feat: more metrics and adding tests

.gitignore

@@ -1 +1,2 @@
 .env
+coverage.out

README.md

@@ -6,29 +6,33 @@ A Prometheus exporter for Octopus Energy smart meter data, using the Kraken Grap
 
 ### Electricity
 
-| Metric | Description |
-|---|---|
-| `octopus_electricity_demand_watts` | Live electricity demand in watts |
-| `octopus_electricity_last_read_timestamp` | Unix timestamp of last electricity reading |
-| `octopus_electricity_unit_rate_pence` | Current unit rate in pence per kWh |
-| `octopus_electricity_standing_charge_pence` | Current standing charge in pence per day |
+| Metric | Source | Description |
+|---|---|---|
+| `octopus_electricity_demand_watts` | GraphQL | Live electricity demand in watts |
+| `octopus_electricity_last_read_timestamp` | GraphQL | Unix timestamp of last electricity reading |
+| `octopus_electricity_consumption_kwh` | REST | Latest half-hourly consumption in kWh |
+| `octopus_electricity_consumption_interval_timestamp` | REST | Unix timestamp of the start of the latest consumption interval |
+| `octopus_electricity_unit_rate_pence` | GraphQL / REST | Current unit rate in pence per kWh (Agile customers get the live half-hourly rate from the REST API) |
+| `octopus_electricity_standing_charge_pence` | GraphQL | Current standing charge in pence per day |
 
 ### Gas
 
 Gas metrics are only exposed if a smart gas meter is found on the account.
 
-| Metric | Description |
-|---|---|
-| `octopus_gas_demand_watts` | Live gas demand in watts |
-| `octopus_gas_last_read_timestamp` | Unix timestamp of last gas reading |
-| `octopus_gas_unit_rate_pence` | Current unit rate in pence per kWh |
-| `octopus_gas_standing_charge_pence` | Current standing charge in pence per day |
+| Metric | Source | Description |
+|---|---|---|
+| `octopus_gas_demand_watts` | GraphQL | Live gas demand in watts |
+| `octopus_gas_last_read_timestamp` | GraphQL | Unix timestamp of last gas reading |
+| `octopus_gas_consumption_kwh` | REST | Latest half-hourly consumption in kWh |
+| `octopus_gas_consumption_interval_timestamp` | REST | Unix timestamp of the start of the latest gas consumption interval |
+| `octopus_gas_unit_rate_pence` | GraphQL | Current unit rate in pence per kWh |
+| `octopus_gas_standing_charge_pence` | GraphQL | Current standing charge in pence per day |
 
 ### Account
 
-| Metric | Description |
-|---|---|
-| `octopus_account_balance_pence` | Account balance in pence (positive = credit, negative = debit) |
+| Metric | Source | Description |
+|---|---|---|
+| `octopus_account_balance_pence` | GraphQL | Account balance in pence (positive = credit, negative = debit) |
 
 Metrics are updated every 60 seconds.
 

cmd/octopus_exporter/account_test.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestGetAccountBalance_Credit(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"viewer":{"accounts":[{"balance":4250}]}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	balance, err := getAccountBalance("token")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if balance != 4250 {
+		t.Errorf("got %v, want 4250", balance)
+	}
+}
+
+func TestGetAccountBalance_Debit(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"viewer":{"accounts":[{"balance":-1500}]}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	balance, err := getAccountBalance("token")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if balance != -1500 {
+		t.Errorf("got %v, want -1500", balance)
+	}
+}
+
+func TestGetAccountBalance_Missing(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"viewer":{"accounts":[{}]}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	_, err := getAccountBalance("token")
+	if err == nil {
+		t.Error("expected error when balance is missing, got nil")
+	}
+}

