fix: more proper setup and lots of quality of life changes (#10)

.github/workflows/pr-check.yml

@@ -5,20 +5,14 @@ on:
     branches: [main]
 
 jobs:
-  build:
+  test:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v3
-
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-
-      - name: Build
-        uses: docker/build-push-action@v6
+      - uses: actions/setup-go@v5
         with:
-          context: .
-          push: false
-          platforms: linux/amd64,linux/arm64
+          go-version-file: go.mod
+
+      - name: Test
+        run: go test -race ./...

.gitignore

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

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.22-alpine AS builder
+FROM golang:1.24-alpine AS builder
 WORKDIR /src
 COPY go.mod go.sum ./
 RUN go mod download
@@ -6,6 +6,7 @@ COPY . .
 RUN CGO_ENABLED=0 go build -o /octopus_exporter ./cmd/octopus_exporter
 
 FROM scratch
+COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
 COPY --from=builder /octopus_exporter /octopus_exporter
 EXPOSE 9359
 ENTRYPOINT ["/octopus_exporter"]

README.md

@@ -1,13 +1,38 @@
 # octopus_exporter
 
-A Prometheus exporter for live electricity consumption data from [Octopus Energy](https://octopus.energy), using the Kraken GraphQL API.
+A Prometheus exporter for Octopus Energy smart meter data, using the Kraken GraphQL API.
 
 ## Metrics
 
-| Metric | Description |
-|---|---|
-| `octopus_live_consumption` | Live electricity demand in watts |
-| `octopus_live_consumption_last_read` | Timestamp of the last meter reading (Unix epoch) |
+### Electricity
+
+| 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 | 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 | Source | Description |
+|---|---|---|
+| `octopus_account_balance_pence` | GraphQL | Account balance in pence (positive = credit, negative = debit) |
 
 Metrics are updated every 60 seconds.
 
@@ -16,12 +41,15 @@ Metrics are updated every 60 seconds.
 | Variable | Required | Description |
 |---|---|---|
 | `OCTOPUS_API_KEY` | Yes | Your Octopus Energy API key |
-| `OCTOPUS_MPAN` | No | Filter by MPAN (recommended if you have multiple meters) |
-| `OCTOPUS_SERIAL` | No | Filter by meter serial number |
-| `OCTOPUS_DEVICE_ID` | No | Use a specific smart device ID directly |
+| `OCTOPUS_MPAN` | No | Filter electricity meter by MPAN |
+| `OCTOPUS_SERIAL` | No | Filter electricity meter by serial number |
+| `OCTOPUS_DEVICE_ID` | No | Use a specific electricity smart device ID directly |
+| `OCTOPUS_GAS_MPRN` | No | Filter gas meter by MPRN |
+| `OCTOPUS_GAS_SERIAL` | No | Filter gas meter by serial number |
+| `OCTOPUS_GAS_DEVICE_ID` | No | Use a specific gas smart device ID directly |
 | `PORT` | No | Port to expose metrics on (default: `9359`) |
 
-If none of `OCTOPUS_MPAN`, `OCTOPUS_SERIAL`, or `OCTOPUS_DEVICE_ID` are set, the exporter will automatically select the first smart meter found on your account. For accounts with multiple meters, use `OCTOPUS_MPAN` or `OCTOPUS_SERIAL` to pin to a specific one.
+If no filter variables are set, the exporter auto-discovers the first smart meter of each type found on the account. Use `OCTOPUS_MPAN` / `OCTOPUS_MPRN` to pin to a specific meter on accounts with multiple meters.
 
 Your API key can be found in the [Octopus Energy developer dashboard](https://octopus.energy/dashboard/new/accounts/personal-details/api-access).
 
