Golang Weighted Response Engine

main.go

package main

import (
	"fmt"
	"math/rand"

	"github.com/go-playground/validator"
)

type RespSpec struct {
	Value  interface{}
	Weight float64
}

type RespEngine struct {
	Config RespEngineConfig
}

type RespEngineConfig struct {
	SpecMap map[string][]RespSpec `validate:"required"`
}

func NewRespEngine(cfg RespEngineConfig) (*RespEngine, error) {
	if err := validator.New().Struct(cfg); err != nil {
		return nil, err
	}
	return &RespEngine{Config: cfg}, nil
}

func (e *RespEngine) FetchResp(procname string) (resp interface{}) {
	// check existence
	spec, exist := e.Config.SpecMap[procname]
	if !exist {
		return nil
	}

	// count value
	totProbability := 0
	for _, v := range spec {
		totProbability += int(v.Weight)
	}

	// iterate correct value
	chosenbar := rand.Float64() * float64(totProbability)
	for _, v := range spec {
		chosenbar -= v.Weight
		if chosenbar <= 0 {
			return v.Value
		}
	}

	return
}

// ***

var ng *RespEngine

func init() {
	var err error
	ng, err = NewRespEngine(RespEngineConfig{
		SpecMap: map[string][]RespSpec{
			"transaction.error": {
				RespSpec{Weight: 1, Value: fmt.Errorf("damn error happened")},
				RespSpec{Weight: 5, Value: fmt.Errorf("damn bigger error probability happened")},
			},
		},
	})
	if err != nil {
		err = fmt.Errorf("cannot start resp engine: %w", err)
		panic(err)
	}
}

// ***

func main() {
	for i := 0; i < 100; i++ {
		fmt.Println(ng.FetchResp("transaction.error"))
	}
}