cmd/octopus_exporter/agile.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"net/url"
+	"time"
+)
+
+// getCurrentAgileRate returns the unit rate (inc. VAT, pence/kWh) for the current
+// half-hour slot from the Agile tariff REST endpoint.
+func getCurrentAgileRate(productCode, tariffCode string) (float64, error) {
+	now := time.Now().UTC()
+	slotStart := now.Truncate(30 * time.Minute)
+	slotEnd := slotStart.Add(30 * time.Minute)
+
+	path := fmt.Sprintf("/v1/products/%s/electricity-tariffs/%s/standard-unit-rates/", productCode, tariffCode)
+	result, err := doREST(path, url.Values{
+		"period_from": {slotStart.Format(time.RFC3339)},
+		"period_to":   {slotEnd.Format(time.RFC3339)},
+	})
+	if err != nil {
+		return 0, err
+	}
+
+	results := toSlice(result["results"])
+	if len(results) == 0 {
+		return 0, errors.New("no Agile rate found for current slot")
+	}
+
+	rate, ok := results[0].(map[string]any)["value_inc_vat"].(float64)
+	if !ok {
+		return 0, errors.New("value_inc_vat missing from Agile rate response")
+	}
+	return rate, nil
+}

cmd/octopus_exporter/agile_test.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestGetCurrentAgileRate_Success(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"count":1,"results":[
+			{"value_exc_vat":21.68,"value_inc_vat":22.764,"valid_from":"2026-04-24T20:00:00Z","valid_to":"2026-04-24T20:30:00Z","payment_method":null}
+		]}`)
+	}))
+	defer srv.Close()
+	octopusREST = srv.URL
+	apiKey = "test"
+
+	rate, err := getCurrentAgileRate("AGILE-24-10-01", "E-1R-AGILE-24-10-01-C")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if rate != 22.764 {
+		t.Errorf("got rate %v, want 22.764", rate)
+	}
+}
+
+func TestGetCurrentAgileRate_NoSlot(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"count":0,"results":[]}`)
+	}))
+	defer srv.Close()
+	octopusREST = srv.URL
+	apiKey = "test"
+
+	_, err := getCurrentAgileRate("AGILE-24-10-01", "E-1R-AGILE-24-10-01-C")
+	if err == nil {
+		t.Error("expected error for empty slot, got nil")
+	}
+}
+
+func TestGetCurrentAgileRate_CorrectPath(t *testing.T) {
+	var capturedPath string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		capturedPath = r.URL.Path
+		fmt.Fprint(w, `{"count":1,"results":[{"value_inc_vat":22.764}]}`)
+	}))
+	defer srv.Close()
+	octopusREST = srv.URL
+	apiKey = "test"
+
+	getCurrentAgileRate("AGILE-24-10-01", "E-1R-AGILE-24-10-01-C")
+
+	want := "/v1/products/AGILE-24-10-01/electricity-tariffs/E-1R-AGILE-24-10-01-C/standard-unit-rates/"
+	if capturedPath != want {
+		t.Errorf("got path %q, want %q", capturedPath, want)
+	}
+}

cmd/octopus_exporter/auth_test.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestGetKrakenToken_Success(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"obtainKrakenToken":{"token":"test-token-123"}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	token, err := getKrakenToken("test-api-key")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if token != "test-token-123" {
+		t.Errorf("got token %q, want %q", token, "test-token-123")
+	}
+}
+
+func TestGetKrakenToken_GraphQLError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"errors":[{"message":"Invalid API key"}]}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	_, err := getKrakenToken("bad-key")
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+}

cmd/octopus_exporter/client.go

@@ -10,7 +10,7 @@ import (
 	"strconv"
 )
 