@@ -35,6 +63,20 @@ docker run -d \
   rwejlgaard/octopus_exporter
 ```
 
+## Docker Compose
+
+```yaml
+services:
+  octopus-exporter:
+    image: rwejlgaard/octopus_exporter:latest
+    restart: unless-stopped
+    environment:
+      OCTOPUS_API_KEY: sk_live_...
+      OCTOPUS_MPAN: "1234567890123"   # optional, auto-discovered if omitted
+    ports:
+      - "9359:9359"
+```
+
 ## Running from source
 
 Requires Go 1.22+.

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, key 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)},
+	}, key)
+	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 +1,56 @@
+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
+
+	rate, err := getCurrentAgileRate("AGILE-24-10-01", "E-1R-AGILE-24-10-01-C", "test")
+	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
+
+	_, err := getCurrentAgileRate("AGILE-24-10-01", "E-1R-AGILE-24-10-01-C", "test")
+	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
+
+	getCurrentAgileRate("AGILE-24-10-01", "E-1R-AGILE-24-10-01-C", "test")
+
+	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

@@ -6,11 +6,20 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"strconv"
+	"strings"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
 )
 
-const octopusGraphQL = "https://api.octopus.energy/v1/graphql/"
+var (
+	octopusGraphQL   = "https://api.octopus.energy/v1/graphql/"
+	httpClient       = &http.Client{Timeout: 15 * time.Second}
+	rateLimitRetries prometheus.Counter
+)
 
 type gqlRequest struct {
 	OperationName string         `json:"operationName,omitempty"`
@@ -39,25 +48,72 @@ func (f *jsonFloat) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
+// executeWithRetry executes an HTTP request, retrying on 429 with exponential
+// backoff (honouring Retry-After when present). Returns the raw response body.
+func executeWithRetry(makeReq func() (*http.Request, error)) ([]byte, error) {
+	const maxRetries = 5
+	backoff := 30 * time.Second
+	for attempt := 0; attempt <= maxRetries; attempt++ {
+		req, err := makeReq()
+		if err != nil {
+			return nil, err
+		}
+		resp, err := httpClient.Do(req)
+		if err != nil {
+			return nil, err
+		}
+		if resp.StatusCode == http.StatusTooManyRequests {
+			resp.Body.Close()
+			if attempt == maxRetries {
+				return nil, errors.New("rate limited: max retries exceeded")
+			}
+			if rateLimitRetries != nil {
+				rateLimitRetries.Inc()
+			}
+			wait := backoff
+			if ra := resp.Header.Get("Retry-After"); ra != "" {
+				if secs, err := strconv.Atoi(ra); err == nil {
+					wait = time.Duration(secs) * time.Second
+				}
+			}
+			log.Printf("rate limited; retrying in %v (attempt %d/%d)", wait, attempt+1, maxRetries)
+			time.Sleep(wait)
+			backoff *= 2
+			continue
+		}
+		raw, err := io.ReadAll(resp.Body)
+		resp.Body.Close()
+		if err != nil {
+			return nil, err
+		}
+		if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+			snippet := strings.TrimSpace(string(raw))
+			if len(snippet) > 200 {
+				snippet = snippet[:200]
+			}
+			return nil, fmt.Errorf("HTTP %d: %s", resp.StatusCode, snippet)
+		}
+		return raw, nil
+	}
+	return nil, errors.New("rate limited: max retries exceeded")
+}
+
 func doGraphQL(req gqlRequest, authToken string) (map[string]any, error) {
 	body, err := json.Marshal(req)
 	if err != nil {
 		return nil, err
 	}
-	httpReq, err := http.NewRequest(http.MethodPost, octopusGraphQL, bytes.NewReader(body))
-	if err != nil {
-		return nil, err
-	}
-	httpReq.Header.Set("Content-Type", "application/json")
-	if authToken != "" {
-		httpReq.Header.Set("Authorization", "JWT "+authToken)
-	}
-	resp, err := http.DefaultClient.Do(httpReq)
-	if err != nil {
-		return nil, err
-	}
-	defer resp.Body.Close()
-	raw, err := io.ReadAll(resp.Body)
+	raw, err := executeWithRetry(func() (*http.Request, error) {
+		httpReq, err := http.NewRequest(http.MethodPost, octopusGraphQL, bytes.NewReader(body))
+		if err != nil {
+			return nil, err
+		}
+		httpReq.Header.Set("Content-Type", "application/json")
+		if authToken != "" {
+			httpReq.Header.Set("Authorization", "JWT "+authToken)
+		}
+		return httpReq, nil
+	})
 	if err != nil {
 		return nil, err
 	}
@@ -67,7 +123,11 @@ func doGraphQL(req gqlRequest, authToken string) (map[string]any, error) {
 	}
