/ldclient_rollout.erl 

%%-------------------------------------------------------------------

%% @doc Rollout data type

%%

%% @end

%%-------------------------------------------------------------------



-module(ldclient_rollout).



%% API

-export([new/1]).

-export([bucket_user/4]).

-export([rollout_user/3]).



%% Types

-type rollout() :: #{

    variations => [weighted_variation()],

    bucket_by  => ldclient_user:attribute()

}.

%% Describes how users will be bucketed into variations during a percentage rollout



-type weighted_variation() :: #{

    variation => ldclient_flag:variation(),

    weight    => non_neg_integer() % 0 to 100000

}.

%% Describes a fraction of users who will receive a specific variation



-export_type([rollout/0]).



%%===================================================================

%% API

%%===================================================================



-spec new(map()) -> rollout().

new(#{

    <<"variations">> := Variations,

    <<"bucketBy">>  := BucketBy

}) ->

    #{

        variations => parse_variations(Variations),

        bucket_by  => BucketBy

    };

new(#{<<"variations">> := Variations}) ->

    #{

        variations => parse_variations(Variations),

        bucket_by  => key

    }.



-spec rollout_user(rollout(), ldclient_flag:flag(), ldclient_user:user()) -> ldclient_flag:variation() | null.

rollout_user(#{variations := WeightedVariations, bucket_by := BucketBy}, #{key := FlagKey, salt := FlagSalt}, User) ->

    Bucket = bucket_user(FlagKey, FlagSalt, User, BucketBy),

    match_weighted_variations(Bucket, WeightedVariations).



-spec bucket_user(ldclient_flag:key(), binary(), ldclient_user:user(), ldclient_user:attribute()) -> float().

bucket_user(Key, Salt, User, BucketBy) ->

    UserValue = ldclient_user:get(BucketBy, User),

    UserSecondary = ldclient_user:get(secondary, User),

    bucket_user_value(Key, Salt, bucketable_value(UserValue), UserSecondary).



%%===================================================================

%% Internal functions

%%===================================================================



-spec parse_variations([map()]) -> [weighted_variation()].

parse_variations(Variations) ->

    F = fun(#{<<"variation">> := Variation, <<"weight">> := Weight}, Acc) ->

            [#{variation => Variation, weight => Weight}|Acc];

        (#{<<"variation">> := Variation}, Acc) ->

            [#{variation => Variation, weight => 0}|Acc];

        (_, Acc)  ->

            Acc

        end,

    lists:foldr(F, [], Variations).



-spec match_weighted_variations(float(), [weighted_variation()]) -> ldclient_flag:variation().

match_weighted_variations(_, []) -> null;

match_weighted_variations(Bucket, WeightedVariations) ->

    match_weighted_variations(Bucket, WeightedVariations, 0.0).



-spec match_weighted_variations(float(), [weighted_variation()], float()) -> ldclient_flag:variation().

match_weighted_variations(_Bucket, [], _Sum) -> null;

match_weighted_variations(_Bucket, [#{variation := Variation}|[]], _Sum) -> Variation;

match_weighted_variations(Bucket, [#{variation := Variation, weight := Weight}|_], Sum)

    when Bucket < Sum + Weight / 100000 ->

    Variation;

match_weighted_variations(Bucket, [#{weight := Weight}|Rest], Sum) ->

    match_weighted_variations(Bucket, Rest, Sum + Weight / 100000).



-spec bucket_user_value(ldclient_flag:key(), binary(), binary() | null, binary()) -> float().

bucket_user_value(_Key, _Salt, null, _Secondary) -> 0.0;

bucket_user_value(Key, Salt, UserAttribute, null) ->

    bucket_hash(<<Key/binary, $., Salt/binary, $., UserAttribute/binary>>);

bucket_user_value(Key, Salt, UserAttribute, Secondary) ->

    bucket_hash(<<Key/binary, $., Salt/binary, $., UserAttribute/binary, $., Secondary/binary>>).



-spec bucket_hash(binary()) -> float().

bucket_hash(Hash) ->

    Sha1 = crypto:hash(sha, Hash),

    Sha1Hex = lists:flatten([[io_lib:format("~2.16.0B",[X]) || <<X:8>> <= Sha1 ]]),

    Sha1_15 = string:substr(Sha1Hex, 1, 15),

    Int = list_to_integer(Sha1_15, 16),

    Int / 1152921504606846975.



-spec bucketable_value(any()) -> binary() | null.

bucketable_value(V) when is_binary(V) -> V;

bucketable_value(V) when is_integer(V) -> list_to_binary(integer_to_list(V));

bucketable_value(V) when is_float(V) -> if V == trunc(V) -> list_to_binary(integer_to_list(trunc(V))); true -> null end;

bucketable_value(_) -> null.