-const octopusGraphQL = "https://api.octopus.energy/v1/graphql/"
+var octopusGraphQL = "https://api.octopus.energy/v1/graphql/"
 
 type gqlRequest struct {
 	OperationName string         `json:"operationName,omitempty"`

cmd/octopus_exporter/client_test.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestJsonFloat_Number(t *testing.T) {
+	var f jsonFloat
+	if err := json.Unmarshal([]byte(`42.5`), &f); err != nil {
+		t.Fatal(err)
+	}
+	if float64(f) != 42.5 {
+		t.Errorf("got %v, want 42.5", f)
+	}
+}
+
+func TestJsonFloat_QuotedString(t *testing.T) {
+	var f jsonFloat
+	if err := json.Unmarshal([]byte(`"42.5"`), &f); err != nil {
+		t.Fatal(err)
+	}
+	if float64(f) != 42.5 {
+		t.Errorf("got %v, want 42.5", f)
+	}
+}
+
+func TestJsonFloat_InvalidString(t *testing.T) {
+	var f jsonFloat
+	if err := json.Unmarshal([]byte(`"not-a-number"`), &f); err == nil {
+		t.Error("expected error for non-numeric string, got nil")
+	}
+}
+
+func TestToSlice_Slice(t *testing.T) {
+	input := []any{1, 2, 3}
+	got := toSlice(input)
+	if len(got) != 3 {
+		t.Errorf("got len %d, want 3", len(got))
+	}
+}
+
+func TestToSlice_Nil(t *testing.T) {
+	if got := toSlice(nil); got != nil {
+		t.Errorf("expected nil, got %v", got)
+	}
+}
+
+func TestToSlice_WrongType(t *testing.T) {
+	if got := toSlice("not a slice"); got != nil {
+		t.Errorf("expected nil for wrong type, got %v", got)
+	}
+}

cmd/octopus_exporter/consumption.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"net/url"
+	"time"
+)
+
+type consumptionReading struct {
+	KWh           float64
+	IntervalStart time.Time
+}
+
+func getLatestConsumption(kind meterKind, id, serial string) (*consumptionReading, error) {
+	var path string
+	switch kind {
+	case electricity:
+		path = fmt.Sprintf("/v1/electricity-meter-points/%s/meters/%s/consumption/", id, serial)
+	case gas:
+		path = fmt.Sprintf("/v1/gas-meter-points/%s/meters/%s/consumption/", id, serial)
+	}
+
+	// Consumption data can lag several hours, so use a 24h window and take the latest entry.
+	result, err := doREST(path, url.Values{
+		"period_from": {time.Now().UTC().Add(-24 * time.Hour).Format(time.RFC3339)},
+		"order_by":    {"period"},
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	results := toSlice(result["results"])
+	if len(results) == 0 {
+		return nil, errors.New("no consumption data in last 24h")
+	}
+
+	latest := results[len(results)-1].(map[string]any)
+	kwh, _ := latest["consumption"].(float64)
+	start, err := time.Parse(time.RFC3339, latest["interval_start"].(string))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse interval_start: %w", err)
+	}
+
+	return &consumptionReading{KWh: kwh, IntervalStart: start}, nil
+}

cmd/octopus_exporter/consumption_test.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestGetLatestConsumption_ReturnsLatestInterval(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"count":2,"results":[
+			{"consumption":0.304,"interval_start":"2026-04-23T22:00:00+00:00","interval_end":"2026-04-23T22:30:00+00:00"},
+			{"consumption":0.512,"interval_start":"2026-04-23T22:30:00+00:00","interval_end":"2026-04-23T23:00:00+00:00"}
+		]}`)
+	}))
+	defer srv.Close()
+	octopusREST = srv.URL
+	apiKey = "test"
+
+	c, err := getLatestConsumption(electricity, "MPAN123", "SERIAL456")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if c.KWh != 0.512 {
+		t.Errorf("got kWh %v, want 0.512", c.KWh)
+	}
+}
+
+func TestGetLatestConsumption_Empty(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"count":0,"results":[]}`)
+	}))
+	defer srv.Close()
+	octopusREST = srv.URL
+	apiKey = "test"
+
+	_, err := getLatestConsumption(electricity, "MPAN123", "SERIAL456")
+	if err == nil {
+		t.Error("expected error for empty results, got nil")
+	}
+}
+
+func TestGetLatestConsumption_GasPath(t *testing.T) {
+	var capturedPath string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		capturedPath = r.URL.Path
+		fmt.Fprint(w, `{"count":1,"results":[
+			{"consumption":1.23,"interval_start":"2026-04-23T22:00:00+00:00","interval_end":"2026-04-23T22:30:00+00:00"}
+		]}`)
+	}))
+	defer srv.Close()
+	octopusREST = srv.URL
+	apiKey = "test"
+
+	getLatestConsumption(gas, "MPRN789", "SERIAL456")
+
+	want := "/v1/gas-meter-points/MPRN789/meters/SERIAL456/consumption/"
+	if capturedPath != want {
+		t.Errorf("got path %q, want %q", capturedPath, want)
+	}
+}