 	if errs, ok := result["errors"].([]any); ok && len(errs) > 0 {
 		if e, ok := errs[0].(map[string]any); ok {
-			return nil, fmt.Errorf("GraphQL error: %s", e["message"])
+			msg, _ := e["message"].(string)
+			if strings.Contains(msg, "JWT") && strings.Contains(msg, "expired") {
+				return nil, errTokenExpired
+			}
+			return nil, fmt.Errorf("GraphQL error: %s", msg)
 		}
 		return nil, errors.New("GraphQL error")
 	}

cmd/octopus_exporter/client_test.go

@@ -0,0 +1,121 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync/atomic"
+	"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)
+	}
+}
+
+func TestExecuteWithRetry_RateLimitRetry(t *testing.T) {
+	var attempts atomic.Int32
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		n := attempts.Add(1)
+		if n < 3 {
+			w.Header().Set("Retry-After", "0")
+			w.WriteHeader(http.StatusTooManyRequests)
+			return
+		}
+		fmt.Fprint(w, `ok`)
+	}))
+	defer srv.Close()
+
+	raw, err := executeWithRetry(func() (*http.Request, error) {
+		return http.NewRequest(http.MethodGet, srv.URL, nil)
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if string(raw) != "ok" {
+		t.Errorf("got body %q, want %q", string(raw), "ok")
+	}
+	if attempts.Load() != 3 {
+		t.Errorf("got %d attempts, want 3", attempts.Load())
+	}
+}
+
+func TestExecuteWithRetry_Non200Error(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusUnauthorized)
+		fmt.Fprint(w, `{"error":"unauthorized"}`)
+	}))
+	defer srv.Close()
+
+	_, err := executeWithRetry(func() (*http.Request, error) {
+		return http.NewRequest(http.MethodGet, srv.URL, nil)
+	})
+	if err == nil {
+		t.Error("expected error for 401, got nil")
+	}
+	if !strings.Contains(err.Error(), "401") {
+		t.Errorf("expected error to contain status code, got: %v", err)
+	}
+}
+
+func TestExecuteWithRetry_ServerError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+		fmt.Fprint(w, `internal server error`)
+	}))
+	defer srv.Close()
+
+	_, err := executeWithRetry(func() (*http.Request, error) {
+		return http.NewRequest(http.MethodGet, srv.URL, nil)
+	})
+	if err == nil {
+		t.Error("expected error for 500, got nil")
+	}
+	if !strings.Contains(err.Error(), "500") {
+		t.Errorf("expected error to contain status code, got: %v", err)
+	}
+}

cmd/octopus_exporter/consumption.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"net/url"
+	"time"
+)
+
+type consumptionReading struct {
+	KWh           float64
+	IntervalStart time.Time
+}
+
+func getLatestConsumption(kind meterKind, id, serial, key 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"},
+	}, key)
+	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, ok := results[len(results)-1].(map[string]any)
+	if !ok {
+		return nil, errors.New("unexpected API response: invalid result entry")
+	}
+	kwh, _ := latest["consumption"].(float64)
+	startStr, ok := latest["interval_start"].(string)
+	if !ok {
+		return nil, errors.New("unexpected API response: missing interval_start")
+	}
+	start, err := time.Parse(time.RFC3339, startStr)
+	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 +1,73 @@
+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
+
+	c, err := getLatestConsumption(electricity, "MPAN123", "SERIAL456", "test")
+	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
+
+	_, err := getLatestConsumption(electricity, "MPAN123", "SERIAL456", "test")
+	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
+
+	getLatestConsumption(gas, "MPRN789", "SERIAL456", "test")
+
+	want := "/v1/gas-meter-points/MPRN789/meters/SERIAL456/consumption/"
+	if capturedPath != want {
+		t.Errorf("got path %q, want %q", capturedPath, want)
+	}
+}
+
+func TestGetLatestConsumption_Non200Error(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusUnauthorized)
+		fmt.Fprint(w, `{"error":"unauthorized"}`)
+	}))
+	defer srv.Close()
+	octopusREST = srv.URL
+
+	_, err := getLatestConsumption(electricity, "MPAN123", "SERIAL456", "bad-key")
+	if err == nil {
+		t.Error("expected error for 401, got nil")
+	}
+}

cmd/octopus_exporter/main.go

@@ -1,9 +1,12 @@
 package main
 
 import (
+	"errors"
 	"log"
 	"net/http"
 	"os"
+	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
@@ -11,8 +14,8 @@ import (
 )
 
 var (
-	apiKey = mustEnv("OCTOPUS_API_KEY")
-	port   = envOrDefault("PORT", "9359")
+	apiKey string
+	port   string
 )
 
