Add simple rate limiter

ratelimit-token-bucket/README.md

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+# Rate limit token bucket
+
+Rate limit abstraction for function calls based on a [token bucket](https://en.wikipedia.org/wiki/Token_bucket) approach.

ratelimit-token-bucket/main.go

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+package main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
+	"time"
+)
+
+// Simple poc function
+type stringReturner func() (string, error)
+
+// RateLimitFunction returns a function doing the same as the original function
+// but with a build in rate limit.
+func RateLimitFunction(f stringReturner, refillInterval time.Duration, refillSize int, bucketSize int) stringReturner {
+
+	remaining := bucketSize
+	refillTicker := time.NewTicker(refillInterval)
+	bmu := &sync.Mutex{}
+	go func() {
+		for range refillTicker.C {
+			bmu.Lock()
+			remaining = min(bucketSize, remaining+refillSize)
+			bmu.Unlock()
+		}
+	}()
+
+	return func() (string, error) {
+		bmu.Lock()
+		defer bmu.Unlock()
+		if remaining <= 0 {
+			return "", errors.New("rate limited")
+		}
+		hello, err := f()
+		// decrease quota
+		remaining--
+		return hello, err
+	}
+}
+
+func main() {
+
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
+	go func() {
+		<-c
+		os.Exit(1)
+	}()
+
+	var printhello stringReturner = func() (string, error) {
+		return "hello", nil
+	}
+	// Every 5 seconds, refill with 2 calls, and start with 3 calls
+	f := RateLimitFunction(printhello, 5*time.Second, 2, 3)
+
+	t := time.NewTicker(1 * time.Second)
+	for range t.C {
+		n := time.Now()
+		val, err := f()
+		if err != nil {
+			fmt.Printf("[%s] %s\n", n.Format(time.TimeOnly), err.Error())
+		} else {
+			fmt.Printf("[%s] %s\n", n.Format(time.TimeOnly), val)
+		}
+	}
+}
+
+// func main() {
+
+// 	t := time.NewTicker(1 * time.Second)
+// 	for range t.C {
+// 		fmt.Println("ce ma?")
+// 	}
+
+// 	select {
+// 	case v, ok := <-t.C:
+// 		fmt.Println("lol", v, ok)
+// 	default:
+// 		fmt.Println("hai ca esti parlit")
+// 	}
+
+// 	time.Sleep(2 * time.Second)
+
+// 	select {
+// 	case v, ok := <-t.C:
+// 		fmt.Println("lol", v, ok)
+// 	default:
+// 		fmt.Println("hai ca esti parlit")
+// 	}
+
+// }