cmd/octopus_exporter/main.go

@@ -11,8 +11,8 @@ import (
 )
 
 var (
-	apiKey = mustEnv("OCTOPUS_API_KEY")
-	port   = envOrDefault("PORT", "9359")
+	apiKey string
+	port   string
 )
 
 func mustEnv(key string) string {
@@ -35,31 +35,40 @@ func gauge(name, help string) prometheus.Gauge {
 }
 
 func main() {
+	apiKey = mustEnv("OCTOPUS_API_KEY")
+	port = envOrDefault("PORT", "9359")
+
 	token, err := getKrakenToken(apiKey)
 	if err != nil {
 		log.Fatalf("failed to get initial token: %v", err)
 	}
 
-	elecDeviceID, err := resolveDeviceID(token, electricity)
+	elecMeter, err := resolveMeter(token, electricity)
 	if err != nil {
 		log.Fatalf("failed to resolve electricity meter: %v", err)
 	}
-	if elecDeviceID == "" {
+	if elecMeter == nil {
 		log.Fatal("no electricity smart meter found on account")
 	}
 
-	gasDeviceID, err := resolveDeviceID(token, gas)
+	gasMeter, err := resolveMeter(token, gas)
 	if err != nil {
 		log.Fatalf("failed to resolve gas meter: %v", err)
 	}
-	if gasDeviceID == "" {
+	if gasMeter == nil {
 		log.Println("no gas smart meter found — gas metrics disabled")
 	}
 
-	// Electricity telemetry
+	// --- Metrics ---
+
+	// Electricity telemetry (live, from GraphQL)
 	elecDemand := gauge("octopus_electricity_demand_watts", "Live electricity demand in watts")
 	elecLastRead := gauge("octopus_electricity_last_read_timestamp", "Unix timestamp of last electricity reading")
 
+	// Electricity consumption (half-hourly kWh, from REST)
+	elecConsumption := gauge("octopus_electricity_consumption_kwh", "Half-hourly electricity consumption in kWh")
+	elecConsumptionInterval := gauge("octopus_electricity_consumption_interval_timestamp", "Unix timestamp of the start of the latest consumption interval")
+
 	// Electricity tariff
 	elecUnitRate := gauge("octopus_electricity_unit_rate_pence", "Current electricity unit rate in pence per kWh")
 	elecStandingCharge := gauge("octopus_electricity_standing_charge_pence", "Current electricity standing charge in pence per day")
@@ -67,20 +76,29 @@ func main() {
 	// Account
 	accountBalance := gauge("octopus_account_balance_pence", "Account balance in pence (positive = credit, negative = debit)")
 
-	toRegister := []prometheus.Collector{elecDemand, elecLastRead, elecUnitRate, elecStandingCharge, accountBalance}
+	toRegister := []prometheus.Collector{
+		elecDemand, elecLastRead,
+		elecConsumption, elecConsumptionInterval,
+		elecUnitRate, elecStandingCharge,
+		accountBalance,
+	}
 