 func mustEnv(key string) string {
@@ -34,32 +37,51 @@ func gauge(name, help string) prometheus.Gauge {
 	return prometheus.NewGauge(prometheus.GaugeOpts{Name: name, Help: help})
 }
 
+func counter(name, help string) prometheus.Counter {
+	return prometheus.NewCounter(prometheus.CounterOpts{Name: name, Help: help})
+}
+
 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)
+	log.Println("discovering meters from account...")
+	candidates, err := getMeters(token)
+	if err != nil {
+		log.Fatalf("failed to discover meters: %v", err)
+	}
+
+	elecMeter, err := resolveMeter(candidates, 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(candidates, 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 +89,36 @@ 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}
+	// Exporter health
+	exporterUp := gauge("octopus_up", "1 if the last poll cycle completed without errors, 0 otherwise")
+	pollErrors := counter("octopus_poll_errors_total", "Total number of collector errors per poll cycle")
+	tokenRefreshCount := counter("octopus_token_refreshes_total", "Total number of successful JWT token refreshes")
+	rateLimitRetries = counter("octopus_rate_limit_retries_total", "Total number of 429 rate-limit retries across all requests")
+
+	toRegister := []prometheus.Collector{
+		elecDemand, elecLastRead,
+		elecConsumption, elecConsumptionInterval,
+		elecUnitRate, elecStandingCharge,
+		accountBalance,
+		exporterUp, pollErrors, tokenRefreshCount, rateLimitRetries,
+	}
 
 	var (
-		gasDemand      prometheus.Gauge
-		gasLastRead    prometheus.Gauge
-		gasUnitRate    prometheus.Gauge
-		gasStandCharge prometheus.Gauge
+		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...)
@@ -93,53 +131,170 @@ func main() {
 		}
 	}()
 
+	// tokenMu guards token across concurrent poll goroutines.
+	var tokenMu sync.RWMutex
+
+	// withToken calls fn with the current token, refreshing once on JWT expiry.
+	withToken := func(fn func(string) error) error {
+		tokenMu.RLock()
+		t := token
+		tokenMu.RUnlock()
+
+		err := fn(t)
+		if !errors.Is(err, errTokenExpired) {
+			return err
+		}
+
+		// Only one goroutine refreshes; others will pick up the new token.
+		tokenMu.Lock()
+		if token == t {
+			newT, e := getKrakenToken(apiKey)
+			if e != nil {
+				tokenMu.Unlock()
+				log.Printf("token refresh failed: %v", e)
+				return err
+			}
+			token = newT
+			tokenRefreshCount.Inc()
+		}
+		newT := token
+		tokenMu.Unlock()
+
+		return fn(newT)
+	}
+
 	for {
-		// Electricity telemetry
-		reading, err := getLiveConsumption(token, elecDeviceID)
-		if err != nil {
-			log.Printf("electricity telemetry error: %v", err)
-			if token, err = getKrakenToken(apiKey); err != nil {
-				log.Printf("token refresh failed: %v", err)
-			}
-		} else {
-			elecDemand.Set(float64(reading.Demand))
-			if t, err := time.Parse("2006-01-02T15:04:05+00:00", reading.ReadAt); err == nil {
-				elecLastRead.Set(float64(t.Unix()))
-			}
+		var (
+			wg        sync.WaitGroup
+			failedAny atomic.Bool
+		)
+
+		fail := func(format string, args ...any) {
+			log.Printf(format, args...)
+			pollErrors.Inc()
+			failedAny.Store(true)
 		}
 
-		// Gas telemetry
-		if gasDeviceID != "" {
-			reading, err := getLiveConsumption(token, gasDeviceID)
-			if err != nil {
-				log.Printf("gas telemetry error: %v", err)
-			} else {
-				gasDemand.Set(float64(reading.Demand))
-				if t, err := time.Parse("2006-01-02T15:04:05+00:00", reading.ReadAt); err == nil {
-					gasLastRead.Set(float64(t.Unix()))
+		collect := func(name string, fn func() error) {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				if err := fn(); err != nil {
+					fail("%s error: %v", name, err)
 				}
-			}
+			}()
 		}
 
-		// Rates
-		rates, err := getRates(token)
-		if err != nil {
-			log.Printf("rates error: %v", err)
-		} else {
-			elecUnitRate.Set(rates.ElectricityUnitRate)
-			elecStandingCharge.Set(rates.ElectricityStandingCharge)
-			if gasDeviceID != "" {
-				gasUnitRate.Set(rates.GasUnitRate)
-				gasStandCharge.Set(rates.GasStandingCharge)
-			}
+		// Electricity telemetry (live demand)
+		if elecMeter.deviceID != "" {
+			collect("electricity telemetry", func() error {
+				return withToken(func(t string) error {
+					reading, err := getLiveConsumption(t, elecMeter.deviceID)
+					if err != nil {
