package application

import (
	"context"
	"crypto/rand"
	"encoding/base64"
	"net/http"
)

type nonceKey struct{}

// NonceMiddleware generates a cryptographic nonce per request and stores it
// in the request context. Retrieve with NonceFromContext.
func NonceMiddleware() Middleware {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			nonce := generateNonce()
			ctx := context.WithValue(r.Context(), nonceKey{}, nonce)
			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}

// NonceFromContext returns the per-request nonce, or empty string if none.
func NonceFromContext(ctx context.Context) string {
	if v, ok := ctx.Value(nonceKey{}).(string); ok {
		return v
	}
	return ""
}

func generateNonce() string {
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		panic("crypto/rand failed: " + err.Error())
	}
	return base64.StdEncoding.EncodeToString(b)
}