 	var (
 		gasDemand            prometheus.Gauge
 		gasLastRead          prometheus.Gauge
+		gasConsumption       prometheus.Gauge
+		gasConsumptionInterval prometheus.Gauge
 		gasUnitRate          prometheus.Gauge
 		gasStandCharge       prometheus.Gauge
 	)
-	if gasDeviceID != "" {
+	if gasMeter != nil {
 		gasDemand = gauge("octopus_gas_demand_watts", "Live gas demand in watts")
 		gasLastRead = gauge("octopus_gas_last_read_timestamp", "Unix timestamp of last gas reading")
+		gasConsumption = gauge("octopus_gas_consumption_kwh", "Half-hourly gas consumption in kWh")
+		gasConsumptionInterval = gauge("octopus_gas_consumption_interval_timestamp", "Unix timestamp of the start of the latest gas consumption interval")
 		gasUnitRate = gauge("octopus_gas_unit_rate_pence", "Current gas unit rate in pence per kWh")
 		gasStandCharge = gauge("octopus_gas_standing_charge_pence", "Current gas standing charge in pence per day")
-		toRegister = append(toRegister, gasDemand, gasLastRead, gasUnitRate, gasStandCharge)
+		toRegister = append(toRegister, gasDemand, gasLastRead, gasConsumption, gasConsumptionInterval, gasUnitRate, gasStandCharge)
 	}
 
 	prometheus.MustRegister(toRegister...)
@@ -94,8 +112,9 @@ func main() {
 	}()
 
 	for {
-		// Electricity telemetry
-		reading, err := getLiveConsumption(token, elecDeviceID)
+		// Electricity telemetry (live demand)
+		if elecMeter.deviceID != "" {
+			reading, err := getLiveConsumption(token, elecMeter.deviceID)
 			if err != nil {
 				log.Printf("electricity telemetry error: %v", err)
 				if token, err = getKrakenToken(apiKey); err != nil {
@@ -107,10 +126,11 @@ func main() {
 					elecLastRead.Set(float64(t.Unix()))
 				}
 			}
+		}
 
-		// Gas telemetry
-		if gasDeviceID != "" {
-			reading, err := getLiveConsumption(token, gasDeviceID)
+		// Gas telemetry (live demand)
+		if gasMeter != nil && gasMeter.deviceID != "" {
+			reading, err := getLiveConsumption(token, gasMeter.deviceID)
 			if err != nil {
 				log.Printf("gas telemetry error: %v", err)
 			} else {
@@ -121,14 +141,46 @@ func main() {
 			}
 		}
 
-		// Rates
+		// Electricity half-hourly consumption (REST)
+		if elecMeter.mpan != "" && elecMeter.serial != "" {
+			c, err := getLatestConsumption(electricity, elecMeter.mpan, elecMeter.serial)
+			if err != nil {
+				log.Printf("electricity consumption error: %v", err)
+			} else {
+				elecConsumption.Set(c.KWh)
+				elecConsumptionInterval.Set(float64(c.IntervalStart.Unix()))
+			}
+		}
+
+		// Gas half-hourly consumption (REST)
+		if gasMeter != nil && gasMeter.mprn != "" && gasMeter.serial != "" {
+			c, err := getLatestConsumption(gas, gasMeter.mprn, gasMeter.serial)
+			if err != nil {
+				log.Printf("gas consumption error: %v", err)
+			} else {
+				gasConsumption.Set(c.KWh)
+				gasConsumptionInterval.Set(float64(c.IntervalStart.Unix()))
+			}
+		}
+
+		// Tariff rates
 		rates, err := getRates(token)
 		if err != nil {
 			log.Printf("rates error: %v", err)
 		} else {
-			elecUnitRate.Set(rates.ElectricityUnitRate)
+			unitRate := rates.ElectricityUnitRate
+			if rates.ElectricityIsAgile && rates.ElectricityProductCode != "" && rates.ElectricityTariffCode != "" {
+				agileRate, err := getCurrentAgileRate(rates.ElectricityProductCode, rates.ElectricityTariffCode)
+				if err != nil {
+					log.Printf("agile rate error: %v", err)
+				} else {
+					unitRate = agileRate
+				}
+			}
+			elecUnitRate.Set(unitRate)
 			elecStandingCharge.Set(rates.ElectricityStandingCharge)
-			if gasDeviceID != "" {
+
+			if gasMeter != nil {
 				gasUnitRate.Set(rates.GasUnitRate)
 				gasStandCharge.Set(rates.GasStandingCharge)
 			}

cmd/octopus_exporter/meters.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"errors"
 	"fmt"
 	"log"
 	"os"
@@ -22,6 +21,13 @@ type meterCandidate struct {
 	deviceID string
 }
 