+						return err
+					}
+					elecDemand.Set(float64(reading.Demand))
+					if ts, err := time.Parse(time.RFC3339, reading.ReadAt); err == nil {
+						elecLastRead.Set(float64(ts.Unix()))
+					}
+					return nil
+				})
+			})
 		}
 
+		// Gas telemetry (live demand)
+		if gasMeter != nil && gasMeter.deviceID != "" {
+			collect("gas telemetry", func() error {
+				return withToken(func(t string) error {
+					reading, err := getLiveConsumption(t, gasMeter.deviceID)
+					if err != nil {
+						return err
+					}
+					gasDemand.Set(float64(reading.Demand))
+					if ts, err := time.Parse(time.RFC3339, reading.ReadAt); err == nil {
+						gasLastRead.Set(float64(ts.Unix()))
+					}
+					return nil
+				})
+			})
+		}
+
+		// Electricity half-hourly consumption (REST)
+		if elecMeter.mpan != "" && elecMeter.serial != "" {
+			collect("electricity consumption", func() error {
+				c, err := getLatestConsumption(electricity, elecMeter.mpan, elecMeter.serial, apiKey)
+				if err != nil {
+					return err
+				}
+				elecConsumption.Set(c.KWh)
+				elecConsumptionInterval.Set(float64(c.IntervalStart.Unix()))
+				return nil
+			})
+		}
+
+		// Gas half-hourly consumption (REST)
+		if gasMeter != nil && gasMeter.mprn != "" && gasMeter.serial != "" {
+			collect("gas consumption", func() error {
+				c, err := getLatestConsumption(gas, gasMeter.mprn, gasMeter.serial, apiKey)
+				if err != nil {
+					return err
+				}
+				gasConsumption.Set(c.KWh)
+				gasConsumptionInterval.Set(float64(c.IntervalStart.Unix()))
+				return nil
+			})
+		}
+
+		// Tariff rates (result needed for optional agile lookup after wg.Wait)
+		var collectedRates *tariffRates
+		collect("rates", func() error {
+			return withToken(func(t string) error {
+				r, err := getRates(t)
+				if err != nil {
+					return err
+				}
+				collectedRates = r
+				return nil
+			})
+		})
+
 		// Account balance
-		balance, err := getAccountBalance(token)
-		if err != nil {
-			log.Printf("account balance error: %v", err)
+		collect("account balance", func() error {
+			return withToken(func(t string) error {
+				balance, err := getAccountBalance(t)
+				if err != nil {
+					return err
+				}
+				accountBalance.Set(balance)
+				return nil
+			})
+		})
+
+		wg.Wait()
+
+		// Agile rate depends on the rates result, so it runs after the parallel phase.
+		if collectedRates != nil {
+			unitRate := collectedRates.ElectricityUnitRate
+			if collectedRates.ElectricityIsAgile && collectedRates.ElectricityProductCode != "" && collectedRates.ElectricityTariffCode != "" {
+				agileRate, err := getCurrentAgileRate(collectedRates.ElectricityProductCode, collectedRates.ElectricityTariffCode, apiKey)
+				if err != nil {
+					fail("agile rate error: %v", err)
+				} else {
+					unitRate = agileRate
+				}
+			}
+			elecUnitRate.Set(unitRate)
+			elecStandingCharge.Set(collectedRates.ElectricityStandingCharge)
+			if gasMeter != nil {
+				gasUnitRate.Set(collectedRates.GasUnitRate)
+				gasStandCharge.Set(collectedRates.GasStandingCharge)
+			}
+		}
+
+		if failedAny.Load() {
+			exporterUp.Set(0)
 		} else {
-			accountBalance.Set(balance)
+			exporterUp.Set(1)
 		}
 
 		time.Sleep(60 * time.Second)

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 {
@@ -47,35 +53,73 @@ func getMeters(token string) ([]meterCandidate, error) {
 
 	var candidates []meterCandidate
 
-	accounts, _ := result["data"].(map[string]any)["viewer"].(map[string]any)["accounts"].([]any)
+	data, _ := result["data"].(map[string]any)
+	viewer, _ := data["viewer"].(map[string]any)
+	accounts, _ := viewer["accounts"].([]any)
 	for _, a := range accounts {
 		props, _ := a.(map[string]any)["properties"].([]any)
 		for _, p := range props {
-			pm := p.(map[string]any)
+			pm, ok := p.(map[string]any)
+			if !ok {
+				continue
+			}
 
 			for _, mp := range toSlice(pm["electricityMeterPoints"]) {
-				mpan, _ := mp.(map[string]any)["mpan"].(string)
-				for _, m := range toSlice(mp.(map[string]any)["meters"]) {
-					serial, _ := m.(map[string]any)["serialNumber"].(string)
-					for _, d := range toSlice(m.(map[string]any)["smartDevices"]) {
-						deviceID, _ := d.(map[string]any)["deviceId"].(string)
+				mpPoint, ok := mp.(map[string]any)
+				if !ok {
+					continue
+				}
