pipelines.go

package main

import (
	"context"
	"errors"
	"fmt"
	"math/rand"
	"time"
)

// Handler handles stream request with context
type Handler interface {
	Get(context.Context, string) (string, error)
}

// NextOrFailure constructs plugins in a chain
func NextOrFailure(ctx context.Context, next Handler, streamID string) (string, error) {
	if next != nil {
		return next.Get(ctx, streamID)
	}

	return "", errors.New("Handler chain terminated")
}

// redisHandler
type redisHandler struct {
}

func (s *redisHandler) Get(ctx context.Context, streamID string) (string, error) {
	result := rand.Intn(10)

	if result < 5 {
		return "", errors.New("redis error")
	}

	return "https://redis.url/" + streamID, nil
}

// cacheHandler
type cacheHandler struct {
	Next Handler
}

func (cache *cacheHandler) Get(ctx context.Context, streamID string) (string, error) {
	result := rand.Intn(10)
	if result < 2 {
		return "", errors.New("Unknown Error")
	}

	if result < 6 {
		return NextOrFailure(ctx, cache.Next, streamID)
	}

	return "https://random.url/" + streamID, nil
}

func init() {
	rand.Seed(time.Now().UTC().UnixNano())
}

func main() {
	redis := &redisHandler{}
	cache := cacheHandler{
		Next: redis,
	}

	result, err := cache.Get(context.Background(), "3210830919510")

	fmt.Println(result, err)
}

pipelines_test.go

package main

import (
	"context"
	"fmt"
	"testing"
)

func TestCacheHandler(t *testing.T) {
	h := cacheHandler{}

	result, err := h.Get(context.Background(), "23131")
	fmt.Println(result, err)
}

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