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strategy_evaluator.go
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strategy_evaluator.go
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// Copyright 2024 The Bucketeer Authors.
//
// 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.
package evaluation
import (
"crypto/md5"
"encoding/hex"
"fmt"
"strconv"
"github.com/bucketeer-io/bucketeer/proto/feature"
)
const max = float64(0xffffffffffffffff)
type strategyEvaluator struct {
}
func (e *strategyEvaluator) Evaluate(
strategy *feature.Strategy,
userID string,
variations []*feature.Variation,
featureID string,
samplingSeed string,
) (*feature.Variation, error) {
switch strategy.Type {
case feature.Strategy_FIXED:
return findVariation(strategy.FixedStrategy.Variation, variations)
case feature.Strategy_ROLLOUT:
variationID, err := e.rollout(strategy.RolloutStrategy, userID, featureID, samplingSeed)
if err != nil {
return nil, err
}
return findVariation(variationID, variations)
}
return nil, ErrUnsupportedStrategy
}
func (e *strategyEvaluator) rollout(
strategy *feature.RolloutStrategy,
userID, featureID, samplingSeed string,
) (string, error) {
bucket, err := e.bucket(userID, featureID, samplingSeed)
if err != nil {
return "", err
}
sum := 0.0
for i := range strategy.Variations {
sum += float64(strategy.Variations[i].Weight) / 100000.0
if bucket < sum {
return strategy.Variations[i].Variation, nil
}
}
return "", ErrVariationNotFound
}
func (e *strategyEvaluator) bucket(userID string, featureID string, samplingSeed string) (float64, error) {
hash := e.hash(userID, featureID, samplingSeed)
// use first 16 characters (hex string) / first 8 bytes (byte array)
intVal, err := strconv.ParseUint(hex.EncodeToString(hash[:])[:16], 16, 64)
if err != nil {
return 0.0, err
}
return float64(intVal) / max, nil
}
func (e *strategyEvaluator) hash(userID string, featureID string, samplingSeed string) [16]byte {
// concat feature test id and user id
// TODO: explain why this makes sense? Why does it make sense to add 'prerequisit' key here?
concat := fmt.Sprintf("%s-%s%s", featureID, userID, samplingSeed)
// returns 16 bytes which, if shown as hex string, has 32 characters
return md5.Sum([]byte(concat))
}