+				mpan, _ := mpPoint["mpan"].(string)
+				for _, m := range toSlice(mpPoint["meters"]) {
+					meterMap, ok := m.(map[string]any)
+					if !ok {
+						continue
+					}
+					serial, _ := meterMap["serialNumber"].(string)
+					devices := toSlice(meterMap["smartDevices"])
+					for _, d := range devices {
+						dMap, ok := d.(map[string]any)
+						if !ok {
+							continue
+						}
+						deviceID, _ := dMap["deviceId"].(string)
 						if deviceID != "" {
 							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(devices) == 0 && serial != "" {
+						candidates = append(candidates, meterCandidate{kind: electricity, mpan: mpan, serial: serial})
+					}
 				}
 			}
 
 			for _, mp := range toSlice(pm["gasMeterPoints"]) {
-				mprn, _ := mp.(map[string]any)["mprn"].(string)
-				for _, m := range toSlice(mp.(map[string]any)["meters"]) {
-					serial, _ := m.(map[string]any)["serialNumber"].(string)
-					for _, d := range toSlice(m.(map[string]any)["smartDevices"]) {
-						deviceID, _ := d.(map[string]any)["deviceId"].(string)
+				mpPoint, ok := mp.(map[string]any)
+				if !ok {
+					continue
+				}
+				mprn, _ := mpPoint["mprn"].(string)
+				for _, m := range toSlice(mpPoint["meters"]) {
+					meterMap, ok := m.(map[string]any)
+					if !ok {
+						continue
+					}
+					serial, _ := meterMap["serialNumber"].(string)
+					devices := toSlice(meterMap["smartDevices"])
+					for _, d := range devices {
+						dMap, ok := d.(map[string]any)
+						if !ok {
+							continue
+						}
+						deviceID, _ := dMap["deviceId"].(string)
 						if deviceID != "" {
 							candidates = append(candidates, meterCandidate{kind: gas, mprn: mprn, serial: serial, deviceID: deviceID})
 						}
 					}
+					if len(devices) == 0 && serial != "" {
+						candidates = append(candidates, meterCandidate{kind: gas, mprn: mprn, serial: serial})
+					}
 				}
 			}
 		}
@@ -84,9 +128,9 @@ 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(candidates []meterCandidate, kind meterKind) (*resolvedMeter, error) {
 	var wantDeviceID, wantID, wantSerial string
 	switch kind {
 	case electricity:
@@ -99,16 +143,6 @@ 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
-	}
-
 	for _, c := range candidates {
 		if c.kind != kind {
 			continue
@@ -127,28 +161,19 @@ 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/meters_test.go

@@ -0,0 +1,209 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestResolveMeter_NoFilters_ReturnsFirst(t *testing.T) {
+	t.Setenv("OCTOPUS_DEVICE_ID", "")
+	t.Setenv("OCTOPUS_MPAN", "")
+	t.Setenv("OCTOPUS_SERIAL", "")
+
+	candidates := []meterCandidate{
+		{kind: electricity, mpan: "1000000000001", serial: "A001", deviceID: "dev1"},
+		{kind: electricity, mpan: "1000000000002", serial: "A002", deviceID: "dev2"},
+	}
+	m, err := resolveMeter(candidates, electricity)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if m == nil {
+		t.Fatal("expected meter, got nil")
+	}
+	if m.mpan != "1000000000001" {
+		t.Errorf("got mpan %q, want 1000000000001", m.mpan)
+	}
+}
+
+func TestResolveMeter_FilterByMPAN(t *testing.T) {
+	t.Setenv("OCTOPUS_DEVICE_ID", "")
+	t.Setenv("OCTOPUS_MPAN", "1000000000002")
+	t.Setenv("OCTOPUS_SERIAL", "")
+
+	candidates := []meterCandidate{
+		{kind: electricity, mpan: "1000000000001", serial: "A001", deviceID: "dev1"},
+		{kind: electricity, mpan: "1000000000002", serial: "A002", deviceID: "dev2"},
+	}
+	m, err := resolveMeter(candidates, electricity)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if m == nil {
+		t.Fatal("expected meter, got nil")
+	}
+	if m.mpan != "1000000000002" {
+		t.Errorf("got mpan %q, want 1000000000002", m.mpan)
+	}
+}
+
+func TestResolveMeter_FilterByDeviceID(t *testing.T) {
+	t.Setenv("OCTOPUS_DEVICE_ID", "dev2")
+	t.Setenv("OCTOPUS_MPAN", "")
+	t.Setenv("OCTOPUS_SERIAL", "")
+
+	candidates := []meterCandidate{
+		{kind: electricity, mpan: "1000000000001", serial: "A001", deviceID: "dev1"},
+		{kind: electricity, mpan: "1000000000002", serial: "A002", deviceID: "dev2"},
+	}
+	m, err := resolveMeter(candidates, electricity)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if m.deviceID != "dev2" {
+		t.Errorf("got deviceID %q, want dev2", m.deviceID)
+	}
+}
+
+func TestResolveMeter_FilterMismatch_ReturnsError(t *testing.T) {