+type resolvedMeter struct {
+	deviceID string
+	mpan     string // electricity
+	mprn     string // gas
+	serial   string
+}
+
 func getMeters(token string) ([]meterCandidate, error) {
 	result, err := doGraphQL(gqlRequest{
 		Query: `{ viewer { accounts { ... on AccountType { properties {
@@ -63,6 +69,10 @@ func getMeters(token string) ([]meterCandidate, error) {
 							candidates = append(candidates, meterCandidate{kind: electricity, mpan: mpan, serial: serial, deviceID: deviceID})
 						}
 					}
+					// Include meters without smart devices so we can still use the REST consumption endpoint.
+					if len(toSlice(m.(map[string]any)["smartDevices"])) == 0 && serial != "" {
+						candidates = append(candidates, meterCandidate{kind: electricity, mpan: mpan, serial: serial})
+					}
 				}
 			}
 
@@ -76,6 +86,9 @@ func getMeters(token string) ([]meterCandidate, error) {
 							candidates = append(candidates, meterCandidate{kind: gas, mprn: mprn, serial: serial, deviceID: deviceID})
 						}
 					}
+					if len(toSlice(m.(map[string]any)["smartDevices"])) == 0 && serial != "" {
+						candidates = append(candidates, meterCandidate{kind: gas, mprn: mprn, serial: serial})
+					}
 				}
 			}
 		}
@@ -84,9 +97,9 @@ func getMeters(token string) ([]meterCandidate, error) {
 	return candidates, nil
 }
 
-// resolveDeviceID finds the device ID for the given meter kind using environment
-// variable filters. Returns ("", nil) if no meter of that kind exists on the account.
-func resolveDeviceID(token string, kind meterKind) (string, error) {
+// resolveMeter finds the meter matching the env var filters for the given kind.
+// Returns (nil, nil) if no meter of that kind exists on the account.
+func resolveMeter(token string, kind meterKind) (*resolvedMeter, error) {
 	var wantDeviceID, wantID, wantSerial string
 	switch kind {
 	case electricity:
@@ -99,14 +112,10 @@ func resolveDeviceID(token string, kind meterKind) (string, error) {
 		wantSerial = os.Getenv("OCTOPUS_GAS_SERIAL")
 	}
 
-	if wantDeviceID != "" && wantID == "" && wantSerial == "" {
-		return wantDeviceID, nil
-	}
-
 	log.Printf("discovering %s meters from account...", kind)
 	candidates, err := getMeters(token)
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
 	for _, c := range candidates {
@@ -127,28 +136,19 @@ func resolveDeviceID(token string, kind meterKind) (string, error) {
 		if wantSerial != "" && c.serial != wantSerial {
 			continue
 		}
+
+		m := &resolvedMeter{deviceID: c.deviceID, mpan: c.mpan, mprn: c.mprn, serial: c.serial}
 		switch kind {
 		case electricity:
-			log.Printf("using electricity meter: MPAN=%s serial=%s deviceID=%s", c.mpan, c.serial, c.deviceID)
+			log.Printf("using electricity meter: MPAN=%s serial=%s deviceID=%s", m.mpan, m.serial, m.deviceID)
 		case gas:
-			log.Printf("using gas meter: MPRN=%s serial=%s deviceID=%s", c.mprn, c.serial, c.deviceID)
+			log.Printf("using gas meter: MPRN=%s serial=%s deviceID=%s", m.mprn, m.serial, m.deviceID)
 		}
-		return c.deviceID, nil
+		return m, nil
 	}
 
