Initial commit: EMS — Energie Management System

Complete self-consumption optimisation system for 7 kWp PV installation:
- Prometheus collector (grid power, SOC, PV, per-phase, compressor)
- Pure decision engine with SOC gates, hysteresis, priority ordering
- Shelly Gen1/Gen2 actuator (SHA-256 Digest auth, PM power readback)
- Viessmann OAuth2 client for DHW temperature control
- PV forecast integration (forecast.solar)
- Wallbox mutual exclusion (VX3 4.6 kW AC output constraint)
- Car-not-charging detection via Shelly PM
- Compressor idle → early SG-Ready release
- Per-phase grid power for single-phase wallbox decisions
- Manual override detection and web UI with override buttons
- Full unit test coverage for decision engine
- systemd service, Makefile, complete documentation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/viessmann/client.go

@@ -0,0 +1,171 @@
+package viessmann
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"net/url"
+	"os"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/tb/ems/internal/config"
+)
+
+const (
+	tokenEndpoint = "https://iam.viessmann-climatesolutions.com/idp/v3/token"
+	apiBase       = "https://api.viessmann.com/iot/v2"
+)
+
+// tokenFile mirrors the JSON structure stored on disk.
+type tokenFile struct {
+	AccessToken     string `json:"access_token"`
+	RefreshToken    string `json:"refresh_token"`
+	TokenType       string `json:"token_type"`
+	ExpiresIn       int    `json:"expires_in"`
+	ValidToTimeDate int64  `json:"validToTimeDate"` // Unix milliseconds
+}
+
+// Client manages Viessmann OAuth2 tokens and sends commands to the IoT API.
+type Client struct {
+	cfg        config.ViessmannConfig
+	httpClient *http.Client
+	logger     *slog.Logger
+	mu         sync.Mutex
+	token      tokenFile
+}
+
+// NewClient creates a new Viessmann client and loads the token from disk.
+func NewClient(cfg config.ViessmannConfig, logger *slog.Logger) (*Client, error) {
+	c := &Client{
+		cfg:        cfg,
+		httpClient: &http.Client{Timeout: 15 * time.Second},
+		logger:     logger,
+	}
+	if err := c.loadToken(); err != nil {
+		return nil, fmt.Errorf("loading token: %w", err)
+	}
+	return c, nil
+}
+
+func (c *Client) loadToken() error {
+	data, err := os.ReadFile(c.cfg.TokenFile)
+	if err != nil {
+		return fmt.Errorf("reading %s: %w", c.cfg.TokenFile, err)
+	}
+	return json.Unmarshal(data, &c.token)
+}
+
+func (c *Client) saveToken() {
+	data, err := json.MarshalIndent(c.token, "", "  ")
+	if err != nil {
+		c.logger.Warn("could not marshal token", "error", err)
+		return
+	}
+	if err := os.WriteFile(c.cfg.TokenFile, data, 0600); err != nil {
+		c.logger.Warn("could not save token file", "error", err)
+	}
+}
+
+// ensureToken refreshes the access token if it expires within 5 minutes.
+// Caller must hold c.mu.
+func (c *Client) ensureToken(ctx context.Context) error {
+	remaining := time.Until(time.UnixMilli(c.token.ValidToTimeDate))
+	if remaining > 5*time.Minute {
+		return nil
+	}
+
+	c.logger.Info("refreshing Viessmann access token", "remaining", remaining.Round(time.Second))
+
+	form := url.Values{}
+	form.Set("grant_type", "refresh_token")
+	form.Set("client_id", c.cfg.ClientID)
+	form.Set("refresh_token", c.token.RefreshToken)
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, tokenEndpoint,
+		strings.NewReader(form.Encode()))
+	if err != nil {
+		return fmt.Errorf("creating token request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("token refresh: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("token refresh returned %d", resp.StatusCode)
+	}
+
+	var fresh struct {
+		AccessToken  string `json:"access_token"`
+		RefreshToken string `json:"refresh_token"`
+		TokenType    string `json:"token_type"`
+		ExpiresIn    int    `json:"expires_in"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&fresh); err != nil {
+		return fmt.Errorf("decoding token response: %w", err)
+	}
+
+	c.token.AccessToken = fresh.AccessToken
+	if fresh.RefreshToken != "" {
+		c.token.RefreshToken = fresh.RefreshToken
+	}
+	c.token.TokenType = fresh.TokenType
+	c.token.ExpiresIn = fresh.ExpiresIn
+	c.token.ValidToTimeDate = time.Now().Add(time.Duration(fresh.ExpiresIn) * time.Second).UnixMilli()
+
+	c.saveToken()
+	c.logger.Info("Viessmann token refreshed")
+	return nil
+}
+
+// featureURL builds the IoT API URL for a device feature.
+func (c *Client) featureURL(feature string) string {
+	return fmt.Sprintf(
+		"%s/features/installations/%s/gateways/%s/devices/%s/features/%s",
+		apiBase,
+		c.cfg.InstallationID,
+		c.cfg.GatewaySerial,
+		c.cfg.DeviceID,
+		feature,
+	)
+}
+
+// SetDHWTemperature sets the domestic hot water target temperature via the Viessmann API.
+func (c *Client) SetDHWTemperature(ctx context.Context, tempC float64) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if err := c.ensureToken(ctx); err != nil {
+		return fmt.Errorf("ensuring token: %w", err)
+	}
+
+	cmdURL := c.featureURL("heating.dhw.temperature.main") + "/commands/setTargetTemperature"
+	body := fmt.Sprintf(`{"temperature":%g}`, tempC)
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, cmdURL, strings.NewReader(body))
+	if err != nil {
+		return fmt.Errorf("creating request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", "Bearer "+c.token.AccessToken)
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("API call: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusNoContent {
+		return fmt.Errorf("Viessmann API returned %d", resp.StatusCode)
+	}
+
+	c.logger.Info("DHW temperature set", "temp_c", tempC)
+	return nil
+}