From e998809d102af40cd99781603da77573a503655f Mon Sep 17 00:00:00 2001
From: andig <cpuidle@gmail.com>
Date: Sat, 13 Sep 2025 15:20:36 +0200
Subject: [PATCH] Tariffs: avoid duplicate cache writes

---
 tariff/proxy.go       | 11 ++++++++++-
 tariff/proxy_cache.go |  2 +-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/tariff/proxy.go b/tariff/proxy.go
index 2caba2b46..b8bbfd0bd 100644
--- a/tariff/proxy.go
+++ b/tariff/proxy.go
@@ -2,7 +2,9 @@ package tariff
 
 import (
 	"context"
+	"crypto/sha256"
 	"errors"
+	"fmt"
 	"slices"
 	"sync"
 	"time"
@@ -14,7 +16,8 @@ import (
 
 // CachingProxy wraps a tariff with caching
 type CachingProxy struct {
-	mu sync.Mutex
+	mu   sync.Mutex
+	hash [32]byte
 
 	key    string
 	ctx    context.Context
@@ -165,6 +168,12 @@ func (p *CachingProxy) cacheGet(until time.Time) (*cached, error) {
 }
 
 func (p *CachingProxy) cachePut(typ api.TariffType, rates api.Rates) error {
+	hash := sha256.Sum256(fmt.Append(nil, rates))
+	if hash == p.hash {
+		return nil
+	}
+
+	p.hash = hash
 	return cachePut(p.key, typ, rates)
 }
 
diff --git a/tariff/proxy_cache.go b/tariff/proxy_cache.go
index e01672fdc..b4fe00ed0 100644
--- a/tariff/proxy_cache.go
+++ b/tariff/proxy_cache.go
@@ -14,7 +14,7 @@ type cached struct {
 }
 
 func cacheKey(typ string, other map[string]any) string {
-	return fmt.Sprintf("%x", sha256.Sum256([]byte(fmt.Sprintf("%s-%v", typ, other))))
+	return fmt.Sprintf("%x", sha256.Sum256(fmt.Appendf(nil, "%s-%v", typ, other)))
 }
 
 func cachePut(key string, typ api.TariffType, rates api.Rates) error {