 	if wantDeviceID != "" || wantID != "" || wantSerial != "" {
-		return "", fmt.Errorf("no %s meter matched the specified filters", kind)
+		return nil, fmt.Errorf("no %s meter matched the specified filters", kind)
 	}
-
-	// No filters set and no meter found — this kind may not be on the account.
-	filtered := 0
-	for _, c := range candidates {
-		if c.kind == kind {
-			filtered++
-		}
-	}
-	if filtered == 0 {
-		return "", nil
-	}
-	return "", errors.New("unexpected: meters found but none selected")
+	return nil, nil
 }

cmd/octopus_exporter/rates.go

@@ -3,22 +3,22 @@ package main
 type tariffRates struct {
 	ElectricityUnitRate       float64
 	ElectricityStandingCharge float64
+	ElectricityProductCode    string
+	ElectricityTariffCode     string
+	ElectricityIsAgile        bool
 	GasUnitRate               float64
 	GasStandingCharge         float64
 }
 
-// electricityTariffFragments covers all known electricity tariff union types.
-const electricityTariffFragments = `
-	... on StandardTariff   { unitRate standingCharge }
-	... on HalfHourlyTariff { standingCharge }
-	... on PrepayTariff     { unitRate standingCharge }
-`
-
 func getRates(token string) (*tariffRates, error) {
 	result, err := doGraphQL(gqlRequest{
 		Query: `{ viewer { accounts { ... on AccountType { properties {
 			electricityMeterPoints {
-				agreements { validTo tariff {` + electricityTariffFragments + `} }
+				agreements { validTo tariff {
+					... on StandardTariff   { unitRate standingCharge productCode tariffCode }
+					... on HalfHourlyTariff { standingCharge productCode tariffCode }
+					... on PrepayTariff     { unitRate standingCharge productCode tariffCode }
+				} }
 			}
 			gasMeterPoints {
 				agreements { validTo tariff { unitRate standingCharge } }
@@ -41,6 +41,13 @@ func getRates(token string) (*tariffRates, error) {
 				if tariff := activeAgreementTariff(mp); tariff != nil {
 					rates.ElectricityUnitRate, _ = tariff["unitRate"].(float64)
 					rates.ElectricityStandingCharge, _ = tariff["standingCharge"].(float64)
+					rates.ElectricityProductCode, _ = tariff["productCode"].(string)
+					rates.ElectricityTariffCode, _ = tariff["tariffCode"].(string)
+					// HalfHourlyTariff has no unitRate field — detect Agile by absence.
+					_, rates.ElectricityIsAgile = tariff["unitRates"]
+					if _, hasUnit := tariff["unitRate"]; !hasUnit {
+						rates.ElectricityIsAgile = true
+					}
 				}
 			}
 

