// Command server is the Nils' MG4 car server: the API the car writes its telemetry,
// consumption and charging sessions to, stored in InfluxDB 2. The car sends live data to ABRP
// itself.
// Dashboards are Grafana's job; Grafana reads the same bucket directly.
package main

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"
)

const (
	minIngestTokenLength      = 24
	minApprovalPasswordLength = 12
)

type config struct {
	listenAddr   string
	influxURL    string
	influxToken  string
	influxOrg    string
	influxBucket string
	ingestToken  string
	approvalPass string
	publicURL    string
}

// loadConfig reads the environment and fails closed: a missing InfluxDB setting or a
// short ingest token stops the server from starting rather than serving something broken.
func loadConfig(getenv func(string) string) (config, error) {
	c := config{
		listenAddr:   getenv("LISTEN_ADDR"),
		influxURL:    getenv("INFLUX_URL"),
		influxToken:  getenv("INFLUX_TOKEN"),
		influxOrg:    getenv("INFLUX_ORG"),
		influxBucket: getenv("INFLUX_BUCKET"),
		ingestToken:  getenv("INGEST_TOKEN"),
		approvalPass: getenv("APPROVAL_PASSWORD"),
		publicURL:    getenv("PUBLIC_URL"),
	}
	if c.listenAddr == "" {
		c.listenAddr = ":8080"
	}
	if c.influxBucket == "" {
		c.influxBucket = "mg4"
	}
	for name, value := range map[string]string{"INFLUX_URL": c.influxURL, "INFLUX_TOKEN": c.influxToken, "INFLUX_ORG": c.influxOrg} {
		if value == "" {
			return config{}, fmt.Errorf("%s is not configured", name)
		}
	}
	if len(c.ingestToken) < minIngestTokenLength {
		return config{}, fmt.Errorf("INGEST_TOKEN must be at least %d characters", minIngestTokenLength)
	}
	// Pairing is optional; when it is on, its password guards token issuance and must not
	// be guessable.
	if c.approvalPass != "" && len(c.approvalPass) < minApprovalPasswordLength {
		return config{}, fmt.Errorf("APPROVAL_PASSWORD must be at least %d characters", minApprovalPasswordLength)
	}
	return c, nil
}

func main() {
	slog.SetDefault(slog.New(slog.NewTextHandler(os.Stderr, nil)))
	cfg, err := loadConfig(os.Getenv)
	if err != nil {
		slog.Error("invalid configuration", "error", err)
		os.Exit(1)
	}

	store := NewInfluxStore(cfg.influxURL, cfg.influxToken, cfg.influxOrg, cfg.influxBucket)
	defer store.Close()
	// Paired cars' tokens must be known before the first request; starting without them
	// would answer every paired car with 401, so a failed load stops the start instead.
	loadCtx, cancelLoad := context.WithTimeout(context.Background(), 30*time.Second)
	devices, err := store.LoadDevices(loadCtx)
	cancelLoad()
	if err != nil {
		slog.Error("paired devices could not be loaded", "error", err)
		os.Exit(1)
	}
	pairing := NewPairing(cfg.approvalPass, devices)
	api := &API{Store: store, IngestToken: cfg.ingestToken, Pairing: pairing, PublicURL: cfg.publicURL}

	srv := &http.Server{
		Addr:              cfg.listenAddr,
		Handler:           api.Routes(),
		ReadHeaderTimeout: 10 * time.Second,
		ReadTimeout:       30 * time.Second,
		WriteTimeout:      30 * time.Second,
		IdleTimeout:       120 * time.Second,
	}

	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()
	go func() {
		slog.Info("listening", "addr", cfg.listenAddr, "bucket", cfg.influxBucket,
			"pairing", pairing.Enabled(), "pairedDevices", len(devices))
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			slog.Error("server failed", "error", err)
			os.Exit(1)
		}
	}()
	<-ctx.Done()
	shutdown, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	if err := srv.Shutdown(shutdown); err != nil {
		slog.Error("shutdown", "error", err)
	}
}