+	t.Setenv("OCTOPUS_MPAN", "9999999999999")
+	t.Setenv("OCTOPUS_DEVICE_ID", "")
+	t.Setenv("OCTOPUS_SERIAL", "")
+
+	candidates := []meterCandidate{
+		{kind: electricity, mpan: "1000000000001", serial: "A001"},
+	}
+	_, err := resolveMeter(candidates, electricity)
+	if err == nil {
+		t.Error("expected error for unmatched filter, got nil")
+	}
+}
+
+func TestResolveMeter_NoMetersOfKind_ReturnsNil(t *testing.T) {
+	t.Setenv("OCTOPUS_DEVICE_ID", "")
+	t.Setenv("OCTOPUS_MPAN", "")
+	t.Setenv("OCTOPUS_SERIAL", "")
+
+	candidates := []meterCandidate{
+		{kind: gas, mprn: "1111111111", serial: "G001"},
+	}
+	m, err := resolveMeter(candidates, electricity)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if m != nil {
+		t.Errorf("expected nil for no electricity meters, got %+v", m)
+	}
+}
+
+func TestResolveMeter_GasFilterByMPRN(t *testing.T) {
+	t.Setenv("OCTOPUS_GAS_DEVICE_ID", "")
+	t.Setenv("OCTOPUS_GAS_MPRN", "2222222222")
+	t.Setenv("OCTOPUS_GAS_SERIAL", "")
+
+	candidates := []meterCandidate{
+		{kind: gas, mprn: "1111111111", serial: "G001"},
+		{kind: gas, mprn: "2222222222", serial: "G002"},
+	}
+	m, err := resolveMeter(candidates, gas)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if m.mprn != "2222222222" {
+		t.Errorf("got mprn %q, want 2222222222", m.mprn)
+	}
+}
+
+func TestGetMeters_ElectricityWithSmartDevice(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"viewer":{"accounts":[{"properties":[{
+			"electricityMeterPoints":[{
+				"mpan":"1000000000001",
+				"meters":[{"serialNumber":"A001","smartDevices":[{"deviceId":"dev1"}]}]
+			}],
+			"gasMeterPoints":[]
+		}]}]}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	candidates, err := getMeters("token")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(candidates) != 1 {
+		t.Fatalf("got %d candidates, want 1", len(candidates))
+	}
+	c := candidates[0]
+	if c.kind != electricity {
+		t.Errorf("kind: got %q, want electricity", c.kind)
+	}
+	if c.mpan != "1000000000001" {
+		t.Errorf("mpan: got %q, want 1000000000001", c.mpan)
+	}
+	if c.deviceID != "dev1" {
+		t.Errorf("deviceID: got %q, want dev1", c.deviceID)
+	}
+}
+
+func TestGetMeters_MeterWithoutSmartDevice(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"viewer":{"accounts":[{"properties":[{
+			"electricityMeterPoints":[{
+				"mpan":"1000000000001",
+				"meters":[{"serialNumber":"A001","smartDevices":[]}]
+			}],
+			"gasMeterPoints":[]
+		}]}]}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	candidates, err := getMeters("token")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(candidates) != 1 {
+		t.Fatalf("got %d candidates, want 1", len(candidates))
+	}
+	if candidates[0].deviceID != "" {
+		t.Errorf("expected empty deviceID for meter without smart device, got %q", candidates[0].deviceID)
+	}
+}
+
+func TestGetMeters_BothElectricityAndGas(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"viewer":{"accounts":[{"properties":[{
+			"electricityMeterPoints":[{
+				"mpan":"1000000000001",
+				"meters":[{"serialNumber":"A001","smartDevices":[{"deviceId":"dev1"}]}]
+			}],
+			"gasMeterPoints":[{
+				"mprn":"1111111111",
+				"meters":[{"serialNumber":"G001","smartDevices":[{"deviceId":"gdev1"}]}]
+			}]
+		}]}]}}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	candidates, err := getMeters("token")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(candidates) != 2 {
+		t.Fatalf("got %d candidates, want 2", len(candidates))
+	}
+	kinds := map[meterKind]bool{}
+	for _, c := range candidates {
+		kinds[c.kind] = true
+	}
+	if !kinds[electricity] {
+		t.Error("expected electricity candidate")
+	}
+	if !kinds[gas] {
+		t.Error("expected gas candidate")
+	}
+}

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 } }
@@ -31,16 +31,27 @@ func getRates(token string) (*tariffRates, error) {
 
 	rates := &tariffRates{}
 
-	accounts, _ := result["data"].(map[string]any)["viewer"].(map[string]any)["accounts"].([]any)
+	data, _ := result["data"].(map[string]any)
+	viewer, _ := data["viewer"].(map[string]any)
+	accounts, _ := viewer["accounts"].([]any)
 	for _, a := range accounts {
 		props, _ := a.(map[string]any)["properties"].([]any)
 		for _, p := range props {
-			pm := p.(map[string]any)
+			pm, ok := p.(map[string]any)
+			if !ok {
+				continue
+			}
 
