From e867ef60cffe45215cad911d4b4aa3e7449d0491 Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Sat, 25 Jul 2026 11:36:28 +0000
Subject: [PATCH] Tariff: fix chargesZones boundaries not taking effect between
 price zones (#32143)

---
 tariff/fixed.go      |  4 +++-
 tariff/fixed_test.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/tariff/fixed.go b/tariff/fixed.go
index 705b9a787..fefca4e2f 100644
--- a/tariff/fixed.go
+++ b/tariff/fixed.go
@@ -2,6 +2,7 @@ package tariff
 
 import (
 	"fmt"
+	"slices"
 	"sort"
 	"time"
 
@@ -77,7 +78,8 @@ func (t *Fixed) Rates() (api.Rates, error) {
 			return nil, fmt.Errorf("no zones for weekday %d", dow)
 		}
 
-		markers := zones.TimeTableMarkers()
+		// include chargesZones boundaries so rate changes there are not swallowed by the coarser price zone markers
+		markers := append(slices.Clone(zones), t.chargesZones.ForDayAndMonth(dow, month)...).TimeTableMarkers()
 
 		for i, m := range markers {
 			ts := dayStart.Add(time.Minute * time.Duration(m.Minutes()))
diff --git a/tariff/fixed_test.go b/tariff/fixed_test.go
index 6be7603d1..56151b33e 100644
--- a/tariff/fixed_test.go
+++ b/tariff/fixed_test.go
@@ -104,3 +104,32 @@ func TestFixedSplitZones(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, expect, rates)
 }
+
+func TestFixedChargesZonesMarkers(t *testing.T) {
+	at, err := NewFixedFromConfig(map[string]any{
+		"price": 0.5,
+		"chargesZones": []struct {
+			Charges float64
+			Hours   string
+		}{
+			{0.1, "0-5:30"},
+		},
+	})
+	require.NoError(t, err)
+
+	tf := at.(*Fixed)
+	tf.clock = clock.NewMock()
+
+	rates, err := tf.Rates()
+	require.NoError(t, err)
+
+	dayStart := now.With(tf.clock.Now()).BeginningOfDay()
+
+	// charges zone ends mid-hour at 05:30 - the price change must take effect there, not at 06:00
+	require.GreaterOrEqual(t, len(rates), 2)
+	assert.Equal(t, dayStart.Add(5*time.Hour), rates[5].Start)
+	assert.Equal(t, dayStart.Add(5*time.Hour+30*time.Minute), rates[5].End)
+	assert.Equal(t, 0.6, rates[5].Value)
+	assert.Equal(t, dayStart.Add(5*time.Hour+30*time.Minute), rates[6].Start)
+	assert.Equal(t, 0.5, rates[6].Value)
+}