// Command behavision-server consumes store events from the broker and serves
// the HTTP API.
//
// One process, two jobs, because they share the database pool and the volume
// does not justify splitting them. If ingest ever needs to scale separately it
// can: nothing in `ingest` knows about HTTP.
package main

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"strings"
	"sync/atomic"
	"syscall"
	"time"

	paho "github.com/eclipse/paho.mqtt.golang"

	"github.com/loyaly/behavision-server/internal/api"
	"github.com/loyaly/behavision-server/internal/assistant"
	"github.com/loyaly/behavision-server/internal/blob"
	"github.com/loyaly/behavision-server/internal/broker"
	"github.com/loyaly/behavision-server/internal/ingest"
	"github.com/loyaly/behavision-server/internal/migrate"
	"github.com/loyaly/behavision-server/internal/secret"
	"github.com/loyaly/behavision-server/internal/store"
	"github.com/loyaly/behavision-server/internal/web"
	"github.com/loyaly/behavision-server/migrations"
)

var version = "dev"

func main() {
	// One binary, two jobs. Provisioning needs the same database URL and the
	// same secret key as the server, and a second image to keep in sync with
	// this one is a second thing to forget to deploy.
	if len(os.Args) > 1 && os.Args[1] == "provision" {
		if err := runProvision(os.Args[2:]); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}
		return
	}
	if len(os.Args) > 1 && os.Args[1] == "broker-init" {
		if err := runBrokerInit(os.Args[2:]); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}
		return
	}
	if len(os.Args) > 1 && os.Args[1] == "migrate" {
		if err := runMigrate(os.Args[2:]); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}
		return
	}
	if err := run(); err != nil {
		log.Fatalf("behavision-server: %v", err)
	}
}

func env(key, def string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return def
}

func run() error {
	logger := log.New(os.Stdout, "", log.LstdFlags|log.LUTC)
	dsn := os.Getenv("DATABASE_URL")
	if dsn == "" {
		return errors.New("DATABASE_URL is required")
	}
	brokerURL := env("MQTT_URL", "tcp://behavision-mqtt:1883")
	brokerUser := os.Getenv("MQTT_USERNAME")
	brokerPass := os.Getenv("MQTT_PASSWORD")
	addr := env("LISTEN_ADDR", ":8080")

	ctx, stop := signal.NotifyContext(context.Background(),
		os.Interrupt, syscall.SIGTERM)
	defer stop()

	st, err := store.Open(ctx, dsn)
	if err != nil {
		return err
	}
	defer st.Close()
	st.UseLogger(logger)
	logger.Print("database connected")

	// Applied here, not by hand, because an upgrade of this product is "copy
	// the new binary and restart it". A migration an operator has to remember
	// to run is a migration that does not get run, and its failure is not a
	// startup error - it is a query referencing a column that is not there,
	// surfacing later on whichever endpoint touches it first.
	//
	// Refusing to start on failure is deliberate: a server running against a
	// schema it does not match writes wrong data, and wrong data outlives the
	// outage that stopping causes.
	if os.Getenv("BEHAVISION_SKIP_MIGRATE") == "1" {
		logger.Print("WARN BEHAVISION_SKIP_MIGRATE=1 - schema not checked")
	} else {
		applied, err := migrate.Apply(ctx, st.Pool(), migrations.FS)
		if err != nil {
			return fmt.Errorf("schema: %w", err)
		}
		if len(applied) == 0 {
			logger.Print("schema up to date")
		} else {
			logger.Printf("schema: applied %s", strings.Join(applied, ", "))
		}
	}

	// Without the key the server still ingests events and serves reports; only
	// enrolment fails, and it fails with a message naming the missing variable.
	// Refusing to start would take a working estate down over a feature that
	// runs once per shop PC.
	if box, err := secret.FromEnv("BEHAVISION_SECRET_KEY"); err != nil {
		logger.Printf("WARN %v - agent enrolment will be refused", err)
	} else {
		st.UseSecrets(box)
	}

	// One hub, shared by the MQTT consumer and the API in this single process.
	// The consumer rings it; live arrival streams answer by re-querying. If
	// this ever runs as more than one instance, an instance will not hear the
	// others' ingest and its streams fall back to their slow tick - latency,
	// not silence, which is why the fallback exists at all.
	hub := api.NewHub()
	consumer := &ingest.Consumer{Store: st, Log: logger, Notify: hub.Notify}

	var brokerUp atomic.Bool
	opts := paho.NewClientOptions().
		AddBroker(brokerURL).
		SetClientID(fmt.Sprintf("behavision-server-%d", time.Now().UnixNano())).
		SetUsername(brokerUser).
		SetPassword(brokerPass).
		SetAutoReconnect(true).
		SetConnectRetry(true).
		SetConnectRetryInterval(5 * time.Second).
		SetKeepAlive(30 * time.Second).
		// Messages are handled one at a time in order. Concurrent handlers
		// would let two events for the same new visitor race and create two
		// visitor rows for one person.
		SetOrderMatters(true)

