bucketing.hpp

#pragma once
 
#include "evaluation_error.hpp"
 
#include <launchdarkly/attribute_reference.hpp>
#include <launchdarkly/context.hpp>
#include <launchdarkly/data_model/flag.hpp>
 
#include <tl/expected.hpp>
 
#include <cstdint>
#include <limits>
#include <optional>
#include <ostream>
#include <string>
#include <variant>
 
namespace launchdarkly::server_side::evaluation {
 
double const kBucketScale = 100'000.0;
 
enum RolloutKindLookup {
    /* The rollout's context kind was found in the supplied evaluation context.
     */
    kPresent,
    /* The rollout's context kind was not found in the supplied evaluation
     * context. */
    kAbsent
};
 
class BucketPrefix {
   public:
    struct KeyAndSalt {
        std::string key;
        std::string salt;
    };
 
    using Seed = std::int64_t;
 
    explicit BucketPrefix(Seed seed);
 
    BucketPrefix(std::string key, std::string salt);
 
    friend std::ostream& operator<<(std::ostream& os,
                                    BucketPrefix const& prefix);
 
   private:
    std::variant<KeyAndSalt, Seed> prefix_;
};
 
using ContextHashValue = double;
 
tl::expected<std::pair<ContextHashValue, RolloutKindLookup>, Error> Bucket(
    Context const& context,
    AttributeReference const& by_attr,
    BucketPrefix const& prefix,
    bool is_experiment,
    std::string const& context_kind);
 
class BucketResult {
   public:
    BucketResult(
        data_model::Flag::Rollout::WeightedVariation weighted_variation,
        bool is_experiment);
 
    BucketResult(data_model::Flag::Variation variation, bool in_experiment);
 
    BucketResult(data_model::Flag::Variation variation);
 
    [[nodiscard]] std::size_t VariationIndex() const;
 
    [[nodiscard]] bool InExperiment() const;
 
   private:
    std::size_t variation_index_;
    bool in_experiment_;
};
 
tl::expected<BucketResult, Error> Variation(
    data_model::Flag::VariationOrRollout const& variation_or_rollout,
    std::string const& flag_key,
    Context const& context,
    std::optional<std::string> const& salt);
 
}  // namespace launchdarkly::server_side::evaluation