cmd/octopus_exporter/rates_test.go

@@ -0,0 +1,122 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestActiveAgreementTariff_ActiveFound(t *testing.T) {
+	mp := map[string]any{
+		"agreements": []any{
+			map[string]any{"validTo": "2020-01-01T00:00:00Z", "tariff": map[string]any{"unitRate": 10.0}},
+			map[string]any{"validTo": nil, "tariff": map[string]any{"unitRate": 26.3}},
+		},
+	}
+	tariff := activeAgreementTariff(mp)
+	if tariff == nil {
+		t.Fatal("expected tariff, got nil")
+	}
+	if tariff["unitRate"].(float64) != 26.3 {
+		t.Errorf("got unitRate %v, want 26.3", tariff["unitRate"])
+	}
+}
+
+func TestActiveAgreementTariff_NoneActive(t *testing.T) {
+	mp := map[string]any{
+		"agreements": []any{
+			map[string]any{"validTo": "2020-01-01T00:00:00Z", "tariff": map[string]any{"unitRate": 10.0}},
+		},
+	}
+	if tariff := activeAgreementTariff(mp); tariff != nil {
+		t.Errorf("expected nil, got %v", tariff)
+	}
+}
+
+func TestActiveAgreementTariff_NoAgreements(t *testing.T) {
+	mp := map[string]any{"agreements": []any{}}
+	if tariff := activeAgreementTariff(mp); tariff != nil {
+		t.Errorf("expected nil, got %v", tariff)
+	}
+}
+
+func TestGetRates_StandardTariff(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"viewer":{"accounts":[{"properties":[{
+			"electricityMeterPoints":[{"agreements":[{"validTo":null,"tariff":{
+				"unitRate":26.32,"standingCharge":54.55,"productCode":"VAR-22-11-01","tariffCode":"E-1R-VAR-22-11-01-C"
+			}}]}],
+			"gasMeterPoints":[]
+		}]}]}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	rates, err := getRates("token")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if rates.ElectricityUnitRate != 26.32 {
+		t.Errorf("unit rate: got %v, want 26.32", rates.ElectricityUnitRate)
+	}
+	if rates.ElectricityStandingCharge != 54.55 {
+		t.Errorf("standing charge: got %v, want 54.55", rates.ElectricityStandingCharge)
+	}
+	if rates.ElectricityTariffCode != "E-1R-VAR-22-11-01-C" {
+		t.Errorf("tariff code: got %q, want %q", rates.ElectricityTariffCode, "E-1R-VAR-22-11-01-C")
+	}
+	if rates.ElectricityIsAgile {
+		t.Error("expected IsAgile=false for StandardTariff")
+	}
+}
+
+func TestGetRates_AgileTariff(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"viewer":{"accounts":[{"properties":[{
+			"electricityMeterPoints":[{"agreements":[{"validTo":null,"tariff":{
+				"standingCharge":54.55,"productCode":"AGILE-24-10-01","tariffCode":"E-1R-AGILE-24-10-01-C"
+			}}]}],
+			"gasMeterPoints":[]
+		}]}]}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	rates, err := getRates("token")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !rates.ElectricityIsAgile {
+		t.Error("expected IsAgile=true for HalfHourlyTariff (no unitRate field)")
+	}
+	if rates.ElectricityProductCode != "AGILE-24-10-01" {
+		t.Errorf("product code: got %q, want %q", rates.ElectricityProductCode, "AGILE-24-10-01")
+	}
+}
+
+func TestGetRates_WithGas(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"viewer":{"accounts":[{"properties":[{
+			"electricityMeterPoints":[{"agreements":[{"validTo":null,"tariff":{
+				"unitRate":26.32,"standingCharge":54.55,"productCode":"VAR-22-11-01","tariffCode":"E-1R-VAR-22-11-01-C"
+			}}]}],
+			"gasMeterPoints":[{"agreements":[{"validTo":null,"tariff":{
+				"unitRate":7.22,"standingCharge":29.11
+			}}]}]
+		}]}]}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	rates, err := getRates("token")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if rates.GasUnitRate != 7.22 {
+		t.Errorf("gas unit rate: got %v, want 7.22", rates.GasUnitRate)
+	}
+	if rates.GasStandingCharge != 29.11 {
+		t.Errorf("gas standing charge: got %v, want 29.11", rates.GasStandingCharge)
+	}
+}

cmd/octopus_exporter/rest.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/url"
+)
+
+var octopusREST = "https://api.octopus.energy"
+
+func doREST(path string, params url.Values) (map[string]any, error) {
+	u := octopusREST + path
+	if len(params) > 0 {
+		u += "?" + params.Encode()
+	}
+	req, err := http.NewRequest(http.MethodGet, u, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.SetBasicAuth(apiKey, "")
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	raw, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	var result map[string]any
+	if err := json.Unmarshal(raw, &result); err != nil {
+		return nil, err
+	}
+	return result, nil
+}