	opts.OnConnectionLost = func(_ paho.Client, err error) {
		brokerUp.Store(false)
		logger.Printf("broker connection lost: %v", err)
	}
	opts.OnConnect = func(c paho.Client) {
		brokerUp.Store(true)
		// Subscribing inside OnConnect, not once after Connect: a reconnect
		// with a clean session drops server-side subscriptions, and without
		// this the process would sit there connected and deaf.
		tok := c.Subscribe("bv/#", 1, func(_ paho.Client, m paho.Message) {
			hctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
			defer cancel()
			if err := consumer.Handle(hctx, m.Topic(), m.Payload()); err != nil {
				// Returning without acking is not possible with this client's
				// auto-ack, so a transient failure is logged loudly rather than
				// silently losing the event. QoS 1 + the agent's own spool mean
				// the event still exists at the far end until we confirm it.
				logger.Printf("ERROR handling %s: %v", m.Topic(), err)
			}
		})
		if tok.Wait() && tok.Error() != nil {
			logger.Printf("subscribe failed: %v", tok.Error())
			return
		}
		logger.Printf("subscribed to bv/# on %s", brokerURL)
	}

	client := paho.NewClient(opts)
	// Connected in the BACKGROUND, and that is the whole point of the comment
	// below: the API must come up even when the broker is down. Waiting here
	// did the opposite. With SetConnectRetry the token does not complete until
	// the broker answers, so an unreachable broker held the HTTP listener down
	// for the full 20 seconds on every start - measured, on a machine with no
	// broker at all. And it was silent: WaitTimeout returns false on a timeout,
	// which short-circuits the && , so the one log line never printed either.
	go func() {
		tok := client.Connect()
		if !tok.WaitTimeout(20 * time.Second) {
			logger.Printf("broker %s not reachable yet - retrying in the background",
				brokerURL)
			return
		}
		if err := tok.Error(); err != nil {
			logger.Printf("initial broker connect failed (will retry): %v", err)
		}
	}()

	apiSrv := &api.Server{
		Store: st,
		Log:   logger,
		// Opening a shop registers its broker login at the same moment, over the
		// same broker credential the ingest side already holds.
		Broker: broker.New(brokerURL, brokerUser, brokerPass, logger),
		Blob:   objectStore(ctx, logger),
		Hub:    hub,
		Bootstrap: api.BootstrapConfig{
			// What an enrolling PC is told to connect to. From the server's own
			// environment, never from the request: an agent asking where to
			// connect must not get to influence the answer.
			MQTTURL: env("AGENT_MQTT_URL", "tls://mcp.loyaly.ai:8883"),
			CACert:  caCert(logger),
			Models:  modelManifest(logger),
		},
	}
	// The assistant. Its tools are the same business questions the screens ask,
	// and every one runs as the signed-in user. Without ANTHROPIC_API_KEY it
	// reports itself off and the UI hides the panel - a supported state, not a
	// startup failure, because everything else on this server still works.
	assistantTools := &assistant.Registry{
		Store:       st,
		SiteChecker: api.BuildSiteSteps,
		Now:         func() time.Time { return time.Now().UTC() },
	}
	assistantClient := &assistant.Client{Tools: assistantTools, Log: logger}
	if assistantClient.Configured() {
		apiSrv.Assistant = assistant.ForAPI(assistantClient)
		logger.Print("assistant enabled")
	} else {
		logger.Print("ANTHROPIC_API_KEY not set - the assistant is off " +
			"(everything else is unaffected)")
	}

	mux := apiSrv.Routes()
	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
		hctx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
		defer cancel()
		dbErr := st.Ping(hctx)
		body := map[string]any{
			"version":   version,
			"database":  dbErr == nil,
			"broker":    brokerUp.Load(),
			"accepted":  consumer.Accepted,
			"duplicate": consumer.Duplicate,
			"dropped":   consumer.Dropped,
		}
		// Degraded, not down: the database is the hard dependency. Reporting
		// unhealthy while the broker reconnects would make an orchestrator
		// restart a process that is working.
		if dbErr != nil {
			body["error"] = dbErr.Error()
			w.WriteHeader(http.StatusServiceUnavailable)
		}
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(body)
	})
	// Anything under /api that matched no route stays JSON. Falling through to
	// the web app would turn a typo'd endpoint into an HTML page arriving where
	// a client expects JSON, and the parse error it causes surfaces three
	// layers from the cause.
	mux.HandleFunc("/api/", func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusNotFound)
		fmt.Fprint(w, `{"error":"not_found","message":"No such endpoint."}`)
	})