 			for _, mp := range toSlice(pm["electricityMeterPoints"]) {
 				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.
+					if _, hasUnit := tariff["unitRate"]; !hasUnit {
+						rates.ElectricityIsAgile = true
+					}
 				}
 			}
 
@@ -58,8 +69,15 @@ func getRates(token string) (*tariffRates, error) {
 
 // activeAgreementTariff returns the tariff map for the agreement with validTo == null.
 func activeAgreementTariff(meterPoint any) map[string]any {
-	for _, ag := range toSlice(meterPoint.(map[string]any)["agreements"]) {
-		agm := ag.(map[string]any)
+	mp, ok := meterPoint.(map[string]any)
+	if !ok {
+		return nil
+	}
+	for _, ag := range toSlice(mp["agreements"]) {
+		agm, ok := ag.(map[string]any)
+		if !ok {
+			continue
+		}
 		if agm["validTo"] == nil {
 			tariff, _ := agm["tariff"].(map[string]any)
 			return tariff

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 +1,32 @@
+package main
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/url"
+)
+
+var octopusREST = "https://api.octopus.energy"
+
+func doREST(path string, params url.Values, key string) (map[string]any, error) {
+	u := octopusREST + path
+	if len(params) > 0 {
+		u += "?" + params.Encode()
+	}
+	raw, err := executeWithRetry(func() (*http.Request, error) {
+		req, err := http.NewRequest(http.MethodGet, u, nil)
+		if err != nil {
+			return nil, err
+		}
+		req.SetBasicAuth(key, "")
+		return req, nil
+	})
+	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
+}

cmd/octopus_exporter/telemetry.go

@@ -3,6 +3,7 @@ package main
 import (
 	"encoding/json"
 	"errors"
+	"fmt"
 )
 
 type telemetryReading struct {
@@ -18,13 +19,14 @@ func getLiveConsumption(token, deviceID string) (*telemetryReading, error) {
 		Query:         "query getSmartMeterTelemetry($meterDeviceId: String!, $start: DateTime, $end: DateTime, $grouping: TelemetryGrouping) {\n  smartMeterTelemetry(deviceId: $meterDeviceId, start: $start, end: $end, grouping: $grouping) {\n    readAt\n    consumption\n    demand\n    __typename\n  }\n}\n",
 	}, token)
 	if err != nil {
-		if err.Error() == "GraphQL error: Signature of the JWT has expired." {
-			return nil, errTokenExpired
-		}
 		return nil, err
 	}
 
-	telemetry := toSlice(result["data"].(map[string]any)["smartMeterTelemetry"])
+	data, ok := result["data"].(map[string]any)
+	if !ok {
+		return nil, fmt.Errorf("unexpected API response: missing data field")
+	}
+	telemetry := toSlice(data["smartMeterTelemetry"])
 	if len(telemetry) == 0 {
 		return nil, errors.New("no telemetry data returned")
 	}

cmd/octopus_exporter/telemetry_test.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestGetLiveConsumption_Success(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"smartMeterTelemetry":[
+			{"readAt":"2026-04-24T10:00:00Z","consumption":"1.23","demand":"456.7"}
+		]}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	reading, err := getLiveConsumption("test-token", "device-123")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if float64(reading.Demand) != 456.7 {
+		t.Errorf("demand: got %v, want 456.7", reading.Demand)
+	}
+	if float64(reading.Consumption) != 1.23 {
+		t.Errorf("consumption: got %v, want 1.23", reading.Consumption)
+	}
+	if reading.ReadAt != "2026-04-24T10:00:00Z" {
+		t.Errorf("readAt: got %q, want %q", reading.ReadAt, "2026-04-24T10:00:00Z")
+	}
+}
+
+func TestGetLiveConsumption_EmptyTelemetry(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"smartMeterTelemetry":[]}}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	_, err := getLiveConsumption("test-token", "device-123")
+	if err == nil {
+		t.Error("expected error for empty telemetry, got nil")
+	}
+}
+
+func TestGetLiveConsumption_MissingDataField(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":null}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	_, err := getLiveConsumption("test-token", "device-123")
+	if err == nil {
+		t.Error("expected error for null data, got nil")
+	}
+}
+
+func TestGetLiveConsumption_GraphQLError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"errors":[{"message":"device not found"}]}`)
+	}))
+	defer srv.Close()
+	octopusGraphQL = srv.URL + "/"
+
+	_, err := getLiveConsumption("test-token", "device-123")
+	if err == nil {
+		t.Error("expected error for GraphQL error, got nil")
+	}
+}