	// Everything else is the head-office web app, embedded in this binary.
	site, err := web.Handler()
	if err != nil {
		return fmt.Errorf("web assets: %w", err)
	}
	mux.Handle("/", site)

	srv := &http.Server{
		Addr:    addr,
		Handler: securityHeaders(mux),
		// Bounded so a slow or hostile client cannot hold a connection open
		// indefinitely on a 2 vCPU box.
		ReadHeaderTimeout: 10 * time.Second,
		ReadTimeout:       30 * time.Second,
		// WriteTimeout is deliberately ZERO, and the arrivals stream is why.
		//
		// A write deadline applies to the WHOLE response, not to each write, so
		// any non-zero value silently severs every event stream that outlives
		// it - a shop screen that dies after 60 seconds and reconnects forever,
		// which looks like a network fault and is not one. ReadTimeout and
		// IdleTimeout still bound a slow or hostile client; what is given up is
		// a cap on how long a client may take to READ a response it asked for.
		WriteTimeout: 0,
		IdleTimeout:  120 * time.Second,
	}
	go func() {
		logger.Printf("http listening on %s", addr)
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			logger.Printf("http server stopped: %v", err)
			stop()
		}
	}()

	<-ctx.Done()
	logger.Print("shutting down")
	shutCtx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
	defer cancel()
	srv.Shutdown(shutCtx) //nolint:errcheck
	client.Disconnect(1000)
	return nil
}

func securityHeaders(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Traefik terminates TLS, so HSTS is set here where the app knows it is
		// only ever served over https.
		w.Header().Set("Strict-Transport-Security", "max-age=31536000")
		w.Header().Set("X-Content-Type-Options", "nosniff")
		w.Header().Set("Referrer-Policy", "no-referrer")
		w.Header().Set("X-Frame-Options", "DENY")
		if strings.HasPrefix(r.URL.Path, "/api/") {
			w.Header().Set("Cache-Control", "no-store")
		}
		next.ServeHTTP(w, r)
	})
}

// caCert reads the CA an agent needs to trust the broker's certificate.
//
// Handed out at enrolment rather than shipped in the installer: the CA can be
// rotated without re-signing and re-distributing every store's software.
func caCert(logger *log.Logger) string {
	path := os.Getenv("AGENT_CA_FILE")
	if path == "" {
		return ""
	}
	b, err := os.ReadFile(path)
	if err != nil {
		logger.Printf("WARN cannot read AGENT_CA_FILE %s: %v - "+
			"enrolling agents will get no CA and cannot verify the broker", path, err)
		return ""
	}
	return string(b)
}

// modelManifest pins which encoder new installs download.
//
// It matters more than it looks: embeddings are model-tagged and vectors from
// two different encoders cannot be compared at all, so a fleet that drifts onto
// two models is a fleet whose sites cannot recognise each other's customers.
func modelManifest(logger *log.Logger) []api.ModelRef {
	path := os.Getenv("AGENT_MODELS_FILE")
	if path == "" {
		return nil
	}
	b, err := os.ReadFile(path)
	if err != nil {
		logger.Printf("WARN cannot read AGENT_MODELS_FILE %s: %v", path, err)
		return nil
	}
	var out []api.ModelRef
	if err := json.Unmarshal(b, &out); err != nil {
		logger.Printf("WARN AGENT_MODELS_FILE is not valid JSON: %v", err)
		return nil
	}
	return out
}

// objectStore configures face-image storage, or returns nil for a deployment
// that stores none.
//
// Nil is a supported, and the default, configuration: this product shipped
// deliberately storing no images at all, and switching them on changes what the
// database is under GDPR and India's DPDP. It should take setting five
// variables, not forgetting to unset them.
//
// The self-test is not optional. The bucket in use is world-readable at the
// bucket level, so "the upload worked" and "the face image is private" are
// different questions, and the second one has to be answered at boot rather
// than discovered later from someone else's search results.
func objectStore(ctx context.Context, logger *log.Logger) api.BlobStore {
	cfg := blob.Config{
		Region:    os.Getenv("DO_SPACES_REGION"),
		Endpoint:  os.Getenv("DO_SPACES_ENDPOINT"),
		Bucket:    os.Getenv("DO_SPACES_BUCKET"),
		AccessKey: os.Getenv("DO_SPACES_ACCESS_KEY"),
		SecretKey: os.Getenv("DO_SPACES_SECRET_KEY"),
		Prefix:    env("DO_SPACES_PREFIX", "behavision/v2"),
	}
	if cfg.AccessKey == "" && cfg.Bucket == "" {
		logger.Print("object storage not configured - visits will carry no images")
		return nil
	}
	store, err := blob.New(cfg)
	if err != nil {
		logger.Printf("WARN object storage disabled: %v", err)
		return nil
	}
	cctx, cancel := context.WithTimeout(ctx, 20*time.Second)
	defer cancel()
	if err := store.Check(cctx); err != nil {
		// Refuse to serve images rather than serve them unsafely. A shop losing
		// photos is a visible, fixable problem; a shop publishing its
		// customers' faces is neither.
		logger.Printf("ERROR object storage self-test failed, images DISABLED: %v", err)
		return nil
	}
	logger.Printf("object storage ready: %s/%s (objects are private)",
		cfg.Bucket, cfg.Prefix)
	return store
}